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Short-Term Population Trends of Isolated Tree-Limit Stands of Pinus sylvestris L. in Central Sweden
Abstract
The annual demographic changes and height increments of small, isolated, tree-limit stands of Pinus sylvestris L. (considered collectively as a single population) were studied during a 10-yr period (1972 to 1981). The individual vitality of specimens forming the population was also followed in detail throughout the study period. No recruitment to the population was recorded during the study period and the population size (total number of live plants) decreased by ca. 13%. The demographic changes were basically controlled by intrinsic factors but proximately executed by damage related to the annual differences in the air temperatures recorded during the initial 2 to 3 mon of the year. Long periods of radiation-controlled high temperatures during these months apparently lower the frost-hardiness, and the young pines, in particular, suffer serious damage by the subsequent onset of low temperatures. The individuals forming such isolated and small-sized tree-limit populations appear to be especially susceptible to this type of damage. Tree vitality in general, and the reproductive phase of life-cycle in particular, may suffer due to selfing and inbreeding. Such populations of pine seem therefore to be doomed to complete extinction, or to very drastic reduction in size within a rather short time after establishment (30 to 40 yr). The Holocene tree-limit history of pine in Scandinavia is briefly discussed in the light of this finding.
... This is the main focus of the present study, which provides updates and a meta-analysis of previous case studies. It highlights recent observations within a regional network of pine treeline monitoring (Kullman 1983(Kullman , 2007(Kullman , 2010 Recorded arboreal changes are richly documented by photographs, supporting their factual nature and character. Despite the tremendous current scientific focus on climate change and associated ecological changes, surprisingly few studies validate predictions of large-scale and profound biogeographic change by in situ observations over sufficiently long periods of time, i.e. at least the past 100 years. ...
... During the period 1973-2023, demographic processes were monitored annually within a system of permanent plots located to the pine treeline ecotone in the Handölan Valley, province of Jämtland (Kullman 1983(Kullman , 1993(Kullman , 2007(Kullman , 2014a; Kullman & Öberg 2022). In addition, some nearby outlier forest groves have been investigated with respect to static age structures (Kullman 1986a(Kullman , 2005cKullman & Öberg 2021), showing a first distinct peak of regeneration by the mid-20th century, which is somewhat later than the warming peak by the late 1930s. ...
... Initially, during a period of relatively cold winters (early 1970s to late 1980s), the density of young saplings at and above the treeline was low and many individuals were in a poor condition, following repeated winter desiccation injuries (Kullman 1981(Kullman , 1983(Kullman , 2014a. Accordingly, the total number of living specimens decreased gradually up to a nadir by the late 1980s. ...
This study focuses, by in situ records and long-term observations, on recent (post-Litte Ice Age), arboreal change in a mountain birch dominated (Betula pubescens ssp. czerepanovii) valley in the Swedish Scandes. During the early Holocene thermal optimum and up to the onset of the mid-Holocene Neoglaciation, Scots pine (Pinus sylvestris) dominated the tree cover of this valley and formed the treeline ecotone adjacent to the early alpine tundra. Subsequently, and consistent with progressive cooling until the late 19th century, prevailing pine stands demised and opened for landscape-level expansion of birch and spruce (Picea abies). A short and distinct break in that process took place by the Medieval Climate warming phase, about 1000-800 years before present. Subsequently, during pre-industrial time, temperatures reached their lowest levels of the entire post-glacial period. This was the so-called Little Ice Age, which ended the long-term Holocene cooling. That cold-climate epoque was broken by the late-19th and early 20th century. Thereafter and up to the present-day, temperatures in the study region (summer and winter) have increased by slightly less than 2 °C. As a consequence, treelines of all species have advanced by a maximum of more than 200 altitudinal meters. Pine displays the most persistent expansion, particularly over the past few decades. "Falangist" occurrences appear in the pure birch forest, tens of kilometers and hundreds of meters, respectively, beyond and above the outposts by the early 20th century. Occasionally, scattered young pine trees now grow close to the birch forest limit and somewhat above. In particular, at sites where pine stands demised during the Little Ice Age, c. AD. 1300-1850, prolific regeneration and insignificant winter mortality are recorded over the past 15 years. In comparison, birch and spruce provide no analogous signs of recent expansion. It may be hypothesized that unabated climate warming and corresponding arboreal progression will profoundly transform the plant cover of this valley, and others alike, into the same pine-dominated state that prevailed during the early Holocene. In other words, a new biogeographic zonation pattern may be on the rise, with pine back as the dominant subalpine species. This option is focused by continued monitoring.
... The present paper highlights the extent and character of a recent strong pulse of pine regeneration in the treeline ecotone. In perspective of long-term monitoring treeline performance since the mid-1970s in the concerned mountain valley, the magnitude of the recent reproductive effort and superabundance of young pine saplings is outstanding with respect of individual density and vigour (Kullman 1983(Kullman , 1993(Kullman , 2007(Kullman , 2014a(Kullman , 2018(Kullman , 2021. Recent sapling densities surpass figures obtained in northern Swedish Lapland, about 100 m below the upper pine stands (Steijlen & Zackrisson 1987). ...
... At the start of a long-term treeline monitoring program by the early-1970s, extant pine treeline stands were in a state of conspicuously declining vigor, which prevailed until the late 1980s. Saplings and young trees were frequently, to various degrees, affected foremost by frost desiccation and reproduction was virtually nil (Kullman 1981(Kullman , 1983(Kullman , 1991(Kullman , 1993. Analogous recession is reported from the treeline in northern Finland (Holtmeier 2003). ...
... The treeline in the study region shifted upslope by a regional maximum of 225 vertical metres during the past 100 years, although with great local variation (Kullman 2017(Kullman , 2021. Within the monitoring system, the density of young pine growth was about 100/ha by the early 1970s (Kullman 1983), to be compared with 40 000-25 000/ha at the present day, as evident from this study. The latter figures are high above the suggested limit for satisfactory regeneration and treeline advance, i. e. 3000-4000 seedlings/ha (Kellomäki et al. 1997). ...
Climate change and response if Picea abies in the treeline ecotone
... This and other procedures (tree coring) could not be used extensively at Ordesa because most individuals were shrubby and multistemmed. This methodology yields an age underestimation of at least 0-5 years, which can be partially removed by showing the age structure in 5-year classes (Kullman, 1983;McCarthy, Luckman & Kelly, 1991;Lloyd, 1996). 454 ...
... It is noteworthy that some climatic conditions positively related to establishment (warm springs, wet summers) are very similar to those favouring radial growth of this species in the Spanish pre-Pyrenees (Gutiérrez, 1991). Reproduction and establishment were associated with warm summers over several successive years in treeline populations of P. sylvestris (Kullman, 1983;. Kullman (1983; found recruitment peaks for treeline populations of P. sylvestris in central Sweden during the late 1950s in response to warm summers. ...
... Reproduction and establishment were associated with warm summers over several successive years in treeline populations of P. sylvestris (Kullman, 1983;. Kullman (1983; found recruitment peaks for treeline populations of P. sylvestris in central Sweden during the late 1950s in response to warm summers. We found similar peaks and a noticeable decrease of establishment after 1960. ...
