How the timberline formed: altitudinal changes in stand structure and dynamics around the timberline in central Japan

Background and Aims

Altitudinal timberlines are thought to move upward by global warming, a crucial topic in ecology. Tall tree species (the conifer Abies mariesii and the deciduous broad-leaved Betula ermanii) dominate the sub-alpine zone between 1600 and 2500 m a.s.l., the timberline, on Mount Norikura in central Japan. Dwarf pine Pinus pumila dominates above the timberline to near the summit (3026 m a.s.l.). This study evaluated how the timberline formed on Mount Norikura by examining altitudinal changes in stand structure and dynamics around the timberline.

Methods

One hundred and twenty-five plots of 10 m × 10 m were established around the timberline (2350–2600 m a.s.l.). Trunk diameter growth rate during 6 years was examined for A. mariesii, B. ermanii and P. pumila. Mortality during this period and mechanical damage scars on the trunks and branches due to strong wind and snow were examined for A. mariesii only.

Key Results

The density, maximum trunk height and diameter of A. mariesii in plots decreased with altitude. The maximum trunk height of B. ermanii decreased with altitude, but density and maximum trunk diameter did not decrease. In contrast, the density of P. pumila abruptly increased from around the timberline. A strong negative correlation was found between the densities of P. pumila and tall tree species, indicating their interspecific competition. Trunk diameter growth rates of A. mariesii and B. ermanii did not decrease with altitude, suggesting that these two tall tree species can grow at the timberline. The ratio of trees with mechanical damage scars increased with altitude for A. mariesii, a tendency more conspicuous for larger trees. The mortality of larger A. mariesii was also greater at higher altitude. Tall tree species may not increase their trunk height and survive around the timberline because of mechanical damage.

Conclusions

This study suggests that the altitudinal location of the timberline is mainly affected by mechanical damage due to strong wind and snow rather than by growth limitation due to low temperature. Therefore, the timberline would not move upward even under global warming if these growth and mortality characteristics do not change for a long time.     

How the scrub height of dwarf pine Pinus pumila decreases at the treeline

Plant height decreases much within narrow altitudinal spans near treelines. We compared the stem age, stem inclination and shoot elongation rates of alpine dwarf pine Pinus pumila between the upper distribution limit (treeline, 2,850 m a.s.l.) and the lower distribution limit (2,500 m a.s.l.) on Mount Norikura in central Japan, to examine how the growth traits of P. pumila change with altitude. The mean stem height at the upper distribution limit (49 cm) was about a quarter of that at the lower distribution limit (187 cm). The mean ratio of stem height to length was lower at the upper distribution limit than at the lower distribution limit, indicating that P. pumila stems inclined more at the higher altitude. The mean stem age at the upper distribution limit (48 years) was less than a half of that at the lower distribution limit (109 years). Although the shoot elongation rate positively correlated with stem length at the two altitudes, the shoot elongation rate at a given stem length was lower at the upper distribution limit than at the lower distribution limit. Thus, less developed scrub at the upper distribution limit than at the lower distribution limit was due to shorter stem age, more creeping stems and lower shoot elongation rates. Generally, wind velocity is greater in higher altitudes. Probably, strong wind reduces the growth and mean stem age of P. pumila stems at the upper distribution limit. Therefore, this study concludes that the scrub height of P. pumila is controlled not only by temperature, but also by strong wind.     

Shoot growth and seasonal changes of nonstructural carbohydrate concentrations at the upper and lower distribution limits of three conifers

