Spatial variability of biotic and abiotic tree establishment constraints across a treeline ecotone in the Alaska range

Throughout interior Alaska (U.S.A.), a gradual warming trend in mean monthly temperatures occurred over the last few decades (approximatlely 2-4 degrees C). The accompanying increases in woody vegetation at many alpine treeline (hereafter treeline) locations provided an opportunity to examine how biotic and abiotic local site conditions interact to control tree establishment patterns during warming. We devised a landscape ecological approach to investigate these relationships at an undisturbed treeline in the Alaska Range. We identified treeline changes between 1953 (aerial photography) and 2005 (satellite imagery) in a geographic information system (GIS) and linked them with corresponding local site conditions derived from digital terrain data, ancillary climate data, and distance to 1953 trees. Logistic regressions enabled us to rank the importance of local site conditions in controlling tree establishment. We discovered a spatial transition in the importance of tree establishment controls. The biotic variable (proximity to 1953 trees) was the most important tree establishment predictor below the upper tree limit, providing evidence of response lags with the abiotic setting and suggesting that tree establishment is rarely in equilibrium with the physical environment or responding directly to warming. Elevation and winter sun exposure were important predictors of tree establishment at the upper tree limit, but proximity to trees persisted as an important tertiary predictor, indicating that tree establishment may achieve equilibrium with the physical environment. However, even here, influences from the biotic variable may obscure unequivocal correlations with the abiotic setting (including temperature). Future treeline expansion will likely be patchy and challenging to predict without considering the spatial variability of influences from biotic and abiotic local site conditions.     

Natural tree collectives of pure oriental spruce [Picea orientalis (L.) Link] on mountain forests in Turkey

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.     

Age and spatial distribution of the world's oldest trees

Extremely old trees have important roles in providing insights about historical climatic events and supporting cultural values, yet there has been limited work on their global distribution and conservation. We extracted information on 197,855 tree cores from 4854 sites and combined it with other tree age (e.g., the OLDLIST) data from a further 156 sites to determine the age of the world's oldest trees and quantify the factors influencing their global distribution. We found that extremely old trees >1000 years were rare. Among 30 individual trees that exceeded 2000 years old, 27 occurred in high mountains. We modeled maximum tree age with climatic, soil topographic, and anthropogenic variables, and our regression models demonstrated that elevation, human population density, soil carbon content, and mean annual temperature were key determinants of the distribution of the world's oldest trees. Specifically, our model predicted that many of the oldest trees will occur in high-elevation, cold, and arid mountains with limited human disturbance. This pattern was markedly different from that of the tallest trees, which were more likely to occur in relatively more mesic and productive locations. Global warming and expansion of human activities may induce rapid population declines of extremely old trees. New strategies, including targeted establishment of conservation reserves in remote regions, especially those in western parts of China and the United States, are required to protect these trees.     

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The study focused on the so-called dark coniferous forest belt on the northern slope of Changbai Mountain, at an altitude of 1100 to 1700 m. Forty tree species, 50 shrub species and 165 herb species were recorded in a series of transects. The main impact factors on forest diversity and proposals for sustainable management of this diversity were studied using an altitude and area gradient pattern method. The results showed that the diversity of dark coniferous forest gradually decreased from lower to upper altitude; while the importance value of key species increased. The methodology used to assess attributes for conservation of dark coniferous forest diversity involved measurement of individual trees, number of species, age structure, stand structure, diameter at breast height (DBH), and cumulative wood storage. Different conservation strategies have been developed and are discussed for different parts of the forest.     