Treeline ecotones are intensively studied to quantify the response of vegetation to environmental changes. We describe here the size, growth-form, and spatial distribution of trees in two alpine forest-pasture ecotones located in the Central Pyrenees (Ordesa and Tessó), dominated by Pinus uncinata Ram. and little affected by anthropogenic disturbances during the last century. Total variation of tree data was partitioned into spatial, environmental, combined, and unexplained components. The influence of understory plants on P. uncinata recruitment was assessed using cover data and detrended canonical correspondence analysis (DCCA). Climatic effects on recent recruitment were also investigated at Tessó. Most individuals at Ordesa were multistemmed and shrubby (krummholz). Krummholz and seedlings showed significant spatial correlation. The spatial component of variation of tree data was greater at Ordesa (26%) than at Tessó (4%). DCCA revealed a significant effect of elevation on the spatial segregation of the size and growth-form classes across both ecotones. At Tessó, recruitment was concentrated close to the treeline, where the cover of the dominant understory shrub (Rhododendron ferrugineum) decreased. The abundance of young individuals in the upper part of this ecotone might produce a future upward displacement of treeline. During the last 60 years, the important episodes of recruitment at Tessó were favoured by wet and warm springs and summers. Ordesa showed a clear spatial trend of distribution of P. uncinata individuals. Most individuals were krummholz, located at greater elevation. Recruitment was associated with krummholz type vegetation, which could buffer seedlings (nurse effect) from the harsh environment and thereby favour the establishment of seedlings.
... Experimental studies suggest that short-term climatic variation may be a critical influence on seedling emergence in several of the shrub species in the study area (Matthews, Petch and Whittaker unpubl. data, see also: Kullman 1983Kullman , 1988). ...
... Experimental studies suggest that short-term climatic variation may be a critical influence on seedling emergence in several of the shrub species in the study area (Matthews, Petch and Whittaker unpubl. data, see also: Kullman 1983Kullman , 1988). ...
... Clearly, up to the time of sampling, successful establishment had been a rare event in the locality of Bnl (80 yr), perhaps enabled by occasional runs of favourable summers (cf. Kullman 1983). Yet, once established, individuals were able to grow to a considerable size and age. ...
Glacier forelands provide valuable sites for the study of patterns and processes of primary succession The Storbreen glacier foreland, south‐central Norway, has previously been the subject of a suite of community‐level approaches Here the focus is population‐level studies of six key pioneer plants Arabis alpina, Deschampsia alpina, Oxyria digyna, Poa alpina, Saxifraga cespitosa and Trisetum spicatum and four heath shrubs Betula nana, Empetrum hermaphroditum, Phyllodoce caerulea and Salix complex ( Salix glauca and S lanata ) Size‐frequency distributions are used as indicators of population phenomena
The optimal conditions for growth and fecundity of Arabis alpina and Saxifraga cespitosa appear to be almost immediately upon deglaciation (< 7 yr), although both achieve their maximum cover on slightly older terrain A similar pattern was noted for the grasses, although their optima come at slightly later times Population phenomena in Oxyria digyna could not be related to terrain age, indicating a differing role of this species within the succession
Among the shrubs a number of demographic and behavioural patterns are identifiable as successional features, and other patterns are explicable in relation to changing histories of disturbance and site moisture relationships Establishment and build‐up in Empetrum hermaphroditum and Salix complex do not appear to be environmentally constrained, in contrast to Betula nana and Phvllodoce caerulea Betula nana is the slowest species to colonize, but occasional early colonists appear healthy and fecund, pointing to a strong environmental sieve at the point of establishment The population patterns varied considerably among the shrub species, the most striking common feature being in mode of establishment Establishment of ramets by vegetative means occurs increasingly on older ground within the foreland (maximum terrain age 230 yr) but only in sites of the mature heath outside the foreland is it the characteristic mode of establishment In exception to this pattern, vegetative establishment of Phyllodoce caerulea is very rare in all conditions studied Discussion focuses upon the importance of population phenomena, seed dispersal and life‐history characteristics in successional change It is concluded that processes involved in species turnover include both allogenic and autogenic elements and that although the two classes are difficult to separate in practice, autogenic factors become more significant whilst species‐environment relations become tighter in later phases of vegetation development
... Both age estimates were positively correlated (R 2 5 0.22, P 5 0.03) with a mean 4 yrs underestimate for the internode counts. Kullman (1983) reported a similar underestimate (1-5 yrs) for P. sylvestris recruits. Following Lloyd (1997), the temporal resolution on the estimates of the germination dates was checked calculating the 95% confidence interval (61.3 yrs) of the age-basal diameter power regression (age 5 11.8 diameter 0.3 , R 2 5 0.82, P , 0.0001, n 5 434). ...
... Therefore, climate seems to be the main driving factor of forest expansion in this isolated stand and in high-elevation alpine treelines under moderate to low grazing pressures. Similar results have been observed in boreal and subalpine forests in northern Europe (Kullman, 1983;Zackrisson et al., 1995;Stö cklin and Kö rner, 1999;Shiyatov, 2003). Furthermore, the recruitment drop in the early 1970s was observed both in the study sites and in the Pyrenees, and coincided with cold summers and falls due to intense cyclonic conditions in NE Spain (Camarero, 1999). ...
To infer future changes in the distribution of tree species in response to climatic variability, we need an understanding of the recruitment dynamics and their climatic controls at the species’ distribution limit. We studied the recruitment processes in an isolated population of Pinus uncinata Ram. located at the southwestern limit of the species’ distribution in Europe (Iberian System, NE Spain). We assessed (1) the temporal patterns of pine recruitment, and (2) how climate influenced recruitment. To reconstruct the recent recruitment episodes and to assess the climatic influence on recruitment and radial growth we employed dendrochronological methods. We mapped, measured the size, and estimated the age of all P. uncinata individuals located within a 50 m × 40 m plot. Additional age data were obtained from individuals located in four nearby 20 m × 20 m plots. The main episodes of tree establishment (early 1960s, late 1980s) coincided with low radial growth during a period with reduced grazing pressure. Grazing pressure and tree recruitment were not related at the spatiotemporal scale of this study. High May, August, and September minimum temperatures and high April precipitation were positively associated with recruitment, whereas high maximum April and June temperatures were negatively associated with recruitment. The studied population was in equilibrium with climate until the late 1990s, one of the warmest decades in the 20th century, when recruitment decreased despite the availability of suitable sites for establishment and the presence of reproductive individuals. We suggest that late-summer temperatures might have a non-linear negative threshold effect on recruitment rather than a linear effect. Despite increasing evidence of climate-induced recruitment episodes in isolated cold mountain forests, threshold effects of temperature on recruitment may imply limited range shifts of these populations in response to climate warming.
... Currently, the study of treeline dynamics focuses on changes in density and tree growth and minor treeline shifts during the last 100 to 150 yr. Treeline dynamics have been studied using ecophysiological (Tranquillini, 1979;Grace, 1989;Komer, 1998) and demographic techniques (Kullman, 1979(Kullman, , 1983(Kullman, , 1987(Kullman, , 1990Scott et aI., 1987;Rochefort et aI., 1994;Szeicz and MacDonald, 1995;Weisberg and Baker, 1995;Lloyd, 1997). However, few authors have explicitly applied spatial analyses to explain the pattern of treeline ecotones (e.g., . ...
... The procedure was 120/ ARCTIC, ANTARCTIC, AND ALPINE RESEARCH not carried out at the Ordesa site because of the multistemmed character of most of the trees that showed less evident scars and would cause greater errors in age estimation. This methodology yields an underestimate of 0 to 5 yr (Kullman, 1983;McCarthy et al., 1991). ...
