The conversion of forests to pastures is the most important human intervention that has shaped the natural landscape into the Anthropocene environment.The Qinghai-Tibet Plateau(QTP),which has both forest drought-lines...The conversion of forests to pastures is the most important human intervention that has shaped the natural landscape into the Anthropocene environment.The Qinghai-Tibet Plateau(QTP),which has both forest drought-lines and alpine treelines with specific ecotone structures,including isolated trees in treeless plant-covers that represent ever existed forest cover according to‘Lonely Tooth Hypothesis’,offers an excellent model in which to examine the extent and timing of human activity on the conversion of forest to pasture.The objectives of this paper are to review(1)palaeo-environmental records of the Early Holocene that indicate when forests were first converted to‘alpine meadows’,and(2)current records of the changing treeline ecotone in the region.‘Alpine meadows’of the QTP are part of the largest conversion of mountain forests into pastures worldwide.This change in forest cover is possibly a consequence of the agro-pastoral transition and the dawn of the Anthropocene on the QTP.To date,however,there is an interdisciplinary gap in knowledge of 5000 years between the palaeo-ecological and the archaeolocical and zoo-archaeological records.Rapid changes of the rural economy and the exodus from remote highland villages to down-country cities have diminished the age-old impacts of summer grazing and pasture management by fire;reforestation is obvious,but often seen exclusively as an effect of Anthropocene global warming.We believe that more interdisciplinary collaborations on the QTP are necessary to increase our understanding of the treelines of the Anthropocene in High Asia.展开更多
Treelines are ecologically unique,fragile,and rich in natural resources.They harbour high species diversity and at the same time are under threat due to anthropogenic activities.Recognizing this,the present study has ...Treelines are ecologically unique,fragile,and rich in natural resources.They harbour high species diversity and at the same time are under threat due to anthropogenic activities.Recognizing this,the present study has been framed to document the patterns of species richness and diversity in the state of Himachal Pradesh,western Himalaya.A total of six treeline sites(three disturbed and three undisturbed)were identified for vegetation sampling.Trees,shrubs,and herbs were sampled at each site using nested plots of 10 m^(2),5 m^(2),and 1 m^(2),respectively.The study exhibits the rich diversity of treeline communities,the patterns of which varied between treeline sites.Altogether,221 species of vascular plants belonging to 47 families and 140 genera were recorded from the area.Amongst families,Asteraceae was the dominant family followed by Apiaceae and Ranunculaceae.The study also revealed the presence of threatened species like Aconitum heterophyllum,Angelica glauca,Bergenia stracheyi,Dactylorhiza hatagirea,Picrorhiza kurroa,and Trillium govanianum etc.at treeline.Moreover,species composition revealed high densities of Betula utilis followed by the under canopy of Rhododendron campanulatum and R.anthopogon at treeline sites.Overall,species richness of herbs,shrubs,and trees were higher at undisturbed site as compared to disturbed one.The diversity indices of herbs and shrubs varied significantly between treeline sites while that of trees was non-significant.At the same time,soil properties showed distinct patterns wherein pH and available nitrogen significantly varied between treeline sites.Present study provides detailed insights into the floristic and ecological aspects of treeline communities from the unexplored ecoregion of western Himalaya.The treelines in the area are anthropogenically depressed and continued land-use activities might result in habitat fragmentation and displacement of plant communities in the near future.展开更多
Treeline ecotone dynamics of Abies spectabilis （D. Don） Mirb. in the Barun valley, Makalu Barun National Park, eastern Nepal Himalaya were studied by establishing seven plots （20 m x variable length） from the fore...Treeline ecotone dynamics of Abies spectabilis （D. Don） Mirb. in the Barun valley, Makalu Barun National Park, eastern Nepal Himalaya were studied by establishing seven plots （20 m x variable length） from the foresfline to the tree species limit： three plots on the south- and north-facing slopes each （S1-S3, N1-N3）, and one plot on the east- facing slope （E） in the relatively undisturbed forests. A dendroecological method was used to study treeline advance rate and recruitment pattern. In all the plots, most trees established in the early 20th century, and establishment in the second half of the 20th century was confined to the foresfline area. Treeline position has not advanced substantially in the Barun valley, with 0nly 22 m average elevational shift in the last 13o years, and with average current shifting rate of 14 cm/yr. Moreover, no significant relationship was found between tree age and elevation on the south-, north-, and east-facing slopes. The number of seedlings and saplings in near the treeline area was negligible compared to that near the foresfline area. Therefore, A. spectabilis treeline response to the temperature change was slow, despite the increasing temperature trend in the region. Beside the temperature change, factors such as high inter-annual variability in temperature, dense shrub cover, and local topography also play an important role in treeline advance and controlling recruitment pattern above the treeline.展开更多