Nonstructural carbohydrate (NSC) concentration in plant organs is an indicator of a balance between carbon sources (i.e., photosynthesis) and sinks (i.e., growth). Understanding how NSC concentrations change with altitude would help determine altitudinal changes in plant growth. This study compared shoot growth and seasonal changes in NSC concentrations of current-year and 1-year-old needles and branch woods between the upper and lower distribution limits of subalpine conifers Abies veitchii (1600–2000 m a.s.l.), A. mariesii (2000–2400 m a.s.l.), and Pinus pumila (2400–2800 m a.s.l.) in Japan. The lengths of 1-year-old shoots were shorter at the upper distribution limits for the three species, and concentrations and branch woods were all high in spring but decreased toward summer, increasing from summer to autumn. No clear difference was found for either parameter between upper and lower distribution limits for each species. Therefore, this study suggests that growth reduction at the upper distribution limits is due to reduction of both sink and source activities, with similar degrees for each species. However, further studies of sink and source activities, such as temperature-dependent photosynthesis and growth traits, are necessary to reveal clearly the cause of this growth reduction in high altitudes.     

Differences in tree and shrub growth responses to climate change in a boreal forest in China

Global climate change has led to rising temperatures and drought in boreal forests in Northeast China. In some areas, shrubs and trees coexist in high altitude and high latitude areas, and their differences with global warming may lead to significant changes in vegetation composition and distribution. Therefore, we compared the relationships between climate and growth for the most widely distributed dwarf shrub (Pinus pumila) and the two dominant tree species (Larix gmelinii and Pinus sylvestris var. mongolica) in boreal forests in the Daxing’an Mountains, China. A total of 340 tree-ring cores from 172 trees and 64 discs from shrubs were collected from four sites and compared the responses of shrub and tree growth to climate patterns using dendrochronological methods. The shrub and two tree species responded differently to interannual climate variance. The negative effect of growing season temperature was greater on growth of L.gmelinii and P. sylvestrisvar.mongolica than on P. pumila, and the promoting effect of winter and spring precipitation was greatest on P. pumila. Compared with the two tree species, P. pumila had a higher temperature threshold and grew over a shorter growing season. Our findings suggested that L. gmelinii and P. sylvestrisvar.mongolica are more susceptible to global warming than the shrubs that coexist with them. However, P.pumila should be studied from an individual perspective in the future due to the dwarf morphology of shrubs and their complex microenvironment.     

Responses to climate by tree-ring widths and maximum latewood densities of two Abies species at upper and lower altitudinal distribution limits in central Japan

This study examined the effects of climate on tree-ring widths and maximum latewood densities of Abies veitchii and Abies mariesii at the upper and lower distribution limits in central Japan. A. veitchii and A. mariesii dominated at the lower and upper parts of the subalpine zone, respectively. Residual chronologies of tree-ring width and maximum latewood density were developed for the two Abies species at the upper and lower distribution limits, and were compared with monthly mean temperatures and monthly sums of precipitation. Tree-ring widths of the two Abies species at the upper and lower distribution limits positively correlated with temperatures during the beginning of the dormant season and during the growing season of the current year, except for A. veitchii at the lower distribution limit, which showed no positive correlation with temperature. Maximum latewood densities of the two Abies species at the upper and lower distribution limits positively and negatively correlated with temperatures and precipitation, respectively, during the growing season of the current year. Therefore, tree-ring widths and maximum latewood densities of the two Abies species were sensitive to low temperature, except for the tree-ring width of A. veitchii at the lower distribution limit with the warmest thermal conditions along the altitude. Global warming is suggested to affect maximum latewood densities and tree-ring widths of the two Abies species along the altitude.     

Competition and disturbance affect elevational distribution of two congeneric conifers