Spatial identifcation and description of ecological boundaries is fundamental to better understanding of treeline dynamics. Ecological boundaries across two contrasting subalpine Pinus uncinata forest-alpine grassland ecotones were delineated within the Central Pyrenees (Ordesa and Tessó sites). Boundaries were delineated using an edge detection algorithm for two-dimensional data (lattice-wombling). Tree density, size-structure, growth-form, and estimated age were used to reveal spatial location of boundaries for several size and growth-form tree classes. Overlap statistics were applied to quantify spatial relationships among boundaries determined for different sets of variables. The most significant and consistent boundaries were those for structural variables at the Ordesa site. At this site, the sequential disposition of bigger and unistemmed trees descending across the ecotone produced boundaries for size-structure and growth-form variables. These boundaries were located along an ordered spatial pattern (altitudinal diagonal). At the Tessó site, there were few consistent boundaries, most of which were developed along the slope. Overlap statistics showed that boundaries at the Ordesa site were more spatially related than were those at the Tessó site. This result held when any set of variables was considered. The studied ecotones describe sharp (Ordesa site) and gradual (Tessó site) structural changes in tree populations, related to situations similar to the ecotone and ecocline concepts, respectively. The possible environmental driving factors producing these patterns are the strong winds and reduced snow cover at higher altitudes at the Ordesa site, and snow avalanches at the Tessó site. Boundary detection through time in permanent plots might be a better tool for monitoring climate-change impact in the forest-alpine grassland ecotone than the subjective location of treelines.
... Lamb, 1982), pine regeneration must be extremely rare, as is also evidenced by the continuous monitoring of the study plot 1974-1986, when only two saplings emerged, both of which died. Regeneration problems are further enhanced by the sparse population structure which, in this area, seems to cause certain inbreeding effects (Kullman, 1983b). Also, the rather thick organic layer which has accumulated due to absence of fires, may constitute a significant obstacle to pine establishment (cf. ...
... Most likely, the operative agent was a long-term deficit in the carbon budget (cf. Bray, 1971;Dahl, 1986), occasionally enhanced by acute weather-induced (late winter-early spring) injuries to the needle mass (Kullman, 1983b). Disturbed root function due to lowered soil temperatures may have been an important mechanism behind the forest decline on the present site with its insignificant snow cover. ...
The natural decline of a virgin high-altitude Pinus sylvestris forest during the Little Ice Age (approximately AD 1300–1850) was studied in the Swedish Scandes. Methods included 14C and cross-dating of wood remnants, soil analyses, year-ring chronologies and age structures. A closed pine forest started a gradual decline in the 11th century or somewhat later, which proceeded until the mid-19th century. Long-term failure of regeneration and premature death of trees are postulated to have caused the forest dieback, mainly owing to a negative shift of the carbon budget, including weather-induced loss of photosynthetic tissue and root disfunction. Temperature measurements on the study site stressed its current marginality. Especially thermal conditions in and close to the ground were deduced to be decisive. The decline of the forest is considered to indicate a long-term lowering during the Little Ice Age of the summer (June-September) mean temperature by 1°C or more, compared with the 1931–1960 mean.
... The radial growth of such outpost individuals reflects particular characteristics in adaptation to stresses and disturbances. During the LIA, occasionally beneficial climatic conditions enabled some seeds to spread and colonize above the upper margin of the closed forest [10][11][12]. Although most seeds and seedlings would die under stressful conditions at the sites above treelines, some seedlings would survive and establish as isolated trees, possibly due to strong growth plasticity to habitat adversity [13][14][15][16]. ...
Trees greater than 150 years old growing in the current treelines were most likely isolated tree outposts above previous treelines of the Little Ice Age (LIA). An intuitive question is, how did these isolated trees grow at such a high elevation in the cold environment? Here, we tackle this question using tree-ring width data of the Northern Hemisphere’s highest treelines at 4900 m a.s.l. (Basu) and 4680 m a.s.l. (Langkazi) on the Tibetan Plateau. The results showed that an age-related exponential growth trend did not exist in most of the ring-width sequences of the sampled trees. The values of ring widths in the isolated trees had a similar pattern of probability distribution during and after the LIA. The coefficients of variation in ring widths of the isolated trees were significantly greater than those of the non-isolated trees in their common growth period. Synchronicity of annual change in radial growth among trees varied in time. These results indicated that the isolated trees in the LIA developed an adaptive ability to slow down radial growth rate and modulate growth synchronicity among individuals in cold stressful environments. Our study highlights growth plasticity in isolated trees above treelines for coping with harsh conditions in the LIA.
... In any case, most of them are affected directly or indirectly by air and soil temperatures. The positive relationship between spring-summer temperature and tree recruitment at treeline has been observed both at altitudinal and latitudinal treelines (Kullman, 1983;Szeicz and MacDonald, 1995;Gutiérrez et al., 1998;Camarero and Gutiérrez, 1999). This relationship is related to temperature requirements, over a period of several summers, for successful seed production, germination and seedling establishment (Zasada et al., 1992;Scott et al., 1997). ...
Spatial identifcation and description of ecological boundaries is fundamental to better understanding of treeline dynamics. Ecological boundaries across two contrasting subalpine Pinus uncinata forest-alpine grassland ecotones were delineated within the Central Pyrenees (Ordesa and Tessó sites). Boundaries were delineated using an edge detection algorithm for two-dimensional data (lattice-wombling). Tree density, size-structure, growth-form, and estimated age were used to reveal spatial location of boundaries for several size and growth-form tree classes. Overlap statistics were applied to quantify spatial relationships among boundaries determined for different sets of variables. The most significant and consistent boundaries were those for structural variables at the Ordesa site. At this site, the sequential disposition of bigger and unistemmed trees descending across the ecotone produced boundaries for size-structure and growth-form variables. These boundaries were located along an ordered spatial pattern (altitudinal diagonal). At the Tessó site, there were few consistent boundaries, most of which were developed along the slope. Overlap statistics showed that boundaries at the Ordesa site were more spatially related than were those at the Tessó site. This result held when any set of variables was considered. The studied ecotones describe sharp (Ordesa site) and gradual (Tessó site) structural changes in tree populations, related to situations similar to the ecotone and ecocline concepts, respectively. The possible environmental driving factors producing these patterns are the strong winds and reduced snow cover at higher altitudes at the Ordesa site, and snow avalanches at the Tessó site. Boundary detection through time in permanent plots might be a better tool for monitoring climate-change impact in the forest--alpine grassland ecotone than the subjective location of treelines.
... Positive plant interactions have been studied in harsh environments like arctic tundra and alpine communities (Carlsson and Callaghan, 1991; Bertness and Callaway, 1994; Kikvidze and Nakhutsrishvili, 1998). The presence of intraspeci®c positive interactions buffering seedlings from extreme conditions at treeline has been inferred by studies revealing preferential establishment in the periphery of adult trees, contagious dispersion and spatial heterogeneity of mortality (Kullman, 1983; Payette and Filion, 1985; Taylor, 1995). Thè`nurse effect'' should be taken into account to understand the potential response of treeline populations to climatic change. ...