Defoliation levels of oriental spruce by Ips typographus (L.) in relation to elevation and exposure

A study concerning the effects of elevation and exposure of the spruce forests on defoliation levels of oriental spruce (Picea orientalis (L.) Link.) by Ips typographus L. was carried out during 2005 and 2006 in Artvin-Hatila National Park, Turkey Nine spruce stands were selected at 3 zones of elevations (1000-1350 m, 1350-1700 m and 1700-2000 m) and at different aspects to assess the role of elevation and exposure in the crown defoliation level and body length of beetles. Influence of bark thickness and trunk diameter at 1.3 m on the damage caused by the pest was investigated as well. The results of the study were as follows: (1) The mean defoliation level was highest at 1700-2000 m following by 1350-1700 m and 1000-1350 m. (2) The highest defoliation levels occurred on southern slopes following by eastern and northern slopes at 1700-2000 m. (3) No statistical differences were found in the mean bark thickness between tree defoliation levels 1, 2, 3 and 4. (4) Mean trunk diameters of dead trees (level 4) were significantly greater than those with defoliation levels 0, 1 and 2. (5) Mean body length of I. typographus at upper zones was significantly higher than those at middle and lower zones.     

Impacts of changing frost regimes on Swedish forests: Incorporating cold hardiness in a regional ecosystem model

Understanding the effects of climate change on boreal forests which hold about 7% of the global terrestrial biomass carbon is a major issue. An important mechanism in boreal tree species is acclimatization to seasonal variations in temperature (cold hardiness) to withstand low temperatures during winter. Temperature drops below the hardiness level may cause frost damage. Increased climate variability under global and regional warming might lead to more severe frost damage events, with consequences for tree individuals, populations and ecosystems. We assessed the potential future impacts of changing frost regimes on Norway spruce (Picea abies L. Karst.) in Sweden. A cold hardiness and frost damage model were incorporated within a dynamic ecosystem model, LPJ-GUESS. The frost tolerance of Norway spruce was calculated based on daily mean temperature fluctuations, corresponding to time and temperature dependent chemical reactions and cellular adjustments. The severity of frost damage was calculated as a growth-reducing factor when the minimum temperature was below the frost tolerance. The hardiness model was linked to the ecosystem model by reducing needle biomass and thereby growth according to the calculated severity of frost damage. A sensitivity analysis of the hardiness model revealed that the severity of frost events was significantly altered by variations in the hardening rate and dehardening rate during current climate conditions. The modelled occurrence and intensity of frost events was related to observed crown defoliation, indicating that 6-12% of the needle loss could be attributed to frost damage. When driving the combined ecosystem-hardiness model with future climate from a regional climate model (RCM), the results suggest a decreasing number and strength of extreme frost events particularly in northern Sweden and strongly increasing productivity for Norway spruce by the end of the 21st century as a result of longer growing seasons and increasing atmospheric CO₂ concentrations. However, according to the model, frost damage might decrease the potential productivity by as much as 25% early in the century.     

Importance of conserving large and old trees to continuity of tree-related microhabitats

Protecting structural features, such as tree-related microhabitats (TreMs), is a cost-effective tool crucial for biodiversity conservation applicable to large forested landscapes. Although the development of TreMs is influenced by tree diameter, species, and vitality, the relationships between tree age and TreM profile remain poorly understood. Using a tree-ring-based approach and a large data set of 8038 trees, we modeled the effects of tree age, diameter, and site characteristics on TreM richness and occurrence across some of the most intact primary temperate forests in Europe, including mixed beech and spruce forests. We observed an overall increase in TreM richness on old and large trees in both forest types. The occurrence of specific TreM groups was variably related to tree age and diameter, but some TreM groups (e.g., epiphytes) had a stronger positive relationship with tree species and elevation. Although many TreM groups were positively associated with tree age and diameter, only two TreM groups in spruce stands reacted exclusively to tree age (insect galleries and exposed sapwood) without responding to diameter. Thus, the retention of trees for conservation purposes based on tree diameter appears to be a generally feasible approach with a rather low risk of underrepresentation of TreMs. Because greater tree age and diameter positively affected TreM development, placing a greater emphasis on conserving large trees and allowing them to reach older ages, for example, through the establishment of conservation reserves, would better maintain the continuity of TreM resource and associated biodiversity. However, this approach may be difficult due to the widespread intensification of forest management and global climate change.     