Climatic change will affect elevational vegetation distribution because vegetation distribution is related to thermal conditions. However, how elevational species distributions are determined by biotic and abiotic factors is not clear. The long‐term plot census along an elevational gradient is indispensable to clarify mechanisms of elevational distribution of tree species. Two congeneric conifers, the less shade‐tolerant Abies veitchii and shade‐tolerant A. mariesii, dominate at low and high elevations, respectively, in the subalpine zone in Japan. This study investigated the population dynamics of the two species at three elevations (low, middle, high) for 13 years to examine why the two species dominated the different elevations from the viewpoints of competition and disturbance. This study showed that growth and survival rates were not highest at the most dominant elevations for each species. At the high elevation where A. mariesii dominated and small disturbances frequently occurred, the recruitment rate of A. mariesii was highest among the three elevations and that of A. veitchii was largely decreased by tree competition. However, A. veitchii was dominant earlier than A. mariesii at the low elevation after large disturbances by the high growth rate of individual trees. Therefore, A. mariesii was superior to A. veitchii at the high elevation because of its high recruitment rate and large reduction of recruitment of A. veitchii due to competition, while A. veitchii was superior to A. mariesii at the low elevation after large disturbances because of higher growth rate than A. mariesii. It is suggested that the elevational distributions of the two species were determined by elevational changes in population dynamics in relation to competition and disturbance. Long‐term observational studies of forest dynamics among various elevations are indispensable to predict the effects of climatic change on vegetation distribution.     

The subalpine vegetation of Mt. Vysokaya, central Sikhote-Alin

The subalpine vegetation structure of Mt. Vysokaya, the Central Sikhote-Alin, is described. This vegetation consists mainly of subalpine spruce-fir forest, a complex of subalpine meadows, shrubs, groves of Betula lanata (B. ermanii s.l.), krummholz of Pinus pumila and alpine tundras. Significant disturbances in the vegetation structure were noted, especially in the forest-tundra ecotone accompanying a sharp reduction of the belts of Betula lanata and Pinus pumila. The altitudinal level of the upper timberline reaches 1600 m a.s.l. which is 250 m less than the expected altitude calculated by Kira's warmth index. An undergrowth of scattered trees of Picea and Betula are growing up to the mountain top. Based on these data and a review of the literature, we concluded that a catastrophic lowering of the timberline and devastation of the subalpine vegetation belt occurred several centuries ago, probably as result of fires.     

Establishment and growth pattern of <Emphasis Type="Italic">Pinus pumila</Emphasis> under a forest canopy in central Kamchatka

We investigated the spatial distribution and growth of the Siberian dwarf pine (Pinus pumila) in a valley–foothill larch–birch (Larix cajanderi–Betula platyphylla as canopy trees) mixed forest of fire origin located in central Kamchatka with the aim of elucidating the ecological features of P. pumila when it is an undergrowth species in a forest. The spatial distribution of all individuals of all tree species was clumped, and the spatial distribution of the two canopy tree species did not repulsively affect that of P. pumila (i.e., its establishment site). These results suggest that the regeneration of P. pumila does not depend on canopy gaps. However, the analysis using a growth model indicated that the canopy trees negatively affected the growth of P. pumila and that the negative effect of L. cajanderi on P. pumila growth was stronger than that of B. platyphylla. The direction of the crown extension of P. pumila was weakly related to the open-space direction. Our results suggest that, although the spatial pattern of establishment of P. pumila is not repulsed by the distribution of canopy trees, the crown can spread horizontally toward the more sparsely populated areas of the canopy trees where they may have higher growth rates.     

山西五台山高山林线的植被景观

 过草本植物群落的分类和排序,结合对乔木和灌木分布的分析,确定了五台山高山林线的几条植被界线以及五台山森林上限附近植被的性质。结果表明：1）阳坡林线的海拔范围为2 605～2 790 m,阴坡林线的海拔范围为2 810～3 015 m;2）草本植物群落随海拔高度的变化比较明显,阴坡和阳坡从郁闭林到山顶均依次分布林下草本层、林缘草甸、亚高山灌丛草甸、高山草甸,草本植物的分布很好地体现了林线内部景观的差异性;3）海拔高度是高山林线附近草本植物群落空间分异的决定性因素。     

Inverse effects of recent warming on trees growing at the low and high altitudes of the Dabie Mountains,subtropical China