We describe the spatial structure of two contrasting subalpine Pinus uncinata forest-alpine grassland ecotones located in the Central Pyrenees (Ordesa and Tessó sites) as a preliminary step to infer the processes that produced their spatial patterns. All trees were mapped and measured within 4200 m2 rectangular plots parallel to the maximum slope and encompassing timberline and treeline. The spatial description of the ecotones was accomplished using several methodologies. Point pattern analysis (Ripley’s K) was first used to quantify the spatial pattern of trees using each stem x–y coordinates. Then, surface pattern analyses (Moran and Mantel spatial correlograms) were used to quantify the spatial pattern of tree characteristics across the ecotone (size, growth-form, estimated age). In the Ordesa site, krummholz individuals showed significant and positive spatial interaction with seedlings. In this site, P. uncinata individuals evolved from shrubby to vertical growth-forms abruptly, producing a steep spatial gradient. In the Tessó site, regeneration was concentrated near the treeline and the spatial gradient was gradual. Both ecotones formed ∼45 m long zones of influence along the slope based on different variables. Wind and snow avalanches seem to be the main controlling factors of the spatial pattern of trees in the sites Ordesa and Tessó, respectively. Our results point out potential different responses of treeline populations to environmental changes according to the spatial pattern.
... 2002. Studies also found that intraspecific positive interactions can buffer seedlings from extreme conditions at treeline (Kullman 1983, Payette and Filion 1985, Taylor 1995. These results suggested that stressful environments may lead to facilitating relationships. ...
Most of the trees at treeline on the Tibetan Plateau are endemic to the Plateau. Yet little is known about these species. The Study focused on the population structure, spatial patterns and associations of the treeline species Abies forestii var. georgei and Juniperus saltuaria at treeline and timberline in Mountain Baima Xueshan on the Southeast Tibetan Plateau. These species form monodominant communities on the north- and south-facing slopes, respectively. Stern density, DBH-distribution, distribution pattern of different tree size classes, and intraspecific spatial association between different tree size classes of both species were analyzed. Spatial structure varied between A. forestii var. georgei and J. saltuaria, and for the same species, the spatial structures were also different from timberline to treeline. Stein density, mean tree height and Young individuals of A. forestii var. georgei were significantly higher than those of J. saltuaria. For the same species, they were different from timberline to treeline, i.e., stem density and mean tree height of both species became lower. Size classes of both species were mainly clustered either at treeline or at timberline but at different scales, and spatial patterns of young J. saltuaria were mainly dominated by random patterns. Clumps of trees created more favorable microenvironments in harsh environments at treeline and timberline. Most tree size classes showed positive intraspecific spatial associations, but positive associations between size classes of J. saltuaria were not as significant as those of A. forestii var. georgei. The south-facing slope was usually subjected to varying intensities of pastoralism. Livestock disturbance greatly changed the microhabitat and reduced the number Of Young individuals. The potential of trees to regenerate was greatly inhibited, while A. forestii var. georgei showed greater regeneration potential. Spatial structures of J. saltuaria were also modified by this kind of human impact.
... Episodic regeneration and mortality at the Picea glauca treeline in Canada is triggered by climatic fluctuations and may influence subsequent recruitment for up to 50 years (Szeicz & MacDonald 1995). Picea abies , Pinus sylvestris , Betula pubescens , and Sorbus aucuparia also establish themselves episodically at Swedish ATs (Kullman 1983(Kullman , 1990. Villalba (1995) found that maximum establishment of Austrocedrus chilensis at the Argentinian forest-steppe ecotone requires favourable climatic conditions to persist for at least 10 years, whereas mortality requires only one or two adverse years. ...
1The short- and long-term dynamics of Nothofagus pumilio were investigated across an altitudinal gradient in Tierra del Fuego. Declining probability of establishment of individuals with increasing altitude (spatial restriction) is expected to lead to increasingly sporadic recruitment towards the alpine timberline (AT) (temporal restriction). Longevity of adult trees and difficulties in establishment at altitude should result in a static AT.2The number of annual growth buds of seedlings suggests that the species regenerates episodically at all altitudes in cycles of a similar length (7–8 years) to those for seed production. Nevertheless, the seedling density in a year of high regeneration (1996) was considerably higher at lower altitudes than at the AT.3Counting of the growth rings of adult individuals revealed a massive episode of establishment between 1800 and 1850 at all altitudes. There was poor establishment between 1920 and 1980. The age range for the entire population fluctuated between 49 and 377 years in 1996.4Although there is no evidence for more frequent recruitment at lower altitudes, differential regeneration ensures that establishment there is more probable.5Individuals at the AT had an average age of 160 years in 1996, suggesting that the border has indeed remained static for at least a century and a half.6The spatial restriction determines that the AT cannot advance until removal of the temporal restriction allows turnover to occur.
Paper can be downloaded from: https://besjournals.onlinelibrary.wiley.com/doi/full/10.1046/j.0022-0477.2001.00636.x
... In any case, most of them are affected directly or indirectly by air and soil temperatures. The positive relationship between spring-summer temperature and tree recruitment at treeline has been observed both at altitudinal and latitudinal treelines (Kullman, 1983; Szeicz and MacDonald, 1995; Gutiérrez et al., 1998; Camarero and Gutiérrez, 1999). This relationship is related to temperature requirements, over a period of several summers, for successful seed production, germination and seedling establishment (Zasada et al., 1992; Scott et al., 1997). ...
Treeline ecotones are regarded as sensitive monitors of the recent climatic warming. However, it has been suggested that their sensitivity depends more on changes in tree density than on treeline position. We study these processes and the effect of climate, mainly air temperature, on tree recruitment and recent treeline dynamics. We selected three relatively undisturbed sites in the Spanish Pyrenees, dominated by Pinusuncinata, and analyzed their recent dynamics at local spatial (0.3–0.5 ha) and short temporal scales (100–300 years). We wanted to establish whether higher temperature was the only climatic factor causing an upward shift of the studied alpine treelines. The data we report show that treelines were ascending until a period of high interannual variability in mean temperature started (1950–95). During the late twentieth century, treeline fluctuation was less sensitive to climate than was the change in tree density within the ecotone. Tree recruitment and treeline position responded to contrasting climatic signals; tree recruitment was favored by high March temperatures whereas treeline position ascended in response to warm springs. We found a negative relationship between mean treeline-advance rate and March temperature variability. According to our findings, if the interannual variability of March temperature increases, the probability of successful treeline ascent will decrease.
... s situated on the margins of blocks I and I1 than on those in blocks IV, where a source of infection was present within the site itself at an early stage of the provenance trial. Furthermore , the weather damage suffered by the contorta plants in the plots of blocks I and I1 would have increased their susceptibility to infection by snow blight (cf. Kullman, 1983). ...
During a nine-year-period ca. 100 provenances of Pinus contorta were investigated annually with respect to different kinds of damage. primarily by parasitic fungi. Damage to Pinus contorta occurred mainly during the first ten years after planting. northern provenances of Pinus contorta were generally more resistant to pathogens than southern provenances. Weather damage occurred almost every year among trees of southern and coastal provenance. Trees of northern provenance also suffered from weather damage due to temperature oscillations during shoot elongation. Severe weather damage predisposed to infection by secondary pathogens. primarily Gremmeniella abietina. Even northern provenances of Pinus contorta were infected by Phacidium infestans in high-altitude stands in northern Sweden. Snow blight infection was. however. of less importance to lodgepole pine than to Scots pine. owing to the rapid early growth of the former. The most productive plants of both Pinus contorta and Pinus sylvestris were attacked by Phacidium infestans. So far vole damage has been the most severe threat to Pinus contorta in northern Sweden. Severe infection by Gremrneniella abietina was recorded after vole attack. even among northern provenances of lodgepole pine. Hitherto Pinus contorta has mainly been infected by the same fungi as Pinus sylvestris, with the exception of Melampsora pinitorqua and Lophodermella sulcigena.
