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Measurement of Sap Flow in Conifers by Heat Transport
... The calculated heat velocity was highly correlated with the applied flow velocity with a unique relationship regardless of the diameter. The latter result confirms the equation of Marshall (1958) which links the sap velocity to the heat velocity with a vessel fraction of around 25 % within samples. The feasibility of outdoor measurements was also successfully tested. ...
... The theoretical equations used to relate the sap flow and heat velocity in xylem are derived from the theory of conduction and convection of heat in porous material (Marshall 1958). ...
... The origin was still close to zero and the sap velocity was about fourfold that of heat pulse velocity. This value could be compared to that given in Marshall 1958, where the sap flow velocity was threefold that of the heat pulse velocity in conifers. ...
... The heat ratio method (HRM) is a pulse method that has been applied in many studies (Vandegehuchte & Steppe, 2012). The HRM technique based on Marshall (1958), and upgraded by Burgess et al. (2001), employs temperature probes inserted into the active xylem at equal distances downstream and upstream from a central heater element. Unlike other techniques that use constant pulses, such as the dissipation family, the heater releases a discrete and momentary heat pulse, after which, temperature is continuously measured by two sensing probes during a time interval (second 63rd to104th after the pulse). ...
... Then they were dried for 7 days at 60 C and were finally weighed to obtain the dry weight. The sap wood water content (m c ) was measured following Equation (1), where w f and wd were the fresh and oven-dried weight of the trunks sample, respectively (Marshall, 1958). ...
... Basic wood density ( p b ) was measured as the dry weight divided by the green volume (Marshall, 1958). The green volume was measured by the water displacement of four wooden cubes per tree (approx. ...
Tree transpiration considerably contributes to evaporative fluxes to the atmosphere in terrestrial ecosystems. Accurate transpiration quantification provides relevant information about forest water use and may benefit adaptive forest management, especially in a global change context. Tree transpiration can be measured by several methods, and sap flow measurements are one of the most valued. However, species-specific validations of these techniques are required to avoid undesirable bias. This is especially relevant in species with low transpiration rates where errors may be relevant , such as Aleppo pine trees (Pinus halepensis Mill.). Moreover, another significant source of uncertainty in sap flow measurements is probe misalignment. Hence, the aim of this study was to correlate transpiration rates estimated by sap flow probes using the heat ratio method (T HRM) and load cells to independently monitor water transpiration in juvenile Aleppo pine trees. The corrections to improve transpiration measures, including misalignment correction, were applied to T HRM results to test if the accuracy of results improved. These measurements were recorded in greenhouse under controlled conditions to implement different environmental conditions. The environmental variables that ruled the experiment, mainly vapour pressure deficit and soil water availability, spanned in a wide range of values. The results showed an accurate linear correspondence between T OBS and T HRM for low and medium values, but moderate underestimations at high transpiration rates were observed. These underestimations were partly removed when applying probe misalignment correction. This study supports the notion that HRM offers accurate Aleppo pine transpira-tion estimations with low and medium values under a variety of abiotic conditions, which also has implications for HRM application in other isohydric species. The results also support the interest in the use of probe misalignment correction to estimate transpiration, mainly when high transpiration values are recorded. The results of this study can be considered as a preliminary approach for future research in order to improve the estimates of the transpiration rates of the Aleppo pine under the limiting conditions of the Mediterranean.
... with single stems at heights of 0.5 and 1.4 m above ground and below branches. The wounding depth was measured around the inserted thermocouples (Marshall, 1958). Due to the destructive sampling required, the sapwood measurements were usually collected at the end of the experiment. ...
... Sapwood moisture content as described by Marshall (1958), was used for calculating heat pulse velocities (Vh) (cm s -1 ); the calculation from Equation 1 is based on the Marshall (1958) idealise 'd' theory which assumes that the HPV probes do not affect the measured heat flow. Thermal diffusivity (k) is allocated at a minimal rate of 2.5 x10 -3 cm 2 s -1 (Marshall, 1958), and this value is used once sapwood properties are obtained: ...
... Sapwood moisture content as described by Marshall (1958), was used for calculating heat pulse velocities (Vh) (cm s -1 ); the calculation from Equation 1 is based on the Marshall (1958) idealise 'd' theory which assumes that the HPV probes do not affect the measured heat flow. Thermal diffusivity (k) is allocated at a minimal rate of 2.5 x10 -3 cm 2 s -1 (Marshall, 1958), and this value is used once sapwood properties are obtained: ...
It is imperative to possess a comprehensive understanding of the water consumption patterns of sweet cherry trees under rainfed conditions. This study investigates the water use of sweet cherry using the heat pulse velocity sap flow method. Tree response to drying soil conditions over two consecutive measurement periods (September 2017 to December 2018) in the eastern Free State, South Africa, is also evaluated. During the post-harvest period (December), there was a continuous increase in daily water consumption by trees, in conjunction with an increase in canopy cover, even though the crop load was reduced. Measured sap flow was positively correlated to net radiation, air temperature, and water vapour pressure deficit. The transpiration rates ranged from 1.2 to 3.5 L d ⁻¹ during the flowering stage (day of year, DOY, 244 – 270) and showed an increasing trend as the days progressed. During the ripening stage (DOY 271 – 292), transpiration rates decreased from 4.5 to 1.1 L d ⁻¹ over the 2018 season. This decreasing trend from the previous growth stage was due to soil drying and scorching weather conditions that led to trees experiencing water stress. Sap flow measurements, however, showed typical characteristics of the diurnal trend during selected days during varying weather conditions. The fraction of transpirable soil water (FTSW) threshold varied for different fruit growth stages and approached 1.0 for different stress levels. FTSW exceeded 0.4 when sweet cherry trees utilised stored soil water, while the transpiration rates declined during prolonged hot days. Moreover, the stress coefficient factor ranged between 0.45 – 0.65 for different growth stages. The daily soil water content varied, and soil evaporation was expected to increase during hot and dry days. In the early stage of a dry spell, soil water content did not directly affect the transpiration rate. Sweet cherry trees are susceptible to soil water deficit at different stages of fruit development. More research is required to understand transpiration as an irrigation management and planning indicator.
... These theoretical methods include the CHP and T-max method, which can measure moderate to high flows (Cohen et al. 1981, Swanson and Whitfield 1981, Green et al. 2003. The HR method, which was originally called 'a method for slow rates of flow' by Marshall (1958) and therefore named the SRF method by Forster (2019), cannot accurately measure high flows. To date, those methods that can measure a range of reverse to high sap flows are the dual method approaches (Forster 2019) and the Sapflow+ method (Vandegehuchte and Steppe 2012). ...
... Heat ratio method Heat pulse velocity V h (cm h −1 ) can be calculated from the ratio of temperature rise of the downstream probe T down (K) to the upstream probe T up (K), assuming an equal distance r (m) from each temperature measurement probe to the heater needle element (Marshall 1958, Burgess et al. 2001: ...
... In Eq. (9), t 0 is the heat pulse duration (s) and all other variables are as previously defined. Vandegehuchte and Steppe (2012) used curve fitting to measure the thermal properties of sapwood and V h was determined from the analytical solution of the fundamental heat conduction-convection equation (Marshall 1958). Applying the heat conduction-convection equation in the axial direction as was done in Ren et al. (2020) simplifies Tree Physiology Online at http://www.treephys.oxfordjournals.org Figure 1. ...
Accurate determination of sap flow over a wide measurement range is important for assessing tree transpiration. However, this is difficult to achieve by using a single heat pulse method. Recent attempts have been made to combine multiple heat pulse methods and have successfully increased the sap flow measurement range. However, relative performance of different dual methods has not yet been addressed, and selection of the numerical threshold used to switch between methods has not been verified among different dual methods. This paper evaluates three different dual methods with respect to measurement range, precision, and sources of uncertainty: (1) the heat ratio (HR) and compensation heat pulse (CHP) method; (2) the HR and T-max method, and (3) the HR and double ratio (DR) method. Field experiments showed that methods #1, #2 with three needles, and #3 compare well with the benchmark Sapflow+ method, having root mean square deviations (RMSD) of 4.7 cm h-1, 3.0 cm h-1 and 2.4 cm h-1, respectively. The three dual methods are equivalent in accuracy (p > 0.05). Moreover, all dual methods can satisfactorily measure reverse, low and medium heat pulse velocities. However, for high velocities (> 100 cm h-1), the HR + T-max (method #2) performed better than the other methods. Another advantage is that this method has a three- instead of four-needle probe configuration, making it less error-prone to probe misalignment and plant wounding. All dual methods in this study use the HR method for calculating low to medium flow and a different method for calculating high flow. The optimal threshold for switching from HR to another method is HR's maximum flow, which can be accurately determined from the Péclet number. This study therefore provides guidance for an optimal selection of methods for quantification of sap flow over a wide measurement range.
... Measurement of the ratio of heat reaching each symmetrically placed outer needle allows for the direction and flow rate of water to be determined within the sapwood. Heat pulse velocity (V h , cm/s) is calculated using Equation (1) [28]: ...
... Thermal diffusivity properties of the wood, sapwood fresh weight, sapwood dry weight, and sapwood fresh volume were determined from values obtained from the literature [28]. Pandanus cookii thermal diffusivity and wound diameter values were obtained from the work of Madurapperuma, Bleby and Burgess [24]. ...
... The approximated wound diameter for the Melaleuca dealbata trees was determined using the methodology of McJannet [22], whereby the diameter is assumed to be equal to the needle width plus one vessel width (0.5 mm) on either side. The default thermal diffusivity value of 2.5 × 10-3 cm 2 /s [28] was then used for both the Eucalyptus tessellaris and Melaleuca dealbata calculations. ...
