Timberline Ecotone Research Articles

Timberlines of the Greek high mountains: status quo at the turn of the millennium

The present review article provides an overview about the timberlines of the Greek high mountains. It informs about the existing tree species and about the altitude, physiognomy and dynamics of the timber-line ecotones. Subsequently, it gives an interpretation of the human influence and the geo-ecological fac-tors, which may have caused the altitudinal limit of tree growth in Greece. A latitudinal and local change in timberline-forming tree species creates high heterogeneity between the research areas and makes this their most remarkable feature. Moreover, in Greece there is no rise in timberline altitude from north to south. In some areas, fir-dieback causes a local decline in timberline altitude, which is the predominant dynamic process. An anthropogenic depression of the forest line is certainly common. Yet, a natural forest cover reaching up to the peak zones of the Greek high mountains is unthinkable. The identified timberline-forming factors and the prevailing site conditions speak against this. In accordance with the Mediterranean climate regime, it is obvious that not only the climatic conditions of winter (frost, snow) determine the limits of tree growth. The (macro- and micro) climatic impacts of summer (drought, high insolation) play a highly important role as well. Against this background, the climate-ecological hindrances to the establishment of trees, i.e. the germination and the survival of seedlings, are identified as key-factors for understanding the Hellenic timberlines (“regeneration hypothesis”). Against the back-ground of global warming, suggestions for further research on the ecology and dynamics of the Greek high mountain timberlines are provided. 

Cover

On the Cover: Centre: Pinus cembra L. is an enigmatic closed-cone pine of the timberline ecotone in the European Alps and the Carpathian Mountains; photograph by Felix Gugerli; pp. 1049–1062. Top right: Feeding aggregation of coney (Cephalopholis fulva, Epinephelidae) in tropical rocky reefs of Fernando de Noronha Archipelago, northeast Brazil; photograph by João Paulo Krajewski; pp. 1163–1176. Top left: Euhadra peliomphala simodae (Jay, 1856) inhabit the southern part of the Izu Peninsula and the Izu Islands in Japan; their great diversity of shell colour is attributed to differences in island elevation; photograph by Shun Ito; pp. 1103–1116. Bottom left: The biodiversity of an aquatic ecosystem is encompassed in the transient traces of environmental DNA left behind by the inhabitants; illustration by Laura L. Hauck; pp. 1151–1162. Bottom right: This circular logo graced the cover of the first issue (March 1974) and initial 14 volumes of the Journal of Biogeography; the golden text celebrates the journal's five decades and 50th anniversary.

Altitude and slope aspects as the key factors affecting the change of C:N:P stoichiometry in the leaf-litter-soil system of alpine timberline ecotones of the Sygera Mountains in Southeast Tibet, China

Understanding the altitudinal distribution patterns of ecological stoichiometry is essential for understanding biogeochemical processes in mountainous forests. However, the changes in ecological stoichiometry throughout the leaf-litter-soil system on the different slope aspects in mountainous forests ecosystems are not fully understood. To fill these gaps, we examined the altitudinal patterns of C:N:P stoichiometry in the leaf-litter-soil system and nutrient resorption of dominant tree species in the alpine timberline ecotones on the sunny and shady slopes of the Sygera Mountains in Southeast Tibet, China. Three timberline plants were selected: Sabina saltuaria (S. saltuaria), Abies georgei (A. georgei) and Rhododendron aganniphum (R. aganniphum). The C, N, and P contents and C:N:P stoichiometry of R. aganniphum in the leaf and foliar litter varied widely along the altitudes, and those of soil showed similar trends. The leaf C:N of R. aganniphum, soil C, and soil C:N on the sunny slope increased with increasing altitudes. Furthermore, the N and P contents in the leaf and foliar litter of timberline plants on the shady slope were significantly higher than those on the sunny slope, whereas the C, C:N, C:P, and N:P ratios in the leaf and foliar litter exhibited the opposite trend. R. aganniphum had the highest nitrogen resorption efficiency (NRE) and phosphorus resorption efficiency (PRE), whereas A. georgei had the lowest. The PRE of R. aganniphum increased with increasing altitudes, which may be driven by the soil C:N ratio. According to leaf N:P ratios and the relative resorption hypothesis, the leaf N:P ratio was 5.55, 8.70 and 2.86 corresponding to NRE equal to PRE for S. saltuaria, A. georgei and R. aganniphum, respectively. It suggests that the timberline ecotones plants in this study were P-limited, although this limitation may not be responsible for the formation of timberlines in the the Sygera Mountains. Varying degrees of correlations exist between element contents, stoichiometry ratios and nutrient resorption efficiency. Overall, our results revealed that altitude and slope aspects are the key factors affecting the change of C:N:P stoichiometry in the leaf-litter-soil system.

