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Water regime of a pine forest under a Mediterranean climate
Abstract
The transpiration (T) of an Aleppo pine (Pinus halepensis Mill.) forest was studied during 1 year to evaluate soil water storage and tree response to water stress in a Mediterranean climate. The heat pulse method was used for continuous measurement (excluding rainy days) of sap flow in the stems of eight trees at hourly intervals. Climatic parameters were measured in the forest for computation of potential transpiration (Tp) using the Penman formula. Extrapolating T of sampled trees to stand T was found to be difficult because of a poor correlation between T and stem diameter. During the rainy season the average daily rate of T was linearly related to Tp and the ratio was 0.62, independent of Tp rate. After the last rainfall, decreased steadily, reaching 0.05 approximately 30 days later; the leaf water potential (ψ1) at sunrise also decreased, from −0.8 to −2.9 MPa. The drop in T and ψ1 indicates that most of the available water in the main root zone had been extracted during less than 30 days after the last rain. Decreasing values of wood thermal diffusivity with the progress of the dry season show that trees may use internally stored water when soil water stress is intense. The integrated T throughout the measurement period was used for estimation of total water uptake by the stand and for evaluation of the amount of water which was available to the trees following the last rain.
... The forest was created for landscaping and recreation and, since planting of the first trees in 1964, it has expanded to become the largest forest in Israel, covering an area of 3000 ha. The forest was established in spite of the professional wisdom of the time, which considered conditions to be too dry, even though over 90% of the planted trees were Aleppo pine, which is a native Mediterranean species whose physiological activity is high during the mild, wet period of winter and early spring (Schiller and Cohen, 1995). Although regarded as a pioneer drought-resistant species that can grow rapidly under a range of conditions, its natural range in Israel does not extend below the 400 mm rainfall isohyet (Zohary, 1962). ...
... The tree-level rate of transpiration was computed from: the heat pulse velocities measured at six depths in the xylem; the physical properties of the wet wood, as determined for P. halepensis by Schiller and Cohen (1995); the area of the conducting xylem sap wood; and the calibration coefficient. The calibration coefficient is the slope of the linear regression between the hourly or daily gravimetrically determined water loss and the calculated sap flux. ...
... The (Schiller and Cohen, 1995). ...
... Improving our understanding of the driving factors that control Aleppo pine responses to climatic conditions is important for managing the species and forecasting its responses to climate variability, extremes, and change. Relationships between various physiological traits and the abiotic environment have been reported in the literature for Aleppo pine [10][11][12]. Studies have demonstrated a strong stomatal regulation in the species and coordination between foliage water potential and stomatal conductance to balance water loss [13]. ...
... It has similarly been reported [40] that the decrease of night temperatures below 10 °C, accompanied by a photoperiod below 12 h, results in low photosynthetic rates in seedlings of Pinus strobus during autumn. The Amax of Mediterranean pines was also found to be controlled by the preceding night temperatures and internal factors during autumn and winter months [41], as well as by extreme preceding summer droughts [10]. Any photoinhibition effects on Amax during the colder months of 2008 can be excluded since Fv/Fm values remained high (above 0.84; data not shown) and the air temperature was not low enough to account for such a response [42]. ...
Aleppo pine (Pinus halepensis Mill.) is widespread in most countries of the Mediterranean area. In Greece, Aleppo pine forms natural stands of high economic and ecological importance. Understanding the species' ecophysiological traits is important in our efforts to predict its responses to ongoing climate variability and change. Therefore, the aim of this study was to assess the seasonal dynamic in Aleppo pine gas exchange and water balance on the leaf and canopy levels in response to the intra-annual variability in the abiotic environment. Specifically, we assessed needle gas exchange, water potential and δ 13 C ratio, as well as tree sap flow and canopy conductance in adult trees of a mature near-coastal semi-arid Aleppo pine ecosystem, over two consecutive years differing in climatic conditions, the latter being less xerothermic. Maximum photosynthesis (Amax), stomatal conductance (gs), sap flow per unit leaf area (Ql), and canopy conductance (Gs) peaked in early spring, before the start of the summer season. During summer drought, the investigated parameters were negatively affected by the increasing potential evapotranspiration (PET) rate and vapor pressure deficit (VPD). Aleppo pine displayed a water-saving, drought avoidance (isohydric) strategy via stomatal control in response to drought. The species benefited from periods of high available soil water, during the autumn and winter months, when other environmental factors were not limiting. Then, on the leaf level, air temperature had a significant effect on Amax, while on the canopy level, VPD and net radiation affected Ql. Our study demonstrates the plasticity of adult Aleppo pine in this forest ecosystem in response to the concurrent environmental conditions. These findings are important in our efforts to predict and forecast responses of the species to projected climate variability and change in the region.
... (3) High winter precipitations between years (n -1) and (n) decrease monocyclism. Plentiful soil water reserve sustains the early development of the first flush in spring (Serre 1976;Schiller and Cohen 1995) decreasing the probability of an early drought which would prevent the induction or elongation of following cycles. However, these winter rains have no influence on tricyclism frequency. ...
... (5) Abundant rainfall in August (n) increases tricyclism and decreases monocyclism. The earlier the summer water stress is released, the faster the later cycle develops (Serre 1976;Schiller and Cohen 1995). When rainfall arrives too late in autumn, no flush develops or the late cycle cannot be seen through successfully and remains short and needleless. ...
... As the soil dried out in the Spring, leading to a concurrent decrease of predawn water potential, transpiration was reduced by stomatal closure. A rather high threshold (between ±1.0 and ±1.5 MPa) of predawn water potential for stomatal closure was found (Fig. 3), in accordance with previous data on Aleppo pine (Scarascia Mugnozza 1980; Aussenac and Valette 1982; Melzack et al. 1985; Grundwald and Schiller 1988; Schiller and Cohen 1995; Tognetti et al. 1997 ). Under Mediterranean conditions , a prompt response of plants to drought is crucial in order to prevent severe tissue dehydration and foliage dieback (Tenhunen et al. 1987; Pereira and Chaves 1993). ...
... The capacity to refill may be crucial in determining the recovery of tree species following drought stress (Grace 1993). If reversible, xylem embolism may be, at least partially, useful: the cavitation of a proportion of vessels may cause a localised release of tension in the surrounding xylem (Dixon et al. 1984) and`sourcesand`sources' of water at high water potential may become available; Schiller and Cohen (1995) showed that Aleppo pine trees can use internally stored water when soil water is scarce. Leading to the increase of whole plant hydraulic resistance, xylem embolism may also contribute to limit water use as soil water is exhausted. ...
The present study was carried out to elucidate the response mechanisms of 50-year-old Pinus halepensis Mill. trees to a long-term and severe drought. The amount of water available to trees was artificially restricted for 12 months by covering the soil with a plastic roof. Over the short term a direct and rapid impact of drought was evident on the water relations and gas exchanges of trees: as the soil dried out in the Spring, there was a concurrent decrease of predawn water potential; transpiration was strongly reduced by stomatal closure. Seasonal changes in the water volume fractions of twig and stem xylem were observed and interpreted as the result of cavitation and refilling in the xylem. When droughted trees recovered to a more favourable water status, refilling of embolized xylem was observed; twig predawn water potentials were still negative in the period when the embolism was reversed in the twig xylem. A few months after the removal of the covering, no differences in whole plant hydraulic resistance were observed between droughted and control trees. Needle and shoot elongation and stem radial growth were considerably reduced in droughted trees; no strategy of trees to allocate carbon preferentially to the stem conducting tissues was apparent throughout the experiment. An after-effect of the drought on growth was observed.
... These measurements were taken on trees adjacent to those in which sap flow was being measured, and of similar stem diameter. The calibration coefficient found previously for other species was also used in the present study (Schiller and Cohen 1995). ...
... Distribution of the sap flow in the trunks of other measured trees followed a similar trend, but in large trees the sapwood area was greater than in small trees. Similar radial distributions of sap flow had been reported earlier for citrus (Cohen et al. 1981), Douglas fir (Cohen et al. 1985) and pine (Schiller and Cohen 1995). The diurnal course of sap flow followed the solar flux density. ...
... In recent years, heat-pulse technique has been widely used to measure tree transpiration, and more and more hydrologists and plant physiologists have been using this technique in their studies (e.g. Liu et al., 1993Liu et al., , 1997Barrett et al., 1995;Schiller and Cohen, 1995;Zang et al., 1996;Chen, 1997, 1998;Hall et al., 1998;Yan et al., 1999;Fernández et al., 2001;Gao et al., 2001;Gong et al., 2001;Bauerle et al., 2002;Sun et al., 2002;Giorio and Giorio, 2003;Wu et al., 2003;Yin et al., 2003;Zhang et al., 2003;Chang and Zhao, 2004). Schiller and Cohen (1995) measured the trunk sap flow of a pine forest in the mediterranean climate. ...
... Liu et al., 1993Liu et al., , 1997Barrett et al., 1995;Schiller and Cohen, 1995;Zang et al., 1996;Chen, 1997, 1998;Hall et al., 1998;Yan et al., 1999;Fernández et al., 2001;Gao et al., 2001;Gong et al., 2001;Bauerle et al., 2002;Sun et al., 2002;Giorio and Giorio, 2003;Wu et al., 2003;Yin et al., 2003;Zhang et al., 2003;Chang and Zhao, 2004). Schiller and Cohen (1995) measured the trunk sap flow of a pine forest in the mediterranean climate. Hall et al. (1998) studied the transpiration from coppiced poplar (Populus trichocarpa ð delroides) and willow (Salix burjatica). ...