Evapotranspiration by phreatophytes in riparian zones makes up a large component of the water balance. However, our understanding of the relative importance of controlling factors such as climatic conditions, species type, depth to groundwater and distance to surface water in riparian zones remains a significant knowledge gap. A field experiment was conducted in an irrigated catchment in North Queensland, Australia, to investigate the factors controlling evapotranspiration by groundwater dependent trees. The sap flow of four tree species was measured, along with soil moisture, groundwater levels and local climatic conditions. The relative influence of species, hydrologic and climate factors, and measured variables were investigated with two non-parametric methods: random forest and Principal Component Analysis (PCA). Field monitoring data revealed differences in sap flow rates and diurnal sap flow trends between species. Distance from surface water explained the most variance in sap flow rates, followed by depth to groundwater and species, based on random forest modeling. The sap flow rates for some of the Eucalyptus tessellaris trees at this site reduced as groundwater levels declined. Overall, results demonstrate the value that can be gained from applying non-parametric methods, such as random forest and PCA, to investigate the relative importance of the factors influencing evapotranspiration.
... Cohen's heatpulse method, or T-max method Invasive (Huber, 1932;Marshall, 1958;Cohen et al., 1981) Advanced Heat ratio (HR) method ...
... Likewise, eosin dye helps measure the conducting capacity of lateral veins of the wheat leaf (Altus et al., 1985). A major disadvantage of using dyes is that it is not known whether they would travel as far as the sap flow before they deposit on the vessel walls (Marshall, 1958). Furthermore, dyes would never indicate variation in speed along a dyed path but only show the maximum speed along such a path (Marshall, 1958). ...
... A major disadvantage of using dyes is that it is not known whether they would travel as far as the sap flow before they deposit on the vessel walls (Marshall, 1958). Furthermore, dyes would never indicate variation in speed along a dyed path but only show the maximum speed along such a path (Marshall, 1958). ...
Sap flow measurement is one of the most effective methods for quantifying plant water use.A better understanding of sap flow dynamics can aid in more efficient water and crop management, particularly under unpredictable rainfall patterns and water scarcity resulting from climate change. In addition to detecting infected plants, sap flow measurement helps select plant species that could better cope with hotter and drier conditions. There exist multiple methods to measure sap flow including heat balance, dyes and radiolabeled tracers. Heat sensor-based techniques are the most popular and commercially available to study plant hydraulics, even though most of them are invasive and associated with multiple kinds of errors. Heat-based methods are prone to errors due to misalignment of probes and wounding, despite all the advances in this technology. Among existing methods for measuring sap flow, nuclear magnetic resonance (NMR) is an appropriate non-invasive approach. However, there are challenges associated with applications of NMR to measure sap flow in trees or field crops, such as producing homogeneous magnetic field, bulkiness and poor portable nature of the instruments, and operational complexity. Nonetheless, various advances have been recently made that allow the manufacture of portable NMR tools for measuring sap flow in plants. The basic concept of the portal NMR tool is based on an external magnetic field to measure the sap flow and hence advances in magnet types and magnet arrangements (e.g., C-type, U-type, and Halbach magnets) are critical components of NMR-based sap flow measuring tools. Developing a non-invasive, portable and inexpensive NMR tool that can be easily used under field conditions would significantly improve our ability to monitor vegetation responses to environmental change.
... The sap flow measurement are based on the two-dimensional conductive and convective heat transfer surrounding a line source of zero dimensions (hereafter heater) (Carslaw and Jaeger, 1959;Green et al., 2003;Marshall, 1958;Swanson, 1994;Vandegehuchte and Steppe, 2013). ...
... Heat pulse velocity, V h (m 3 m -2 s -1 or m s -1 ), is related to sap flux density, J sap (Green et al., 2003;Marshall, 1958;Swanson, 1994;Vandegehuchte and Steppe, 2013) ...
... Because V h is required to estimate J sap , all heat pulse methods need to derive V h from measured temperature changes resulting from the release of heat pulse by the heater. Marshall (1958) developed an analytical solutions to Eq. (1) with instantaneous and infinite line heat ...
Accurate measurement of plant transpiration is critical to gaining a better understanding of plant water use and exploration of the influence of plants on regional and even global climate. Heat tracer-based sap flow (HTSF) techniques are currently the dominant method to estimate plant transpiration at the individual plant level. However, the majority of current research focuses on specific applications or the evaluation of the method itself, and there is a lack of an overall analysis of HTSF methods. The objectives of this study were: (i) to briefly review the theories and categories of the various HTSF methods, and (ii) to undertake a bibliometric analysis of the use of HTSF methods in measuring plant transpiration. Each HTSF method is described mathematically and their application and pros and cons are briefly discussed. A bibliometric analysis was conducted using 3964 papers published between 1992 and 2020 archived in the Web of Science core collection. The analysis identified publication trends, the most productive authors, organizations, and countries, as well as the most utilized HTSF method (i.e., thermal dissipation) and journals in which these papers were published. In addition, world distribution maps of the use of HTSF methods and tree species measured were drawn based on 741 selected publications with in situ measurements.
... Volumetric sap flow (Q) can then be estimated for an instrumented tree by multiplying v s by the area of sapwood (Forster, 2017). Marshall (1958) established much of the theoretical framework behind heat pulse based sap flow methods using a two probe configuration with an implanted heater and downstream temperature sensor, although the first reference to a heat pulse method was made by Huber (1932). The work developed an analytical solution to the conduction equation including convection by sap within an infinite medium given by ...
... where T is temperature rise measured at the thermocouple at a distance of r = (x 2 + y 2 ), Q is heat from the heat pulse, α is thermal diffusivity [L 2 T -1 ], t is time since application of the heat pulse, and v h is heat pulse velocity. Marshall (1958) solved , T-max method, and heat ratio method (HRM) (Fernández, 2017;Swanson, 1994). The various heat pulse based methods have been developed mainly to accommodate varying rates of sap flow among woody plants and mitigate measurement error. ...
... The T-max method was developed by Cohen et al. (1981) with a two-probe configuration consisting of a line heater and temperature sensor located 15 mm downstream. Cohen et al. (1981) adapted the analytical theory developed by Marshall (1958) to ...
Mountain meadows in the western USA are experiencing increased rates of conifer encroachment due to climate change and land management practices. Past research has focused on conifer removal as a meadow restoration strategy, but there has been limited work on conifer transpiration in a pre-restoration state. Meadow restoration by conifer removal has the primary goal of recovering sufficient growing season soil moisture necessary for endemic, herbaceous meadow vegetation. Therefore, conifer water use represents an important hydrologic output toward evaluating the efficacy of this active management approach. This study quantified and evaluated transpiration of encroached conifers in a mountain meadow using sap flow prior to restoration by tree removal. We report results of lodgepole pine transpiration estimates for an approximate 1-year period and an evaluation of key environmental variables influencing water use during a dry growing season. The study was conducted at Rock Creek Meadow (RCM) in the southern Cascade Range near Chester, CA, USA. Sap flow data were collected in a sample of lodgepole pine and scaled on a per-plot basis to the larger meadow using tree survey data within a stratified random sampling design (simple scaling). These estimates were compared to a MODIS evapotranspiration (ET) estimate for the meadow. The 1-year period for transpiration estimates overlapped each of the 2019 and 2020 growing seasons partially. The response of lodgepole pine transpiration to solar radiation, air temperature, vapor pressure deficit, and volumetric soil water content was investigated by calibrating a modified Jarvis-Stewart (MJS) model to hourly sap flow data collected during the 2020 growing season, which experienced below average antecedent winter precipitation. The model was validated using spatially different sap flow data in the meadow from the 2021 growing season, also part of a dry year. Calibration and validation were completed using a MCMC approach via the DREAM(ZS) algorithm and a generalized likelihood (GL) function, enabling model parameter and total uncertainty assessment. We also used the model to inform transpiration scaling for the calibration period in select plots in the meadow, which allowed comparison with simple scaling transpiration estimates. Average total lodgepole pine transpiration at RCM was estimated between 220.57 ± 25.28 and 393.39 ± 45.65 mm for the entire campaign (mid-July 2019 to mid-August 2020) and between 100.22 ± 11.49 and 178.75 ± 20.74 mm for the 2020 partial growing season (April to mid-August). The magnitude and seasonal timing were similar to MODIS ET. The model showed good agreement between observed and predicted sap velocity for the 2020 partial growing season (RMSE = 1.25 cm h-1), with meteorological variables modulating early growing season sap flow and volumetric soil water content decline imposing transpiration decrease in the late growing season. The model validation performed similarly to calibration in terms of performance metrics and the influence of meteorological variables. The consistency of the declining volumetric soil water content effect during the late growing season between periods could not be evaluated due to an abridged validation period. Overall, the implementation GL-DREAM(ZS) showed promise for future use in MJS models. Lastly, the model derived transpiration estimates for the 2020 partial growing season showed some of the potential utility in using the MJS model to scale sap flow at the study locale. It also highlights some of the key limitations of this approach as it is executed in the present study.
... Global change scenarios not only predict increasing temperature and changes in 40 precipitation patterns, but also higher drought intensity and longer duration (IPCC, 2021). The heat ratio method (HRM) has been used in many articles (Vandegehuchte and Steppe,64 2012) and is quite reliable for determining transpiration (Fernández et (Swanson, 1994); the detection of low and reverse flows due 67 to a rapid thermal response (Burgess et al. 2001;Marshall, 1958). The heat pulse in the 68 HRM is discrete, unlike other techniques that use constant pulses. ...
... The heat pulse in the 68 HRM is discrete, unlike other techniques that use constant pulses. Due to rapid pulse 69 diffusion when conduction and convection effects are comparable to one another, 70 temperature rises at a point and reaches its maximum value before the centre of the heat 71 pulse goes up to that point (Marshall, 1958). 72 However, the HRM presents several calculation steps to convert the measurements of (Quézel, 2000). ...
... Sap wood water content (mc) 141 was measured following Eq. (1), where wf and wd were the fresh and oven-dried weight 142 of the trunks sample, respectively (Marshall, 1958). (1) ...