Impact of minimum winter temperatures on the population dynamics of Dendroctonus frontalis.

Predicting population dynamics is a fundamental problem in applied ecology. Temperature is a potential driver of short-term population dynamics, and temperature data are widely available, but we generally lack validated models to predict dynamics based upon temperatures. A generalized approach involves estimating the temperatures experienced by a population, characterizing the demographic consequences of physiological responses to temperature, and testing for predicted effects on abundance. We employed this approach to test whether minimum winter temperatures are a meaningful driver of pestilence from Dendroctonus frontalis (the southern pine beetle) across the southeastern United States. A distance-weighted interpolation model provided good, spatially explicit, predictions of minimum winter air temperatures (a putative driver of beetle survival). A Newtonian heat transfer model with empirical cooling constants indicated that beetles within host trees are buffered from the lowest air temperatures by approximately 1-4 degrees C (depending on tree diameter and duration of cold bout). The life stage structure of beetles in the most northerly outbreak in recent times (New Jersey) were dominated by prepupae, which were more cold tolerant (by >3 degrees C) than other life stages. Analyses of beetle abundance data from 1987 to 2005 showed that minimum winter air temperature only explained 1.5% of the variance in interannual growth rates of beetle populations, indicating that it is but a weak driver of population dynamics in the southeastern United States as a whole. However, average population growth rate matched theoretical predictions of a process-based model of winter mortality from low temperatures; apparently our knowledge of population effects from winter temperatures is satisfactory, and may help to predict dynamics of northern populations, even while adding little to population predictions in southern forests. Recent episodes of D. frontalis outbreaks in northern forests may have been allowed by a warming trend from 1960 to 2004 of 3.3 degrees C in minimum winter air temperatures in the southeastern United States. Studies that combine climatic analyses, physiological experiments, and spatially replicated time series of population abundance can improve population predictions, contribute to a synthesis of population and physiological ecology, and aid in assessing the ecological consequences of climatic trends.     

Modelling forest succession in two southeastern Canadian mixedwood ecosystem types using the ZELIG model

The gap model ZELIG was validated for red spruce–balsam fir–yellow birch and yellow birch–sugar maple–balsam fir forest types in southern Quebec, Canada. Long-term historical data originating from the Lake Edward Experimental Forest, La Mauricie National Park, were used. The effect of the variation in plot size, representing the space within which trees uptake site resources, was also examined. Several species were included in both forest types: red spruce (Picea rubens Sarg.), balsam fir (Abies balsamea (L.) Mill.), yellow birch (Betula alleghaniensis Britton), white birch (Betula papyrifera Marsh.), red maple (Acer rubrum L.), sugar maple (Acer saccharum Marsh.), American beech (Fagus grandifolia Ehrh.), eastern hemlock (Tsuga canadensis (L.) Carr.) and northern white cedar (Thuja occidentalis L.). The pattern of change in basal area growth varied among species, ranging from a steady increase to a more or less rapid decline. There was a good agreement between observations and predictions for yellow birch, red spruce, red maple, sugar maple, balsam fir and northern white cedar. Plot size had a significant impact on the dynamics of the different species. Depending on the species, the decline was accelerated, the amplitude of the fluctuations varied, or the maximum basal area reached changed. Predicted regeneration varied among species and the number of seedlings generally increased with increase in plot size. The pattern of development for most species was related to their life characteristics. The results highlighted the fact that there is a critical lack of knowledge and data on the dynamics of regeneration from the seedling to the sapling stages for the two forest types studied, which resulted in poor predictions for some species. As the life characteristics varied among species, the use of only one plot size for all species may not be realistic.     