Tamarix elongata Ledeb is a desert shrub found in the desert region of Northwest China and is commonly cultivated as a sand-holding plant in this region. To understand its water requirement and the effects of climate conditions on its growth, trunk xylem sap flows of irrigated 8-year-old Tamarix elongata Ledeb plants were monitored continuously with heat-pulse sap flow meters for the entire season. Soil moisture contents at 0–300 cm layer depth were also measured with a tube type time domain reflectometry (Tube-TDR). Meteorological factors, i.e. solar radiation, air temperature, relative humidity and wind speed were simultaneously monitored by an automatic weather station at the site. Daily and seasonal variations of the trunk sap fluxes and their correlations with the meteorological factors, reference evapotranspiration and soil moisture contents in the root-zone were analysed. The results indicated that frost influenced the trunk sap flux greatly under irrigated conditions, although the flux generally fluctuated with the variation of environmental factors and showed a mean trunk sap flux of 4·18 l d−1. There was a significantly exponential relationship between sap flux and the reference value of crop evapotranspiration, with a correlation coefficient of R2 = 0·7172. The sap flux also had a significant correlation with the soil water contents at a depth of 150–300 cm from soil surface (R2 = 0·5014). The order of the main meteorological factors affecting the sap flux of Tamarix elongata Ledeb trees was solar radiation > air temperature > vapour pressure deficit > relative humidity > wind speed. Copyright © 2007 John Wiley & Sons, Ltd.
... These measurements were taken on trees adjacent to those in which sap flow was being measured, and of similar stem diameter. The calibration coefficient found previously for other species was also used in the present study (Schiller and Cohen 1995). ...
... Distribution of the sap flow in the trunks of other measured trees followed a similar trend, but in large trees the sapwood area was greater than in small trees. Similar radial distributions of sap flow had been reported earlier for citrus (Cohen et al. 1981), Douglas fir (Cohen et al. 1985) and pine (Schiller and Cohen 1995). The diurnal course of sap flow followed the solar flux density. ...
Expanding the area of tree plantations in the Negev desert of Israel requires prior quantification of the water resources
in small watersheds. Combined hydrological and physiological measurements were used to study a “liman” (floodwater irrigated
plot) in the Negev highlands, where Eucalyptus and other tree species are grown successfully. The amount of water flowing into the liman, surplus water flowing out of the
liman, temporal soil moisture distribution, and water uptake by the trees were determined. Depending on rainfall intensity
and distribution during the season, the liman received 2 – 3 times the total seasonal rainfall. Although the study was conducted
during a year with a negligible amount of rainfall, the transpiration rate was closely correlated with potential transpiration
throughout the year. The amount of water extracted from the soil was less than the time-integrated transpiration rate from
the trees, suggesting that a water source other than soil water storage was available to the trees. We suggest that the trees
extracted water from the rock fractures and/or utilized the lateral flows over the rock/soil interface.
... Whole tree estimates of water use are becoming increasingly important in forest science (Wullschleger et al. 1998). Forest hydrologists rely on such information to help resolve issues of water resource management (Schiller, Cohen 1995;Loustau et al. 1996), as well as to evaluate the role of transpiration in forest and woodland hydrology (Barrett et al. 1996;Kupec, Deutscher 2017). The effect of transpiration has also been linked to intra-daily variations in streamflows in forest stands, although, so far, there is no generally accepted model to explain how streamflow declines https://doi.org/10.17221/191/2022-JFS ...
Sap flow represents water transport from roots to leaves through the xylem and is used to describe tree transpiration. This paper proposed and tested a procedure to estimate sap flow by calculating global radiation in a digital model of the tree canopy surface obtained by unmanned aerial vehicle imaging. The sap flow of nine trees was continuously measured in the field. In the digital surface model, individual canopies were automatically delineated, their parameters were determined and the global radiation incident on their surface on specific days was calculated. A polynomial relationship was found between sap flow and the calculated incident solar radiation during the morning hours with a coefficient of determination of 0.98, as well as a linear relationship between the decrease in radiation and sap flow during the afternoon with a correlation coefficient of 0.99. Using the Random Forest machine learning method, a model predicting the sap flow of the trees was created based on the global radiation and canopy parameters determined from the digital surface model of tree canopies. The resulting model was deployed on additional days and compared to field measurements of sap flow, achieving a correlation coefficient of 0.918. In addition, two linear regression models were created for a tree group, achieving coefficients of determination of 0.66 and 0.90.
... The species benefited from periods of high available soil water (normally autumn to spring) [126,127]. These drought episodes do no influence directly moisture content at branches and leaf level [58,128], so that direct measurement of LFMC% of Mediterranean pines should not be considered as the only appropriate indicator to monitor wildfire risk. Moreover, strong drought conditions and consequently high evapotranspiration carries physiological responses in branches and needles of Pinus halepensis. ...
Pinus halepensis forests, as Mediterranean-type ecosystems, are subject to high levels of wildfire risk in times of drought, with meteorological conditions of water stress and very high temperatures, mainly in summer. Considering the difficulty of knowing the phenological state of this species, the objective of this research was to evaluate the possibility of implementing the electrical responses (voltage and short-circuit current) as a variable in fire risk management models, compared to live fuel moisture. On the one hand, the obtained results demonstrate non-significant differences between the moisture content of the different fractions of the living branches (base and half of the branch and live fuel), even in times of drought with hydric stress and very high temperatures. Live fuel moisture of Pinus halepensis does not show significant seasonal variations under the influence of extreme fire risk factors. For this reason, it should be complemented with other variables for fire risk management models. On the other hand, the differences registered in the electrical signal show oscillations with significant variations, which are strongly correlated with the periods of extremely favourable meteorological conditions for wildfires. So, the voltages measured show ranges that correspond with great accuracy to the FWI. Voltage variation is dependent on the hydraulic dynamic plant behaviour and a result of the physiological response of pine trees to abiotic stress of drought. It is an easy-to-measure electrical parameter as well as a very reliable indicator with a high correlation with wildfire risk. Thus, electrical responses could add more knowledge about the phenological state of the trees in dependence on stress climatic conditions, allowing integration of these variables in the preventive wildfire modelling and management.
... Accurate estimation of tree water is important for rational water use, forest production, climate change, and ecosystem functions (Asbjornsen et al., 2011;Pieruschka et al., 2010). Such information helps to resolve issues of water resource management (Barrett et al., 1996;Cienciala and Lindroth, 1995;Lindroth et al., 1995;Loustau et al., 1996;Schiller and Cohen, 1995). Estimation of tree water use is important for better management of catchments that supply water to people (Chiew et al., 2009). ...
Hydrological and vegetation models, with the help of various micro-meteorological methods, are widely used to calculate water fluxes. Correctly estimating these fluxes requires accurate transpiration measurements. Tree water use is known to be influenced by many factors but there is scant literature on the factors influencing tree water use in tropical forest areas. This study presents the first systematic review of research into tree water use in the tropics. The aim of the study was to understand the research trends and the influence of tree functional traits on water use. The study found a clear bias in research focus on geographic area and species group selection. The results indicate that water use increases in tropical tree species with increased tree size, sapwood area, leaf area index, and seed mass. On the other hand, wood density is negatively correlated with tree water use. Season is highly significant in explaining variations in tree water use, as was leaf phenology. Tropical trees’ water use significantly increases during the dry season. Native trees use more water than exotic trees species. Brevi-deciduous trees uptake significantly more water than evergreen and deciduous species during the dry season. These tree traits and their relationship with water use can provide a tool for better understanding ecohydrological processes, which can support improved plantation management and conservation of water resources. This systematic review identified research gaps that, if addressed, could inform the development of hydrological and vegetation models for the efficient management of water resources.
... Also, tree transpiration can be up-scaled to stand transpiration by estimating stand basal area of conducting sapwood of each tree. In Mediterranean pine forests, several studies monitored transpiration with an hourly or half-hourly resolution (Schiller and Cohen, 1995;Fernandes et al. 2016;Eliades et al. 2018), but the main limitation of sap flow measurements is that only accounts for transpiration of the individuals measured. For correct estimations of shrubs transpiration and evaporation from the soil other type measurements or estimations are needed (i.e. ...
Water scarcity is the main limiting factor for Mediterranean pine forests and its availability conditions both forest functionality and ecosystem services. In a global change context, the predicted increments in aridity in these areas render the need for in-depth ecohydrological knowledge. In this chapter, we review the main functional characteristics of Mediterranean pine forests for coping with drought episodes and aridity, their water-related interactions with soil and atmosphere, and current and predicted water balance responses to hydrologically oriented forest management. Mediterranean pine forests contribute poorly to runoff and deep percolation, while tree transpiration often represents about 50% of total precipitation, and actual evapotranspiration (ETa) values can reach up to 90–100%. Under certain conditions, the ETa contribution to atmospheric water vapor might play a key role in forming summer storms, which represent a significant amount of total precipitation. However in dense pine forests, some management practices, such as conveniently applied thinning, are needed to improve the availability of water resources for ecosystems and society by reducing ETa and increasing deep percolation.
... As mentioned above, it disturbs macropores continuity and therefore, in terms of soil water conservation, it is beneficial during the drying phase since it hinders evaporation. Furthermore, under tillage management, top layer drying is controlled only by evaporation whereas, under weed cover, it also depends on plant transpiration which can be significant during the dry season (Schiller and Cohen, 1995). Here the measurements of soil moisture were conducted during a typically dry Mediterranean summer when soil moisture is at its minimum. ...
Soil erosion is a threat for the sustainability of agriculture and severely affects the Mediterranean crops. Olive groves are among the rainfed agriculture lands that exhibit soil and water losses due to the impact of unsustainable practices such as conventional tillage and herbicides abuse. To achieve a more sustainable olive oil production, alternative, greener crop management practices need to be tested in the field. Here, a weed cover (CW) treatment is tested at an olive tree plantation that has undergone conventional mechanical tillage for 20 years and results were compared against an adjacent control plantation that maintained tillage as a weed control strategy (CO). Both plantations were under the same tillage management for centuries and macroscopic analysis confirms they are otherwise comparable. Compared to the CO, where tilled soil cover was zero, 20 years of CW (weeds cover 64%; litter cover 5%) had led to significantly higher values of soil bulk density and soil organic matter. Results from rainfall simulation experiments at 55 mm h⁻¹ on 0.25 m² plots under CO (N = 25) and CW (N = 25) show that as a result of the improved soil structure, CW (i) reduced soil losses by two orders of magnitude (140 times), (ii) decreased runoff yield by one order of magnitude (from 2.65 till 27.6% of the rainfall), (iii) significantly reduced runoff sediment concentration (from 18.6 till 1.43 g l⁻¹), and (iv) significantly delayed runoff generation (CO = 273 s; CW = 788 s). These results indicate that weed cover is a sustainable land management practice in Mediterranean olive groves and promotes sustainable agriculture production in mountainous areas under rainfed conditions, which are typically affected by high erosion rates such those found in the CO plots. Due to the spontaneous recovery of plant cover, we conclude that weed cover is an excellent nature-based solution to increase in the soil organic matter content and soil erosion reduction in rainfed olive orchards.