Tree transpiration considerably contributes to evaporative fluxes to the atmosphere in terrestrial ecosystems. Accurate transpiration quantification promotes the knowledge of water consumption by forests and could favour an adaptive forest management, especially in a global change context. Tree transpiration can be measured by a wide range of methods, and one of the valued ones is sap flow measurements. However, species-specific validations of techniques are required. Hence the objectives of this study were to validate transpiration rate measurements by the heat ratio method (HRM) in juvenile Aleppo pine trees (Pinus halepensis Mill.) by using the probe misalignment correction proposed by Larsen et al. (2020). This study simultaneously recorded the transpiration rate by tree sap flow following the HRM technique (THRM) and tree water losses by load cells (TOBS). These measurements were taken in combination with the environmental variables that control this process such as different vapour pressure deficit (VPD) ranges of air and the soil relative extractable water (REW). The results showed an accurate linear correspondence between TOBS and the transpiration rate measurements both without and with probe misalignment correction, THRM and THRM MIS, respectively, but interestingly underestimations at high transpiration rates were observed. However, underestimations were removed when applying probe misalignment correction. THRM MIS showed a good relation between the VPDxREW interaction. This study supports the notion that HRM offers accurate low values under a wide range of abiotic conditions, and is useful in isohydric species with low transpirations rates like Aleppo pine. To conclude, our results support the validation of both transpiration rate measurements by the THRM and probe misalignment correction in Aleppo pine under different environmental laboratory conditions.
... Several studies analyzed and monitored PWS through various correlated physiological variables [33][34][35], whereas others focused on developing approaches, methods, and sensors that can operate continuously and remotely [33,34,36]. Stomatal conductance (gs) [35], leaf turgor [37], stem diameter variation [38-40], leaf thickness (LT) [41], water potential [27,42,43], relative water content (RWC) [44,45], and sap flow (SF) [42,46,47] can be indirect indicators or proxies of water stress deficit. Each of these physiological variables has a certain response to water availability. ...
... -Need to be corrected -Unable to measure low sap flow rates and reverse flow [46] (ii) Heat ratio method Measures the ratio of the increase in temperature - ...
... The compensation heat pulse method (CHPM), introduced by Marshall [46], is a technique intended to study SF [114,122,126,127]. Since its introduction, simple instrumentation, robust probes, and reliable measurements have been developed [112]. ...
Global climate change presents a threat for the environment, and it is aggravated by the mismanagement of water use in the agricultural sector. Since plants are the intermediate component of the soil–plant–atmosphere continuum, and their physiology is directly affected by water availability, plant-based approaches proved to be sensitive and effective in estimating plant water status and can be used as a possible water-saving strategy in crop irrigation scheduling. This work consists of two parts: the first part extensively reviews the plant-based methods and approaches that are most applied to monitor the plant water status (PWS), the different technologies available, the gaps, and the possibility of further improvements in establishing a sustainable irrigation schedule. The various approaches are described, and the differences between conventional and recent improved methods are analyzed. The second part is an extensive dataset survey of 83 publications from 2012 to 2022 that applied the main monitoring methodologies and approaches for water status assessment in fruit and nut tree crops cultivated in a Mediterranean climate. The aim of this work is to serve as a practical reference to deepen reader knowledge on PWS and enhance researchers to identify gaps and potential advances in designing user-friendly monitoring technologies.
... L'objectif de cette recherche est de mesurer la transpiration de différentes espèces d'arbre suivant un gradient climatique dans les parcs agroforestiers et d'investiguer son impact potentiel sur des cultures en vue de formuler des recommandations de gestion des parcs. (Marshall, 1958). Le principe de cette méthode est d'insérer dans les tissus du xylème un senseur HRM 30 composé de 3 sondes : une sonde chauffante au milieu, une en bas et une autre en haut de la sonde chauffante qui contiennent des thermocouples. ...
... Par la suite la surface de l'aubier (Burgess et al., 2001) a été estimée. La vitesse de propagation de la chaleur (Vh) en cm h -1 est calculée selon Marshall (1958). ...
RESUME Objectif : Les facteurs climatiques influencent la transpiration des arbres. L’objectif de cette recherche est de mesurer la transpiration de différentes espèces d’arbre suivant un gradient climatique dans les parcs agroforestiers et d’investiguer son impact potentiel sur des cultures en vue de formuler des recommandations de gestion des parcs agroforestiers. Méthodologie et résultats : Les parcs agroforestiers à Vitellaria paradoxa et Parkia biglobosa en association avec Sorghum bicolor (L.) Moench situés dans trois zones agroécologiques sont étudiés. La méthode de ratio de chaleur et de flux de sève ont été utilisées pour mesurer la transpiration des arbres. Les rendements en grains en dessous du houppier ont été mesurés. La transpiration des arbres a augmenté avec la diminution de la précipitation et l’augmentation de la température, et est plus marquée chez V. paradoxa. Les rendements en grains du sorgho ont été modestement expliqués par la transpiration des arbres en fonction des espèces d’arbres. Conclusion et application des connaissances : Les compétitions pour l’accès à l’eau dépendraient peu de la pluviométrie, mais plus de l’importance de l’évapotranspiration qui varie suivant les espèces d’arbres. L’application des options de gestion des arbres qui réduirait la transpiration des arbres permettrait d’améliorer la performance des cultures à travers une réduction de la compétition arbre-culture pour l’accès à l’eau dans les parcs agroforestiers Mots clés : agroforesterie, changement climatique, température, précipitation 18182 Coulibaly et Zombre, J. Appl. Biosci. Vol: 175, 2022 Effet du gradient climatique sur la transpiration des arbres dans les parcs agroforestiers au Burkina Faso (Afrique de l’Ouest) Climatic gradient effect on trees transpiration in agroforestry parklands in Burkina Faso (West Africa) ABSTRACT Objective: Climatic factors influence tree transpiration. The objective of this research is to measure the transpiration of different tree species along a climatic gradient in agroforestry parklands and to investigate its potential impact on crops in order to formulate agroforestry parklands management recommendations. Methodology and results: Agroforestry parklands with Vitellaria paradoxa and Parkia biglobosa in association with Sorghum bicolor (L.) Moench located in three agroecological zones were studied. Heat ratio and sap flow methods were used to measure tree transpiration. Grain yields below the crown were measured. Tree transpiration increased with decreasing precipitation and increasing temperature, and is more pronounced in V. paradoxa. Grain yields of sorghum were modestly explained by tree transpiration depending on tree species. Conclusion and application of results: Competition for water access was found to depend little on rainfall, but more on the amount of evapotranspiration, which varied among tree species. The application of tree management options that would reduce tree transpiration would improve crop performance by reducing tree-crop competition for water in agroforestry parklands.
... Microcores (15mm and 25 mm long, 2mm diameter, Trephor (Rossi et al., n.d.) microcorers (from CMC, Italy on behalf of UNIVERSITA' di PADOVA)) were taken near all 36 target oak probeset installation positions. These were used to determine wood hydraulic properties (Edwards and Warwick, 1984;Marshall, 1958) for sap flux calculations (see also stage 4, Table A2 and definitions Table A1). In summer 2021 280 woodcores taken from some of the target oaks were further analysed to check the conversion (xylem woody matrix) factors from heat velocity to sap velocity and to verify the active xylem radial width. ...
... At stage 3, the Green and Clothier (1988) polynomial factors were used for wound compensation. For stage 4, the conversion factor c1 was derived (Eq.(A4) and Eq.(A5)) to calculate xylem sap velocity from heat velocity in oakwood (Edwards and Warwick, 1984;Marshall, 1958). Measurement of wet and dry woodcores and microcores previously described provided data for derivation. ...
Predicting how increased atmospheric carbon dioxide levels will affect water usage by whole mature trees remains a challenge. The present study focuses on diurnal (i.e. daylight) water usage of old growth oaks within an experimental treatment season from April to October inclusive. Over five years, from 2017 to 2022, we collected 12,259 days of individual tree data (770,667 diurnal sap flux measurements across all treatment months) from eighteen oaks (Quercus robur L.) within a large-scale manipulative experiment at the Birmingham Institute of Forest Research (BIFoR) Free-Air CO2 Enrichment (FACE) temperate forest in central England, UK. Sap flux data were measured using the compensation heat pulse (HPC) method and used to calculate diurnal tree water usage per day (TWU) across the leaf-on seasons. Six trees were monitored in each of three treatments: FACE infrastructure arrays of elevated (+150 mmol mol-1) CO2 (eCO2); FACE infrastructure control ambient CO2 (aCO2) arrays; and control Ghost (no-treatment-no-infrastructure) arrays. For each tree, sap flux demonstrated a circumferential imbalance across two orientations of the stem. Median and peak (95 %ile) diurnal sap flux increased in the spring from first leaf to achieve peak daily values in summer months (July, August) for all trees in the study. TWU increased similarly, declining more slowly towards full leaf senescence (Oct/ Nov). Water usage varied between individual oaks in July of each year. TWU was linearly proportional to tree bark radius, Rb, at the point of probeset insertion ca. 1.1–1.3 m above ground level (ca. 3.1 litres d-1 mm-1 radius; 274 mm ≤ radius ≤ 465 mm). We also found that bark radius is a very good proxy for canopy area, Ac. Ac was linearly proportional to Rb (ca. 616.5 m2 mm-1 radius), which implies a mean July water usage of almost 5 litres m-2 of projected canopy area in the BIFoR FACE forest. In comparing seasonal responses, TWU was seen to vary by treatment season precipitation amounts and in response to cloudy days, also seen from the diurnal sap flux data. We normalised TWU by individual tree bark radius Rb, which we call TWUn. TWUn treatment comparisons differed year on year. Trees treated with eCO2 compared to the aCO2 controls exhibited different median TWUn results both within and between treatment years, but with no consistency in this difference. Infrastructure control trees exhibited higher TWUn than Ghost, no-infrastructure, trees, especially for the larger trees. The greater TWUn may be due to one or more of several factors: the installation or operation of FACE infrastructure; or to array-specific differences in soil moisture, slope, soil respiration; or sub-dominant tree species presence. The results indicate the importance of infrastructure controls in forest FACE experiments. This first set of plant water usage results encourages the conclusion that old growth oak forests cope well with eCO2 conditions in the FACE(sic) of climate change. From our tree-centred viewpoint, the results reported improve our understanding of future-forest water dynamics of old growth forest and could contribute to the development of more realistic dynamic vegetation models.