Substrate supply, fine roots, and temperature control proteolytic enzyme activity in temperate forest soils

Temperature and substrate availability constrain the activity of the extracellular enzymes that decompose and release nutrients from soil organic matter (SOM). Proteolytic enzymes are the primary class of enzymes involved in the depolymerization of nitrogen (N) from proteinaceous components of SOM, and their activity affects the rate of N cycling in forest soils. The objectives of this study were to determine whether and how temperature and substrate availability affect the activity of proteolytic enzymes in temperate forest soils, and whether the activity of proteolytic enzymes and other enzymes involved in the acquisition of N (i.e., chitinolytic and ligninolytic enzymes) differs between trees species that form associations with either ectomycorrhizal or arbuscular mycorrhizal fungi. Temperature limitation of proteolytic enzyme activity was observed only early in the growing season when soil temperatures in the field were near 4 degrees C. Substrate limitation to proteolytic activity persisted well into the growing season. Ligninolytic enzyme activity was higher in soils dominated by ectomycorrhizal associated tree species. In contrast, the activity of proteolytic and chitinolytic enzymes did not differ, but there were differences between mycorrhizal association in the control of roots on enzyme activity. Roots of ectomycorrhizal species but not those of arbuscular mycorrhizal species exerted significant control over proteolytic, chitinolytic, and ligninolytic enzyme activity; the absence of ectomycorrhizal fine roots reduced the activity of all three enzymes. These results suggest that climate warming in the absence of increases in substrate availability may have a modest effect on soil-N cycling, and that global changes that alter belowground carbon allocation by trees are likely to have a larger effect on nitrogen cycling in stands dominated by ectomycorrhizal fungi.     

Predicting the decomposition of Scots pine, Norway spruce, and birch stems in Finland.

Models were developed for predicting the decomposition of dead wood for the main tree species in Finland, based on data collected from long-term thinning experiments in southern and central Finland. The decomposition rates were strongly related to the number of years after tree death. In contrast to previous studies, which have used the first-order exponential model, we found that the decomposition rate was not constant. Therefore, the Gompertz and Chapman-Richard's functions were fitted to the data. The slow initial decomposition period was mainly due to the fact that most dead trees remained standing as snags after their death. The initial period was followed by a period of rapid decomposition and, finally, by a period of moderately slow decomposition. Birch stems decomposed more rapidly than Scots pine and Norway spruce stems. Decomposition rates of Norway spruce stems were somewhat lower than those of Scots pine. Because the carbon concentration of decaying boles was relatively stable (about 50%) the rate of carbon loss follows that of mass loss. Models were also developed for the probability that a dead tree remains standing as a snag. During the first years after death, the probability was high. Thereafter, it decreased rapidly, the decrease being faster for birch stems than for Scots pine and Norway spruce stems. Almost all stems had fallen down within 40 years after their death. In Scots pine and Norway spruce, most snags remained hard and belonged to decay class 1. In birch, a higher proportion of snags belonged to the more advanced decay classes. The models provide a framework for predicting dead wood dynamics in managed as well as dense unthinned stands. The models can be incorporated into forest management planning systems, thereby facilitating estimates of carbon dynamics.     

Detecting Rare Species with Random or Subjective Sampling: a Case Study of Red-Listed Saproxylic Beetles in Boreal Sweden

Abstract:  Efficient sampling design in field studies is important for economical and statistical reasons. We compared two ways to distribute sampling effort over an area, either randomly or subjectively. We searched for red-listed saproxylic (wood-living) beetles in 30 spruce stands in boreal Sweden by sifting wood from dead trees. We randomly selected positions within each stand with a geographic positioning system and sampled the nearest dead tree (random sample). In the same stand we also sampled dead trees that, based on literature, were likely to host such species (subjective sampling). The subjective sampling (two to five samples per stand, depending on stand size) was compared with the higher, random sampling effort (fixed level of 12 samples/stand). Subjective sampling was significantly more efficient. Red-listed species were found in 36% of the subjective samples and in 16% of the random samples. Nevertheless, the larger random effort resulted in a comparable number of red-listed species per stand and in 13 detected species in total (vs. 12 species with subjective sampling). Random sampling was less efficient, but provided an unbiased alternative more suitable for statistical purposes, as needed in, for example, monitoring programs. Moreover, new species-specific knowledge can be gained through random searches.     