... Still, to our knowledge, limited information is available about the radial patterns of sap flux and its seasonal and diurnal fluctuation, in relation to climate, in P. halepensis at eastern Mediterranean ecosystems. Mostly, if not solely, the relevant literature refers to Aleppo pine plantations in Israel, such as the works of Schiller and Cohen [40] who first reported on the radial profile of sap flux in this species and Cohen et al. [35] who studied the radial sap flux gradients of Aleppo pines under different climatic conditions. ...
Research Highlights: The radial gradient of sap flux density (Js) and the effects of climatic factors on sap flow of Aleppo pine were assessed at different time scales in an eastern Mediterranean ecosystem to improve our understanding of the species water balance. Background and Objectives: Aleppo pine’s sap flow radial profile and responses to environmental parameters in the eastern Mediterranean were, to our best knowledge, originating to date from more arid planted forests. Information from natural forests in this region was lacking. Our objectives were to (a) determine the species’ radial variability in Js on a diurnal and seasonal basis and under different climatic conditions, (b) scale up to tree sap flow taking into account the radial profile of Js and (c) determine the responses of Aleppo pine’s sap flow over the year to climatic variability. Materials and Methods: Js was monitored in Aleppo pine in a natural forest in northern Greece with Granier’s method using sensors at three sapwood depths (21, 51, and 81 mm) during two periods differing in climatic conditions, particularly in soil water availability. Results: Js was the highest at 21 mm sapwood depth, and it declined with increasing depth. A steeper gradient of Js in deep sapwood was observed under drier conditions. The same patterns of radial variability in Js were maintained throughout the year, but the contribution of inner sapwood to sap flow was the highest in autumn when the lower seasonal Js was recorded in both study periods. Not taking into account the radial gradient of Js in the studied Aleppo pine would result in a c. 20.2–27.7 % overestimation of total sap flow on a sapwood basis (Qs), irrespective of climatic conditions. On a diurnal and seasonal basis, VPD was the strongest determinant of sap flux density, while at a larger temporal scale, the effect of soil water content was evident. At SWC > 20% sap flow responded positively to increasing solar radiation and VPD, indicating the decisive role of water availability in the studied region. Moreover, in drier days with VPD > 0.7 KPa, SWC controlled the variation of sap flow. Conclusions: There is a considerable radial variability in Js of the studied Aleppo pine and a considerable fluctuation of sap flow with environmental dynamics that should be taken into account when addressing the species water balance.
... The model predicts that water uptake can reach zero when the root-soil layers approach desiccation. This extreme forest water stress during the summer and autumn was reported by Schiller and Cohen (1995) and Baraket et al. (2019) . The deeper water depletion in DS compared to DZ is highly dependent upon the type of soil. ...
Aleppo pine (Pinus halepensis Mill.) is one of the most drought-tolerant pine species and it is distributed over large drought-prone Mediterranean regions. The determination of the water balance of the soil-crop-climate and its fluctuation is difficult to achieve, due to the spatial variation in site conditions (Schiller and Cohen, 1998). The objectives of this study are to (1) estimate crop water requirements (ETc) and actual evapotranspiration (ETa) of Tunisian Aleppo pine and (2) study the impact of climate change on water balance, using the WEAP-MABIA Module (Yates et al.,2005a; 2005b; Jabloun and Sahli, 2012) based on the FAO Irrigation and Drainage publication 56 (Allen et al., 1998).
... The model predicts that water uptake can reach zero when the root-soil layers approach desiccation. This extreme forest water stress during the summer and autumn was reported by Schiller and Cohen (1995) and Baraket et al. (2019) . The deeper water depletion in DS compared to DZ is highly dependent upon the type of soil. ...
https://repository.incredibleforest.net/oppla-factsheet/20188
... Les physiologistes s'intéressent, entre autre, aux mécanismes de la régulation stomatique (Hinckley et al. 1994 ;Meinzer et al. 1995), ou encore aux rôles des réserves d'eau dans les différentes organes des arbres dans la régulation des flux . Les forestiers comptent sur ces informations pour les aider à résoudre les problèmes de gestion de la ressource en eau (Schiller et Cohen, 1995 ;, ou pour évaluer le rôle de la transpiration dans le bilan hydrologique des peuplements forestiers (Barrett et al. 1996) ou encore pour quantifier les besoins en eau des forêts (Cienciala et Lindroth 1995 ;Goldhamer et al. 2003 ;Intrigliolo et Castel 2004 ;Steppe et al. 2008.) Précisément, notre travail a porté sur le hêtre (Fagus sylvatica L.), espèce feuillue européenne majeure, qui occupe une large place dans la filière-bois en France. ...
... These measurements are very useful for examining the effect of changes in forest structure on stand water balance and for providing information on the physiological regulation of transpiration. Forest ecologists can utilize those estimates of tree water uptake derived from sap flow to evaluate the role of transpiration in forest hydrology (Barrett et al., 1996;Ewers et al., 2002), and to address issues of water resource management (Schiller and Cohen, 1995;Oishi et al., 2008). For the Qinghai spruce, the sap flow velocity was measured with the heat pulse method, and was overestimated by about 5.6% (Chang et al., 2014a). ...
... However, this was not the case in the drier year of 2015, when the water potential of Aleppo pine was lower and less variable, and all trees approached the reported threshold for stomatal closure (between -2.0 and -2.8 MPa; see e.g. Klein et al., 2011;Klein et al., 2013;Schiller & Cohen, 1995;Tognetti et al., 1997). On the other hand, the high water potential and depleted isotope values of oaks during 2013 point to the access to deep water reservoirs where water is more easily available, as has been reported for other deep-rooting species (Filella & Peñuelas, 2003b;Flanagan et al., 1992;Grossiord et al., 2016). ...
Understanding inter- and intra-specific plant interactions and competition over water is challenging because of the lack of effective approaches for accessing and monitoring root distribution and activity. In this context, stable isotopes are excellent eco-hydrological tracers that allow characterizing the dynamics of water uptake patterns in trees and shrubs. Here, we studied biotic interactions for water uptake between two typical Mediterranean tree species, Aleppo pine (Pinus halepensis) and holm oak (Quercus ilex), coexisting in a mixed forest. We measured stable isotope composition (18O and 2H) of xylem water in all trees found in the studied stand during one growing season, covering an exceptionally long summer drought and subsequent recovery. We applied point-process statistics together with stand density information to evaluate tree-to-tree interactions for water use. In pines, we observed a clear uncoupling between soil and xylem water isotope composition after two months of persistent drought. Conversely, the isotope composition of xylem water in oaks tracked observed changes in the soil during the first two months of drought, but began to depart from soil values after three months. These results suggest that during drought the oaks were able to keep active for longer using alternative soil water sources, not available for the pines. Point-process statistics revealed more positive isotope compositions at distances below 4-6 m, but only between con-specific individuals (i.e. pine-pine, oak-oak). These intra-specific responses were first seen in the pines (after two months of drought) and subsequently in oaks (after three months), coinciding with the onset of soil-xylem uncoupling for each species. On the other hand, the isotope composition of individual oaks decreased with increasing neighbor pine density, but increased in response to oak density. Conversely, the pines showed more positive values with increasing oak density. Our results suggest that the use of shallow water in oaks is limited by the presence of pines, which force them to shift to deep-soil water use, whereas pines have more restricted access to deep water in the presence of oaks, leading to more positive isotope values. According to the dynamics of interaction patterns, we conclude that inter-specific differences in pine-oak mixed forests hold two components: a static, spatial component determined by root distribution, and a dynamic, physiological component related to water uptake capacity within the soil profile.
... Direct measurements of tree sap flow are very useful to examine the effect of changes in forest structure on stand water balance and to provide information on the physiological regulation of transpiration. Forest ecologists can utilize those estimates of tree water uptake derived from sap flow to evaluate the role of transpiration in forest hydrology (Barrett et al., 1996;Ewers et al., 2002), to quantify the water requirements of coexisting species (Granier et al., 1996;Oren et al., 1998), and to address issues of water resource management (Schiller and Cohen, 1995;Oishi et al., 2008). For example, previous studies have suggested that under a forest soil water deficit, management techniques such as tree thinning or controlling shrub layers to reduce competition for water may be necessary in some stands to increase water availability for plant growth (Breda et al., 1995;Moore et al., 2004;Domec et al., 2012). ...
Our objectives are (1) to compare tree sap flux density (Js in g cm�2 d�1) and stomatal conductance (Gs in mmolm�2 s�1) across five dominant species, red maple (Acer rubrum), sweetgum (Liquidambar styraciflua), tulip poplar (Liriodendron tulipifera), loblolly pine (Pinus taeda), and oak species (Quercus spp.), (2) to quantity riparian buffer stand transpiration (Es in mmd�1), and (3) to link riparian buffer Es of residual trees to stream discharge. In June 2010, the above species were instrumented with sap flow sensors in a pair (HF1 and HF2) of 12 hectare gauged watersheds. HF1 was clearcut, leaving a 15.2-m riparian buffer around the stream, and HF2 was the reference. Trees were harvested in the riparian buffer reducing HF1 riparian buffer basal area by 27%. The riparian buffer growing season net radiation increased from 11.9Wm�2 preharvest to an average of 24.3Wm�2 postharvest. HF1 stream growing season discharge increased dramatically (150%) from the preharvest to postharvest period. HF1 2010 preharvest growing season soil moisture was 22.5%. HF1 postharvest growing season soil moisture was 28.5% in 2011, 26.5% in 2012, and 27.2% in 2013. HF2 canopy cover, energy input, and soil moisture showed little change over the same period. From preharvest to postharvest, mean daily growing season Js of trees in HF1 increased in all species. A reduction in HF1
Gs was less evident over the study vapour pressure deficit range in loblolly pine, red maple, and tulip poplar than in oak and sweetgum during the postharvest period. HF1 residual trees in the riparian buffer used 43% more water in growing season postharvest (314 mm) than growing preharvest (220 mm) period. This resulted in an 8% reduction in stream discharge because of an increase in riparian buffer Es. Although clearcutting increased stream discharge, we conclude that the increase in transpiration by the residual trees in the riparian buffer will, at least, partially mitigate the hydrologic effects of forest removal through increased transpiration.