Understanding how tree rings of different species at different elevations respond to climate, and whether their relationship is stable over time is crucial not only for credible palaeoclimatic reconstructions, but also for better awareness of forest growth dynamics and therefore making scientific management decisions against a background of global warming. In this work, six tree-ring chronologies of Pinus taiwanensis at three sites from 800 to 1550 m above sea level (asl), and Pinus massoniana at three sites from 500 to 650 m asl were developed in the Dabie Mountains (DBS), subtropical China. In recent decades, only P. taiwanensis at 1550 m asl showed a positive growth-trend. Both P. taiwanensis at 800 m asl and three low-altitude P. massoniana at 500–650 m asl showed negative growth trends. Climate-growth relationship analyses revealed that 1) temperature was the dominant climatic factor that controlled tree-ring growth in DBS. It exerted most influence on trees growing at the lower and upper limit, than for trees growing at altitudes from 650 to 1450 m asl. Only precipitation in October positively influenced tree growth of P. massoniana at all three sites and P. taiwanensis at 800 m asl; 2) There was a shift in temperature’s impact on trees, that was from significantly negative relationship at the four lower altitudes, mainly for the current growing-season, to significantly positive relationship in previous February–July period at the highest altitude. The higher the altitude, the more significant the lag effect of temperature on trees; 3) The influence of temperature on tree growth at most altitudes were variable over time. The positive influence of temperature on trees at 1550 and 1450 m asl was comparatively stable during the early period of instrumental records. It strengthened evidently since the early 1990s, which is coincidental with the timing of the evident temperature increase in DBS. On the contrary, the negative impacts of temperature on tree growth at 800, 650 and 500 m asl had weakened since the early 1990s. Besides the increase of water use efficiency of trees, we speculated that the increasing influence of precipitation in May and July weakened the relationship between temperature and tree rings at low altitudes. This work points out that the upper and lower limits of forest in DBS offer the preferred locations for future sampling in climate reconstruction, but the stability of tree growth and climate over time should be considered. Moreover, forest management should give priority to altitude factors, in addition to tree species representation.     

Effects of climate on diameter growth of co-occurring Fagus sylvatica and Abies alba along an altitudinal gradient

In high-elevation forests, growth is limited by low temperatures, while in Mediterranean climates drought and high temperatures are the main limiting factors. Consequently, the climate-growth relationships on Mont Ventoux, a mountain in the Mediterranean area, are influenced by both factors. Two co-occurring species were studied: silver fir (Abies alba Mill.) and common beech (Fagus sylvatica L.), whose geographical distribution depends on their low tolerance to summer drought at low altitude/latitude, and low temperatures (late frost and short length of the growing season) at high altitude/latitude. Firs and beeches distributed along an elevational gradient were investigated using dendroecological methods. Silver fir growth was found to be more sensitive to summer water stress than beech. On the other hand, beech growth was more impacted by extreme events such as the 2003 heat wave, and negatively related to earlier budburst, which suggests a higher sensitivity to late frost. These results are confirmed by the different altitudinal effects observed in both species. Beech growth decreases with altitude whereas an optimum of growth potential was observed at intermediate elevations for silver fir. Recent global warming has caused a significant upward shift of these optima. As found for the period 2000–2006, rising temperatures and decreasing rainfall may restrain growth of silver fir. If these trends continue in the future beech might be favored at low altitudes. The species will have a reduced capacity to migrate to higher altitudes due to its sensitivity to late frosts, although an upward shift of silver fir is likely.     

Needle browning and death in the flagged crown of Abies mariesii in the timberline ecotone of the alpine region in central Japan

In the flagged crown, which is asymmetric growth formed by severe stresses during winter in alpine regions, needles of evergreen conifers often became brown and died in early spring, but did not in a cushion-shaped crown. Needle browning and death is thought to occur by increasing transpiration due to a thinner cuticle or mechanical damage to the cuticle by wind-born snow and ice particles. To confirm whether the needle browning and death in the flagged crown of Abies mariesii Mast., in the alpine region of Japan conform with this concept, we assessed mechanical damage of the needle cuticle in a timberline ecotone and evaluated the effect of cuticle thickness on cuticular resistance. Mechanical damage on needle cuticles of A. mariesii was not observed. In the cushion-shaped crown, epicuticular wax covered the cuticle and plugged stomatal antechambers. In the flagged crown, epicuticular wax was mostly absent. Cuticular resistance in the flagged crown was lower than that in the cushion-shaped crown. However, the cuticle in the flagged crown was thicker than that in the cushion-shaped crown. The needle browning and death in the flagged crown of A. mariesii occurred even though needle cuticles were not mechanically damaged. The thicker cuticle of the flagged crown may play a role in other stresses. To estimate desiccation stress in relation to the cuticle, we need to elucidate not only cuticular resistance and cuticle thickness, but also cuticle quality and structure.     