Elevational pattern, structure, and regeneration status of woody taxa along a semi-disturbed timberline ecotone in northwestern Himalayas

The composition, structure, and patterns of vegetation undergo a noticeable shift along the elevational gradient, and this is regulated by various abiotic variables, primarily the elevation and edaphic characteristics. The present study investigated the change in community characteristics of woody vegetation along a vertical gradient from 2800 m till 4000 m in parts of upper Bani Wildlife Sanctuary in Jammu and Kashmir. In all, 40 woody species were recorded including 11 trees and 29 shrubs with a distinctive hump shaped pattern that becomes steeper with the rising elevation. Quercus semecarpifolia Sm. and Betula utilis D.Don. exhibited a wide elevational range (3000–3500 m asl), eventually forming the climatic climax along southern and northern aspects. The diversity and phytosociological attributes peaked at intermediate elevation with H¯=1.74 recorded for trees and H¯=2.48 observed for shrubs. The average density and basal cover for trees and shrubs ranged between 75.50 Nha−1 & 20.09 m2ha−1 and 69.31 Nha−1 & 4.50 m2ha−1, respectively. The species turnover rate was recorded high in case of trees (0.11–0.77) and low for shrubs (0.17–0.29). A modest density of 114 seedlings ha−1 and 249 saplings ha−1 was recorded across the forest types. The low seedling (0.22) and sapling (0.48) per tree ratio indicated a low regeneration performance anticipating a very slow upslope movement of the tree line. This may result in population decline of a few select species in future, necessitating effective monitoring and management intervention for which these findings will be helpful.

Phenocam observed flowering anomaly of Rhododendron arboreum Sm. in Himalaya: a climate change impact perspective.

Flowering exhibits a significant relationship with environmental stimuli and changes. Effect of photoperiodism and vernalization have been well studied in flowering phenology; however, the effect of soil temperature on flowering is less explored which is one of the major factors of vegetation growth in alpine ecosystem. This study thus focuses on the effects of soil and air temperature on flowering response of Rhododendron arboreum Sm., a Himalayan tree species, which is also an indicator of spring initiation in high altitude regions. To monitor the flowering pattern, we employed automated phenocam, which was set up at 3356 masl in Tungnath (Indian Alpine region of Uttarakhand) for time-lapse photography of timberline ecotone. Soil and air temperature were recorded continuously at the timberline ecotone. Three years (2017 to 2020) of datasets were used for the present study. The phenocam observations displayed an interesting event in the year 2019-2020 with complete absence of flowering in R. arboreum population at Tungnath timberline ecotone. From the soil temperature data, an increase in winter (Dec-Jan, during which floral buds form) soil temperature, by > 1°C, and no accumulation of freezing degree-days were found for the year 2019-2020. Air temperature however did not display any relationship with the failure of flowering, ruling out aerial chilling or frost injury of floral buds. From the results, a possible relationship between soil temperature and flowering can be suggested pointing towards necessary root apex vernalization stimulus in shallow rooted Rhododendrons. However, the dependency of flowering in Rhododendrons on winter soil temperature further requires continuous monitoring and more observations to make concrete inferences.

Remarkable Variation in the Process of Hg Accumulation in Timberline Forests Indicates an Aggravated Hg Burden in Alpine Forests Under Climate Warming

AbstractSignificant knowledge gaps in mercury (Hg) cycling challenge our ability to assess the effectiveness of the Minamata Convention on Mercury in reducing human and wildlife Hg exposure due to the complicated impacts of climate change. In this study, we comprehensively quantified the Hg spatial distribution and determined the Hg stable isotopes to understand the Hg sources and accumulation pathways in forests along the timberline ecotone, an ecosystem that provides an early bellwether of global warming effects. Our results show that although there were subtle variations in meteorological and environmental conditions among the <50 m elevation variation, a spruce to shrub vegetation structure shift led to a distinct decrease in vegetation and soil Hg pool sizes by 36%–56% along the timberline ecotone. Further Hg isotopic evidence verified that vegetation‐induced atmospheric Hg0 deposition was the main source for Hg accumulation in soils, and the source contribution of such input decreases from 73% to 45% along the timberline ecotone. Our results indicate that if global warming induced a spruce tree line upward shift, it would significantly promote the atmospheric Hg burden, thus resulting in a conspicuous “Hg hotspot”. We recommend further studies to assess the Hg ecological risk promoted by global warming in alpine ecosystems.