... Episodic regeneration and mortality at the Picea glauca treeline in Canada is triggered by climatic fluctuations and may influence subsequent recruitment for up to 50 years (Szeicz and McDonald, 1995). Picea abies, Pinus sylvestris, Betula pubescens and Sorbus aucuparia also establish themselves episodically at Swedish alpine timberlines (Kullman, 1983Kullman, , 1990). Establishment at the alpine timberline is infrequent because high seed production and adequate dispersal to safe sites are rarely followed by the favourable environmental conditions needed during early growth (Arno, 1984) and low browsing pressure (Cuevas, 2002). ...
Distribution area of oriental spruce [Picea orientalis (L.) Link.] in the world is only in the north-east of Turkey and Caucasian. Because of being the semi monopoly tree with respect to its distribution and representing the upper forest line, it is necessary to analyse, evaluate and model the stand structures of oriental spruce forests in Turkey. In this research, some sampling plots were selected in timberline and treeline in the subalpine forest zone in Turkey. In these sampling plots some information about occurrence and development of the tree collectives was obtained. A total of 12 sampling plots (6 in timberline and 6 of them in treeline) were studied and horizontal and vertical stand profiles were obtained, while number of trees ranges between 2-86 in the tree collectives in treeline and in timberline 3-12. According to this, area per tree in treeline and in timberline is determined as 1.02 m2 and 3.75 m2 on an average respectively. Mean age of trees to reach breast height is 43 years in treeline sampling plots and 22 years in timberline sampling plots. According to the ratio of h (mean height) / d1.30 (diameter at breast height), stand stability values were calculated and it was determined if the stands were stable on the basis of the sampling plots. Stability values of the sampling plots changed between 33 and 75.
We describe the spatial pattern of a subalpine forest-alpine pasture ecotone in the Central Pyrenees, that includes altitudinal timberline and treeline, and it is dominated by Pinus uncinata Ram. A rectangular (30 x 140 m) plot was located crossing the ecotone with its longest side parallel to the slope. We measured for each P. uncinata individual inside the plot: location (coordinates x, y), and structure (e. g. height) and growth form variables (number and type —living or dead, vertical or shrubby— of stems per individual). P. uncinata individuals were classified according to their size (adults, poles, saplings and seedlings) and growth form (krummholz —shrubby and multistemmed individuals— and krummholz with vertical stems). We described quantitatively the type of substrate (bare soil, organic matter, gravel and rock) and cover of herbs, shrubs and P. uncinata using transects parallel to the slope. The ecotone structure was described through: (1) point pattern (Ripley’s K) and (2) surface pattern analyses (spatial correlograms of height); (3) the detection and description of boundaries using density, size or growth form variables; (4) the synthesis of variations of presence and diversity of substrates and herbs and shrubs; and (5) the ordination of quadrats (the plot was previously subdivided into 115 6 x 6 m quadrats), according to their spatial position in the ecotone, the type of substrate, the cover of herbs and shrubs and the number, size and growth form of P. uncinata individuals. Most P. uncinata living individuals were krummholz, located above the timberline. Krummholz individuals showed significant and positive spatial interaction with seedlings. Bigger, vertical and unistemmed individuals predominated in the lower area of the ecotone, in the forest. The change of height with increasing elevation was abrupt and masked an underlying pattern of patches of trees with similar height in the forest. The structure variables were more sensitive because they produced a greater number of boundaries. These boundaries were arranged forming a “diagonal” (in the lower and upper areas of the ecotone for big and small individuals, respectively) because of the sequential location of progressively bigger unistemmed individuals descending across the ecotone. The shrubby individuals were associated with rocky substrates, that decreased in the forest, where organic matter predominated. The snow-wind interaction can explain the location of the studied timberline that could be considered a local phenomenon. Krummholz can buffer seedlings against the harsh climatic conditions of this ecotone (strong wind, reduced snowpack, low temperature). The spatial location of the different classes of individuals, the spatial interaction between seedlings and krummholz individuals, and changes of growth form (from shrubby to vertical growth form or vice versa) can cause some inertia in the response of ecotone P. uncinata populations to environmental changes.
The altitudinal tree-limit of Scots pine (Pinus sylvestris L.) has been surveyed at the population level since the early- and mid-1970s in the Swedish Scandes. Elevational tree-limit advance was recorded for the majority of sites, despite statistically stable, although highly fluctuating climate with clusters of exceptionally cold winters and many relatively cool summers. The new tree-limit derived from pines established in the late 1950s. Tree-limit rise was concurrent with net population decline for the period 1972 to 1991, mainly as a result of failing regeneration. The main factor of individual vitality depression and mortality was deduced to be winter desiccation. The progressive tree-limit has a tendency for slow upslope advance during periods of climatic stability, even if punctuated by shorter events of unfavorable climate. Pine tree-limit dynamics is suggested to be a complex of climate/age/disturbance interactions. The tree-limit may decline altitudinally mainly in response to secular climate cooling, which makes it best suited for surveying sustained climatic trends and analogous paleoclimatic reconstruction. 51 refs., 12 figs., 1 tabs.
The dynamic nature of Swedish (and Scandinavian) alpine tree-limits is reviewed in the perspective of recent research covering: 1) the long-term Holocene perspective, 2) the Little Ice Age, 3) the post-Little Ice Age warming, and 4) the recent cooling. Species have responded individualistically, particularly stressing the regenerative strategies. Vegetative regeneration and phenotypic plasticity provide relative stability to the altitudinal range limits of mountain birch Betula pubescens tortuosa, spruce Picea abies and rowan Sorbus aucuparia in contrast to Scots pine Pinus sylvestris. -from Author
Treeline ecotones are intensively studied to quantify the response of vegetation to environmental changes. We describe here the size, growth-form, and spatial distribution of trees in two alpine forest-pasture ecotones located in the Central Pyrenees (Ordesa and Tesso), dominated by Pinus uncinata Ram. and little affected by anthropogenic disturbances during the last century. Total variation of tree data was partitioned into spatial, environmental, combined, and unexplained components. The influence of understory plants on P. uncinata recruitment was assessed using cover data and detrended canonical correspondence analysis (DCCA). Climatic effects on recent recruitment were also investigated at Tesso. Most individuals at Ordesa were multistemmed and shrubby (krummholz). Krummholz and seedlings showed significant spatial correlation. The spatial component of variation of tree data was greater at Ordesa (26%) than at Tesso (4%). DCCA revealed a significant effect of elevation on the spatial segregation of the size and growth-form classes across both ecotones. At Tesso, recruitment was concentrated close to the treeline, where the cover of the dominant understory shrub {Rhododendron ferrugineum) decreased. The abundance of young individuals in the upper part of this ecotone might produce a future upward displacement of treeline. During the last 60 years, the important episodes of recruitment at Tesso were favoured by wet and warm springs and summers. Ordesa showed a clear spatial trend of distribution of P. uncinata individuals. Most individuals were krummholz, located at greater elevation. Recruitment was associated with krummholz type vegetation, which could buffer seedlings (nurse effect) from the harsh environment and thereby favour the establishment of seedlings.