... Direct measurements of tree sap flow are very useful to examine the effect of changes in forest structure on stand water balance and to provide information on the physiological regulation of transpiration. Forest ecologists can utilize those estimates of tree water uptake derived from sap flow to evaluate the role of transpiration in forest hydrology (Barrett et al., 1996;Ewers et al., 2002), to quantify the water requirements of coexisting species (Granier et al., 1996;Oren et al., 1998b), and to address issues of water resource management (Schiller and Cohen, 1995;Oishi et al., 2008). For example, previous studies have suggested that under a forest soil water deficit, management techniques such as tree thinning or controlling shrub layers to reduce competition for water may be necessary in some stands to increase water availability for plant growth (Bréda et al., 1995;Moore et al., 2004;Domec et al., 2012). ...
Our objectives are 1) to compare tree sap flux density (Js in g cm-2 d-1), and stomatal conductance (Gs in mmol m-2 s-1) across five dominant species, red maple (Acer rubrum), sweetgum (Liquidambar styraciflua), tulip poplar (Liriodendron tulipifera), loblolly pine (Pinus taeda), and oak species (Quercus spp.), 2) to quantity riparian buffer stand transpiration (Es in mm d-1), and 3) to link riparian buffer Es of residual trees to stream discharge. In June 2010, the above species were instrumented with sap flow sensors in a pair (HF1 and HF2) of 12 hectare gauged watersheds. HF1 was clearcut, leaving a 15.2 meter riparian buffer around the stream and HF2 was the reference. Trees were harvested in the riparian buffer reducing HF1 riparian buffer basal area by 27%. The riparian buffer growing season net radiation increased from 11.9 W m-2 preharvest to an average of 24.3 W m-2 postharvest. HF1 stream growing season discharge increased dramatically (150%) from the preharvest to postharvest period. HF1 2010 preharvest growing season soil moisture was 22.5%. HF1 postharvest growing season soil moisture was 28.5% in 2011, 26.5% in 2012 and 27.2% in 2013. HF2 canopy cover, energy input, and soil moisture showed little change over the same period. From preharvest to postharvest, mean daily growing season Js of trees in HF1 increased in all species. A reduction in HF1 Gs was less evident over the study vapor pressure deficit range in loblolly pine, red maple, and tulip poplar than in oak and sweetgum during the postharvest period. HF1 residual trees in the riparian buffer used 43% more water in growing season postharvest (314 mm) than growing preharvest (220 mm) period. This resulted in an 8% reduction in stream discharge due to an increase in riparian buffer Es. Although clearcutting increased stream discharge, we conclude that the increase in transpiration by the residual trees in the riparian buffer will, at least, partially mitigate the hydrologic effects of forest removal through increased transpiration. This article is protected by copyright. All rights reserved.
... Whole-tree and whole-stand water use estimates are of great importance in different aspects of forest science (Wullschleger et al. 1998), which is shown by the fact that they are for instance utilised to resolve water resource management issues (Schiller and Cohen 1995;Dragoni et al. 2005) or to evaluate the role of transpiration in forest hydrology (Barrett et al. 1996;Roberts 2007). ...
Key message
Our study shows that sap flow in
Avicennia marina
varies significantly throughout the sapwood and that spatial patterns in sap flux density are dependent on meteorological conditions.
Abstract
Sap flux density measurements are used worldwide as a relatively inexpensive means to provide estimates of whole-tree and whole-stand water use in forest ecosystems. However, erroneous upscaling from point measurements to the entire sapwood area remains an issue, since sap flow is hardly ever constant throughout the tree. In this study, two widely used sap flow methodologies (the Heat Ratio or HR method and the Heat Field Deformation or HFD method) are used to assess radial and azimuthal variations in sap flux density in three mature trees of the mangrove species Avicennia marina in Brisbane, Australia. The genus Avicennia is characterised by secondary growth via successive cambia, resulting in an atypical sapwood pattern of xylem patches braided with phloem strings. Water use estimates were calculated in different ways. At first, spatial variation was ignored when upscaling from point measurements. Then, radial and azimuthal variations were incorporated subsequently by measuring at different depths and aspects around the tree. Ignoring azimuthal variation led to over- or underestimations of up to 102 %, while radial variation accounted for discrepancies of up to 25 %. Furthermore, the influence of changing meteorological conditions was assessed, which showed that radial profiles changed in shape during rain events, such that maximum sap flow rates occurred at different depths compared to dry periods. Our study thus indicates that spatial variation in sap flux density is highly unpredictable in A. marina due to its hydraulic architecture, and that changing meteorological conditions alter the pattern of this variation. These two factors should be accounted for when assessing whole-tree water use.
... It was previously shown that the proportion of annual rainfall transpired by a planted P. halepensis stand increases with progress from a relatively humid to a relatively arid region. In a region having 280-mm average annual rainfall-Yatir Forest, adjacent to our southern sites-transpiration of the P. halepensis trees amounted to 80 % of annual rainfall (Schiller and Cohen 1998), compared with 69 % in a 700-mm year −1 region (Ramat Hanadiv) (Schiller and Cohen 1995). Subsequent studies in Yatir Forest found lower proportions: 49-66 % in 200449-66 % in -200649-66 % in (Klein et al. 2013Ungar et al. 2013);37 % in 2007(Raz-Yaseef et al. 2010 and 57 % in 2010 (Klein et al. 2014). ...
We investigated forest responses to global warming by observing: (1) planted Pinus halepensis forests, (2) an aridity gradient—with annual precipitation (P) ranging from ~300 to ~700 mm, and (3) periods of wet and dry climate that included the driest period during at least the last 110 years. We examined: (1) how the length of climatic integration periods to which trees are most responsive varies in space and time, (2) the extent to which competition modulates growth decline during drought (2011) and subsequent recovery (2012) years. The temporal scale of rainfall that was most influential on growth shortened in progressing southward, and in the drier than in the wetter period. Long-term underground water storage, as reflected in the relationship of growth to multiple-year rainfall, remained significant up to the point where P ≈ 500 mm. Under drier conditions (P < 500 mm) in both space and time, influential rainfall scales shortened, probably reflecting a diminishing role of water storage. These drier locations are the first from which the species would be likely to retreat if global warming intensified. Competition appeared to set an upper limit to growth, while growth variation among individual trees increased as competition-intensity decreased. That upper limit increased in 2012 compared with 2011. The observed insensitivity of slow-growing trees to competition implies that mortality risk may be density independent, when even any potential for higher soil moisture availability in open stands is lost to evapotranspiration before it can benefit tree growth.
... Estimates of water use by plants are becoming increasingly important to forest science. Researchers apply water use estimates to predict the control of canopy conductance and transpiration [14,26,46], where this information is useful to help troubleshooting the water resources management [37,24,32], the role of transpiration in native forests [3] and to quantify the demand for water in short rotation forests and in plantations of Eucalyptus sp [10,40,41]. ...
This study aimed at characterizing leaf ecophysiological behavior of two clones of Eucalyptus sp related to environmental variables such as photosynthetically active radiation (Qleaf) and vapor pressure deficit of the atmosphere (VPD) at two scales (pot and plot), as well as promoting a change of information obtained from a smaller scale to a higher one. The study was conducted at UNICAMP, Sao Paulo, Brazil. For data transpiration (E) and stomata conductance (Gs) porometry an infrared gas analyzer was used. Local environmental variables associated with Qleaf and VPD were recorded by the automatic station of CEPAGRI/UNICAMP installed at the study site. At all scales, individuals were under the same range of predawn leaf water potential (0 to -0.5 MPa). The scaling of information was performed by applying the ecophysiological model, to simulate the E and Gs as a function of Qleaf and VPD. The exchange of E and Gs were consistently above the plot scale when compared to the pot scale for the two clones under study. The proposed models were effective in the extrapolation of E and Gs between different scales, but the best results were obtained in the relations E, Gs and Qleaf.
... Following this principle, we could draw the conclusion that detected unusual increase in photosynthetic activity of Aleppo pine and holm oak in 2005, emerged as a result of optimal climatic setting with high irradiance and sufficient water availability, most probably contributes to an increase of carbon reserve in support of the new enhanced needle growth in successive dry summer. In addition to storing carbon, Aleppo pine can internally store water which can be later used when soil water is scarce (Schiler and Cohen, 1995). However, according to Breda et al. (2006) water storage capacity in trees is rather negligible when compared to the amount of water transpired every day; it could sustain only 1-2 days of transpiration. ...
... Measuring leaf or twig xylem water potential is among the several methods for estimating plant water content (Levitt, 1980;Borghetti et al., 1998;Chuvieco et al., 2002). Indeed, a number of studies for low elevation Mediterranean tree or shrub species of TMVB-MMVB document the significant drop in water potential (and thus moisture content) as drought increases within a year or between years (Otieno et al., 2006 for Quercus suber;Martínez-Vilalta et al., 2003 for Arbutus undo and Quercus ilex.; Schiller and Cohen, 1995;Borghetti et al., 1998 for Pinus halepensis). All the above are in support of our original hypothesis. ...