C:N:P Stoichiometry in Leaf-Litter-Soil System, Nutrient Resorption and Stoichiometric Homeostasis of Alpine Timberline Ecotones and Adjacent Areas of Sejila Mountain in Southeast Tibet, China

C:N:P Stoichiometry in Leaf-Litter-Soil System, Nutrient Resorption and Stoichiometric Homeostasis of Alpine Timberline Ecotones and Adjacent Areas of Sejila Mountain in Southeast Tibet, China

Spatiotemporal dynamics of encroaching tall vegetation in timberline ecotone of the Polar Urals Region, Russia

Previous studies discovered a spatially heterogeneous expansion of Siberian larch into the tundra of the Polar Urals (Russia). This study reveals that the spatial pattern of encroachment of tree stands is related to environmental factors including topography and snow cover. Structural and allometric characteristics of trees, along with terrain elevation and snow depth were collected along a transect 860 m long and 80 m wide. Terrain curvature indices, as representative properties, were derived across a range of scales in order to characterize microtopography. A density-based clustering method was used here to analyze the spatial and temporal patterns of tree stems distribution. Results of the topographic analysis suggest that trees tend to cluster in areas with convex surfaces. The clustering analysis also indicates that the patterns of tree locations are linked to snow distribution. Records from the earliest campaign in 1960 show that trees lived mainly at the middle and bottom of the transect across the areas of high snow depth. As trees expanded uphill following a warming climate trend in recent decades, the high snow depth areas also shifted upward creating favorable conditions for recent tree growth at locations that were previously covered with heavy snow. The identified landscape signatures of increasing tall vegetation, and the effects of microtopography and snow may facilitate the understanding of treeline dynamics at larger scales.

Effects of single plant functional type loss on microbial community composition and litter decomposition in an alpine timberline ecotone

Biodiversity loss likely occurs in alpine ecosystems under climate warming. However, little is known about the effect of plant functional type loss on the litter decomposition rate and microbial community composition. To test whether single functional type loss has a significant impact on the litter decomposition and microbial community composition, we conducted a litterbag experiment by randomly removing a single functional type from the litter mixtures of six functional types (evergreen conifer, evergreen shrubs, deciduous shrub, graminoid, forb and fern). Moreover, incubation sites were established in two vegetation types with contrasting microclimatic conditions in an alpine timberline ecotone. Based on a two-year decomposition experiment, we found that random loss of the single plant functional type did not significantly affect the mass loss rates and microbial community biomass and structure in the two vegetation types. Moreover, most losses of single plant functional type affected the investigated mass loss rates and microbial parameters in an additive way. In contrast, there were significant effects of vegetation type on the microbial community composition, irrespective of plant functional type loss treatments. We conclude that mass loss rates and microbial parameters in litter mixtures are largely predictable from those in individual plant functional type in the alpine timberline ecotone. Our findings suggest that, under climate change scenarios, losses of single plant functional type possibly induced by upward shifts of alpine plants would alter the microbial community composition in litters only under the condition of changes in microclimatic factors (i.e., moisture and temperature), which would have a profound impact on alpine ecosystems.

Indian Himalayan Timberline Ecotone in Response to Climate Change – Initial Findings

This article enumerates the findings of a team research on the Indian Himalayan timberline ecotone, with focus on three sites (located in Kashmir, Uttarakhand and Sikkim). Timberline elevation increased from west to east, was higher in the warmer south aspect than the cooler north aspect, and was generally depressed. Betula, Abies, Rhododendron and Juniperus were important treeline genera. The Himalaya has not only the highest treelines (Juniperus tibetica, at 4900 m), but also the widest elevational range (>1700 m). Remotely sensed data revealed that the timberline is a long, twisting and turning ecotone, traversing a length of 8–10 km per km horizontal distance. Surface temperature lapse rate in the monsoonal regions was lower (–0.53°C/100 m elevation) than generally perceived and varied considerably with season, being the lowest in December. The Himalayan treeline species are not water-stressed at least in monsoonal regions, predawn tree water potential seldom getting below –1 MPa. The upward advance of Rhododendron campanulatum (a krummholz species) may deplete alpine meadows with climatic warming. Tree-ring chronology indicated that winter warming may be favouring Abies spectabilis . Early snowmelt increased growth period and species richness. Treelines generally are stable in spite of decades of warming. Dependence of people on timberline was still high; so economic interventions are required to reduce the same.

