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Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In cold regions, there is a close relationship between vegetation and the underlying permafrost. While the vegetation protects the permafrost, the permafrost also provides the necessary water, nutrients, and physical support for the vegetation. As the most sensitive area of alpine vegetation to environmental changes, alpine timberlines respond rapidly to permafrost degradation. Based on the data from meteorological stations and remote sensing in Mount Wutai, the distribution and change in surface frost numbers under the influence of vegetation and alpine timberlines in Mount Wutai from 2001 to 2021 were produced. The results show that from 2001 to 2021, along with the continuous degradation of permafrost, the alpine timberline showed an upward followed by a slight downward trend. From 2000 to 2014, the alpine timberline consistently moved upward, with the melting of permafrost, which produces water playing a positive role. In 2014–2021, the permafrost near the timberline in the study area disappeared, and the upward trend in the alpine timberline was blocked, even downward in some areas. Analysis of the above phenomena shows that in the process of permafrost degradation, the functions of supporting and fixing roots as well as water storage for overlying forest vegetation by permafrost will be lost sequentially, which will have an impact on the growth of the vegetation and make the upward trend in NDVI in the growing season blocked. The process of permafrost degradation is beneficial to vegetation growth but is unfavorable at the end of the degradation period, which is reflected in the phenomenon of the alpine timberline rising and then falling. [ABSTRACT FROM AUTHOR]

Purpose: Soil microbial communities and related key ecological processes play critical roles in timberline delineation and soil carbon balance in alpine ecosystems, which are highly vulnerable to climate change. Accordingly, understanding their geographical differentiation will facilitate recognition of ecosystem functions and improve soil carbon models. In this study, we explored the biogeographic patterns of soil bacterial communities and their mechanisms in maintaining soil carbon balance in an alpine timberline ecosystem of the Sygera Mountains, Southeast Tibet. Materials and methods: Soil samples were collected from typical forest belts above and below the timberline. The abundance and composition of bacterial communities, as well as functional genes, were assessed using the gene chip technology. The relationship of key microbial taxa, functional genes, and soil carbon maintenance was investigated using random forest analysis, multi-model inference, and structural equation modeling. Results and discussion: The shrubland soil bacterial community exhibited greater diversity compared with the coniferous forest community, with higher Shannon Index and more functional genes at the taxonomic and functional levels, respectively. Bacterial community composition differed between the two forest types, with copiotrophic bacteria more abundant in shrubland, and oligotrophic bacteria more abundant in coniferous forest. The shrubland community was also more efficient at utilizing labile organic carbon, while the coniferous forest community utilized recalcitrant organic carbon more efficiently. Genes related to labile carbon degradation were more intense in shrubland, while genes related to recalcitrant carbon degradation were more concentrated in the coniferous forest. Soil temperature and C:N ratio were dominant drivers of bacterial community composition and function. Besides key soil-environment and microbial properties, certain bacterial taxa and functional genes also exerted unique roles in soil carbon variation. Conclusions: Significant differences exist in soil bacterial community composition and functions between the two forest types above and below the timberline of the Sygera Mountains. These differences may be attributed to soil temperature and soil C:N ratio. Coupling these microbial variables into the earth system model can improve the predictive power of the carbon feedback process in terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

In the permafrost zone, the vegetation growth condition is closely related to the permafrost occurrence state. Changbai Mountain is the highest peak in Northeast China and is also a permafrost distribution area, where the vegetation shows an obvious vertical distribution pattern, and the alpine timberline has a clear boundary. The intersecting zone of alpine timberline is an ecologically fragile area that can be used as an external signal amplifier and is an important site for monitoring climate change. In this study, the surface frost number and alpine timberline in the Changbai Mountain area were analyzed through combining ground and remote-sensing data, using the freezing number model and support vector machine method. The results show that the distribution characteristics of alpine timberline and permafrost at elevation are correlated, there is a response mechanism of alpine timberline to the degradation of permafrost, and the upward migration rate of alpine timberline has increased in the last 20 years. The continuous degradation of permafrost will change the environment of vegetation growth, which, in turn, will affect the global carbon cycle process. Focusing on the state of permafrost will help us to understand climate change in depth, and we can respond to a series of impacts caused by ecological changes in cold regions in advance. [ABSTRACT FROM AUTHOR]