Deep-rooted plants (phreatophytes) survive the Mediterranean dry season by utilizing rainfall accumulating belowground from past rainfall events. This adaptation potentially influences their moisture content when acting as living fuel for forest fires. Other shallow-rooted herbaceous plants (therophytes) survive drought as seeds, acting as very flammable fine fuel because their biomass totally desiccates in summer. We investigated the effects that these ecological adaptations (functional-structural) may have in shaping the fire regime in the Mediterranean by: (a) separating precipitation (P) and temperature (T) to longer (entire hydrological year) and shorter (seasonal and monthly) temporal scales, (b) correlating the above with burnt area (BA) and number of fires (NF) from the thermo- and medio-Mediterranean vegetation belts (TMVB-MMVB; the most arid and flammable belts), (c) comparing correlations with those from regions of more moist climate and related vegetation. Spatial scales ranged from provinces of Greece and southern France, to combined data for Greece, Italy, France and Spain. We focused on 1985–2008 (and its sub periods); one of the driest periods for the Mediterranean, with large fire occurrence. Clearly, where the TMVB-MMVB prevail P outweighs T in determining BA, having a rather equal contribution in explaining NF. In the driest areas increased P accumulating from autumn, but mostly supplied in winter, suppressed BA the following summers, likely because it improved moisture content in pheatophytic vegetation (living fuel). This impact was reduced in more humid regions, where fires suppression was related to increased summer P that makes fuel damp. In contrast, increased late-spring P promoted BA and NF likely by increasing biomass accumulation from therophytic vegetation (fine fuel). Indications for the resistance of pheatophytic plants to fire following wet winters are already evident in the recent fire regime of northern Mediterranean countries. This function may strengthen under a drier climate and could assist early fire-danger prognosis.
... Lagergren and Lindroh (2002) working on Scots pine (P. sylvestris) observed a steep decline in the sap flow rates with increasing vapour pressure deficit (VPD) of the air while (Schiller and Cohen, 1995) observed that the transpiration rates of P. halepensis dropped at a rate as much as 0.5 mm d À1 (on cloudless days) after the last rains. In our study however, VPD levels exceeding 3.50 kPa were prevalent during the dry summer and autumn months and this possibly contributed to the lowering of the transpiration rates. ...
Self-established stands of alien invasive pine trees are common in many parts of South Africa and elsewhere. They mainly invade non-riparian settings but sometimes invade riparian habitats. There are clear visual differences in the physical attributes of trees that occupy riparian and non-riparian zones. We have little information whether the differences between trees growing in these contrasting habitats reflect their water-use. The goal of this study was to establish the water-use of alien invasive pines growing adjacent to and away from a perennial stream, and to determine the driving factors behind the variations. The study was conducted in a self-established 20-year-old mixed pine forest occupied by roughly equal proportions of Pinus pinaster and Pinus halepensis. Individual tree transpiration rates were measured using the heat pulse velocity (HPV) sap flow method. Evapotranspiration (ET) from entire stands was determined from the surface energy balance equation using sensible heat flux data collected using a boundary layer scintillometer and measurements of the available energy (net radiation – soil heat flux). A simple two-layer model in which the stand ET was calculated as the algebraic sum of the outputs from transpiration (E) and soil evaporation sub-models was evaluated at the two contrasting sites. Annual transpiration and ET rates were higher in the riparian zone at 980 and 1417 mm compared to 753 and 1190 mm, respectively in the non-riparian area. The model predicted stand transpiration fairly accurately for both sites (average R2 > 0.75), but was less accurate for evapotranspiration (average R2 < 0.70) due to the difficulties in simulating soil evaporation. No significant differences in sap velocities were found between trees at the two sites so the greater water-use of trees in the riparian zone was due to the larger basal area per stem. Based on the measured transpiration data we conclude that self-sown pine stands growing in riparian zones use at least 36% more water than those occurring in non-riparian settings justifying the high priority given to clearing invasive trees in riparian zones.
... In wet years, however, the advantage of the northern aspects may be realized. In such years the soil water content may be high enough to allow, for example, prolonged physiological activity on the northern aspects in spring and early summer (Klein et al., 2005; Schiller and Cohen, 1995). The contrast between northern and southern aspects will then appear, because cessation of physiological activity is reached faster in the latter. ...
... The Mediterranean pine ecosystems studied are characterized by lower soil water capacity (≅100 mm) and lower precipitation (≅ 600 mm·year –1 ), which is distributed mainly outside of the vegetative period. These characteristics, combined with an elevated vapor pressure deficit, make the soil water regime the major controlling factor for this type of ecosystem (Schiller and Cohen 1995, 1998; Borghetti et al. 1998; Nicault et al. 2001). In the MAIDEN model, soil water stress expresses its control over assimilation by reducing stomatal conductance (Misson 2004, eq. 6). ...
A process-based model (MAIDEN, modeling and analysis in dendroecology) is compared with statistical response functions to analyze the climate-growth relationship for two different species (sessile oak (Quercus petraea (Matt.) Liebl.) and Aleppo pine (Pinus halepensis Mill.)) growing in contrasting climates (temperate and Mediterranean). Growth data were obtained using dendroecological sampling procedures. Results obtained with both methods are consistent, but the MAIDEN model provides a more explanatory analysis than classical statistical tools. Analyses with MAIDEN indicate that oak stomatal conductance is sensitive to atmospheric vapor deficit, whereas precipitation and soil water deficit are not limiting factors in the study area. In contrast, the soil water regime is the major controlling factor of bole growth variability for Aleppo pine. The model shows that remobilization of the carbohydrate reserves in spring is of major importance for leaf and root expansion, and it affects the subsequent bole increment of oak. Because the amount of carbon that can be mobilized in spring is linked to carbon stored the previous year, these processes explain how the growth of oak trees is linked in this way from one year to the next. In contrast, the MAIDEN model shows that carbohydrate-reserve dynamics, phenology, and bole growth are less connected for Aleppo pine trees.
... Sap flow measurements are the most useful technique for obtaining transpiration data, because other techniques such as the eddy covariance method cannot provide reliable measurements during and after rainfall (Mizutani et al., 1997); in contrast, sap flow measurements have the advantage that the instrumentation can be easily installed at accessible points on the tree, such as at the base of the stem. Since 1990s, the sap flow technique has been widely used to measure plant transpiration (e.g., Barrett et al., 1995;Schiller and Cohen, 1995;Edwards and Jèermák, 1996;Hall et al., 1998;MacNish et al., 2000;Green et al., 2003;O'Brien et al., 2004;Nicolas et al., 2005;Chang et al., 2006;Kume et al., 2006;Kigalu, 2007;McDowell et al., 2008;Xia et al., 2008;Yue et al., 2008). Sap flow data are generally obtained using two main measurement methods to quantify plant transpiration (Swanson, 1994;Kigalu, 2007): the heatpulse velocity, based on heat compensation theory, can measure the upstream xylem sap velocity and sapflow rate within a stem section (Dugas, 1990), but this technique is invasive and may damage the plant; the stem heat-balance method is less invasive, and estimates sap velocity (Steinberg et al., 1989;Ishida et al., 1991;Batho et al., 1994;Boersma and Weibel, 1995) using a small heater wrapped around the plant's stem or a branch to supply heat to that section of the plant, and therefore creates less damage to the plants (Kigalu, B. LIU, W. ZHAO AND B. JIN 2007). ...
A case study was conducted in a desert–oasis ecotone in the middle of China's Heihe River basin to reveal the response of sap velocity to environmental variables. We measured sap flow in the branches and stems of desert shrubs (Nitraria sphaerocarpa and Elaeagnus angustifolia) using sap-flow gauges, and simultaneously measured environmental variables at the study site. The relationships between sap velocity and the environmental variables were analysed using redundancy analysis. The diurnal variation in sap velocity was best described by a bimodal curve, except for the branches of N. sphaerocarpa, which followed a unimodal curve. Sap flow began about 1 h earlier in the branches than in the stems. The dynamic variations in sap velocity were remarkably similar for the two species at a given position (stem vs branch) but differed between the two positions for each species. Redundancy analysis and Kendall's tau analysis indicated that precipitation had the greatest influence on sap velocity in the stem, whereas precipitation duration significantly affected sap velocity in the branches of the desert shrubs (R2 = 0·85 and 0·73, respectively). The variation in sap velocity could be described by a multiple linear regression against the meteorological variables, and the simulated value was significantly linearly correlated with the measured value (0·861 ≤ R2 ≤ 0·938, P < 0·0001). Copyright © 2010 John Wiley & Sons, Ltd.
... Since the 1990s, a modified heat pulse technique has been widely used to measure tree transpiration (e.g. Barrett et al., 1995;Schiller and Cohen Y, 1995;Edwards and Jèermák, 1996;Hall et al., 1998;MacNish et al., 2000;Fernández et al., 2001;Gong et al., 2001;Roberts et al., 2001;Ffolliott et al., 2003;Giorio and Giorio, 2003;Green et al., 2003;NN Zhang et al., 2003;Kluitenberg and Ham, 2004;Williams et al., 2004;Nicolas et al., 2005). The heat pulse technique based on the heat compensation theory can measure the xylem upstream sap velocity and sap flow rate under natural conditions and thus determine the tree canopy transpiration. ...
The aim of this study was to obtain the diurnal and seasonal changes of trunk sap flow in desert-living Caragana korshinskii so as to understand its water requirement and ecological significance. The experiment was carried out with 15-year old Caragana korshinskii grown in north-west China under natural conditions. Heat pulse sensors based on the heat compensation theory were applied to measure the trunk sap flow, and soil moisture content at 0–300 cm layer, using tube-type time domain reflectometry (Tube-TDR). The solar radiation, the maximum and minimum air temperatures, relative humidity, wind speed, wind direction and precipitation were measured at a standard automatic weather station. The diurnal and seasonal variations of sap flow rate, the sap velocity at different positions in the trunk and the sap flow rate under different weather conditions were analysed. And the correlation between the sap flow rate and the meteorological factors was also analysed. Results showed that the trunk sap flow varied regularly in the diurnal term and the sap flow velocity decreased with the probe-inserted depth into the sapwood. Magnitude of sap flow changed considerably between sunny and rainy days. The order of the main meteorological factors affecting the sap flow rate of Caragana korshinskii shrubs were: vapour pressure deficit > solar radiation > air temperature > wind speed. The close correlation between daily sap flow rate and meteorological factors in the whole growing season can be used to estimate the transpiration of Caragana korshinskii. Copyright © 2007 John Wiley & Sons, Ltd.