Criteria and indicator for assessing threat on Himalayan birch (B. utilis) at timberline ecotone of Nanda Devi Biosphere Reserve: A world heritage site, Western Himalaya, India

Abstract Western Himalayan timberline are mainly dominated by Betula utilis (Himalayan birch) and closely associated with Abies spectabilis, Quercus semicarpifolia and Taxus baccata and formed the ecotone between the coniferous forest and alpine areas. Himalayan birch is socio-culturally and ecologically valued and considered a keystone species which plays significant role in the functioning of timberline ecosystem. A total of 13 timberline ecotone of pure Himalayan birch forests were selected to assess the magnitude of threat on dominant plant species using rapid threat assessment and rapid vulnerability assessment. It form the basis to design appropriate criteria, indicators and scores (ranging from 1 to 4) to rank the plant species under various threat categories. Besides, phytosociological studies were undertaken for assessment of species diversity, density and regeneration potential. The paper highlighted individual of Himalayan birch is declining in adult stages, however growth and vigor observed in seedling and sapling stages. Despite, Himalayan birch was found the most vulnerable species with a threat score of 29 followed by Taxus baccata and Juniperus communis. The annual exploitation of Himalayan birch estimated about 927.10 ​kg capita−1 yr−1 fuelwood and 551.15 ​gm capita−1 yr−1 bark by the people involved in collection of Ophiocordyceps sinensis. The current trends of unsustainable exploitation would facilitate the decline in population of the some ecological important species particularly Himalayan birch. Therefore, this study suggests the appropriate policies and strategies for conservation and management of Himalayan birch on one hand and socio-economic development of local communities on the other.

Dynamics and Drivers of the Alpine Timberline on Gongga Mountain of Tibetan Plateau-Adopted from the Otsu Method on Google Earth Engine

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.

Mixture of plant functional groups inhibits the release of multiple metallic elements during litter decomposition in alpine timberline ecotone

Mixed litter decomposition is a common phenomenon in nature and is very important for the circulation of material through an ecosystem. Different plant functional groups (PFGs) are likely to interact during decomposition. It is unclear how mixed decomposition influences the release of multiple metallic elements, and the biogeochemical circulation mechanism in the alpine ecosystem remains elusive. In this study, a two-year experiment on decomposition of mixed litter from six dominant PFGs was conducted at two elevations in an alpine timberline ecotone using the litterbag method. First, the results suggested that PFG identity had greater impacts on the release of all metallic elements than elevation. The release rates of potassium (K), calcium (Ca), magnesium (Mg) and copper (Cu) in graminoid, deciduous shrub and forb litter were significantly higher than those in evergreen conifer, evergreen shrub and mixed litter. Second, the release of metallic elements showed non-additive effects during mixed litter decomposition. K, Ca, Mg, sodium (Na), Cu, and aluminium (Al) exhibited antagonistic effects, while Fe exhibited a synergistic effect. The antagonistic effects on Na, K, Ca and Cu release increased with increasing elevation, while the antagonistic effects on Mg, Al and Mn release decreased with increasing elevation. Third, Al and Fe showed high levels of accumulation. The K release rate decreased while Al and Fe accumulation increased with plant litter upward shift. In conclusion, mixtures of PFGs inhibits the release of multiple metallic elements during litter decomposition in the alpine timberline ecotone. We speculate that an upward shift in PFGs in response to climate warming will slow the release of K and accelerate the enrichment of Fe and Al in alpine timberline ecotones.

The importance of seasonal environmental factors in the foraging habitat selection of Alpine Ring Ouzels Turdus torquatus alpestris