Uncertainty still exists on the directions and intensity of changes in leaf herbivory under scenarios of global warming. We, therefore, conducted an investigation on insect herbivory along an elevational gradient to explore how leaf herbivory may respond to future climate warming using a space-for-time substitution approach. We hypothesize that the leaf herbivory for alpine woody species should decline with elevation. We also guess the leaf herbivory may not differ between different leaf-age groups, for the old leaves are less attractive to insect due to their lower nutrients. To approve these assertions, we measured different aspects of leaf herbivory, i.e., the intensity (leaf area consumed per damaged leaf), frequency (percentage of leaves damaged), and rate (percentage of consumed leaf area over the total number of leaves), across different leaf-age groups for Rhododendron aganniphum var. schizopeplum along an elevational gradient (4280–4640 m) in the Sergymla Mountains, southeast Tibet. Related leaf traits of leaf mass per area (LMA) and nitrogen (Nmass), as well as total phenolics for 1-year-old leaves, were also investigated. In contrast with our expectation, the rate of herbivory did not vary with elevation, while the frequency and intensity reflected increasing and declining patterns, respectively. LMA and total phenolics tended to increase with elevation, while Nmass significantly declined. Further analysis indicated that Nmass and total phenolics mainly explained the variation of frequency of herbivory, while Nmass reflected a significant effect on the variation of intensity. No differences in herbivory were found between the leaf-age groups. Our results suggest that the lower intensity of leaf herbivory at higher elevations is mainly associated with the declined nutritional levels, while the higher frequency might be related to the higher costly anti-herbivore defenses like phenolics and the lower nutritional levels. Although the older leaves are exposed to herbivore attacks for a longer time, they possessed the same herbivory levels as current-year leaves partly due to their lower nitrogen concentrations. Both supporting the nutrient limitation hypothesis, i.e., plants with lower leaf nutrient levels possess less leaf herbivory. In all, the herbivory on the alpine Rhododendron is small in magnitude, but given the higher herbivory (for intensity at least) under persistent warming conditions and its potential impacts on mediating plant–insect interactions, insect herbivory should be included in predictions of climate change impacts on alpine ecosystems. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Northwest A & F University - Natural Science Edition is the property of Editorial Department of Journal of Northwest A&F University (Natural Science Edition) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The spatiotemporal change in the alpine timberline, an ecosystem ecotone, is an ideal indicator for use in climate change research. In order to gain a quantitative understanding of the response of the alpine timberline to climate change, the Hengduan Mountains region of China was selected as a study area and a series of 136 Landsat images covering this area that were acquired in 1985, 1995, 2005 and 2015 were collected. First, the alpine timberline was retrieved and the spatiotemporal dynamics of the timberline were explored. The effect of topography on the location of the alpine timberline was also analyzed. The results indicate that the average elevation of the timberline increased by about 55 (±8.54) m from 3992.58 m in 1985 to 4047.60 m in 2015; however, there was obvious spatial heterogeneity in these changes. On the whole, the average elevation of the timberline on shaded slopes (northern, northeastern, and northwestern slopes) were found to be about 160 m higher than on sunward slopes (southern, southeastern, and southwestern slopes). It was also found that, over the period 1985–2015, there has been an obvious acceleration in the upward tendency of the alpine timberline. Finally, the climate variables that are driving this timberline shift were identified and evaluated using the partial least squares (PLS) regression method. The results indicate that the average annual temperature (TEM_Year), total precipitation during the growing season (PRE_Grow), and growing season temperature (TEM_Grow) were the significant positive factors driving the rise in the timberline elevation; the total annual precipitation (PRE_Year) was found to have an unexpected negative influence. Besides, other climatic factors (e.g., strong winds) and non-climate variables (e.g., human influence and soil properties) should be also included in future related studies to enhance the understanding of the link between forest vegetation and climate change under extreme conditions.