Climate change – Bad news for montane forest herb layer species?

Global warming presents a threat to plant species distributed at montane or alpine altitudes if the topography does not allow upward shifts in distribution ranges. Nevertheless, the species might also benefit from increasing temperatures and secondary effects on dominant species (e.g. bark beetle outbreaks or summer drought affecting the canopy species). As a consequence, disturbance frequency in montane forests might increase and light availability for herb layer species will increase. We addressed these interactions in a common garden experiment in Central Germany at different altitudes, representing cold and moist vs. warm and dry conditions. We investigated three montane species with different life forms, including a herb (Trientalis europaea), a grass (Calamagrostis villosa) and a dwarf shrub (Vaccinium myrtillus) under three shading treatments (3%, 28% and 86% of full sunlight). We hypothesized that montane species are at a disadvantage in the lowland, with the dwarf shrub suffering more than the grass. Furthermore, we hypothesized an antagonistic interaction of increased temperature and increased light conditions. While T. europaea and V. myrtillus showed only slightly responses to low altitude conditions, C. villosa displayed a nearly fifteen fold increase in biomass production, despite higher observed herbivory levels in the lowland. We failed to show an antagonistic effect of increased temperature and increased light availability, as all study species suffered from deep shade conditions and grew best under full light conditions at both sites. In conclusion, both improved temperature and light conditions might be principally beneficial for the investigated boreal species, in particular for the grass species C. villosa.     

What role do plant–soil interactions play in the habitat suitability and potential range expansion of the alpine dwarf shrub Salix herbacea?

Mountain plants may respond to warming climates by migrating along altitudinal gradients or, because climatic conditions on mountain slopes can be locally very heterogeneous, by migrating to different microhabitats at the same altitude. However, in new environments, plants may also encounter novel soil microbial communities, which might affect their establishment success. Thus, biotic interactions could be a key factor in plant responses to climate change. Here, we investigated the role of plant–soil feedback for the establishment success of the alpine dwarf shrub Salix herbacea L. across altitudes and late- and early snowmelt microhabitats. We collected S. herbacea seeds and soil from nine plots on three mountain-slope transects near Davos, Switzerland, and we transplanted seeds and seedlings to substrate inoculated with soil from the same plot or with soils from different microhabitats, altitudes and mountains under greenhouse conditions. We found that, on average, seeds from higher altitudes (2400–2700 m) and late-exposed snowbeds germinated better than seeds from lower altitudes (2200–2300 m) and early-exposed ridges. However, despite these differences in germination, growth was generally higher for plants from low altitudes, and there were no indications for a an home-soil advantage within the current range of S. herbacea. Interestingly, seedlings growing on soil from above the current altitudinal distribution of S. herbacea grew on average less well than on their own soil. Thus, although the lack of a home-soil advantage in the current habitat might be beneficial for S. herbacea in a changing environment, migration to habitats beyond the current altitudinal range might be limited, probably due to missing positive soil-feedback.     