To infer future changes in the distribution of tree species in response to climatic variability, we need an understanding of the recruitment dynamics and their climatic controls at the species' distribution limit. We studied the recruitment processes in an isolated population of Pinus uncinata Ram. located at the southwestern limit of the species' distribution in Europe (Iberian System, NE Spain). We assessed (1) the temporal patterns of pine recruitment, and (2) how climate influenced recruitment. To reconstruct the recent recruitment episodes and to assess the climatic influence on recruitment and radial growth we employed dendrochronological methods. We mapped, measured the size, and estimated the age of all P. uncinata individuals located within a 50 m X 40 in plot. Additional age data were obtained from individuals located in four nearby 20 in X 20 m plots. The main episodes of tree establishment (early 1960s, late 1980s) coincided with low radial growth during a period with reduced grazing pressure. Grazing pressure and tree recruitment were not related at the spatiotemporal scale of this study. High May, August, and September minimum temperatures and high April precipitation were positively associated with recruitment, whereas high maximum April and June temperatures were negatively associated with recruitment. The studied population was in equilibrium with climate until the late 1990s, one of the warmest decades in the 20th century, when recruitment decreased despite the availability of suitable sites for establishment and the presence of reproductive individuals. We suggest that late-summer temperatures might have a non-linear negative threshold effect on recruitment rather than a linear effect. Despite increasing evidence of climate-induced recruitment episodes in isolated cold mountain forests, threshold effects of temperature on recruitment may imply limited range shifts of these populations in response to climate warming.
Climatic change may alter vegetation composition and structure, but the response to climatic change can be expected to be spatially heterogeneous. Tree populations in the alpine forest–tundra ecotone, for example, may find only certain locations to be favourable for regeneration and growth. If monitoring and detection of vegetation responses to climatic change is to be most successful, the monitoring system must be tuned to the locations where a response is most likely. We used the grass geographical information system (gis) to map population parameters indicating potential change throughout the forest–tundra ecotone (FTE) of Rocky Mountain National Park (RMNP). Seedling density in patch forest and krummholz openings, as well as annual krummholz height growth, were measured in the field. These parameters were then modelled over the heterogeneity of the FTE environment, using principle components regression analysis. The grass gis was used to extrapolate the resulting predictive equations to the entire RMNP FTE. Potential FTE responses to climate change were evaluated in the context of species-specific differences in how tree seedling density and krummholz height growth are associated with the present environment. For example, climate change leading towards moister conditions, causing currently xeric environments to become more mesic, might increase the spatial extent of existing tree invasion into patch forest openings. This would increase the potential for widespread conversion of patch forest to closed forest. Present population parameters extrapolated spatially may provide a useful guide to where future change is likely.
Seeds of mountain birch (Betula pubescens Ehrh. ssp. tortuosa (Ledeb.) Nyman) were sown on permanent plots in three contrasting habitats close to the birch tree-limit in Central Sweden. The habitats differed mainly in regard to the length of the growth period, as determined by the pattern of local snow-accumulation. Germination success, seedling demography (1981–1983) and related aspects of the early stages were studied. Germination was found to start shortly after snowmelt in the year after ripening, in all three habitats. The conclusion is that germination is not the crucial phase of the life-cycle. In the habitat with the longest growth period, and where spontaneous birch stands are present, mortality mainly occurred in summer, evidently caused by soil drought. With shortening of the growth period, however, mortality during the winter became increasingly important. Survival was clearly correlated with the length of the growth period and the autumn height of seedlings. Factors which affect ecesis determine the altitude of the tree-limit and the long-term stability of the mountain birch forest ecosystem.
The influence of climate on the population dynamics of trees must be inferred from indirect sources of information because the long lifespans of trees preclude direct observation of population growth and decline. Important insights about these processes come from 1) observations of the life histories and ecologies of trees in contemporary forests, 2) evidence of recent treeline movements in remote areas unaffected by human disturbance, and 3) results of experiments performed on forest simulation models. Each line of evidence indicates that tree population responses are influenced by many factors: including lifespans, seed productivity and dispersibility, phenotypic plasticity, genetic variability, competition, and disturbance. Some population characteristics should allow rapid changes in population sizes, while others should confer stability in times of environmental fluctuation. Interactions between controlling factors should result in a wide array of possible responses to climatic change. Interpretations of late-Quaternary forest dynamics must be based on an understanding of the biological processes involved in population responses to environmental variations.
Species monitoring is the regular observation and recording of changes in status and trend of species in a certain territory.
The primary purpose of monitoring is to collect information that can be used to examine the outcomes of management actions
and to guide management decisions. Here, we analyze plant species monitoring to provide a first overview on efforts made to
monitor trends in vascular plant biodiversity in Europe. Our study is based on an assessment of 63 plant monitoring schemes
from Europe (collected into a database “DaEuMon”), and 33 schemes found with literature screening. Altogether, the monitoring
schemes cover 354 vascular plant species, of which 69 are listed in Annex II of the EU Habitats Directive (=EU protected
species; Annex II includes 420 species). In most cases, an EU protected plant species occurs in 3 countries but is monitored
in only 1 country. Scientific interest was the main reason for launching a monitoring scheme in 21% of the schemes from the
database, but in 58% of the schemes from the literature survey. The current schemes collect insufficient data particularly
on the dynamics of the extent and distribution pattern of species. We conclude that planning to publish monitoring data when
designing a scheme would improve the quality and general effect of monitoring programs. The needs to cover the taxonomic diversity
and the integration of different scales, as well as the inclusion of monitoring in the context of different types of sustainable
management would require a strong emphasis in the development of monitoring schemes.
We describe the structure of a subalpine forest-alpine pasture ecotone in the Central Pyrenees, that includes altitudinal timberline and treeline, and it is dominated by Pinus uncinata Ram . We measured for each P. uncinata 21individual located inside a rectangular plot parallel to the slope: the location and several structural and groivth form variables (number and type of stems per individual). Then, P. uncinata individuals were classified according to their size (adults, poles, saplings and seedlings) and growth form (krummholz —shrubby and multistemmed individuals—, krummholz with vertical stems). The ecotone structure was described through the study of groivth form and size changes of P. uncinata individuals across the ecotone and related to the area climate, that is characterized by maximum snow thickness in spring (April) and strong N-NW-W winds. Most of living individuals were krummholz, located above the timberline in the area where seedlings were abundant. Bigger, vertical and unistemmed individuals predominated in the forest. The structure or growth form changes were sharp across the ecotone. Crown injuries due to wind effects were evident in shrubby individuals and predominated in those directions that showed stronger winds during the year. The snow-wind interaction can explain partially the location of the studied timberline that could be considered a local phenomenon. The spatial location of the different classes of individuals, the spatial interaction between seedlings and krummholz individuals, and the changes of growth form (from arborescent to shrubby or vice versa) can modify the response of these P. uncinata populations to climate changes.