As an important ecotone, the alpine timberline is the boundary between closed-canopy montane forest and alpine vegetation, and is highly sensitive to global and regional climate changes. We provided a way to identify and extract the alpine timberline in Yarlung Zangpo Grand Canyon Nature Reserve by using remote sensing data and spatial analysis based on land use/land cover classification and NDVI distribution characteristics. Combining DEM data, the influence of slope and aspect on the distribution of alpine timberline was explored. The results showed that the alpine timberline in Yarlung Zangpo Grand Canyon is transitional timberline, with the upper boundary approximately distributed at the elevation of 3422–4373 m, the lower boundary at approximately 3270–4164 m, with a width of about 110–280 m. Alpine timberline was mainly distributed on steep and very steep slopes ranging from 25° to 45°. The maximum elevation of both the upper and lower boundaries occurred on steep slopes. The distribution of alpine timberline varies with aspects, with sunny slopes having a higher boundary than shady slopes. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The radial growth of trees in alpine timberline is particularly sensitive to climate change. We sampled and disposed tree-ring cores of three coniferous tree species including Juniperus saltuaria , Abies forrestii , and Larix potaninii at alpine timberline in Yading Nature Reserve. The standard tree-ring chronology was used to explore the response of radial growth of different timberline species to climate change. The results showed that radial growth of L. potaninii increased after 2000, while that of A. forrestii declined after 2002, and J. saltuaria showed a significant decreasing growth trend in the past 10 years. Such results indicated divergent growth responses to climate factors among the three tree species at alpine timberline. The radial growth of J. saltuaria was sensitive to temperature, and was positively correlated with the minimum temperature from previous October to current August, the mean tempera-ture from previous November to current April and from current July to October, but was negatively associated with the relative humidity from current July to October. The radial growth of A. forrestii showed negative correlation with mean temperature and the maximum temperature from May to June in the current year, while it exhibited positive association with the relative humidity and the Palmer drought severity index from May to June in the current year. L. potaninii radial growth was positively associated with mean temperature and the maximum temperature of November-December in the previous year, the maximum temperature of current March and mean temperature of current August. The temporal stability of climate-growth relationship varied among different timberline species. The positive correlation between radial growth of A. forrestii and J. saltuaria and temperature gradually decreased, while the posi-tive relationship of L. potaninii radial growth and temperature gradually increased. Under the background of climate warming, rapid rise in surface air temperatures may promote the radial growth of L. potaninii , while inhibit that of J. saltuaria and A. forrestii , which may change the position of regional timberline.

Climate change is a major cause of changes in alpine and polar vegetation, particularly at the edges of distributions. In temperate regions, these changes are expected to occur at the timberline of alpine zones. On Mt. Fuji, the highest mountain in Japan, the timberline is located 2400–2500 m above sea level. Over a 40-year period (1978–2018), we researched changes in the timberline vegetation of Mt. Fuji. A permanent belt transect extending from the upper timberline to subalpine zones was set up in August 1978. Tree diameters and heights were recorded at the establishment of the transect and every 20 years afterwards. Over the 40 years of the study, the timberline advanced rapidly upwards, and the degree of vegetation cover above the timberline increased remarkably. Notably, the expansion of Salix reinii into the upper part of the timberline facilitated the subsequent spread of Larix kaempferi into this zone. Seedlings of L. kaempferi were particularly abundant at the upper timberline and became established on the uppermost part of the slope. The shape of L. kaempferi at the upper timberline changed from a prostrate form to an upright tree form. We conclude that the upward advance of the alpine timberline observed on Mt. Fuji is due to climate change.

The alpine timberline, an ecosystem ecotone, indicates climatic change and is tending to shift toward higher altitudes because of an increase in global warming. However, spatiotemporal variations of the alpine timberline are not consistent on a global scale. The abundant and highest alpine timberline, located on the Tibetan Plateau, is less subject to human activity and disturbance. Although many studies have investigated the alpine timberline on the Tibetan Plateau, large-scale monitoring of spatial-temporal dynamics and driving mechanisms of the alpine timberline remain uncertain and inaccurate. Hence, the Gongga Mountain on the southeastern Tibetan Plateau was chosen as the study area because of the most complete natural altitudinal zonation. We used the Otsu method on Google Earth Engine to extract the alpine timberline from 1987–2019 based on the normalized difference vegetation index (NDVI). Then, the alpine timberline spatiotemporal patterns and the effect of topography on alpine timberline distribution were explored. Four hillsides on the western Gongga Mountain were selected to examine the hillside differences and drivers of the alpine timberline based on principal component analysis (PCA) and multiple linear regression (MLR). The results indicated that the elevation range of alpine timberline was 3203–4889 m, and the vegetation coverage increased significantly (p < 0.01) near the alpine timberline ecotone on Gongga Mountain. Moreover, there was spatial heterogeneity in dynamics of alpine timberline, and some regions showed no regular trend in variations. The spatial pattern of the alpine timberline was generally high in the west, low in the east, and primarily distributed on 15–55° slopes. Besides, the drivers of the alpine timberline have the hillside differences, and the sunny and shady slopes possessed different driving factors. Thus, our results highlight the effects of topography and climate on the alpine timberline on different hillsides. These findings could provide a better approach to study the dynamics and formation of alpine timberlines.