Species inhabiting mountain ecosystems are expected to be particularly vulnerable to environmental change, yet information on their basic ecology is often lacking. Knowledge from field‐based empirical studies remains essential to refine our understanding of the impact of current habitat alterations and for the consequential development of meaningful conservation management strategies. This study focuses on a poorly investigated and vulnerable mountain bird species in Europe, the Ring Ouzel Turdus torquatus. Our aim was to identify the species’ key ecological requirements during the crucial period of nestling provisioning in the context of environmental change. We radiotracked and observed Alpine Ring Ouzels in a high‐density population, investigating their pattern of foraging habitat selection in 2015 and 2017, and evaluated the transferability of these results over a wider geographical range across the SW Swiss Alps. Foraging birds selected, consistently in space and time, short grass swards (< 10 cm) with interspersed patches of accessible and penetrable soils, at intermediate moisture levels (around 40–65% volumetric water content). In Alpine ecosystems, this microhabitat configuration is typically widespread during the spring snowmelt, but extremely seasonal, with a rapid decrease in its availability over the course of the breeding season. This underlines the high vulnerability of the Ring Ouzel to environmental change: an earlier snowmelt could generate a temporal mismatch between the peak of the breeding effort and optimal foraging conditions; however, abandoning grazing activities on semi‐wooded Alpine pastures may further decrease foraging habitat suitability through taller and denser grass swards, and subsequent woody vegetation encroachment. This study provides a mechanistic appraisal of the challenges Ring Ouzels will face in the future, as well as initial guidelines for targeted habitat management within timberline ecotones.

Faunal abundance along timberline ecotone in western Himalaya with reference to anthropogenic pressure and season: a case study

High anthropogenic pressure not only affects individual species, but also has a negative impact on overall ecosystem health and its resilience capability, especially in the ecosystem transition zone, such as “timberline ecotone”. Timberline ecotone in western Himalaya is currently facing dual threat due to climate change and anthropogenic pressures. The present study aims to enhance our understanding about how various mammal and bird species use this ecotone across seasons and gradient of anthropogenic pressure, using standard animal abundance estimation method in the state of Uttarakhand, India. Ten mammalian species, five birds of prey, four pheasant, and fifty-three small bird species were found to use timberline ecotone during different seasons. The timberline ecotone experiences high anthropogenic pressure during summer and monsoon. The abundance of mammal such as Himalayan musk deer (β = − 1.62 ± 0.50, P < 0.01) and pheasant such as Himalayan monal (β = − 0.38 ± 0.15, P < 0.01) were found to be negatively influenced by wood cutting, livestock grazing. The density and species richness of small birds were comparatively higher in moderately disturbed sites than that of highest or least disturbed sites. In addition, the small bird species composition varied significantly across sites with different anthropogenic pressure. This study revealed the differential impact of anthropogenic pressure on various mammalian and bird species, which utilized timberline ecotone seasonally or year round. Furthermore, the result of the present study also indicated faunal species (e.g., Himalayan musk deer), which could be used as indicator species to understand impact and magnitude of anthropogenic pressure on timberline ecotone.

Seedling Survival at Timberline Is Critical to Conifer Mountain Forest Elevation and Extent

Conifer mountain forests influence a large portion of the World’s human population by providing a host of critical economic, sociological, and ecosystem services. Although the causes of the elevational, transitional boundaries of these forests (i.e. upper and lower timberlines) have been questioned for over a century, these investigations have focused predominately on the growth limitations of saplings or mature trees at the upper alpine boundary. Yet, the elevational movement of timberlines is dependent initially on new seedling establishment in favorable microsites that appear to be generated by ecological facilitation. Recent evidence suggests that this facilitation is critical during the initial 1-2 years of growth when survival may be less than a few percent, only cotyledons are present, and survival occurs only in favorable microsites created by inanimate objects (e.g. boulders, dead stems), microtopography, or already established vegetation. Dramatic changes in tree form (e.g. krummholz mats) across the timberline ecotone also plays an important role in generating microsite facilitation. These favorable, facilitated microsites have been characterized broadly as experiencing low sky exposure during summer (day and night) and leeward wind exposure during winter that generates protective snow cover, all of which are needed for new seedling survival. Thus, determining the specific microclimate and edaphic characteristics of favorable microsites, and their frequency at timberline, will provide a more mechanistic understanding and greater predictability of the future elevation and extent of conifer mountain forests. In addition, although the ecophysiological advantages of a needle-like leaf morphology is well established for adult conifer trees, the advantage of this phylogenetically unique trait in emergent seedlings has not been thoroughly evaluated. Understanding seedling ecophysiology and the functional morphology that contributes to survival, plus the nature and frequency of favorable microsites at timberline, will enable more reliable estimates of future elevational shifts in conifer mountain forests. This approach could also lead to the development of a valuable and sensitive tool for forest managers interested in evaluating future changes in these forests under increased large-scale infestation and drought mortality, as well as for current scenarios of predicted climate change.