... All the indexes were determined at 8:00 AM, 10:00 AM, 12:00 PM PM, 4:00 PM, and 6:00 PM on each day during three consecutive days, in each of the nological stages. The in situ water potential and sap flow rates were determined simultaneously a bottom of culms according to the methods of Dixon et al. [40] and Marshall [41], re tively, by using a PSY1 Stem Psychrometer and a SFM1 Stem Psychrometer (ICT Int tional, Armidale, NSW, Australia), so as to determine the water storage levels in the c (Figure 2). High transpiration pull in the midculm, associated with a low rate of sap and low water potential at the base of the culm, indicated an adequate supply of w stored in the culms to carry out photosynthesis and transpiration reactions. ...
... High transpiration pull in the midculm, associated with a low rate of sap and low water potential at the base of the culm, indicated an adequate supply of w stored in the culms to carry out photosynthesis and transpiration reactions. The in situ water potential and sap flow rates were determined simultaneously at the bottom of culms according to the methods of Dixon et al. [40] and Marshall [41], respectively, by using a PSY1 Stem Psychrometer and a SFM1 Stem Psychrometer (ICT International, Armidale, NSW, Australia), so as to determine the water storage levels in the culms (Figure 2). High transpiration pull in the midculm, associated with a low rate of sap flow and low water potential at the base of the culm, indicated an adequate supply of water stored in the culms to carry out photosynthesis and transpiration reactions. ...
Reasonable management could produce the good growth of bamboo plants. There are few studies in bamboo that integrate phenology and ecophysiological traits; in this case, water relations, photosynthetic rates and carbohydrate content in different organs of Neosinocalamus affinis were determined. The moisture content was easily affected by the local precipitation and showed a similar trend in leaves and branches, with the highest values in July and August, but did not vary significantly between vegetative phenological stages in culms. The emergence and growth of shoots caused an apparent decrease in the moisture content of 1-year culms. NSC content showed a similar trend in culms and branches in classes of different ages and decreased progressively from March through November and then increased in the following months. Net photosynthetic rate and transpiration pull showed the highest values in July and then decreased constantly, which implied that a great deal of water was consumed for photoassimilate synthesis. The net photosynthetic rates of leaves were significantly affected by the water status of culms in the dry season, but correlated significantly only with the leaf water content in the wet season for the sufficient water supply. The transpiration pulls, water potential and sap flow rates revealed the water status of culms better than the water content of culms. The shoot germination and growth of N. affinis were more dependent on the photoassimilate accumulation in the early stage from May to July. There was no real dormancy period for N. affinis due to its apparent photoassimilate accumulation and water flow in January. This suggested that proper irrigation was essential during leaf and branch extension during the dry season.
... Heat-pulse methods -based on the fundamental conduction-convection equation presented by Marshall (1958) -offer an alternative to the more commonly used thermal dissipation methods. Heat pulse methods measure the velocity (V h ) of a short heat pulse ($2 s) which can then be converted to SFD and whole-tree flow based on the physiological parameters of the sap wood. ...
... where B is a correction coefficient that corresponds to a specific wound size. Pulse velocity is converted to sap flux density (g cm À2 s À1 ), using measured properties of the wood [34]: ...
Accurate estimation of transpiration in individual trees is important for understanding plant responses to environmental drivers, closing the water balance in forest stands and catchments, and calibrating earth system models, among other applications. However, the cost and power consumption of commercial systems based on sap flow methods still limit their usage. We developed and tested a cost-effective (<$150), simple to construct, and energy efficient sap flux device based on the heat pulse method. Energy savings were achieved by reducing the voltage of heat pulses and using an internal clock to completely shut down the device between pulses. Device accuracy was confirmed by laboratory estimates of sap flow made on excised branches of Acer saccharum and Tsuga canadensis (adjusted R² = 0.96). In a 174-d field installation of 12 devices, batteries (eight rechargeable Ni-MH AA) needed to be replaced every 14 days. Sap flux measurements in the field tracked expected variations in vapor pressure deficit and tree phenology. The low cost, compact design, reliability, and power consumption of this device enable sap flux studies to operate with more replication and in more diverse ecological settings than has been practical in the past.
... Transpiration measurements have a long history and have been obtained in a variety of ways [6][7][8]. Marshall [9] measured the rate of sap flow in conifers using the principles of heat transport to estimate the tree transpiration. McNaughton and Black [10] used the energy balance to measure the evapotranspiration from a young Douglas fir forest. ...
... Only a section of the xylem tissue contains sap, and in our study the sap flow velocity (V s , mm h −1 ) was calculated following the method used by Marshall [9] and modified by Barrett et al. [12]: ...
Transpiration is fundamental to the understanding of the ecophysiology of planted forests in arid ecosystems, and it is one of the most uncertain components in the ecosystem water balance. The objective of this study was to quantify differences in whole-tree transpiration estimates obtained with a heat ratio probe in a secondary Qinghai spruce (Picea crassifolia) forest. To do this, we analyzed the sap flux density values obtained with sensors installed in (1) holes drilled in the preceding growing season (treatment) and (2) holes drilled in the current year (control). The study was conducted in a catchment in the Qilian Mountains of western China. The results showed that an incomplete diameter at breast height (DBH) range contributed to 28.5% of the overestimation of the sapwood area when the DBH > 10 cm and 22.6% of the underestimation of the sapwood area when the DBH < 5 cm. At daily scales, there were significant differences in both the quantity and magnitude of the sap flux density between the treatment and control groups. Furthermore, a linear regression function (R2 = 0.96, p < 0.001), which was almost parallel to the 1:1 reference line, was obtained for the sap flux density correction for the treatment group, and the daily sap flux density and whole-tree transpiration were underestimated by 36.8 and 37.5%, respectively, at the half-hour scale. This study illustrates uncertainties and a correction function for sap flow estimations in young Qinghai spruce trees when using heat ratio sensors with minimal damage over multiple growing seasons.
... Where k is the thermal diffusivity of the wood, set to 0.0025 cm 2 s − 1 in the study (Marshall et al., 1958). x is the distance between the heating needle and any probe, fixed at 0.5 cm, v 1 and v 2 are the increases in temperature in paired thermistors (Burgess, et al., 2001). ...
... The instrument SFM1 measured the sap velocity using heat ratio method (Schoppach et al., 2021), which measures temperature change ratio of two thermistors (Burgess et al., 2001). The thermal diffusivity of cotton stem for calculating the sap velocity of plant stem (V h , cm·h -1 ) was 0.002 5 cm 2 ·s -1 (Marshall, 1958;Chen et al., 2022). ...
Background
Water deficit is an important problem in agricultural production in arid regions. With the advent of wholly mechanized technology for cotton planting in Xinjiang, it is important to determine which planting mode could achieve high yield, fiber quality and water use efficiency (WUE). This study aimed to explore if chemical topping affected cotton yield, quality and water use in relation to row configuration and plant densities.
Results
Experiments were carried out in Xinjiang China, in 2020 and 2021 with two topping method, manual topping and chemical topping, two plant densities, low and high, and two row configurations, i.e., 76 cm equal rows and 10+66 cm narrow-wide rows, which were commonly applied in matching harvest machine. Chemical topping increased seed cotton yield, but did not affect cotton fiber quality comparing to traditional manual topping. Under equal row spacing, the WUE in higher density was 62.4% higher than in the lower one. However, under narrow-wide row spacing, the WUE in lower density was 53.3% higher than in higher one (farmers’ practice). For machine-harvest cotton in Xinjiang, the optimal row configuration and plant density for chemical topping was narrow-wide rows with 15 plants m ⁻² or equal rows with 18 plants m ⁻² .
Conclusion
The plant density recommended in narrow-wide rows was less than farmers’ practice and the density in equal rows was moderate with local practice. Our results provide new knowledge on optimizing agronomic managements of machine-harvested cotton for both high yield and water efficient.
... Additionally, we placed different sap flow meters (SFM1 instrument, ICT International, Australia): one at northwestern side of the maple and three surrounding the birch treeś stem (north, northwest and south). All sap flow sensors work according to the heat ratio method by Marshall (1958). Dendrometers (DR Radius Dendrometer, Ecomatik, Dachau, Ger170; accuracy max. ...
... The sapwood core was weighed after drying in the oven at 103 °C for 48 h (Sun et al. 2022a). The thermal diffusivity (k (mm 2 /s)) of sapwood measures the transient thermal response of sapwood to temperature change and is calculated using Eq. 1 (Marshall 1958). ...
Key message
The high-quality sap flow dataset of Melaleuca styphelioides could assists local councils in assessing tree water use and aids in the development of an urban tree sustainable planting management plan
Trees have a vital part to play in urban ecosystems, offering ecological, economic, and social advantages in addition to beautifying our suburbs. Knowledge of tree water use in urban environments is crucial for facilitating urban greening when there is a perception that growing trees on the street verge on expansive soils poses a risk to pavement and buildings. Information on long-term water use by individual trees in an urban environment is essential for local councils in developing urban tree management plans for sustainable planning of trees; however, this information is scarce. Micrometeorological models have commonly been used to estimate the canopy transpiration of plants in the absence of sap flow data. However, the reliability and accuracy of these models have rarely been assessed using sap flow measurements at the field site. This study aimed to provide the water use data of four individual Australian native Melaleuca styphelioides Sm. using sap flow instruments over 25 months. Tree transpiration, estimated based on three commonly used micrometeorological models using weather parameters and tree characteristics, was assessed and compared with sap flow measurements by employing the linear regression statistical analysis. The results revealed that the modified Penman–Monteith (PM) model demonstrated the highest level of accuracy among the evaluated models, consistently yielding lower errors and providing more reliable estimates of tree water use. This suggests that this model may be more appropriate for predicting plant water use in situations where sap flow data are unavailable.