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Alpine timberline is particularly sensitive to global climate change, with the danger of losing essential ecosystem services in high elevational regions. Its evolution is generally linked to annual average thermal regimes, and is regarded as an indicator of climate warming. However, the effect of uneven seasonal climate change stressed by the Hijioka et al. (2014) on alpine timberline dynamics in terms of both position migration and species composition remains unclear. Here, we documented approximately 6000 years of postglacial alpine timberline evolution on Mt. Tabai in the monsoon-dominated East Asian subtropical–temperate transition. We analyzed three high-resolution lacustrine sediment sequences located below, within, and above the current alpine timberline, an ecotone between the forest line and treeline, respectively. The timberline position appears to have varied coincidently with the temperature effect of cold East Asian Winter Monsoon (EAWM), implying that enhanced EAWM shortened the duration of the growing season and reduced forest survival at the alpine timberline. Unlike position migration, however, timberline species composition depends on summer precipitation. We found that drought-tolerant herb and shrub species were much more sensitive to variations in the water-bearing East Asian Summer Monsoon (EASM) than mesophytic trees at the alpine timberline. Our results suggest that prediction of future timberline dynamics should consider uneven seasonal climate changes. [ABSTRACT FROM AUTHOR]

Changes to global climate patterns have the potential to alter the structure of soil microbial communities which are key components of terrestrial ecosystems. High altitude ecosystems are both temperature and Nitrogen-limited and the biota therein is sensitive to these conditions. Temperatures and nitrogen (N) depositions in the eastern Qinghai–Tibet Plateau are predicted to sharp rise by the end of this century. This study aimed to better understand the effects of warming and N addition treatments alone and in combination on an alpine meadow ecosystem near the timberline zone in the eastern region of the Qinghai–Tibet Plateau. The field experiment included replicated plots with an ambient treatment alone or with low N (5 g N m −2 a −1 ), intermediate N (15 g N m −2 a −1 ), and high N (30 g N m −2 a −1 ) (Control, LN, MN, HN) and open top chambers warming treatment alone, or LN and HN additions (W, WLN, WHN) to study the interactive effects of the warming and N additions on the soil microbial community as determined by phospholipid fatty acids (PLFAs). Microbial communities and their allied soil and plant properties were examined after 3 years of the treatments. The strength of the relationship between the treatments and their direct and indirect effects on the microbial communities, soil and plant properties were determined using a structural equation model (SEqM). The results indicated that N addition significantly changed surface soil microbial communities, in particular, decreased the fungi: bacteria ratio (F:B) ( p < 0.01). The warming differentially influenced some specific microbial biomarkers, such as fungal PLFAs which decreased, and actinobacterial PLFAs, which increased, under warming ( p < 0.05). The combination of the warming and N addition showed significantly positive interactive effects ( p < 0.001) on soil microorganisms (i.e. the biomass of general bacteria, Gram-positive bacteria, fungi and etc.) in these alpine soils. The SEqM results show the direct effects of the warming treatment on soil microorganisms were less than those from the N additions. Moreover, warming and N addition had stronger indirect, than direct, effects on the soil microbial community via induced changes in soil properties and plant community. The total effect of warming on the soil microbial community was stronger than that of the N additions. The results suggested interactive effects of the warming and N addition on soil microorganisms in an near timberline alpine ecosystem in the eastern Qinghai-Tibet Plateau. [ABSTRACT FROM AUTHOR]