Woody species Structure as Influenced by Biotic Regimes at Timberline Ecotone in the Eastern Himalaya: Implications for Management

Woody species Structure as Influenced by Biotic Regimes at Timberline Ecotone in the Eastern Himalaya: Implications for Management

Elevational transects of modern pollen samples: Site-specific temperatures as a tool for palaeoclimate reconstructions in the Alps

The potential of quantitatively reconstructing climate from modern pollen assemblages from high mountain environments has been widely debated but seldom tested. We analysed the pollen deposition in 53 surface samples (mosses) in relation to July temperature in two elevational transects in the European Alps. Each surface-sample site was assigned climate data derived from the local-scale climate. We compared our results with a larger calibration set extracted from the European Modern Pollen Database (EMPD) and centred on the European Alps. This also was assigned local climate data. The main calibration set (234 pollen samples) had Alnus harmonized at genus level; in contrast, a second set was selected (174) that retained the taxonomic resolution of Alnus viridis, which is one of the main climate indicators in the timberline ecotone. The overall and individual pollen responses to July temperature were inferred by canonical correspondence analysis (CCA), generalized linear regression (eHOF) and weighted averaging (WA). Quantitative climate reconstructions for each sample site of the two elevational transects were obtained using transfer functions, that is, WA and WA partial least squares (WA-PLS) regressions. In each calibration set, around 30% of the pollen taxa show a relationship with July temperature through monotonic or unimodal functions. The best transfer function obtained has a good statistical performance, with a determination coefficient ( r2) of 0.74. We propose new calibration procedures formulated to include the full climate space of the modelled taxa, as well as to account for uphill pollen transport in the high mountains and for human activity.

Vascular plants distribution in relation to topography and environmental variables in alpine zone of Kedarnath Wild Life Sanctuary, West Himalaya

The present study was carried out in Tungnath alpine meadows of Kedarnath Wild Life Sanctuary, Western Himalaya from subalpine to upper alpine zone. A total of four summits were selected along an altitudinal gradient and sampled for detailed vegetation analysis using multi summit approach as per Global observation research initiative in alpine environments (GLORIA). Species richness, diversity, and evenness among four summits as well as the interaction between environmental variables with plant communities were assessed. Monthly mean soil temperature was calculated using data retrieved from geo-precision temperature logger in order to identify the trend of soil temperature among different season and altitudinal gradient and its implications to plant communities. Soil samples were analyzed from each summit by collecting randomized composite soil samples. The indirect non-metric multidimensional scaling (NMDS) and direct canonical correspondence analysis (CCA) tools of ordination techniques to determine the linkage between plant species from various sample summits and biotic/abiotic environmental gradients were used in the present study. The results of the study demonstrated increase in species richness as soil temperature increases, the ecotone representing summits were found most warm summits followed by highest species richness. Annual soil temperature increased by 1.43°C at timberline ecotone. Whereas, at upper alpine zone the soil temperature increased by 0.810C from year 2015 to 2016. Sorensen’s similarity index was found to be increased between subalpine and upper alpine zone with increase in the presence of subalpine plant species at upper alpine zone. Both the ordination tools separate the subalpine summit and their respective vegetation from summits representing timberline ecotone and upper alpine zone. Soil pH, altitude, soil cation exchange capacity were found as the key abiotic drivers for distribution of plant species.

Temperature change along elevation and its effect on the alpine timberline tree growth in the southeast of the Tibetan Plateau

Smith fir (Abies georgei var. smithii), which is the timberline constructive tree species in the cool slope of Mt. Sygera in the southeast of Tibet, plays a very important role in maintaining the timberline completeness and indicating global climate change. This study uses the instrumental recorded meteorological data along the altitude from 3600 to 4400 m at every 200 m in the growing season, investigates the smith fir growth biomass from 2006 to 2010 in the same timberline ecotone, and makes a non-linear regression analysis to determine the relationship between the alpine tree growth biomass and its in-situ environment condition. The results showed that the cool and warm slope share different air temperature lapse rates, which were −0.48 °C (100 m)−1 in the warm slope and −0.54 °C (100 m)−1 in the cool slope, respectively. However, the dominant timberline tree species in the warm slope was Sabina saltuaria, and it can reach as high as 4570 m, which is approximately 170 m higher than that in the cool slope. Moreover, the smith fir in the cool slope was only distributed in the range of elevation from approximately 3600 to 4400 m. The altitude of approximately 3800 m was the appropriate altitude for the growing smith fir, where the mean air temperature in the growing season was about 9.0 °C, and the young smith fir tree can form more biomass. The results suggested that alpine forest chose a suitable environment where trees can grow more in the prolonged succession, but not in the warmer or cooler condition, it could be seen as a biological evidence for climate change.