[es] Describimos la estructura de un ecotono bosque subalpino-pastos alpinos en los Pirineos Centrales, que incluye los límites altitudinales del bosque y del árbol y está dominado por Pinus uncinata Ram . Para cada individuo de P. uncinata situado dentro de una parcela rectangular paralela a la pendiente anotamos su localización y medimos diversas variables estructurales o deforma (número y tipo de pies por individuo). Estos individuos fueron clasificados según su tamaño (adultos, jóvenes, vastagos y plántulas) y forma («krummholz» —individuos arbustivos policórmicos—, krummholz con pies verticales). La estructura del ecotono se describió mediante los cambios de tamaño y forma de los individuos de P. uncinata a lo largo del ecotono y en relación con el clima de la zona, que se caracteriza por espesores de nieve máximos en primavera (abril) y fuertes vientos del N-NW-W. La mayoría de los individuos vivos eran krummholz, situándose por encima del límite del bosque y mostrando proximidad espacial con las plántulas. Los individuos grandes, verticales y unicórmicos predominaban en el bosque. Los cambios estructurales o deforma de los individuos eran bruscos a lo largo del ecotono. Los daños de las copas debidos al viento eran evidentes en individuos arbustivos y predominaban en las direcciones de viento más fuertes durante todo el año. La interacción nieve-viento permite explicar en parte la localización de este límite del bosque que puede considerarse un fenómeno local. La situación espacial de las distintas clases de individuos, la interacción espacial entre plántulas y krummholz más los cambios deforma de crecimiento (de arbustiva a arbórea o viceversa) pueden modificar la respuesta de estas poblaciones de P uncinata a cambios climáticos.
[fr] Nous avons analysé la structure d'un ecotone marqué par le passage de la forêt subalpine à la prairie alpine dans les Pyrénées Centrales. Cet écotone incluant les limites altitudinales de la forêt et des arbres est dominé par le Pinus uncinata Ram . A l'intérieur d'une parcelle rectangulaire parallèle à la pente, nous avons mesuré la position de chaque tige de P. uncinata ainsi que plusieurs paramètres décrivant la structure et la forme des arbres (abondance et type de tige par individus). Nous avons classifié les individus de ce pin selon leur taille (adulte, «pole», gaulis et semis) et leur forme de croissance (krummholz —à tiges multiples et à port arbustif, krummholz à tiges verticales). La structure de l'écotone a été décrite par l'analyse des formes de croissance et de la taille des individus de P. uncinata et celle-ci fut a été reliée aux particularités du climat régional lequel se caractérise par une accumulation maximale de la neige au printemps (april) et la dominance des vents du N-NW-W. La majorité des individus vivants étaient constitués de krummholz et se retrouvaient au delà de la limite altitudinale de la forêt, a l'endroit même où les semis abondaient. Les individus de fort diamètre, à tige verticale et unique dominaient surtout dans l'étage forestier. Les changements dans la structure ou les formes de croissance étaient très marqués le long de l'écotone. Les dommages à la cime causés par les vents étaient fréquents chez les individus à port arbustif et prédominaient selon l'orientation des vents dominants. L'interaction entre la direction des vents et l'accumulation de la neige au sol peut expliquer, en partie, la localisation actuelle de la limite des arbres dans l'écotone étudié. La position de l'écotone semble être le reflet des conditions locales. La localisation spatiale des différentes classes d'individus, l'interaction spatiale entre les semis et les krummholz, de même que les changements dans le port des arbres (arborescent à arbustif et vice versa) peuvent modifier la réponse des populations de P. uncinata aux changements climatiques.
Describimos el patrón espacial de un ecotono bosque subalpino-pastos alpinos, que incluye los límites altitudinales del bosque y del árbol, dominado por Pinus uncinata Ram. y localizado en los Pirineos Centrales. Situamos una parcela rectangular (30 x 140 m) cruzando el ecotono con su lado mayor paralelo a la pendiente. Para cada individuo de R uncinata dentro de la parcela medimos: su localización (coordenadas x, y), y variables estructurales (p. ej. altura) y de forma de crecimiento (número y tipo -vivo o muerto, vertical o arbustivo- de pies por individuo). Los individuos vivos de P. uncinata se clasificaron según su tamaño (adultos, jóvenes, vástagos y plántulas) y forma de crecimiento (krurmnhoIz -individuos arbustivos policórmicos-, krummholz con pies verticales). Describimos cuantitativamente el tipo de sustrato (suelo, materia orgánica, grava, roca) y la cobertura de herbáceas, arbustos y P. uncinata usando transectos paralelos a la pendiente. La estructura del ecotono se describió mediante: (a) los análisis del patrón de puntos (K de Ripley) y (b) del patrón de superficies (correlogramas espaciales de la altura); (c) la detección y descripción de fronteras usando la densidad o variables de tamaño y forma de crecimiento de los indidividos ; (d) la síntesis de las variaciones en la presencia y diversidad de sustratos y de herbáceas y arbustos-, y (e) la ordenación de los cuadrados en que subdividimos la parcela (115 cuadrados de 6 x 6 m), de acuerdo a su posición espacial en el ecotono, al tipo de sustrato, a la cobertura de herbáceas y arbustos y al número, tamaño y forma de crecimiento de los individuos de P. uncinata. La mayoría de los individuos vivos de P. uncinata eran krummhoIz, situándose por encima del límite del bosque. Los individuos krummholz mostraron interacción espacial positiva con las plántulas. En el área inferior del ecotono, los individuos grandes, verticales y unicórmicos...
Since the turn of the century population research, in the form of provenance experiments, has been in the foreground of forest genetics and breeding. The use and distribution of hardy and well-growing materials has formed an important object in advanced forestry practice. Norway spruce (Picea Abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) are the two valuable conifer species in northern Europe. The background of work and the results have been discussed by numerous scientists. References are here made especially to papers by Langlet and by Eiche (see references).
With the pressure chamber, the water potential of red spruce stems (Picea rubens) was measured in four altitudinal zones, including timberline, on Mount Monadnock, New Hampshire, during two winters. Average water potential over all zones and dates was -1.14 (sd @= 0.57, range -0.1 to -4.0) MPa for 545 stems from 91 trees. More variation in water potential occurred within single trees than between juvenile and adult trees, and than among altitudinal zones or among seasons. Temperature data from maximum-minimum thermometers and from thermistors implanted into trunks and soil show that bulk water flow periodically occurs in winter. The slow decline in water potential of branches excised in winter, and scanning electron micrographs of plugged stomates, indicate that high diffusion resistances maintain needles within the relatively high levels of water potential measured in this study. Our results disagree with traditional concepts, support the conclusions of Slatyer (1976) and Marchand and Chabot (1978), and indicate that the mechanisms behind the variability in water status of modular parts of single trees must be understood before the causes, timing, and consequences of winter death in timberline trees can be unraveled.
The extent and causes of winter desiccation were studied in three tree-line species on Mt. Washington, New Hampshire. We did not find excessively low relative water contents in intact foliage of balsam fir (Abies balsamea [L.] Mill.) or black spruce (Picea mariana [Mill.] BSP.) during the winter. Relative water contents were lowest following damage by ice abrasion and in intact stems of paper birch (Betula papyrifera Marsh.). Winter transpiration in conifer foliage is very low perhaps due to several dormancy-related mechanisms. Transpiration is further reduced by high wind speeds which maintain thermal equilibrium between leaf and air. Thus winter desiccation is not universal at tree line and is probably related to factors other than the high-wind regime.
Cold hardiness in Taxus baccata L. was investigated over the winter months in six widely-separated provenances of England. It was found that the degree of cold hardiness varied according to season, the maximum tolerance to cold normally being achieved in mid-winter (January). Hardiness declined rapidly in the early spring, when populations from all provenances proved to be vulnerable to tissue damage under severe fromst conditions. Between-provenance variation was also examined, and proved to be largely random, displaying no marked clinal features. There is, however, no doubt that populations in the northeast of England are in greater potential danger of sustained tissue damage, expecially during the spring months, than those elsewhere in the country; and this may explain the relative scarcity of stands of native yew in this region.