In alpine regions, elevational gradients in environmental parameters are reflected by structural and functional changes in plant traits. Elevational changes in plant water relations have also been demonstrated, but comparable information on root hydraulics is generally lacking. We analyzed the hydraulic efficiency (specific hydraulic conductivity k, entire root system conductance K) and vulnerability to drought-induced embolism (water potential at 50 % loss of conductivity Ψ) of the roots of Pinus cembra trees growing along an elevational transect of 600 m. Hydraulic parameters of the roots were compared with those of the stem and related to anatomical traits {mean conduit diameter ( d), wall reinforcement [( t/b)]}. We hypothesized that temperature-related restrictions in root function would cause a progressive limitation of hydraulic efficiency and safety with increasing elevation. We found that both root k and K decreased from low (1600 m a.s.l.: k 5.6 ± 0.7 kg m s MPa, K 0.049 ± 0.005 kg m s MPa) to high elevation (2100 m a.s.l.: k 4.2 ± 0.6 kg m s MPa, K 0.035 ± 0.006 kg m s MPa), with small trees showing higher K than large trees. k was higher in roots than in stems (0.5 ± 0.05 kg msMPa). Ψ values were similar across elevations and overall less negative in roots ( Ψ −3.6 ± 0.1 MPa) than in stems ( Ψ −3.9 ± 0.1 MPa). In roots, large-diameter tracheids were lacking at high elevation and ( t/b) increased, while d did not change. The elevational decrease in root hydraulic efficiency reflects a limitation in timberline tree hydraulics. In contrast, hydraulic safety was similar across elevations, indicating that avoidance of hydraulic failure is important for timberline trees. As hydraulic patterns can only partly be explained by the anatomical parameters studied, limitations and/or adaptations at the pit level are likely. [ABSTRACT FROM AUTHOR]

Birch (Betula) trees and forests are found across much of the temperate and boreal zones of the Northern Hemisphere. Yet, despite being an ecologically significant genus, it is not well studied compared to other genera like Pinns, Picea, Larix, Juniperus, Quercus, or Fagus. In the Himalayas, Himalayan birch (Betula utilis) is a widespread broadleaf timberline species that survives in mountain rain shadows via access to water from snowmelt. Because precipitation in the Nepalese Himalayas decreases with increasing elevation, we hypothesized that the growth of birch at the upper timberlines between 3900 and 4150 m above sea level is primarily limited by moisture availability rather than by low temperature. To examine this assumption, a total of 292 increment cores from 211 birch trees at nine timberline sites were taken for dendroecological analysis. The synchronous occurrence of narrow rings and the high interseries correlations within and among sites evidenced a reliable cross-dating and a common climatic signal in the tree-ring width variations. From March to May, all nine treering- width site chronologies showed a strong positive response to total precipitation and a less-strong negative response to temperature. During the instrumental meteorological record (from 1960 to the present), years with a high percentage of locally missing rings coincided with dry and warm pre-monsoon seasons. Moreover, periods of below-average growth are in phase with well-known drought events all over monsoon Asia, showing additional evidence that Himalayan birch growth at the upper timberlines is persistently limited by moisture availability. Our study describes the rare case of a drought-induced alpine timberline that is comprised of a broadleaf tree species. [ABSTRACT FROM AUTHOR]

Norway spruce trees in the subalpine forests of the European Alps are frequently attacked by the needle rust Chrysomyxa rhododendri. The obligate parasite undergoes a complex life cycle with a host shift between rhododendrons ( Rhododendron sp.) and Norway spruce [ Picea abies (L.) Karsten] and causes a yellowing and defoliation of the current-year needles in summer. Infected trees show several anatomical, morphological and physiological modifications, including a decrease in pigment content and net photosynthesis of infected needles, lower biomass production and reduced radial and height growth. The consequences are diminished timber yield and cripple growth. Because of repeated heavy infections in recent years, forest managers report increasing difficulties in both natural regeneration and afforestation at high elevation sites, where rhododendrons occur. This review gives a summary of the present knowledge about the effects of C. rhododendri infections on Norway spruce, including so far unpublished findings and with particular attention to the phenomena of resistant trees. Implications for subalpine forests and counter strategies are discussed. [ABSTRACT FROM AUTHOR]