Relation between extinction and assisted colonization of plants in the arctic‐alpine and boreal regions

Assisted colonization of vascular plants is considered by many ecologists an important tool to preserve biodiversity threatened by climate change. I argue that assisted colonization may have negative consequences in arctic‐alpine and boreal regions. The observed slow movement of plants toward the north has been an argument for assisted colonization. However, these range shifts may be slow because for many plants microclimatic warming (ignored by advocates of assisted colonization) has been smaller than macroclimatic warming. Arctic‐alpine and boreal plants may have limited possibilities to disperse farther north or to higher elevations. I suggest that arctic‐alpine species are more likely to be driven to extinction because of competitive exclusion by southern species than by increasing temperatures. If so, the future existence of arctic‐alpine and boreal flora may depend on delaying or preventing the migration of plants toward the north to allow northern species to evolve to survive in a warmer climate. In the arctic‐alpine region, preventing the dispersal of trees and shrubs may be the most important method to mitigate the negative effects of climate change. The purported conservation benefits of assisted colonization should not be used to promote the migration of invasive species by forestry.     

Projected vegetation changes for the American Southwest: combined dynamic modeling and bioclimatic-envelope approach

This study focuses on potential impacts of 21st century climate change on vegetation in the Southwest United States, based on debiased and interpolated climate projections from 17 global climate models used in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Among these models a warming trend is universal, but projected changes in precipitation vary in sign and magnitude. Two independent methods are applied: a dynamic global vegetation model to assess changes in plant functional types and bioclimatic envelope modeling to assess changes in individual tree and shrub species and biodiversity. The former approach investigates broad responses of plant functional types to climate change, while considering competition, disturbances, and carbon fertilization, while the latter approach focuses on the response of individual plant species, and net biodiversity, to climate change. The dynamic model simulates a region-wide reduction in vegetation cover during the 21st century, with a partial replacement of evergreen trees with grasses in the mountains of Colorado and Utah, except at the highest elevations, where tree cover increases. Across southern Arizona, central New Mexico, and eastern Colorado, grass cover declines, in some cases abruptly. Due to the prevalent warming trend among all 17 climate models, vegetation cover declines in the 21st century, with the greatest vegetation losses associated with models that project a drying trend. The inclusion of the carbon fertilization effect largely ameliorates the projected vegetation loss. Based on bioclimatic envelope modeling for the 21st century, the number of tree and shrub species that are expected to experience robust declines in range likely outweighs the number of species that are expected to expand in range. Dramatic shifts in plant species richness are projected, with declines in the high-elevation evergreen forests, increases in the eastern New Mexico prairies, and a northward shift of the Sonoran Desert biodiversity maximum.     

Application of decision tools to ethical analysis in biodiversity conservation

Achieving ethically responsible decisions is crucial for the success of biodiversity conservation projects. We adapted the ethical matrix, decision tree, and Bateson's cube to assist in the ethical analysis of complex conservation scenarios by structuring these tools so that they can implement the different value dimensions (environmental, social, and animal welfare) involved in conservation ethics. We then applied them to a case study relative to the decision-making process regarding whether or not to continue collecting biomaterial on the oldest of the two remaining northern white rhinoceroses (Ceratotherium simum cottoni), a functionally extinct subspecies of the white rhinoceros. We used the ethical matrix to gather ethical pros and cons and as a starting point for a participatory approach to ethical decision-making. We used decision trees to compare the different options at stake on the basis of a set of ethical desiderata. We used Bateson's cube to establish a threshold of ethical acceptability and model the results of a simple survey. The application of these tools proved to be pivotal in structuring the decision-making process and in helping reach a shared, reasoned, and transparent decision on the best option from an ethical point of view among those available.     