In northern Quebec, black spruce (Picea mariana [Mill.] B.S.P.) occurs throughout the hemiarctic zone along with white spruce and larch. Black spruce reproduces mostly vegetatively by layering. Population study of a clonal stand located in the Lake Minto area, northern Quebec, was undertaken to provide a better understanding of these populations. The smooth straight line trend of age, height, and diameter distributions indicated a stable population. The inverse J-shaped depletion model suggested by the population structure was similar to those described for southern stable tree populations. The inverse exponential model which best described the population implied a constant death rate through time. Clonal population growth was little disturbed by climatic change. Small variations (statistically not significant) that were still apparent in the growth curve could be related to more or less favorable growth periods. In the forest tundra, where disturbances are mostly linked to climatic changes, the opportunistic use of both vegetative and seed reproduction constituted an important asset for black spruce populations. Spatial growth pattern of the black spruce clone was determined using cartographic data related to above- and belowground components of the population. Because it reproduced mainly by layering, the black spruce clonal stand displayed a radial development. Older individuals were found near the middle of the stand while regeneration was most active on the border. Few living ramets occurred in the immediate center of the clonal stand while rotten roots and stems were found buried in the soil organic layer. These rotten structures were probably the remains of individuals that gave birth to the clone. Spatial distribution of above and belowground structure showed three units that resulted from the decay of branch connection between layerings. If the population were to expand, these units would be expected to develop either towards stability or towards extinction depending on topography and space available.
When first-year shoots of Picea engelmannii cultivated in New Zealand were artificially frozen and then thawed, the needles developed damage patterns which seem identical to those seen in natural krummholz of the same species in Colorado. In the same experiment, needles from Pinus contorta plants of krummholz form were more susceptible to freezing damage than needles from vigorous, erect saplings. This raises the possibility that freezing rather than water stress may be the primary cause of winter desiccation in inadequately matured krummholz shoots.
The cuticular resistance of Pinus albicaulis Engelm. needles was estimated throughout the 1979 growing season at altitudes of 2730, 2800, and 2940 m in the Sierra Nevada of California to determine differences in rate and degree of culticle maturation within the timberline ecotone. Cuticular transpiration was measured using excised fascicles within constant humidity chambers at 20°C and 44% relative humidity. Foliage from the forest limit (2730 m) began growth earlier and developed rapidly, while transition zone (2800 m) and krummholz (2940 m) foliage growth was delayed and developed more slowly. Cuticular resistances of needles at season's end were significantly lower with increasing altitude (p = 0.01). Our findings using transpiration rates predicted under estimated winter conditions, support the hypothesis that the shorter growing seasons of higher altitudes, slower growth, and the resulting lower cuticular resistance may be important in the winter desiccation of exposed foliage at high altitudes.
The temperatures of needles of 10- to 15-year-old trees of Pinussilvestris L. growing in a frost hollow in Sweden were measured with an ultraminiature thermocouple. The measurements were made in the spring of 1977, during days of variable cloudiness. During periods of full sun and very low wind speed the temperature of the needles exceeded that of the surrounding air by 12 to 15 °C.
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Seedlings of Pinus silvestris (L.) and Picea abies ((L.) Karst.), 16 weeks old, were hardened under various photo- and thermoperiods. Dehardening after a period of chilling was followed by exposure to various temperatures under long and short day conditions. The degree of frost hardiness of the seedlings was determined in freezing tests at -7°, - 11° and - 17°C. Damage caused by freezing was evaluated by measurement of conductivity. Short day conditions were of importance to hardening in both species, the most effective photoperiods being 6-12 hours. Shorter photoperiods (2-4 hours) were less effective. Low temperatures did not cause hardening under long-day conditions, but increased hardiness under short photoperiods, especially in pine. Night temperature had a greater influence on hardening in pine than did day temperature. Dehardenirng appeared to depend more on temperature than on photoperiod. Dehardening was a much faster process than hardening.
Changes in the natural level of frost hardiness of shoots of four provenances of Picea sitchensis were monitored over two growing seasons by detaching shoots from 7 to 10-year-old trees growing in a nursery in Scotland, and subjecting them to freezing temperatures under conditions which simulated night frosts. Six seasonal phases of frost hardiness were identified (Fig. 3).
During each autumn, killing temperatures (the level of hardiness) decreased from −5°C to below −20°C, beginning several weeks after shoot elongation ceased. Alaskan provenances hardened in September, apparently in response to shortening day lengths alone, whereas an Oregon provenance did not harden until November, after repeated frosts. Queen Charlotte Islands provenances were intermediate.
From November to March all provenances were hardy to below −20°C, which is adequate to prevent direct freezing injury at most plantation sites.
In March-April, several weeks before bud-burst, old shoots dehardened to killing temperatures of about −10°C in response to warm temperatures, and southerly provenances did so before northerly ones.
During bud-burst the newly-emerging shoots were hardy to only −3°C to −5°C until they were about 3.5 cm long. All provenances burst bud at the same time and were equally frost susceptible at this time.
During May-July the elongating shoots fluctuated in hardiness between −5°C and −10°C apparently in response to fluctuating ambient temperatures.
In August 1980 there was a period of late summer dehardening to killing temperatures of about −3°C. Seasonal changes in hardiness are discussed in relation to changes in shoot growth and environmental factors. The main opportunities for selecting frost hardy genotypes seem to be in the rate of autumn hardening, the time of pre-bud burst dehardening, and the time of bud-burst.
Excerpt
Introduction
Recent studies of population genetics, as summarized in the Cold Spring Harbor Symposium for 1955 (Lerner, 1955; Dobzhansky, 1955), have shown us that natural populations of cross-fertilizing organisms normally possess an enormous store of hidden variability, in the form of recessive genes for which their individuals are heterozygous. In the past, this variability has been regarded as a load of deleterious genes which the population must bear as insurance for the future. Now, however, we have a large enough number of examples pointing toward the superior adaptiveness of heterozygotes per se (Lerner, 1954, 1955; Dobzhansky, 1955), so that we can regard some of this hidden variability as of positive value to the population.
Viewed in this light, the tendency of many populations of higher plants to dispense with such variability, and to deviate in the direction of self-fertilization, or toward the substitution of asexual reproduction for the sexual method,...
Genetic systems associated with coloniz-ing ability in predominantly self-pollinated species The Genetics of Coloniz-ing Species
- R W Allard
Allard, R. W., 1965: Genetic systems associated with coloniz-ing ability in predominantly self-pollinated species. In Baker, H. G. and Stebbins, G. L. (eds.), The Genetics of Coloniz-ing Species. New York: Academic Press, 49-75.
Studier av metoder f6r plantering av gran och tall pa akermark i sodra och mellersta Sverige. Studia Forestalia Suecica, 50. 332 pp. (In Swedish with German summary Geographic variation in drought and winter hardiness of common pine
- U Barring
- Z P Biryukova
- N N Kharlamova
Barring, U., 1967: Studier av metoder f6r plantering av gran och tall pa akermark i sodra och mellersta Sverige. Studia Forestalia Suecica, 50. 332 pp. (In Swedish with German summary.) Biryukova, Z. P. and Kharlamova, N. N., 1982: Geographic variation in drought and winter hardiness of common pine. The Soviet Journal of Ecology, 12(4): 223-227.
1967: Marginal populations and provenance research
- J P Bujtenen
- Van
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