Abstract: It is still unknown if the variation of leaf energy content across altitudinal gradients is caused by varying climatic factors or species replacement. We test whether there is an altitudinal increase in leaf energy properties within a single species, which is mainly due to the decreasing air temperature with altitude. We collected samples for Bergenia purpurascens Engl. (an evergreen herb) at every 10 m in altitude from outside the timberline forest (4320 m) to the hilltop (4642 m) in the Sergyemla Mountains, southeastern Tibet. We measured mass- and area-based leaf construction cost (CCm, CCa) and their components: nitrogen concentration (Nmass), ash concentration (AC), the heat of combustion (HC), and specific leaf area (SLA), as well as leaf lignin concentration (LC) and new leaf dry mass per plant (NLDM). As altitude increased, CCm, CCa, HC, and LC increased, whereas Nmass, SLA, AC, and NLDM decreased. CCm and CCa were positively correlated with HC and LC but negatively with Nmass, SLA, AC and NLDM. CCm, CCa and HC were negatively correlated with mean air temperature. The data indicated that some high-HC constituents like lignin rather than protein contributed to the observed pattern of leaf energy properties. For high-altitude plants, having relatively high leaf CCm and HC can be regarded as a growth strategy for sustaining carbon gain and maximizing nitrogen-use efficiency. Since CC tends to decrease with increasing air temperature, evergreen herbs at high altitude are expected to construct relatively “cheaper” leaves in response to global warming. [Copyright &y& Elsevier]

The aims of this study were to describe the biometrics and the spatial and age structure of a population of Norway spruce, to compare vertically connected sections of the timberline ecotone, and to assess the possibility of regeneration of a Norway spruce population under the conditions of the ecotone developing above the former pastoral timberline in the Hrubý Jeseník Mountains, Czech Republic. In the first stage, we established the age of the populations by means of an age-girth nonlinear regression model in a research polygon (RP) with an area of 3.5 ha. The degree of coverage was determined by using geographic information system methods. The total number of cones in the RP was counted, and 50 cones were taken for laboratory investigation of their germination capacity and the number of seeds per cone. The distribution of trees in clonal generations was examined for 10 clonal groups, and the characteristics of layering were explored by measuring the preserved layered branches. To verify the trends found in the first stage of research, we conducted an analysis of the age of all specimens on 8 control plots (50 m 3 30 m) in other parts of the mountain range. The results show that the timberline ecotone is rising gradually and that the forest-free area may become significantly reduced. Up to 3 generations of trees of clonal origin were found in the RP. A greater intensity of vegetative regeneration was observed in the upper section of the RP. Moreover, the seed-based regeneration proved to be successful in the RP, and living, germinating seeds were found even in the top parts of the RP. [ABSTRACT FROM AUTHOR]

Chrysomyxa rhododendri is a rust which infects Picea abies growing near the alpine timberline. Attacked needles are normally shed, but few remain on shoots. We hypothesised that these needles increase transpiration of Picea during winter. Partly damaged, completely damaged and healthy needles of an infected tree as well as healthy needles of a resistant tree were compared in a microscopy analysis, and needle conductance of shoots was measured gravimetrically. Despite needle shedding, more than 6% of needles remaining on infected tree shoots were damaged. Partly damaged needles showed local brownish areas in the periphery and completely damaged needles necrotic parenchyma and epidermal tissues. Cuticular conductance of affected shoots was up to 25.23 ± 2.75 mmol m−2 s−1 at moderate water potential and thus twofold higher than in the resistant tree. Needle shedding reduces negative effects of Chrysomyxa infections during summer, but remaining damaged needles impair tree water relations in winter. [ABSTRACT FROM AUTHOR]

For assessing the impact of soil temperature on tree growth in remote areas such as the alpine timberline, we introduce a new method for soil temperature manipulations. This new approach is based on roofing of the rooting zone and allows either soil cooling or soil warming without significantly influencing soil water availability and the above ground microclimate. [ABSTRACT FROM AUTHOR]

Spatial pattern of nonstructural carbohydrates (NSC) was analyzed in two alpine timberline species ( Abies georgei and Juniperus saltuaria) growing at the timberline in Sergyemla Mountain, southeastern Tibetan Plateau. We aimed to examine the effect of canopy height and leaf age on balance between carbon uptake and consumption of timberline tree species in extremely environmental condition. The results showed that no significantly vertical variation in sugars, starch or NSC (soluble sugars plus starch) in A. georgei was found for any aged needles. Also, there were no significant differences among vertical gradients in both current and last-year leaves for J. saltuaria. However, different-aged needles/leaves showed significant differences in NSC concentrations in both A. georgei and J. saltuaria. For A. georgei, needle mean NSC across vertical canopies showed a significant increase from current-year to 2-year needles ( P < 0.05), followed by a gradual decrease from 2- to 5-year needles ( P < 0.05), whereas for J. saltuaria, last-year leaves had significant higher NSC except sugars compared with current-year leaves across canopies ( P < 0.01). The observed trends of NSC along vertical canopy heights and leaf ages suggested that, in extreme environmental condition, not only light-induced carbon acquisition in photosynthesis but also carbohydrate export from leaves should be taken into account to explain the spatial pattern of NSC. [ABSTRACT FROM AUTHOR]