Climate sensitivity of purple cone spruce (Picea purpurea) across an altitudinal gradient on the eastern Tibetan Plateau

Picea purpurea (Purple cone spruce) is a dominant and widely distributed tree species in the subalpine area of the Wanglang Nature Reserve. We investigated variations in radial growth and its response to climate in P. purpurea along an altitudinal gradient. In this study, P. purpurea chronologies were developed from three altitudinal sites ranging from 2850 to 3250 m above sea level. Correlation analysis and principal component analysis were used for all the chronologies to detect the growth patterns at different altitudes. Correlation analysis was used to assess the relationships between chronologies and climatic factors. Tree-ring widths among the three elevations were all positively correlated with June maximum temperature in the current year. Radial growth at the higher altitude was more sensitive to temperature than those of the two lower altitudes. Ring-widths at the low and middle sites were mainly negatively affected by temperatures in the previous growing season (June and August). Spruce growth at the upper site was strongly positively affected by temperatures in the previous winter, the current spring and current growing season. Climatological analysis revealed that elevation-dependent and elevation-independent signals were present in this semi-humid subalpine area. Precipitation was not the main factor affecting the tree growth in the growing season throughout the study area. The noteworthy findings were that the lag effects of temperatures to spruce growth was more significant at the low and middle altitude sites, and spruce growth at the high altitude site clearly benefited from the warmer climate before and during the growing season. This study will provide a basis for better predicting forest dynamics and carrying out vegetation restoration in the future.     

The trade-off between cold resistance and growth determines the <Emphasis Type="Italic">Nothofagus pumilio</Emphasis> treeline

The upper and poleward limit of tree distribution are usually determined by abiotic factors such as low temperature and strong winds. Thus, cold resistance is a key element for survival in high altitudes and latitudes where conditions can reduce plant growth. A trade-off between resource allocation to cold resistance and growth could emerge in populations frequently exposed to low temperatures like those in the treeline zone. We studied annual height growth and ice nucleation temperature in Nothofagus pumilio (Nothofagaceae) populations growing in its extremes of altitudinal distribution and in 3 sites situated on a latitudinal gradient in the Chilean Andes. Additionally, gas exchange, water and nitrogen use efficiency and total soluble sugar (TSS) were also measured as possible mechanisms for survival in high altitudes. Individuals from the treeline populations showed lower annual height growth and lower ice nucleation temperatures compared with those from lower populations. In the same way, individuals from more poleward populations showed lower annual height growth and lower ice nucleation temperatures. Gas exchange, water and nitrogen use efficiency and TSS were also higher in the high altitude populations. The results obtained support the hypothesis of trade-off, because the upper and poleward populations showed more cold resistance but a lower height growth. Additionally, we show that cold resistance mechanisms do not impact the physiological performance, suggesting possible adaptation of the high altitude populations. Low temperatures may be affecting cellular growth instead of photosynthesis, creating a pool of carbohydrates that could participate in cold tolerance. Other abiotic and biotic factors should be also assessed to fully understand the distributional range of Nothofagus species.     

Concurrent biotic interactions influence plant performance at their altitudinal distribution margins

Recent studies have shown that biotic interactions can shape species' distributions, but empirical data on multiple biotic interactions are scarce. Therefore, we examined effects of plant–plant and plant–herbivore interactions on plant survival, growth and reproduction at different altitudes. For these purposes we conducted a factorial neighbor removal and large herbivore exclusion experiment with six transplant species (three tall forbs with their main distribution at low altitudes and three small forbs with their main distribution at high altitudes) on Låkta?ohkka Mountain, northern Sweden, replicated at two altitudes (ca 600 and 900 m a.s.l.) and consequently a 2.1°C difference in summer air temperatures. Overall transplant survival was 93%. Two out of three tall forbs grew better at low than at high altitudes, while no significant differences in growth between altitudes were found for any of the three small forbs. Since the main difference in abiotic conditions between the altitudes was most likely in temperature (as the sites were topographically and edaphically matched as closely as possible), this result indicates that climatic warming could induce upward migration of tall low‐altitude forbs. Negative plant–plant interactions prevailed at both altitudes, and we found indications that competition may set the lower altitudinal limits of some small tundra forbs. Thus, increased competition in response to climate warming may potentially shift the lower margins of high‐altitude forbs' distributions upward. Large mammalian grazers reduced the growth of tall forbs and enhanced the flowering of small forbs, and grazers could thus at least partly counteract the anticipated warming‐induced distribution shifts.     