... In this study, surviving trees had consistently higher mean ring density, latewood density, latewood proportion and maximum ring density than their dead counterparts. Some authors (Waring and Running, 1978;Schiller and Cohen, 1995;Domec and Gartner, 2002;Beedlow et al., 2007) suggest that in Douglas-fir ring density components are related to adaptive hydraulic properties of wood: higher latewood/earlywood ratio for density could be then interpreted as a strategy to grow in favourable initial wet conditions during the spring and dry stressing conditions in the summer. Trees lacking such capacity of drastically changing their density over the growing season would be penalized. ...
Microdensity profiles of Douglas-fir's clones and weather data were used to study phenotypic plasticity (dendroplasticity). Within-ring microdensity was interpreted as the variation of tree response to drought constraints during selected growing seasons. An original norm of reaction was obtained by pairing evident points of abrupt changes in tree-ring microdensity profiles and in weather indices. The coefficients of the non-linear models adjusted to the reaction norms were analysed as dendroplasticity variables. Dendroplasticity variables were significantly different between geographical locations, years and clones. Heritability of the dendroplasticity variables ranged from low to high and was similar to heritability values of microdensity variables such as mean ring density (MRD). Coefficients of genetic variation of dendroplasticity variables were intermediate between those of wood density and growth variables. Dendroplasticity variables were phenotypically and genetically related to ring microdensity variables, more strongly to latewood variables. Dendroplasticity provides retrospective, synthetic and easy-to-interpret information about tree response to the variation of the balance between water availability and water demand during the growing season. The proposed model of dendroplasticity is described by a number of parameters that are linked to a biological meaning. Our results suggest that there is a potential for adaptation to drought in Douglas-fir, with two mechanisms involved: at individual level, short-term plastic response during the growing season and, at population level, long-term, between-generation, evolution process.
... Daily cumulative transpiration of the magnitude observed in the large trees in this study are rare in the literature, primarily because most studies have been carried out on smaller material in the higher latitudes, where evaporative demand tends to be lower. In conifers, individual tree transpiration of dominant and co-dominant trees on the order of 50±100 kg per day is typical (Schiller and Cohen, 1995;Arneth et al., 1996;Loustau et al., 1996;Wullschleger et al., 1998), Fig. 3. Sap¯ow, conductance and meteorological data from a 220-year-old Abies amabilis stand during two days in 1994 with similar vapor pressure de®cit and net radiation regimes. (A) Sap¯ow rate per unit leaf area for the largest tree measured. ...
We measured sap ¯ow at the branch and tree levels, and calculated tree transpiration at the stand level, in a 220-year-old Abies amabilis (Dougl.) Forbes forest. Temporal and spatial patterns of branch sap ¯ow rate per unit leaf area re¯ected differences in canopy position and diurnal variation in radiation exposure. Average leaf area normalized branch conductance of upper canopy branches ranged from 0.50 to 1.01 mm s À1 . Maximum leaf area normalized tree sap ¯ow rates were similar to those previously measured in a younger A. amabilis forest (about 80 g m À2 leaf area h À1), but dominant trees in the old growth stand transpired approximately three times more per day (up to 281 kg H 2 O per day) than dominant trees in the younger forest. This difference was attributed primarily to leaf area: dominant trees in the old growth stand had approximately three times more leaf area than those in the younger Abies stand. Crown conductance on a ground area basis varied by an order of magnitude between the smallest and largest trees measured (maximum 4.84 mm s À1 and mean 1.44 mm s À1 versus maximum 37.54 mm s À1 and average 12.16 mm s À1 , respectively). There was considerable spatial and temporal variation in stomatal versus boundary layer control of transpiration as expressed by the O decoupling coef®cient. O for the largest measured tree ranged from less than 0.1 to greater than 0.6, and remained above 0.3 for more than 9% of the daylight hours monitored. The degree of decoupling decreased with tree size, with O of the smallest tree sampled never exceeding 0.3. Daily stand transpiration ranged from less than 0.4 mm to greater than 3.3 mm depending on radiation and vapor pressure de®cit. # 2001 Elsevier Science B.V. All rights reserved.
... Nevertheless, these empirical models have very weak predictive power, so their assessments of climatic change's impact on tree growth are questionable. Indeed, classical response functions (based on monthly temperature and precipitation) show a limited ability to take the water budget properly into account (Rathgeber 2002), although it is known to be a key factor governing tree growth in Mediterranean regions (Querejeta et al. 2001; Schiller and Cohen 1995 , 1998). On the other hand, some attempts have been made to use process - based models that directly simulate tree radial growth ( Deleuze and Houllier 1998 ; Fritts et al . ...
The potential effects of global changes on forests are of increasing concern. Dendrochronology, which deals with long-term records of tree growth under natural environmental conditions, can be used to evaluate the impact of climatic change on forest productivity. However, assessment of climatic change impacts must be supported by accurate and reliable models of the relationships between climate and tree growth. In this study, a bioclimatic model is used to explore the relationships between tree radial growth and bioclimatic variables closely related to the biological functioning of a tree. This model is at an intermediate level of complexity between purely empirical and process-based models. The method is illustrated with data for 21 Aleppo pine (Pinus halepensis Mill.) stands grown under a Mediterranean climate in south-east France. The results show that Aleppo pine growth is mainly controlled by soil water availability during the growing season. The bioclimatic variable which best expresses the observed inter-annual tree growth variations is the actual evapotranspiration (AET). Four parameters were adjusted to simulate dendrochronological data: the soil water capacity, the wilting point, the minimum temperature for photosynthesis, and the end of the growing season. The bioclimatic model gives better results than the standard response function and provides better insight into the functional processes involved in tree growth. The convincing results obtained by the bioclimatic model as well as the limited numbers of parameters it requires demonstrate the feasibility of using it to explore future climatic change impacts on Aleppo pine forests.
... The objectives of the studies conducted in forests were to determine the water regimes under Mediterranean climate conditions, as a guiding tool for sustainable forest management (Schiller and Cohen 1995). The studies were conducted in the northern and southern regions of Israel. ...
We studied the radial pattern of sap velocity (v) in trunks of six forest species: Cupressus sempervirens L; Eucalyptus camaldulensis F. Muell; Pinus halepensis Mill. (Alleppo pine); Quercus aegilops L. ssp. ithaburensis [Decne] Boiss; Quercus calliprinos Webb; Quercus rotundifolia Lam. (Syn. Quercus ilex spp. Rotundifolia) and three fruit species: Citrus
sinensis L. Osback; Malus domestica cv. Golden Delicious; Persea americana Mill. Data was selected from measurements made over a period of 15 years. For each species, at least data of 1–2 weeks measured on days with clear sky and after a rain event or irrigation were analyzed. Measurements were made with the T
max heat pulse method, and six points were measured along the radius of the trunk. Two types of radial pattern were found; in one type the highest v value was recorded near the cambium, decreasing toward the heartwood; and the other type had low v near the cambium increasing toward a depth of 12 to 20 mm below the cambium and decreasing with depth to the heartwood. There was large interspecies variability of v in both the pattern of radial gradient with depth and the distance between the cambium and the border of conducting sapwood. Variations in radial pattern of v between trees within species were generally small with a coefficient of variation of 4–20%. The mean fractions of volumetric flow in the 0–16 and 0–24 mm layers below the cambium were 59% and 79% of the total flow, respectively. The distance between the cambium and the border between conducting and non-conducting sapwood varied from 31 to 66 mm in the various species. The radial distribution of sap velocity with azimuth around the trunk had a coefficient of variation similar to that found between trees of the same species. The amplitude of the azimuthal variation changed during the day; it was high in the mornings and evenings and low at noon. The variation of sap velocity in three azimuths was more affected by the structure of each individual trunk than by the position with respect to the sun.
The chapter portrays the history of afforestation efforts since 1880 of a desolated country lacking forests. It describes the big efforts to expand the afforested area aiming mainly at the prevention of soil erosion, beautification of the country and recreation. The Mediterranean pine species used and their management problems arising as the result of use of unsuitable seed sources are described.
In dryland areas, knowledge of plant water requirements and water use strategies of species are essential for use in afforestation, to ensure the establishment of seedlings in the first summer after planting. In this context, we used minilysimeters to estimate the daily whole-plant transpiration requirements in seedlings of Pinus halepensis, Pistacia lentiscus and Quercus coccifera, which are frequently used in afforestation. This estimate was calculated according to the following two conditions: high-soil moisture and a drought period. The results in both conditions indicated the highest daily rate (0.90–1.33 L m−2 day−1) for Q. coccifera, P. lentiscus was moderate (0.50–0.75 L m−2 day−1) and P. halepensis showed the lowest rate (0.37–0.44 L m−2 day−1). Species response under drought conditions was in accordance with their drought-avoidance strategy. P. halepensis and P. lentiscus displayed a water-saver mechanism, while Q. coccifera exhibited a water-spender mechanism. Our results show that the use of minilysimeters is a suitable method to determine whole-seedling transpiration rate and to accurately estimate the water requirements of species used for afforestation in dryland areas.
Available online: http://www.sciencedirect.com/science/article/pii/S0140196315300410
The SF100 Heat pulse sensors based on the heat compensation theory were applied to study the diurnal and seasonal changes of trunk sap flows for Caragana korshinskii. The soil moisture content at 0 - 300 cm layer was measured with a tube-type time domain reflectometry (Tube-TDR) . The solar radiation, the maximum and minimum air temperature, relative humidity, wind speed, wind direction and precipitation etc. were also measured with an automatic weather station where the reference crop evapotranspiration was provided simultaneously. The diurnal and seasonal variations of sap fluxes, the flow velocity at different positions in the trunk and the sap fluxes under different weather conditions were analyzed. The correlation between the sap flux and the meteorological factors was also analyzed by SPSS 11.0 statistical software. Results showed that the trunk sap flow varied regularly in the diurnal term and the sap flow velocity decreased wilh the inserted depth into the sapwood. Magnitude of sap flow changed considerably between sunny and rainy days. The order of the main meteorological factors affecting the sap flux of Caragana korshiniskii trees were: vapor pressure deficit > solar radiation > air temperature > wind speed.