Drought stress can cause xylem embolism in trees when the water potential (Ψ) in the xylem falls below specific vulnerability thresholds. At the alpine timberline, frost drought is known to cause excessive winter embolism unless xylem vulnerability or transpiration is sufficiently reduced to avoid critical Ψ. We compared annual courses of Ψ and embolism in Picea abies, Pinus cerebra, Pinus mugo, Larix decidua, and Juniperus communis growing at the timberline vs. low altitude. In addition, vulnerability properties and related anatomical parameters as well as wood density (Dt) and wall reinforcement (wall thickness related to conduit diameter) were studied. This allowed an estimate of stress intensities as well as a detection of adaptations that reduce embolism formation. At the alpine timberline, Ψ was lowest during winter with corresponding embolism rates of up to 100% in three of the conifers studied. Only Pinus cembra and Larix decidua avoided winter embolism due to moderate Ψ. Minor embolism was observed at low altitude where the water potentials of all species remained within a narrow range throughout the year. Within species, differences in Ψ50 (Ψ at 50% loss of conductivity) at high vs. low altitude were less than 1 MPa. In Picea abies and Pinus cembra, Ψ50 was more negative at the timberline while, in the other conifer species, Ψ50 was more negative at low altitude. Juniperus communis exhibited the lowest (-6.4 ± 0.04 MPa; mean ± ) and Pinus mugo the highest Ψ50 (-3.34 ± 0.03 MPa). In some cases, Dt and tracheid wall reinforcement were higher than in previously established relationships of these parameters with Ψ50, possibly because of mechanical demands associated with the specific growing conditions. Conifers growing at the alpine timberline were exposed to higher drought stress intensities than individuals at low altitude. Frost drought during winter caused high embolism rates which were probably amplified by freeze-thaw stress. Although frost drought had a large effect on plant water transport, adaptations in hydraulic safety and related anatomical parameters were observed in only a few of the conifer species studied. [ABSTRACT FROM AUTHOR]

Abstract: Research has shown that some plants respond to enhanced UV-B radiation by producing smaller and thicker leaves, by increasing the thickness of epidermis and concentration of UV-B absorbing compounds of their surface layers and activation of the antioxidant defence system. The response of high-altitude plants to UV-B radiation in controlled conditions is often less pronounced compared to low-altitude plants, which shows that the alpine timberline plants are adapted to UV-B. These plants may have a simultaneous co-tolerance for several stress factors: acclimation or adaptation to the harsh climate can also increase tolerance to UV-B radiation, and vice versa. On the other hand, alpine timberline plants of northern latitudes may be less protected against increasing UV-B radiation than plants from more southern latitudes and higher elevations due to harsh conditions and weaker preadaptation resulting from lower UV-B radiation exposure. It is evident that more long-term experimental field research is needed in order to study the interaction of climate, soil and UV-B irradiance on the timberline plants. [Copyright &y& Elsevier]

We investigated carbon (C) uptake and respiratory losses of an adult Pinus cembra tree at the alpine timberline throughout an entire year by means of an automated, multiplexing gas exchange system. These chamber measurements were then combined with biomass data for scaling up the C budget to the tree level. Integrated over an entire year, the cumulative C gain of the tree under study was 23.5 kg of C in 2002. The daily C balance was negative for 5 months and the estimated total wintertime respiratory losses were 9% of the amount of C fixed during the growing season. The total annual C loss of the tree consumed 55% of the annual net C gain and the remaining surplus was stored in new tissues (36%) and used for fine root growth (9%). Thus, the overall C budget of P. cembra at the upper timberline is balanced fairly well, although the C sink strength in fine roots is strongly limited owing to low root zone temperatures when compared to conifers at lower elevation sites. [ABSTRACT FROM AUTHOR]