Patterns of Genetic Variation across Altitude in Three Plant Species of Semi-Dry Grasslands

Background

Environmental gradients caused by altitudinal gradients may affect genetic variation within and among plant populations and inbreeding within populations. Populations in the upper range periphery of a species may be important source populations for range shifts to higher altitude in response to climate change. In this study we investigate patterns of population genetic variation at upper peripheral and lower more central altitudes in three common plant species of semi-dry grasslands in montane landscapes.

Methodology/Principal Findings

In Briza media, Trifolium montanum and Ranunculus bulbosus genetic diversity, inbreeding and genetic relatedness of individuals within populations and genetic differentiation among populations was characterized using AFLP markers. Populations were sampled in the Swiss Alps at 1800 (upper periphery of the study organisms) and at 1200 m a.s.l. Genetic diversity was not affected by altitude and only in B. media inbreeding was greater at higher altitudes. Genetic differentiation was slightly greater among populations at higher altitudes in B. media and individuals within populations were more related to each other compared to individuals in lower altitude populations. A similar but less strong pattern of differentiation and relatedness was observed in T. montanum, while in R. bulbosus there was no effect of altitude. Estimations of population size and isolation of populations were similar, both at higher and lower altitudes.

Conclusions/Significance

Our results suggest that altitude does not affect genetic diversity in the grassland species under study. Genetic differentiation of populations increased only slightly at higher elevation, probably due to extensive (historic) gene flow among altitudes. Potentially pre-adapted genes might therefore spread easily across altitudes. Our study indicates that populations at the upper periphery are not genetically depauperate or isolated and thus may be important source populations for migration under climate change.     

Effects of altitude and competition on growth and mortality of the conifer Abies sachalinensis

Altitudinal gradients are convenient subjects to investigate plant responses to air temperature. Plant growth and mortality are also affected by competition at any altitude. This study investigated the effects of altitude and competition on absolute diameter growth rate (ADGR) and mortality of the conifer Abies sachalinensis by using 13-year data. This study was done at two altitudes (200 and 1,000 m a.s.l.) in northern Japan. Local crowding by conifers and broad-leaved trees reduced ADGR of target trees. ADGR was lower in high altitude than low altitude at any DBH and any degree of local crowding because of the short growing season. Observed size-dependent mortality was a U-shaped pattern against DBH at the two altitudes. Smaller and larger trees tended to die of suppression (standing-dead) and disturbances (stem-broken and uprooting), respectively. Mortality of standing-dead trees was negatively correlated with ADGR, irrespective of altitude, i.e., ADGR was a good predictor of mortality. Thus, mortality of standing-dead trees was estimated to be greater at high altitude than low altitude at any degree of local crowding because ADGR was lower at high altitude than low altitude. By contrast, mortality due to disturbances was slightly greater at low altitude than high altitude. Thus, this study showed that a short growth period decreases growth and increases mortality due to suppression at high altitude. Although global warming may increase growth and survival of individual trees at high altitude by prolonging the growth period, prediction on mortality due to disturbances needs caution because the mortality is largely affected by frequency and intensity of disturbances.     

秦岭太白红杉林分布及太白山高山林线特征的定量分析

采用正交试验设计在秦岭太白山设置了12个太白红杉林分,用样方方法对太白红杉种群进行了调查,用正交分析法和"DataProcessingSystem"数据处理软件对影响太白红杉林分布的5个生态因子进行了分析。结果表明:5个生态因子中,海拔梯度的变化是影响太白红杉林分布的主导因子,5个生态因子在影响太白红杉林分布中的作用地位是:海拔>坡度>土壤厚度>坡向>风向。并对描述太白红杉林的5个指标进行了主成分分析,并对高山林线进行了定量描述,胸高直径是描述太白红杉林的主要成分,海拔3400m是太白山太白红杉郁闭林的上限。