The present book is a collection of ten original research articles and reports, associated with selected topics in agricultural chemistry. The discussed issues are organized in four sections: Classification and labeling of active substances in plant protection products, Environmental and stress plant physiology and behavior, Antimicrobial and antioxidant potential of plant extracts, and Pollutants analysis and effects. The information provided in this book should be of interest for academic researchers and for agriculturalists. Available from: http://www.intechopen.com/books/agricultural-chemistry
Functional convergence in water use of trees across species from diverse geographic locations was examined using data on tree water use parameters, with the intention of gaining an understanding on the capacity for water transport for trees with varying structural and functional traits. Wood density (ρw), which is reported to have a negative exponential relation with sap flow density (SFD), showed a bell-shaped curve when the daily SFD data from 101 tree species belonging to 35 angiosperm and gymnosperm families were plotted. The species came from 23 different geographical locations representing all continents. Trees were most efficient in water transport when the ρw was between 0.51 and 0.65 g cm−3. When the ρw increased or decreased from this range, there was a gradual fall in their water transport rate as indicated by lower daily SFD. The unexpected reduction in SFD with decreasing ρw is explained in terms of reduced conductance in the transport pathway, which is a precaution taken by the tree for avoiding cavitation or implosion in larger conducting tubes, which is characteristic of low density wood. The development of severe leaf water potential variations, which is frequently reported in such trees, supports this notion. The SFD versus ρw relation has a potentially wide applicability in predicting water use by forest stands with varying ρw. In addition, the occurrence of a high number of tree species with ρw values in the range of 0.51–0.65 g cm−3 across all continents examined points towards the importance of ρw in the evolutionary process as related to efficient functioning of the water transport mechanism.
The sensor measuring stem water content based on SWR (standing wave ratio) principle was presented in this paper. Laboratory and field tests were performed to examine the feasibility of SWR (standing wave ratio) sensor to monitor changes in the moisture storage of the woody parts of trees. To serve as wave guides for the SWR signal, pairs stainless steel rods (50 mm long, 3 mm in diameter, and 30 mm separation) were driven into parallel pilot holes drilled into woody parts of trees, and a cable testing oscilloscope was used to determine the output voltage of the transmission line. A laboratory calibration test was performed on two sapwood samples, so that the relation between the volumetric water content and the output voltage could be determined over a range of water contents. At the same time, root-zone soil water content was measured to evaluate the root-zone environment of the tree.
We hypothesized that for similar trunk circumferences and leaf masses, under similar climatic conditions, the canopy structure of Cupressus sempervirens L. influences transpiration rate such that the faster transpiring var. horizontalis exhausts the winter's allocation of rainfall earlier, to its own subsequent detriment. To verify this assumption, heat pulse velocity measurements, by means of the heat pulse method, were done at eight periods during the year in the stem xylem of eight matched pairs of trees, each pair composed of a var. horizontalis and a var. pyramidalis tree of similar dimensions. Results showed that during the daylight hours in winter and spring, midday sap flow velocity of var. horizontalis trees was greater than that of var. pyramidalis trees of similar trunk circumferences and foliage mass. Hence, the calculated average daily transpiration of var. horizontalis trees was nearly 50% greater than that of var. pyramidalis trees. During the wet period (November to May), mean daily transpiration of var. horizontalis exceeded, with 2.91 dm(3) per tree, that of var. pyramidalis. This amount adds up to an additional water consumption of similar to500 dm(3) per tree during 170 clear-sky days within that period. This higher water consumption by var. horizontalis reduces the spatial soil-water storage and availability in the late spring and early Summer, thereby prolonging the water stress period that might become critical under droughty winter conditions. Thus, at afforestation sites under given soil and bedrock conditions, e.g., spatial and temporal water availability for each tree, the canopy structure will be the decisive factor influencing the development (time and amount) of the soil-water stress.
Increased understanding of transpiration by dryland oaks in the woodlands of the south-western United States and northern Israel has been obtained from studies in the two countries. Transpiration was estimated in both studies by the heat pulse velocity (HPV) method in stands of Quercus emoryi, a drought-deciduous species growing in the south-western United States, and stands supporting Q. ithaburensis, a deciduous oak, and Q. calliprinos, an evergreen oak, in northern Israel. Estimates of daily transpiration rates by individual trees and annual transpiration amounts on a stand basis indicate that depending on the species and stand structure, 45–80% of the precipitation inputs to the stands sampled are represented by transpiration component of the respective hydrologic cycles.
Structure of needle head and seal mechanism are key problems of tree trunk injection. It analyzed the current structure of needle head and seal mechanism, demonstrated the shortages for its sealing principle in this paper. A ring-shaped drill of tree trunk injector was successfully developed. The push in force of needle head is measured by CMT5105. Because the special form of the needles, the needle has good performance of sealing located in cambium and can expand its diameter as it goes into the tree trunk but not crack. In tree trunk injection tests, the needle can inject large volume of nutrition solutions and achieved remarkable economic results.
Transpiration (T), needle water stress (MPa) and the water balance of an Aleppo pine (Pinus halepensis Mill.) plantation, growing in an arid region at the edge of the Israeli Negev desert, were studied during 1 yr. The heat pulse technique for the measurement of the heat flow velocity was used for the estimation of the sap flow velocity, i.e., transpiration, in the stems of 16 trees (27% of the trees in a plot of 1000 m2). A pressure chamber was used to determine the needle water potential (MPa). Climatic parameters were measured in the forest for the computation of the potential transpiration (Tp) by means of the Penman–Montheith equation. During the rainy period, the transpiration (T) rate was maintained at a level between 1 and 2 mm day−1, which then dropped after the last rain; the decrease of T in small trees (diameter at breast height [DBH]12 cm). In May, T dropped to a nondetectable rate (about 0.02 mm day−1) and remained at this level till the next significant rain in December. A maximum T/Tp ratio of 0.3, which is nearly half of the ratio found previously in an Aleppo pine plantation under Mediterranean climatic conditions (Schiller and Cohen, 1995), was recorded in February. This difference between the two sites, in T/Tp ratio, is attributed to the difference in the basal area of the trees between the two sites. Needle water potential at sunrise decreased from −0.8 MPa in the rainy period to more than −3.0 MPa during the dry period. The integrated T throughout the measurement period was used to estimate the total water uptake by the stand, which was 210.1 mm, i.e., 93% of the effective rainfall, or 80.2% of the total annual rainfall.
As a result of predicted regional climatic changes the need to select for the more drought-tolerant genotypes (ecotypes) among
Mediterranean conifers has become clear. Aleppo pine (Pinus halepensisMill.) seems to be one of the most drought-tolerant pine species. Nevertheless, the existence of geographical trends in their
genetic differentiation indicates potentially large differences in drought-tolerance among provenances. This assumption was
verified by the finding of large variation among provenances in their internal water relations. Hence, the aim of this study
was to compare the ecophysiological behaviour of several Aleppo pine provenances under contrasting climatic conditions. Growth
parameters (height and diameter) and survival rate were measured in two provenance trials, one planted under sub-desertic
conditions at the northern edge of the Negev desert, and the second under thermo-Mediterranean climatic conditions in the
central coastal plains, Israel. Ecophysiological parameters such as: predawn needle water potential, sap flow in the xylem
(i.e. transpiration), photosynthesis and water-use efficiency were measured in trees of selected provenances. The results
suggest that it is not possible to predict provenance performance under harsh conditions from their performance under more
favourable ones. Therefore, selection must be carried out under the exact conditions in which the trees from the resultant
selection will be planted. The present study clearly emphasises the need for broad selection programs of P. halepensis.
Pinus halepensis (Mill.) forest canopy transpiration was measured, using the heat-pulse method, in a forest plantation growing under semi-arid
climatic conditions at the edge of the Israeli Negev desert, during 3 successive hydrological years (2003–2006). The daily
transpiration rates were related to soil water content and ambient meteorological parameters measured by the flux tower erected
in the geographical centre of the forest. The overall measured and estimated canopy transpiration (Tcanopy) of 300 trees ha−1 summed to 148, 181 and 135 mm year−1, representing ∼65%, ∼48% and ∼60%, respectively, of the annual rainfall in the hydrological years 2003–2004, 2004–2005, 2005–2006.
Summed daily Tcanopy during the measurement periods in the 3 hydrological years constituted ∼59%, ∼51%, and ∼70%, respectively, of the summed
ecosystem evapotranspiration (ET, mm day−1) during the day (0600–1,900 h); furthermore, summed daily Tcanopy constituted ∼14%, ∼20% and ∼15%, respectively, of the summed potential evapotranspiration (PET, mm day−1). The importance of rain-storm intensity, in addition to rain-storm amounts, in this semi-arid area was revealed. The hydrological
years 2003–2004 and 2005–2006 had similar rain amounts of 231 and 224 mm, respectively, but very different storm intensities:
hence, very different impacts on the soil profile water content were observed, resulting in very different daily transpiration
(T) rates and different T/PET ratios. Slope aspect influences on daily Tcanopy rates were more pronounced in droughty years. Trees growing on north-facing slopes transpired less than those on the plateau
or south-facing slopes, a situation which enables fine-tuning of the stocking density on the different slope aspects.
When the heat pulse velocity method of measuring sap flux in trees is based on idealized heat transport theory, it seriously
underestimates actual water flow. Two-dimensional numerical solution of the physical heat flow system demonstrates that both
sensor thermal properties and sap flow interruption in the vicinity of implanted probes cause significant departure from the
idealized theory. New numerical solutions to the practical heat pulse problem are given and applied to earlier experimental
data. Transpiration rates thus determined in conifers agree within 5% of those measured by weighing lysimetry or in a diffuse
porous hardwood within 10% of those calculated from a climatized cuvette. A table of numerical solutions applicable to the
most widely published heat pulse sensing configuration is given.
Transpiration of Aleppo pine was studied in three hilly regions of Israel (Hills of Judea, Mt. Carmel, and Mt. Cana'an). In spite of differences in the ecological factors of the localities tested, fluctuations and pattern of transpiration rate were similar in all of them. During the dry period of July-December no significant changes were noted in transpiration and soil-moisture percentage. The first rains, however, accompanied by favorable temperatures raised the transpiration rate. During the driest and hottest months, when all climatic factors (sun energy, temperature, etc.), including intensity of evaporation, reached their highest values, transpiration are dropped considerably. This phenomenon was particularly noticeable during @'hamsin@' (hot and dry desert winds) days, when evaporation rate increases two- to threefold, temperature reaches its highest values, and relative air humidity drops to its lowest value.
surface, which is related to the surface saturation deficit. We show that this diffusion resistance model is not applicable either to vegetation canopies or to soil, and we have developed a combination formula relating the evaporation from a drying soil to the potential evaporation. This method uses the surface temperature as the only additional measurement to the standard combination formula .for potential evaporation, and it compares favorably with the energy balance-Bowen ratio method over a drying soil.