... The methodological base developed by now makes it possible to measure the characteristics of moisture flow in the xylem (xylem flow-sap flow) in tree trunks with a high time resolution [10,11,13,14,18]. Based on it, various types of measuring instruments have been developed in which the supplied heat is used as a tracer. ...
in the trunks of white fir (Abies nephrolepis), the analysis of the main factors of the process of moisture transport in tree trunks, and the results of modeling hourly series of xylem flow rates. The analysis of factors was made with the use of the method of principal components, and the reproduction of individual
series of xylem consumption was based on a multiple linear regression model. The evaluated volume of the transported moisture flux in fir trees over the vegetation period in 2020 varied from 1720 to 5620 L, depending on tree diameter, and the mean daily velocity of stem sap flow in the xylem varied from 0.3 to 1.0 cm/h. Regression analysis was used to find the optimal structure of the empirical model, which includes two predictors — air temperature and humidity. The empirical coefficients of regression equations were determined for each tree based on calibration samples. The results of testing on long enough test samples showed that the model series of xylem discharge on a complete sample (from May to October) for three test trees out of four
are close to the measured values: the coefficient of correlation is 0.79–0.88, Nash–Sutcliffe coefficient is 0.62–0.85. The simulation efficiency improves significantly when samples for individual months are used: the correlation coefficient is 0.87‒0.94, the Nash–Sutcliffe coefficient is 0.73‒0.97.
... J s was calculated using the Dual Method Approach (Forster 2019(Forster , 2021. This method combines the heat ratio method (HRM) (Marshall 1958, Burgess et al. 2001) and the Tmax method (Cohen et al. 1981). Thereby, the method defines slow and reverse flow assuming conductive heat transfer (using HRM). ...
Beneficial and negative effects of species interactions can strongly influence water fluxes in forest ecosystems. However, little is known about how trees dynamically adjust their water use when growing with interspecific neighbours. Therefore, we investigated the interaction effects between Fagus sylvatica (European beech) and Picea abies (Norway spruce) on water use strategies and aboveground structural characteristics. We used continuous in-situ isotope spectroscopy of xylem and soil water to investigate source water dynamics and root water uptake depths. P. abies exhibited a reduced sun-exposed crown area in equally mixed compared to spruce dominated sites, which was further correlated to a reduction in sap flow of −14.5 ± 8.2%. Contrarily, F. sylvatica trees showed +13.3 ± 33.3% higher water fluxes in equally mixed compared to beech dominated forest sites. Although a significantly higher crown interference by neighboring trees was observed, no correlation of water fluxes and crown structure was found. High time-resolved xylem δ2H values showed a large plasticity of tree water use (−74.1‰ to −28.5‰), reflecting the δ2H dynamics of soil and especially precipitation water sources. F. sylvatica in equally mixed sites shifted water uptake to deeper soil layers, while uptake of fresh precipitation was faster in beech dominated sites. Our continuous in-situ water stable isotope measurements traced root water uptake dynamics at unprecedented temporal resolution, indicating highly dynamic use of water sources in response to precipitation and to neighbouring species competition. Understanding this plasticity may be highly relevant in the context of increasing water scarcity and precipitation variability under climate change.
... The sap ow was continuously measured in a time interval of 30 minutes from cotton owering to harvesting times.The instrument SFM1 measures sap velocity using heat ratio method(Schoppach et al., 2021), which measures temperature change ratio of two thermistors(Burgess et al., 2001). The thermal diffusivity of cotton stem for calculating sap velocity of a plant stem (V h , cm hr − 1 )was 0.0025 cm 2 s − 1(Marshall, 1958;Chen et al., 2022).Plant transpiration (cm 3 hr − 1 ) was the production of sap area of a plant (cm 2 )and sap velocity (cm hr − 1 ). Say velocity was output of the instrument measurements and sap area of cotton plant was measured at eld condition. ...
Improving crop yield, quality and water use are crucial in dealing with climate change and water scarcity in arid regions. With the advent of wholly mechanized technology for cotton planting in Xinjiang, it is important to determine the mode with optimizing row configuration, plant density and topping. This study aims to explore the effects of two plant densities, chemical topping vs manual topping under two different common row configurations, i.e. 76 cm equal rows and 10+66 cm narrow-wide rows, which are used for matching harvest machine. The cotton growth, yield, fiber quality and transpiration,were investigated. Experiments were carried out in Xinjiang China, in 2020 and 2021. Seed yield was high in 10 plants m ⁻² for equal rows and 15 plants m ⁻² for narrow-wide rows. Chemical topping increased fiber length by 2.1% comparing to the traditional manual. Micronaire was 9.6% higher in equal rows than in narrow-wide rows. Under equal row spacing, the WUE in 18 plants m ⁻² and was 62.4% higher than in 10 plants m ⁻² . Under narrow-wide row spacing, the WUE in 15 plants m ⁻² was 53.3% higher than in 25 plants m ⁻² . For machine-harvest cotton in Xinjiang, the optimal managements for both high yield and water saving could be 15 plants m ⁻² , narrow-wide rows and applying chemical topping.The results provide a useful approach for optimizing cotton managements and water use.
... The system used in this experiment was developed by ICT International Pty Ltd (SFM1) to measure the water uptake rate in liters per hour (L.h − 1 ). It uses the principle of the Heat Ratio Method (Burgess et al., 2001;Marshall, 1958) to measure high, low and reverse flow rates in both small woody stems and roots as well as in large trees. ...
... Measuring plant sap flow has long been a traditional method to quantify transpiration. Various techniques have been employed in this field, including the dye method, isotope tracing method, gravimetric method, magnetic fluid mechanic method, whole-tree container method, rapid weighing method, and heat technique [10][11][12][13]. In forest environments, traditional methods such as the whole-tree container method and rapid weighing method may introduce potential errors during sampling and measurement. ...
The measurement of plant sap flow has long been a traditional method for quantifying transpiration. However, conventional direct measurement methods are often costly and complex, thereby limiting the widespread application of tree sap flow monitoring techniques. The concept of a Virtual Measurement Instrument (VMI) has emerged in response to this challenge by combining simple instruments with Artificial Intelligence (AI) algorithms to indirectly assess specific measurement objects. This study proposes a tree sap flow estimation method based on environmental factors and AI algorithms. Through the acquisition of environmental factor data and the integration of AI algorithms, we successfully achieved indirect measurement of tree sap flow. Accounting for the time lag response of the flow to environmental factors, we constructed the Magnolia denudata sap flow estimation model using the K-Nearest Neighbor (KNN), Random Forest (RF), Backpropagation Neural Network (BPNN), and Long Short-Term Memory network (LSTM) algorithms. The research results showed that the LSTM model demonstrated greater reliability in predicting sap flow velocity, with R2 of 0.957, MAE of 0.189, MSE of 0.059, and RMSE of 0.243. The validation of the target tree yielded an R2 of 0.821 and an error rate of only 4.89% when applying the model. In summary, this sap flow estimation method based on environmental factors and AI provides new insights and has practical value in the field of tree sap flow monitoring.
... Sap flow calculation was based on the Dual Method Approach (DMA, Forster, 2019, 2020), combining the Heat Ratio Method (Marshall, 1958;Burgess et al., 2001) and the T max method (Cohen et al., 1981). ...
The microclimate within forest stands might change rapidly in space and time due to the complex three-dimensional structure of forests. We are nowadays able to map the structure of forest stands in high detail, due to advances in Light Detection and Ranging (LiDAR) technologies such as terrestrial laser scanning (TLS). But measurements of microclimatic properties are often still bound to sensors which are only able to provide point measurements. Therefore, we propose a novel method to map the surface temperatures of a mature forest stand based on sensor fusion of TLS and thermal imaging as a time series. We provide insights into small scale temperature changes like sun flecks, or different bark structures. The results were also indicative of a cooling effect on tree trunks due to the uptake of cooler soil water, which is directly linked to the sap flux within the tree. While being only a first proof of concept of this method, our study provides a successful characterisation of spatio-temporal dynamics in trunk temperatures and indicates a potential promising correlation with ecohydro-logical processes. Our results suggest this novel technology to open various opportunities for future research and ecosystem monitoring.
... Wound correction coefficients described by Burgess et al. (2001) were used to correct HPV signals for sapwood wounding. Sap flux densities obtained from a method described by Marshall (1958), were finally converted to tree total Sapflow values using the calculation of the sum of the cross-sectional area for individual tree stems and the products of sap flux densities. Daily, monthly, and annual Sapflow volumes for each tree were assumed to equate to transpiration (T). ...
... The sap flow rate (Q, cm h -1 ) was calculated from heat pulse velocity according to424 Burgess et al. V h is the uncorrected heat pulse velocity (cm h -1 ); k is the thermal diffusivity of fresh wood (for which429 the nominal value is given as 0.0025 cm 2 s -1 )(Marshall, 1958); x is the distance between the heater and 430 either of the temperature probes (the distance being 5 mm in our case); v 1 and v 2 are increases in of the water (1.00 g cm -3 ). The sap flow data of each root was corrected for probe misalignment,436 according toBurgess et al. (1998). ...
Many tree species have developed extensive root systems that allow them to survive in arid environments by obtaining water from a large soil volume. These root systems can transport and redistribute soil water during drought by hydraulic redistribution (HR). A recent study revealed the phenomenon of evaporation-driven hydraulic redistribution (EDHR), which is driven by evaporative demand (transpiration). In this study, we confirmed the occurrence of EDHR in Chinese white poplar (Populus tomentosa) through root sap flow measurements. We utilized micro-computed tomography technology to reconstruct the xylem network of woody lateral roots and proposed conceptual models to verify EDHR from a physical perspective. Our results indicated that EDHR is driven by the internal water potential gradient within the plant xylem network, which requires three conditions: high evaporative demand, soil water potential gradient, and special xylem structure of the root junction. The simulations demonstrated that during periods of extreme drought, EDHR could replenish water to dry roots and improve root water potential up to 38.9%-41.6%. This highlights the crucial eco-physiological importance of EDHR in drought tolerance. Our proposed models provide insights into the complex structure of root junctions and their impact on water movement, thus enhancing our understanding of the relationship between xylem structure and plant hydraulics.