Determination of set-back lines on eroding coasts. Example of the beaches of the Gulf of Lions (French Mediterranean Coast)

The study presented here describes a method for defining set-back lines along eroding coasts. The method (a mathematical model) combines the long-term shoreline retreat trend with short-term shoreline erosion (during storms). Simulations are carried out for 2030 and compared with the beach width to determine whether the shoreline is likely to shift onshore. The mathematical model is applied to the Frontignan and Carnon beaches (south of France). Both sites possess hard engineering coastal structures and downdrift erosion on the natural beaches. The set-back lines indicate that beaches with groynes are generally wide enough to resist shoreline retreat, while the downdrift “natural” beaches are not. We discuss the possible utilisation of set-back line estimations.     

A dendroecological study on Pinus nigra Arn. at different altitudes of northern slopes of Kazdaglari, Turkey

This study was carried out to investigate the relationship between tree ring widths of Pinus nigra in Kazdaglari having humid and very humid climatic conditions. Sixty two trees were cut from 24 sampled points from different altitudes in Kazdaglari to measure treering widths. To determine the responses to the climate, correlation coefficients between treering widths and climatic data were calculated during biological years from October of the previous year to September of the current year In lower altitudes, where climate type is humid, spring and summer precipitation affect the growth of tree rings, but they are not statistically limiting factors. In higher altitudes, this effect is weaker. As a result, we can conclude that the negative effects of the drought are still not clear on the Pinus nigra trees under humid and very humid climatic conditions and at the northern slopes in submediterranean mountainous regions in Turkey.     

Spatio-temporal analysis of alpine ecotones: A spatial explicit model targeting altitudinal vegetation shifts

There is general agreement in literature that Alpine vegetation belt ecotones have shown a trend of upward migration in the last few decades. Despite the potential of such shifts as indicators of global change effects in mountain ecosystems, there are relatively few works focused on their assessment in a systematic and spatially explicit way. In this work our aim is to quantify the altitudinal shifts and analyse the spatial pattern dynamics of mountain ecotones. We developed a novel procedure to delineate the current and former state of three characteristic mountain ecotones, which we formalised as forest, tree and tundra lines. Our approach is based on the recognition of altitudinal extreme outposts identified with ecotone locations at a slope scale. The integration of multi-temporal datasets allows the identification and quantification of altitudinal advances and retreats in the outpost locations for a given period. We tested the method in a section of the Italian Alps for the period 1957-2003. Results show a general trend of an increase in altitude for the three ecotones, despite the occurrence of occasional decreases. We estimate decadal altitude increments of 25 m for forest line, 13 m for treeline and 11 m for tundra line. We also identified changes in ecotone spatial morphology between the two dates, with significant implications in connectivity and colonisation dynamics.     

Divergence in ectomycorrhizal communities with foreign Douglas-fir populations and implications for assisted migration

Assisted migration of forest trees has been widely proposed as a climate change adaptation strategy, but moving tree populations to match anticipated future climates may disrupt the geographically based, coevolved association suggested to exist between host trees and ectomycorrhizal fungal (EMF) communities. We explored this issue by examining the consistency of EMF communities among populations of 40 year-old Douglas-fir (Pseudotsuga menziesii var. menziesii) trees in a common-garden field trial using four provenances from contrasting coastal climates in southwestern British Columbia. Considerable variation in EMF community composition within test sites was found, ranging from 0.38 to 0.65 in the mean similarity index, and the divergence in EMF communities from local populations increased with site productivity. Clinal patterns in colonization success were detected for generalist and specialist EMF species on only the two productive test sites. Host population effects were limited to EMF species abundance rather than species loss, as richness per site averaged 15.0 among provenances and did not differ by transfer extent (up to 450 km), while Shannon's diversity index declined slightly. Large differences in colonization rates of specialist fungi, such as Tomentella stuposa and Clavulina cristata, raise the possibility that EMF communities maladapted to soil conditions contributed to the inferior growth of some host populations on productive sites. The results of the study suggest locally based specificity in host-fungal communities is likely a contributing factor in the outcome of provenance trials, and should be a consideration in analyzing seed-transfer effects and developing strategies for assisted migration.