Daily total transpiration was linearly related to heat pulse velocities measured once each day at mid-day or averaged for 4- to 14-hour periods centred on mid-day. The correlation coefficients were higher than 0.98 in every case. Because the sky was clear throughout most of this study, heat pulse velocities were quite constant throughout the daylight hours. If variable cloudiness had occurred, HPV's for the longer time periods would probably have shown significantly higher correlations than the one reading at mid-day.Heat pulse velocity was shown to be a function of transpiration and water movement into storage. If HPV's were negligible during darkness, then an HPV taken during daylight was fairly indicative of the same hour's transpiration. Significant HPV's during darkness indicated movement into stem storage rather than vapor loss alone, so that any hour's transpiration value was essentially independent of the comparable hour's velocity reading.
A survey of plantations over 30 years old in the Judean mountains and in the Shephela region was conducted to determine quantitative effects of the bedrock on the growth of Aleppo pine. Site quality was found to be strongly affected by both the lithological and moisture-retaining characters (rather than by the geological age). Mean height growth was lowest on limestone, and highest on marl and chalk, with dolomite occupying an intermediate position.
Net photosynthesis, transpiration, dark respiration rates and stomatal and mesophyll resistances were studied in young potted seedlings of Pinus halepensis Mill. under gradually decreasing soil and leaf water potentials. Stomatal resistance under non-limiting xylem water potentials was 6–7 times higher than mesophyll resistance. Stomata started to close at threshold xylem water potentials of −0.8 MPa, whereas mesophyll resistance started to increase at about −1.4 MPa. Decreasing xylem water potentials increased the CO2 compensation point and decreased the water use efficiency (expressed by the photosynthesis to transpiration ratio) and dark respiration rate. It is concluded that at least part of the drought resistance characteristics of P. halepensis are associated with a sensitive stomatal mechanism which enables an efficient control of water loss.
Sap flow measurements in the trunk and potential transpiration computed from meteorological data were used during two irrigation seasons to determine orchard water requirement. Standard commercial irrigation was applied except for two trees which were irrigated every 3 days to maintain unlimited soil water availability and used as reference trees. Measured transpiration was proportional to potential transpiration. The ratio between the two, averaged for all trees, was approximately 0.3 when soil water availability was not limiting falling to 0.2 when soil water potential in the main root zone dropped to -90 kPa. This ratio was successfully used to schedule orchard irrigation at an arbitrarily chosen reduction of 20% in the ratio as measured on the first day after irrigation. Yield of individual trees was highly correlated with their seasonally accumulated transpiration. Analysis of variability in transpiration between trees led to the conclusion that orchard transpiration may be determined with acceptable accuracy by this approach which can, therefore, be used to schedule orchard irrigation.
Traditional meteorological estimates of evapotranspiration include empirical crop factors which are inadequate for scheduling high frequency irrigation. The performance of a transpiration model was tested and adapted to suit the operational requirements of automated irrigation systems. Hourly measurements of global solar radiation, air temperature, humidity and wind speed, obtained from an automatic weather station are inputs to the model. Additional inputs include daily updated data of plant height and leaf area index. This information is processed to determine the active coupling surface between the crop and the atmosphere. The model takes into account the resistance of the leaf to diffusion of water vapor.
Calculated transpiration, based on the model, matched very closely measurements of latent heat flux in an irrigated cotton field. It was also in good agreement with water uptake measured in stems of the cotton plants using a heat pulse technique. The test also showed that implementation of the model in the field under study would have improved the efficiency of water application.
A method combining sensible heat flux measurement based on temperature and vertical wind speed fluctuations, and energy balance, was used to estimate evaporation above the canopy and the understorey of a Pinus pinaster (Ait.) stand in Les Landes forest. The problems of the horizontal homogeneity of net radiation and sensible heat flux under the canopy, and of estimating heat storage, are reviewed. The differences between above- and below-canopy evaporation are compared with sap flow on five experimental days. Except for one overcast day with little tree transpiration, the method fits sap flow within ± 15%.
Measurements of sap flow made on eight trees in a stand of Maritime pine (Pinus pinaster Ait.) are presented, and compared with potential evaporation and concurrent measurements of stomatal conductance, water potential, and the total vapour flux as measured by eddy correlation instrumentation. When the probable transpiration from the understorey is taken into account, there is good agreement between the two methods.
Recent atmospheric and wind tunnel data on the heat, mass and momentum transfer above natural and artificial surfaces indicate a general increase in the quantity kB-1 (= In(zo/zp), where zp is the roughness length appropriate to the quantity p) between aerodynamically smooth and fully rough flow. Below a roughness Reynolds number, u*zo/v, of about 100, kB-1 appears to be a single valued function of u*zo/v, closely approximated by the assumption of a molecular sub-layer for heat and water vapour fluxes. Beyond u*zo/v = 100, there is no unique value of kB-1, but rather the observations suggest that the behaviour falls into either of two categories. For surfaces comprised of arrays of widely spaced solid roughness elements, kB-1 continues to increase (with some evidence for a plateau being reached by about u*zo/v = 1,000, when kB-1 ≃ 10), whilst for surfaces comprised of randomly distributed fibrous roughness elements, kB-1 gradually decreases with increasing roughness Reynolds number beyond about 10
La mesure du potentiel de sève (Ψѕ) au cours des étés 1977 et 1979 a permis de caractériser les potentialités hydriques de quatre stations forestières du versant sud du Mont Ventoux (Vaucluse, France) et les réponses de dix espèces forestières aux facteurs climatiques. Pendant l’été 1977 particulièrement pluvieux, les réserves en eau du sol ont été satisfaisantes dans toutes les stations. Des différences systématiques de potentiel de base (Pв) ont été observées et s’expliquent par des évapotranspirations potentielles (ETP) plus élevées sur les stations de basse altitude. Par contre, pendant l’été 1979, le climat a été typiquement méditerranéen. L’alimentation en eau des arbres a alors été conditionnée par les réserves en eau et l’ETP. Les mesures régulières de potentiel de base ont permis de montrer que dans les stations climatiquement difficiles, les arbres avaient développé un enracinement susceptible d’exploiter les réserves profondes d’eau, alors que dans les stations climatiquement plus favorables les arbres ont, en année sèche, des difficultés à s’alimenter en eau, probablement à cause d’un enracinement plus superficiel. Associées aux mesures régulières de potentiel minimum diurne (Pm), les mesures de Pв ont permis la détermination des potentiels de base critique (Pво). Cedrus atlantica, Quercus ilex, Quercus pubescens et Acer opulifolium maintiennent leurs activités transpiratoires et photosynthétiques jusqu’à des niveaux de grande sécheresse (Pво entre - 30 et - 35 bars). Par contre, les pins bloquent leur activité transpiratoire vers - 15 ou - 17 bars. Sur le plan sylvicole, il apparaît que le cèdre peut être installé à des altitudes inférieures aux limites actuelles de la cédraie. Mais, en relation avec les conditions édaphiques, il pourra s’agir de peuplements clairs et le reboisement économique de ces zones difficiles passe par la constitution d'îlots de semenciers susceptibles d’étendre les peuplements à la faveur de séquences climatiques favorables.
The hydrological cycle in vegetation
- Rutter
Rutter, A.J., 1975. The hydrological cycle in vegetation. In: J.L. Monteith (Editor), Vegetation and the Atmosphere, Vol. 1, Academic Press, London, pp. 111-154.
An Introduction to Environment Biophysics Determination of orchard water requirement by a combined trunk sap flow and meteor-ological approach
- G S Campbell
Campbell, G.S., 1977. An Introduction to Environment Biophysics. Springer, Berlin. Cohen, Y., 1991. Determination of orchard water requirement by a combined trunk sap flow and meteor-ological approach. |trig. Sci., 12: 93-98.
Evaporation and environment. In: The State and Movement of Water in Living Organisms
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Monteith, J.L., 1964. Evaporation and environment. In: The State and Movement of Water in Living Organisms. Proc. 19th Syrup. Soc. Exp. Biol., Swansea. Academic Press, New York, pp. 205-234.
The Soils of Ramat ha'Nadiv (southern Carmel). Yad ha'Nadiv and The Society for the Protection of Nature in Israel, Tel Aviv
- Kaplan
Kaplan, M., 1989. The Soils of Ramat ha'Nadiv (southern Carmel). Yad ha'Nadiv and The Society for the Protection of Nature in Israel, Tel Aviv. Research Report 2, 54 pp. (in Hebrew).
Ecological studies of the vegetation on old walls Agricultural Research Organization, Division of Forestry
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Karschon, R., Weinstein, A. and Heth, D., 1987. Ecological studies of the vegetation on old walls. Agricultural Research Organization, Division of Forestry, Ilanot, Israel, Leaflet 56.
Study of the Differences in Effects of Forest and Other Vegetative Covers on Water. Israel Ministry of Agriculture, Soil Conservation and Drainage Division
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Rosenzweig, D., 1972. Study of the Differences in Effects of Forest and Other Vegetative Covers on Water. Israel Ministry of Agriculture, Soil Conservation and Drainage Division, Research Unit, Tel Aviv. Research Report 33 (in Hebrew).
Ecological studies of the vegetation on old walls. Agricultural Research Organization, Division of Forestry, Ilanot, Israel
- Karschon
The Geology of Ramat ha'Nadiv (southern Carmel). Yad ha'Nadiv and the Society for the Protection of Nature in Israel, Tel Aviv
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Study of the Differences in Effects of Forest and Other Vegetative Covers on Water. Israel Ministry of Agriculture, Soil Conservation and Drainage Division, Research Unit, Tel Aviv
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