... (Ginestar & Castel, 1995) . (Marshall, 1958) . 21 / 3 9838 / 1 3322 / 3 -3333 / 3 22 / 3 8554 / 1 3325 / 3 -3334 / 3 23 / 3 3221 / 2 3328 / 3 -3334 / 3 24 / 3 3195 / 2 3331 / 3 -3335 / 3 21 / 3 1832 / 2 3339 / 3 -3331 / 3 29 / 3 3449 / 2 3341 / 3 -3339 / 3 3 / 3 4839 / 2 ...
Abstract
Introduction
The lack of giving attention to the water needs of trees can lead to water wastage or water stresses in trees. Accurate irrigation of trees requires the availability of information on the amount and manner of water consumed in trees. However, for the precise implementation of irrigation, a reliable method of measuring the plant's water requirements is needed to avoid water stress. Existing methods of measuring the water requirement of trees can often be used for a part of the tree (such as stem or leaf) and require the presence of the user and spend time and money, so these methods are often used in research applications.
Materials and Methods
A sap-flow meter device was also developed to make a heat pulse in a tree trunk every 15 minutes. The device consists of measuring probes, a processor unit, and a data logger. In order to evaluate, the device the probes were installed on the trunk of the Ficus Benjamina tree in a controlled environment, at two different heights, and the results of the sap flow through the vascular tissue were compared with the data obtained by the lysimetric method. The Ficus Benjamina tree with a trunk diameter of 3.5 cm and height of 196 cm was prepared in the summer of 2022. By measuring the speed of destruction of the heat pulse and using the theorem of heat transfer, and assuming that heat transfer is done only through the sap flow from vascular tissue, the amount of sap flow was estimated by the Heat ratio method (HRM).
The trunk was triple drilled 1.5 mm in diameter and 25mm in depth. After drilling, the probes were placed in the holes. In order to avoid heat transfer from the probes to the outside, the trunk was covered by Glass wool insulation (Figure 3). To measure the reliability of the device, the lysimetric method was used to measure the tree transpiration. For this purpose, the soil surface of the pot was covered with cellophane so that the evaporation and weight reduction of the pot were done only from the leaves of the tree. Every hour, the weight of the pot was measured by a digital scale. Changes in the weight of the pot indicate the amount of water evaporated. In other words, this water has been transferred through the vascular tissue of the tree trunk.
Results and Discussion
The results showed that the sap-flow meter device measures the amount of water consumption of the tree with a little overestimation compared to the value obtained by the lysimetric method. Sap flow and transpiration follow a similar trend so that it increases during the day and reaches their peak value in the middle of the afternoon. This value reached 17.98 ml.h-1 for sap flow and 16 ml.h-1 for transpiration (by lysimetric method), followed by a rapid decrease in the late afternoon as the air was cooled. In addition, the results of device measurements showed spraying irrigation on the leaves lowers the speed and amount of sap flow. Water spraying on the leaves affects the speed of sap flow, so that when the canopy gets wet, water evaporation from the leaf surface made them colder, and the speed of sap flow decreases significantly.
The v1/v2 ratio is not constant with time, and selecting the appropriate measurement starting time is essential for the working cycle of the device for the data acquisition. It is essential to measure (by the device) the difference between temperature probes 40 seconds after heat pulse generation. The sap flow and transpiration followed a similar trend during the experiments, the sap flow and transpiration increased during the daytime and reached their peak value in the middle of the afternoon, which is 17.98 ( ) for the first day and 19.75 ( ) sap flow in the second day. The related lysimetric method transpirations reached 16 ( ), followed by a rapid decrease in the late afternoon.
Conclusion
According to the obtained results, the following are deduced from the developed device:
Sap flow and transpiration follows a similar trend during the test period, and the estimated value of the sap flow is 30 percent higher than that of the lysimetric method.
The device was able to show the effect of surface irrigation well, irrigation by spray affects the speed of sap flow so that when the canopy gets wet, the speed of sap flow decreases noticeably. Sap flow and transpiration are directly proportional to air temperature, and canopy temperature, and inversely proportional to relative humidity.
The results showed that the heat pulse method after calibration can reliably estimate the amount of sap flow in the vascular tissue of trees.
Keywords
Sap flow Water tension Heat ratio method Lysimetric
... The heat pulse velocities, calculated according to Burgess et al. (2001) were corrected for wounding caused by the drilling, using wound correction coefficients described by Swanson and Whitfield (1981). The corrected heat pulse velocities were then converted to sap flux densities according to the method presented by Marshall (1958). The data was also corrected for the density and moisture fraction of the wood according to the procedure by Burgess et al. (2001). ...
All commercial apple fruit (Malus Domestica (Borkh) exported from semi-arid regions are grown under irrigation with drip and micro sprinkler systems being the most widely used. Few studies have directly compared the physiological responses of fruit trees to these systems in detail leading to uncertainties around their performance. This study investigated variations in transpiration rates, tree water status, growth, water use partitioning, fruit yield and quality for trees growing on deep sandy soils under these two systems. Data were collected in a mature Royal Gala orchard in South Africa over three growing seasons. Tree transpiration was quantified using the heat ratio method of monitoring sap flow while the soil water balance approach was used to derive the evapo-transpiration (ET) rates. Leaf level results showed that one day after irrigation on hot dry days, the stomatal conductance was, on average, almost double for trees under micro than those under drip irrigation. There was more stress under drip with the minimum midday leaf water potential dropping to under-1.80 MPa compared to only around-1.20 MPa under micro sprinklers. Consequently, the tree transpiration per unit leaf area was substantially higher under micro sprinkler (2.9 L/m 2 /d) compared to 2.3 L/m 2 /d under drip (P ≤ 0.05). Canopy growth was slower under drip with peak leaf area index (LAI) around 2.1 compared to 2.7 under the micro sprinkler system. The micro sprinkler system had a more active ground cover than the drip. At peak canopy cover in summer, up to 28% of ET was derived from the orchard floor under micro compared to only 15% under drip. However, fruit size and fruit quality were lower under drip compared to micro sprinkler irrigated trees. The study highlights that while water savings are high under drip irrigated orchards on sandy soils, trees tend to experience considerable water stress culminating in smaller fruit of compromised quality.
... There are several methods that correlate transpiration with sap flow and have been used in research concerning the use of water by plants, such as the thermal dissipation method [8,9], the heat equilibrium method [10,11] and the heat pulse velocity method, mainly the heat ratio method, initially proposed by [12] and later improved by [13]. This method has advantages over other methods, as it allows the measurement of low (slow) and reverse (negative) flows [14,15], which helps in the correct determination of the percentage of sap flow that is destined for rehydration and redistribution in the root system. ...
Brazilian mahogany (Swietenia macrophylla King) is a forest species of economic and environmental interest due to its wood’s great finish and its use in recovering and recomposing ecosystems. However, clarification on how this species uses water resources is still necessary. This study proposes to evaluate sap flow and transpiration behavior in young Brazilian mahogany plants under variable conditions of soil water potential. We conducted the study in a protected environment and cultivated the plants in weighing lysimeters wherein the soil underwent potential variations between -10 kPa and -35 kPa during periods of water restriction, rehydration, and full irrigation. To quantify water use in the mahogany plants, we measured sap flow through heat pulses, transpiration through the weighing lysimeters, and evapotranspiration by weather variables. Sap flow and transpiration are affected negatively by soil water potential variation. The leaves lost water to the atmosphere under water deficit conditions, even with the absence of upward sap flow. Sap flow was restored four days after irrigation had resumed.
... Assume-se que o transporte daágua do solo até a atmosfera realiza-se de forma contínua e que a movimentação daágua no interior do caule seja similar ao deslocamento daágua em meio poroso (Marshall, 1958). Os métodos normalmente utilizados para a medição de fluxo de seiva são baseados em princípios de termometria. ...
... All sensors were installed at breast height. The measured increase in sapwood temperature following the release of a heat pulse downstream and upstream of the heater is calculated into heat pulse velocity (V h ) according to Marshall (1958) as ...
Root water uptake (RWU) is an important critical zone process, as plants can tap various water sources and transpire these back into the atmosphere. However, knowledge about the spatial and temporal dynamics of RWU and associated water sources at both high temporal resolution (e.g. daily) and over longer time periods (e.g. seasonal) is still limited. We used cavity ring-down spectroscopy (CRDS) for continuous in situ monitoring of stable water isotopes in soil and xylem water for two riparian willow (Salix alba) trees over the growing season (May to October) of 2020. This was complemented by isotopic sampling of local precipitation, groundwater, and stream water in order to help constrain the potential sources of RWU. A local eddy flux tower, together with sap flow monitoring, soil moisture measurements, and dendrometry, was also used to provide the hydroclimatic and ecohydrological contexts for in situ isotope monitoring. In addition, respective bulk and twig samples of soil water and xylem water were collected to corroborate the continuous in situ data. The monitoring period was characterised by frequent inputs of precipitation, interspersed by warm dry periods, which resulted in variable moisture storage in the upper 20 cm of the soil profile and dynamic isotope signatures. This variability was greatly damped at 40 cm, and the isotopic composition of the subsoil and groundwater was relatively stable. The isotopic composition and dynamics of xylem water were very similar to those of the upper soil, and analysis using a Bayesian mixing model inferred that overall ∼90 % of RWU was derived from the upper soil profile. However, while for the soil water signatures, the direct equilibrium method showed good comparability with in situ results, for xylem water, the cryogenic extractions signatures were only moderately or not at all comparable. Sap flow and dendrometry data indicated that soil water availability did not seriously limit transpiration during the study period, though it seemed that deeper (>40 cm) soil water provided a higher proportion of RWU (∼30 %) in a drier period in the late summer. The study demonstrates the utility of prolonged real-time monitoring of natural stable isotope abundance in soil–vegetation systems, which has great potential for the further understanding of ecohydrological partitioning under changing hydroclimatic conditions.
... (birch). More recently, the much less destructive thermometric methods (Marshall, 1958;Granier, 1985) became the dominant approach to investigate sap flux velocities and the role of dye tracers was mainly reduced to a supplementary mean to determine conducting sapwood areas (Dawson, 1998;McJannet et al., 2007;Lubczynski et al., 2017). ...