The application of quantitative wood anatomy (QWA) in dendroclimatic analysis offers deep insight into the climatic effect on tree-ring formation, which is crucial in understanding the forests' response to climate change. However, interrelations between tree-ring traits should be accounted to separate climatic signals recorded during subsequent stages of cell differentiation. The study was conducted in the South Siberian alpine timberline on Pinus sibirica Du Tour, a species considered unpromising in dendroclimatology. Relationships between tree-ring width, cell number N, mean and maximum values of radial diameter D, and cell wall thickness (CWT) were quantified to obtain indexed anatomical chronologies. Exponential functions with saturation D(N) and CWT(N) were proposed, which explained 14–69% and 3–61% of their variability, respectively. Indexation unabated significance of the climatic signals but separated them within a season. Analysis of pointer years and climatic extremes revealed predominantly long-term climatogenic changes of P. sibirica radial growth and QWA and allowed to obtain QWA-based 11-year filtered reconstructions of vegetative season climatic characteristics (R2adj = 0.32–0.66). The revealed prevalence of low-frequency climatic reactions is probably explained by a strategy of slow accumulation and utilization of resources implemented by P. sibirica. It makes this species' QWA a promising proxy for decadal climatic variations in various intra-seasonal timeframes. [ABSTRACT FROM AUTHOR]

Climate change is a major cause of changes in alpine and polar vegetation, particularly at the edges of distributions. In temperate regions, these changes are expected to occur at the timberline of alpine zones. On Mt. Fuji, the highest mountain in Japan, the timberline is located 2400–2500 m above sea level. Over a 40-year period (1978–2018), we researched changes in the timberline vegetation of Mt. Fuji. A permanent belt transect extending from the upper timberline to subalpine zones was set up in August 1978. Tree diameters and heights were recorded at the establishment of the transect and every 20 years afterwards. Over the 40 years of the study, the timberline advanced rapidly upwards, and the degree of vegetation cover above the timberline increased remarkably. Notably, the expansion of Salix reinii into the upper part of the timberline facilitated the subsequent spread of Larix kaempferi into this zone. Seedlings of L. kaempferi were particularly abundant at the upper timberline and became established on the uppermost part of the slope. The shape of L. kaempferi at the upper timberline changed from a prostrate form to an upright tree form. We conclude that the upward advance of the alpine timberline observed on Mt. Fuji is due to climate change. [ABSTRACT FROM AUTHOR]

The alpine timberline, an ecosystem ecotone, indicates climatic change and is tending to shift toward higher altitudes because of an increase in global warming. However, spatiotemporal variations of the alpine timberline are not consistent on a global scale. The abundant and highest alpine timberline, located on the Tibetan Plateau, is less subject to human activity and disturbance. Although many studies have investigated the alpine timberline on the Tibetan Plateau, large-scale monitoring of spatial-temporal dynamics and driving mechanisms of the alpine timberline remain uncertain and inaccurate. Hence, the Gongga Mountain on the southeastern Tibetan Plateau was chosen as the study area because of the most complete natural altitudinal zonation. We used the Otsu method on Google Earth Engine to extract the alpine timberline from 1987–2019 based on the normalized difference vegetation index (NDVI). Then, the alpine timberline spatiotemporal patterns and the effect of topography on alpine timberline distribution were explored. Four hillsides on the western Gongga Mountain were selected to examine the hillside differences and drivers of the alpine timberline based on principal component analysis (PCA) and multiple linear regression (MLR). The results indicated that the elevation range of alpine timberline was 3203–4889 m, and the vegetation coverage increased significantly (p < 0.01) near the alpine timberline ecotone on Gongga Mountain. Moreover, there was spatial heterogeneity in dynamics of alpine timberline, and some regions showed no regular trend in variations. The spatial pattern of the alpine timberline was generally high in the west, low in the east, and primarily distributed on 15–55° slopes. Besides, the drivers of the alpine timberline have the hillside differences, and the sunny and shady slopes possessed different driving factors. Thus, our results highlight the effects of topography and climate on the alpine timberline on different hillsides. These findings could provide a better approach to study the dynamics and formation of alpine timberlines. [ABSTRACT FROM AUTHOR]