A vast majority of studies investigating the source depths in the soil of root water uptake with the help of water stable isotopes implicitly assumes that the isotopic signatures of root water uptake and xylem water are identical. In this study we show that this basic assumption is not necessarily valid, since water transport between the root tips and an observed point above the root zone is not instantaneous. However, to our knowledge no study has yet tried to explicitly assess the distribution of water transport velocities within the xylem. With a dye tracer experiment we could visualize how the transport of water through the xylem happens at a wide range of velocities which are distributed unequally throughout the xylem. In an additional virtual experiment we could show that, due to the unequal distribution of transport velocities throughout the xylem, different sampling approaches of water stable isotopes might effectively lead to xylem water samples with different underlying age distributions.
... 3a). Following the release of a heat pulse, the ratio of temperature 204 increase between downstream and upstream thermistor was measured and the heat pulse 205 velocity was calculated following Eq.k is thermal diffusivity of fresh wood set to 0.0025 cm 2 s -1(Marshall 1958), x is the208 distance between the needles (0.5 cm), and v 1 and v 2 are the increases in temperature in the 209 downstream and upstream thermistor, respectively. Installation of the needles required drilling 210 into the conductive area called sapwood. ...
... Tree transpiration (mm day À1 ) was estimated using sap flow sensors cm À2 h À1 ) by accounting for sap and wood densities, specific heat capacities, and sapwood water content (Burgess et al., 2001;Marshall, 1958). An average wood density of 563.78 kg m À3 and water content of 38% were determined in two wood cores extracted from each of 10 trees in 2017 with increment borers (Haglöf Sweden, Sweden). ...
Land use affects evapotranspiration rates and is a primary driver of the catchment water balance. The water balance of two catchments in southeastern Australia dominated by either grazed pasture or blue gum (Eucalyptus globulus) plantation was studied, focusing on the patterns of evapotranspiration (ET) throughout the year. Rainfall, streamflow, and groundwater levels measured between 2015‐2019 were combined to estimate annual ET using a water balance equation. In the pasture, eddy covariance was used to measure ET from the catchment. Sap flow measurements were used to estimate tree transpiration in May 2017 – May 2018 and Feb 2019 – Feb 2021 in two different plots within the plantation. The tree transpiration rates were added to interception, estimated as a percentage of annual rainfall, to calculate ET from the plantation catchment. ET in the pasture showed strong seasonal cycles with very low ET rates in summer and ET rates in spring that were larger than the transpiration rates in the plantation, where trees transpired consistently throughout the year. The estimated annual ET from the water balance equation was comparable to ET estimated from other measurements. In the pasture, ET on average accounted for 88% of annual rainfall, while ET in the plantation was on average 93% of rainfall, exceeding it in the years with annual rainfall lower than about 500 mm. The difference between the ET rates in the plantation and the pasture was approximately 30 to 50 mm y‐1. The larger ET rates in the plantation were reflected in a gradual decrease in the groundwater storage. The larger ET rates were enough to cause a decrease in groundwater storage in the plantation but not in the pasture, where groundwater levels remained stable. This article is protected by copyright. All rights reserved.
... Of the various approaches to measurement of sap flow, the compensation heat-pulse method (CHPM) 22,23 has been successfully used in many studies including on apple 24 , pear 25 and olive 26 . In this study we have used the CHPM to investigate how sweet cherry tree water use responds to climatic variables, as influenced by rain covered and netted PCS, throughout the season. ...
Protected cropping systems (PCS) alter the plant growing environment, though understanding of this in ventilated systems and how the new climate affects tree water uptake is limited. Sap flow sensors and weather stations were deployed in 16-year-old ‘Lapins’ on ‘Colt’ rootstock cherry trees under a ventilated Voen PCS and in an adjacent bird netted PCS. Average and maximum temperatures were consistently higher (14.7 °C and 22.9 °C) while total daily solar radiation and average wind were consistently lower (12.9 MJ/m² and 0.2 m/s) in rain covered, in contrast to netted, PCS (13.9 °C, 21.3 °C, 13.7 MJ/m² and 0.9 m/s). Over the season, a threefold lower daily sap flow rate was observed under rain covered PCS. Using generalised additive modelling (GAM), the influence of individual climate parameters on sap flow were predicted. Whilst sap flow was only slightly affected by relative humidity (RH) less than 60%, above this threshold sap flow rapidly declined under rain covered PCS whereas sap flow more gradually declined above 20% RH under netted PCS. Overall, our novel modelling approach led to the discovery of the 60% RH critical threshold on predicted sap flow and the indirect effect that wind speeds have on sap flow under PCS.
... For example, the most established methods to quantify the amount of water transpired by trees are based on heat dissipation. Sensor needles are inserted at discrete points into the sapwood to relate heat dissipation to sap flow velocities (Granier 1987;Marshall 1958;Smith and Allen 1996). For estimating whole tree water use, sap flow velocities must be integrated over the sapwood area, which requires an accurate estimation of sapwood depth. ...
The cells in tree sapwood form a network of interconnected conduits which enables the transport of water and nutrients from the tree roots to the canopy. Sapwood depth must be assessed when tree water use is estimated from sap flow velocities. However, current approaches to assess sapwood depth are either not applicable universally, or require expensive instruments, the application of chemicals or laborious field efforts. Here, we present a new method, which estimates sapwood depth by thermal imaging of increment cores. Using a low-cost thermal camera for mobile devices, we show that the sapwood–heartwood boundary is detectable by a sharp increase in temperature. Estimated sapwood depths agree with dye estimates (R² = 0.84). We tested our approach on a broad range of temperate and tropical tree species: Quercus robur, Pinus sylvestris, Swietenia macrophylla, Guazuma ulmifolia, Hymenaea courbaril, Sideroxylon capiri and Astronium graveolens. In nearly all species, the methods agreed within 0.6 cm. Thermal imaging of increment cores provides a straightforward, low-cost, easy-to-use, and species-independent tool to identify sapwood depth. It has further potential to reveal radial differences in sapwood conductivity, to improve water balance estimations on larger scales and to quickly develop allometric relationships.
Miniaturized silicon thermal probes for plant’s sap flow measurement, or micro sap flow sensors, have advantages in minimum invasiveness, low power consumption, and fast responses. Practical applications in sap flow measurement has been demonstrated with the single-probe silicon micro sensors. However, the sensors could not detect flow directions and require estimating zero sap flow output that leads to significant source of uncertainty. Furthermore, silicon-needles would break easily during the insertion into plants. We present the first three-element micro thermal sap flow sensor packaged on a durable printed circuit board needle that can measure bidirectional flows with improved dynamics and precision. The performance of the newly designed calorimetric flow sensor was confirmed through precision calibration and field test on tomato stems. A calibration curve for a tomato stem was obtained with a sensitivity of 0.299 K/(µL mm⁻² s⁻¹) under the maximum temperature increase of 4.61 K. Results from the field test for one month revealed a correlation between the measured sap flux density and related conditions such as solar radiation, vapor pressure deficit, sunshade and irrigation. The developed sensor will contribute to practical long-term sap flow monitoring for small and delicate plants with minimal physical invasion.
Terrestrial water fluxes are substantially mediated by vegetation, while the distribution, growth, health, and mortality of plants are strongly influenced by the availability of water. These interactions, playing out across multiple spatial and temporal scales, link the disciplines of plant ecophysiology and ecohydrology. Despite this connection, the disciplines have provided complementary, but largely independent, perspectives on the soil‐plant‐atmosphere continuum since their crystallization as modern scientific disciplines in the late 20th century. This review traces the development of the two disciplines, from their respective origins in engineering and ecology, their largely independent growth and maturation, and the eventual development of common conceptual and quantitative frameworks. This common ground has allowed explicit coupling of the disciplines to better understand plant function. Case studies both illuminate the limitations of the disciplines working in isolation, and reveal the exciting possibilities created by consilience between the disciplines. The histories of the two disciplines suggest opportunities for new advances will arise from sharing methodologies, working across multiple levels of complexity, and leveraging new observational technologies. Practically, these exchanges can be supported by creating shared scientific spaces. This review argues that consilience and collaboration are essential for robust and evidence‐based predictions and policy responses under global change.
We measured the tree transpiration of 9-year-old, Eucalyptus grandis x Eucalyptus urophylla clonal hybrid (GU) trees in the commercial forestry area of northern KwaZulu-Natal, South Africa. Transpiration was measured using the heat ratio method over two consecutive hydrological years (2019/20 and 2020/21) and up-scaled to a stand level. Leaf area index (LAI), quadratic mean diameter, and soil water content (SWC) were measured over the same period using an LAI 2200 plant canopy analyser, manual dendrometers and CS616 sensors, respectively. The depth to groundwater was estimated to be approx. 28 m, using a borehole next to our study site. Results showed that transpiration followed a seasonal pattern, with daily mean of 2.3 mm‧tree−1‧day−1 (range: 0.18 to 4.55 mm‧tree−1‧day−1) and 3.3 mm‧tree−1‧day−1 (range: 0.06 to 6.6 mm‧tree−1‧day−1) for 2019/20 and 2020/21, respectively. Annual GU transpiration was higher than that found by international studies under similar conditions, but was within the same transpiration range as Eucalyptus genotypes in the KwaMbonambi area. Plantation water productivity, calculated as a ratio of stand volume to transpiration, was higher than for other published studies, which was attributed to a very high productive potential of the study site. Multiple regression using the random forests predictive model indicated that solar radiation, SWC and air temperature highly influence transpiration. There is a high possibility that our GU tree rooting system extracted water in the unsaturated zone during the dry season. Due to the use of short-term results in this study, the impact of GU on water resources could not be quantified; however, previous long-term paired catchment studies in South Africa concluded that Eucalyptus has a negative impact on water resources. Further research is suggested with long-term measurements of transpiration and total evaporation and an isotope study to confirm the use of water by GU trees in the unsaturated zone.
The vast majority of studies investigating the source depths in the soil of root water uptake with the help of stable water isotopes implicitly assumes that the isotopic signatures of root water uptake and xylem water are identical. In this study we show that this basic assumption is not necessarily valid, since water transport within a plant's xylem is not instantaneous. However, to our knowledge, no study has yet tried to explicitly assess the distribution of water transport velocities within the xylem. With a dye tracer experiment, we were able to visualize how the transport of water through the xylem happens at a wide range of velocities which are distributed unequally throughout the xylem. In an additional virtual experiment we could show that, due to the unequal distribution of transport velocities throughout the xylem, different sampling approaches of stable water isotopes might effectively lead to xylem water samples with different underlying age distributions.
We monitored stable water isotopes in liquid precipitation and atmospheric water vapour (δ v ) using in situ cavity ring‐down spectroscopy (CRDS) over a 2 month period in an urban green space area in Berlin, Germany. Our aim was to better understand the origins of atmospheric moisture and its link to water partitioning under contrasting urban vegetation. δ v was monitored at multiple heights (0.15, 2 and 10 m) in grassland and forest plots. The isotopic composition of δ v above both land uses was highly dynamic and positively correlated with that of rainfall indicating the changing sources of atmospheric moisture. Further, the isotopic composition of δ v was similar across most heights of the 10 m profiles and between the two plots indicating high aerodynamic mixing. Only at the surface at ~0.15 m height above the grassland δ v showed significant differences, with more enrichment in heavy isotopes indicative of evaporative fractionation especially after rainfall events. Further, disequilibrium between δ v and precipitation composition was evident during and right after rainfall events with more positive values (i.e., values of vapour higher than precipitation) in summer and negative values in winter, which probably results from higher evapotranspiration and more convective precipitation events in summer. Our work showed that it is technically feasible to produce continuous, longer‐term data on δ v isotope composition in urban areas from in situ monitoring using CRDS, providing new insights into water cycling and partitioning across the critical zone of an urban green space in Central Europe. Such data have the potential to better constrain the isotopic interface between the atmosphere and the land surface and to thus, improve ecohydrological models that can resolve evapotranspiration fluxes.
Our understanding of the movement and storage of water in typical Caatinga plants is still limited and often disregarded in water balance calculations. This is why the objective of this work was to evaluate the water storage dynamic in typical trees of the Caatinga biome during the dry, rainy and transition period by gauging the water content levels that cause the onset of leaf emergence. In a preserved Caatinga forest, soil and stem water content of six trees of the representative species catingueira ( Caesalpinia pyramidalis Tul.) were monitored with low‐cost capacitive sensors. Leaf moisture, leaf area index, leaf and stem water volume, and sap flow density were measured. The emergence of leaves occurred with a stem moisture of 0.32 m ³ m ⁻³ , and the leaf area index was maximum with a stem moisture of 0.34 m ³ m ⁻³ . Catingueira plants are able to absorb water below the soil water potential commonly determined as the permanent wilting point (−1.5 MPa). The volume of water stored in the plants represents 108% of the average volume stored in the Boqueirão reservoir during the study period.
Warming across the western United States continues to reduce snowpack, lengthen growing seasons, and increase atmospheric demand, leading to uncertainty about moisture availability in montane forests. As many upland forests have thin soils and extensive rooting into weathered bedrock, deep vadose‐zone water may be a critical late‐season water source for vegetation and mitigate forest water stress. A key impediment to understanding the role of the deep vadose zone as a reservoir is quantifying the plant‐available water held there. We quantify the spatiotemporal dynamics of rock moisture held in the deep vadose zone in a montane catchment of the Rocky Mountains. Direct measurements of rock moisture were accompanied by monitoring of precipitation, transpiration, soil moisture, leaf‐water potentials, and groundwater. Using repeat nuclear magnetic resonance and neutron‐probe measurements, we found depletion of rock moisture among all our monitored plots. The magnitude of growing season depletion in rock moisture mirrored above‐ground vegetation density and transpiration, and depleted rock moisture was from ∼0.3 to 5 m below ground surface. Estimates of storage indicated weathered rock stored at least 4%–12% of mean annual precipitation. Persistent transpiration and discrepancies between estimated soil matric potentials and leaf‐water potentials suggest rock moisture may mitigate drought stress. These findings provide some of the first measurements of rock moisture use in the Rocky Mountains and indicated rock moisture use is not just confined to periods of drought or Mediterranean climates.
Climate‐induced fire regimes may change species abundance and species composition in affected forest types, potentially altering pyro‐eco‐hydrologic feedbacks. In some fire‐prone forests across the globe, eco‐hydrologic thresholds (changing points, or tipping points, in ecohydrology when vegetation shifts from one steady vegetation to another) are being exceeded due to changes in relationships between climate, fire and vegetation. Following compound disturbances, forests may fail to maintain ecological resilience. Under multiple burn conditions, Eucalyptus regnans F. Muell. forests in south east Australia are highly vulnerable to ecological tipping points. In Victoria, over 189 000 ha of obligate seeder forests have been burned two or more times within 18 years. These short return‐interval fires allow Acacia dealbata to become the dominant overstorey species. Such a dramatic species replacement may result in a new evapotranspiration (ET) regime, leading to a new hydrologic state. Stand scale dynamic models were combined with field estimated ET in E. regnans and A. dealbata forests aged 10, 35 and 75/80 years. We found that long‐term forest structure, ET and water yield significantly diverge between E. regnans and A. dealbata forests with increasing age. These divergences imply a non‐equilibrium state after A. dealbata replaces E. regnans under high‐frequency fire conditions. In senescing A. dealbata , understorey transpiration contribution of 29.8% to system ET was similar to that of overstorey transpiration (31.2%), indicating the understorey and overstorey contribute equally to total ET at the final stage of Acacia forests. In contrast, in 75‐year‐old E. regnans forests, understorey contribution to the total system evapotranspiration is about 16%. This suggests that, after the Acacia life cycle finishes, the ET regime will transit into a new state that will be dominated by shrubby understorey species. Our findings suggest that this climate‐induced species replacement would decrease long‐term ET, inferring an increase in streamflow.
Transpiration is a globally important component of evapotranspiration. Careful upscaling of transpiration from point measurements is thus crucial for quantifying water and energy fluxes. In spatially heterogeneous landscapes common across the boreal biome, upscaled transpiration estimates are difficult to determine due to variation in local environmental conditions (e.g., basal area, soil moisture, permafrost). Here, we sought to determine stand‐level attributes that influence transpiration scalars for a forested boreal peatland complex consisting of sparsely‐treed wetlands and densely‐treed permafrost plateaus as land cover types. The objectives were to quantify spatial and temporal variability in stand‐level transpiration, and to identify sources of uncertainty when scaling point measurements to the stand‐level. Using heat ratio method sap flow sensors, we determined sap velocity for black spruce and tamarack for two‐week periods during peak growing season in 2013, 2017 and 2018. We found greater basal area, drier soils, and the presence of permafrost increased daily sap velocity in individual trees, suggesting that local environmental conditions are important in dictating sap velocity. When sap velocity was scaled to stand‐level transpiration using gridded 20 x 20 m resolution data across the ~10 ha Scotty Creek ForestGEO plot, we observed significant differences in daily plot transpiration among years (0.17 to 0.30 mm), and across land cover types. Daily transpiration was lowest in grid‐cells with sparsely‐treed wetlands compared to grid‐cells with well‐drained and densely‐treed permafrost plateaus, where daily transpiration reached 0.80 mm, or 30 % of the daily evapotranspiration. When transpiration scalars (i.e., sap velocity) were not specific to the different land cover types (i.e., permafrost plateaus and wetlands), scaled stand‐level transpiration was overestimated by 42 %. To quantify the relative contribution of tree transpiration to ecosystem evapotranspiration, we recommend that sampling designs stratify across local environmental conditions to accurately represent variation associated with land cover types, especially with different hydrological functioning as encountered in rapidly thawing boreal peatland complexes. This article is protected by copyright. All rights reserved.
Measurements of the thermal properties of the skin can serve as the basis for a noninvasive, quantitative characterization of dermatological health and physiological status. Applications range from the detection of subtle spatiotemporal changes in skin temperature associated with thermoregulatory processes, to the evaluation of depth-dependent compositional properties and hydration levels, to the assessment of various features of microvascular/macrovascular blood flow. Examples of recent advances for performing such measurements include thin, skin-interfaced systems that enable continuous, real-time monitoring of the intrinsic thermal properties of the skin beyond its superficial layers, with a path to reliable, inexpensive instruments that offer potential for widespread use as diagnostic tools in clinical settings or in the home. This paper reviews the foundational aspects of the latest thermal sensing techniques with applicability to the skin, summarizes the various devices that exploit these concepts, and provides an overview of specific areas of application in the context of skin health. A concluding section presents an outlook on the challenges and prospects for research in this field.
Biogeoscience is a rapidly growing interdisciplinary field that aims to bring together biological and geophysical processes. This book builds an enhanced understanding of ecosystems by focusing on the integrative connections between ecological processes and the geosphere, hydrosphere and atmosphere. Each chapter provides studies by researchers who have contributed to the biogeoscience synthesis, presenting the latest research on the relationships between ecological processes, such as conservation laws and heat and transport processes, and geophysical processes, such as hillslope, fluvial and aeolian geomorphology, and hydrology. Highlighting the value of biogeoscience as an approach to understand ecosystems, this is an ideal resource for researchers and students in both ecology and the physical sciences.
The specific heat of wood. of Agr
- F Dunlop
DUNLOP, F. The specific heat of wood. of Agr. Bull. 110. 1912
Untersuchung fiber den Transpirationstrom der Nadelholzer und den Wasserbedarf von Fichte und Liirche
- A Schubert
SCHUBERT, A. Untersuchung fiber den Transpirationstrom der Nadelholzer und den Wasserbedarf
von Fichte und Liirche. Tharandt. Forst. Jahrb.
90: 821-883. 1939.
IDENTIFICATION AND ESTIMATION OF CATABOLIC
PATHWAYS OF GLUCOSE IN FRUITS1'2
The specific heat of wood
DUNLOP, F. The specific heat of wood. U. S. Dept.
of Agr. Bull. 110. 1912.