Numerous studies have reported that treelines are moving to higher elevations and higher latitudes.Most treelines are temperature limited and warmer climate expands the area in which trees are capable of growing.Hence...Numerous studies have reported that treelines are moving to higher elevations and higher latitudes.Most treelines are temperature limited and warmer climate expands the area in which trees are capable of growing.Hence,climate change has been assumed to be the main driver behind this treeline movement.The latest review of treeline studies was published in 2009 by Harsch et al.Since then,a plethora of papers have been published studying local treeline migration.Here we bring together this knowledge through a review of 142 treeline related publications,including 477 study locations.We summarize the information known about factors limiting tree-growth at and near treelines.Treeline migration is not only dependent on favorable growing conditions but also requires seedling establishment and survival above the current treeline.These conditions appear to have become favorable at many locations,particularly so in recent years.The review revealed that at 66%of these treeline sites forest cover had increased in elevational or latitudinal extent.The physical form of treelines influences how likely they are to migrate and can be used as an indicator when predicting future treeline movements.Our analysis also revealed that while a greater percentage of elevational treelines are moving,the latitudinal treelines are capable of moving at greater horizontal speed.This can potentially have substantial impacts on ecosystem carbon storage.To conclude the review,we present the three main hypotheses as to whether ecosystem carbon budgets will be reduced,increased or remain the same due to treeline migration.While the answer still remains under debate,we believe that all three hypotheses are likely to apply depending on the encroached ecosystem.Concerningly,evidence is emerging on how treeline migration may turn tundra landscapes from net sinks to net sources of carbon dioxide in the future.展开更多
Alpine treeline, as a prominent ecological boundary between forested mountain slopes and alpine meadow/shrub, is highly complex in altitudinal distribution and sensitive to warming climate. Great efforts have been mad...Alpine treeline, as a prominent ecological boundary between forested mountain slopes and alpine meadow/shrub, is highly complex in altitudinal distribution and sensitive to warming climate. Great efforts have been made to explore their distribution patterns and ecological mechanisms that determine these patterns for more than 100 years, and quite a number of geographical and ecophysiological models have been developed to correlate treeline altitude with latitude or a latitude related temperature. However,on a global scale, all of these models have great difficulties to accurately predict treeline elevation due to the extreme diversity of treeline site conditions.One of the major reasons is that "mass elevation effect"(MEE) has not been quantified globally and related with global treeline elevations although it has been observed and its effect on treeline elevations in the Eurasian continent and Northern Hemisphere recognized. In this study, we collected and compiled a total of 594 treeline sites all over the world from literatures, and explored how MEE affects globaltreeline elevation by developing a ternary linear regression model with intra-mountain base elevation(IMBE, as a proxy of MEE), latitude and continentality as independent variables. The results indicated that IMBE, latitude and continentality together could explain 92% of global treeline elevation variability, and that IMBE contributes the most(52.2%), latitude the second(40%) and continentality the least(7.8%) to the altitudinal distribution of global treelines. In the Northern Hemisphere, the three factors' contributions amount to 50.4%, 45.9% and 3.7% respectively; in the south hemisphere, their contributions are 38.3%, 53%, and 8.7%, respectively. This indicates that MEE, virtually the heating effect of macro-landforms, is actually the most significant factor for the altitudinal distribution of treelines across the globe, and that latitude is relatively more significant for treeline elevation in the Southern Hemisphere probably due to fewer macro-landforms there.展开更多
There are differing views regarding the climatic factors that limit radial growth of Qilian juniper （Juniperus przewalskii Kom.） at the upper treelines on the northeastern Tibetan Plateau. In this study, trees from ...There are differing views regarding the climatic factors that limit radial growth of Qilian juniper （Juniperus przewalskii Kom.） at the upper treelines on the northeastern Tibetan Plateau. In this study, trees from an upper tree northeastern Tibetan Plateau were selected to limits the radial growth of Qilian juniper. Using ine site in the Anyemaqen Mountains of the present new evidence that low temperature a signal-free regional curve standardization （SF-RCS） method, a ring-width chronology for Qilian juniper was developed extending from AD 1082 to 2010. The results of correlation analysis between tree-ring index and instrumental climatic variables showed that both winter （December in the previous year and January in the current year） and summer （July and August in the current year） temperatures were signifi- cantly and positively correlated with the tree-ring index. Precipitation in June was also significantly and positively correlated with the tree-ring index, but was not as important as low temperature in controlling tree growth. To test the key limiting climatic factor for tree radial growth at different altitudes, an indicator termed the ＂relative distance to upper treeline＂ （RDUT） was developed to quantify the representativeness of collected samples for the forest＇s upper treeline. The RDUT showed that the upper 20% of the forest belt may be an important boundary in terms of capturing the temperature signal from tree-ring width at the upper treelines on the northeastern Tibetan Plateau. Our findings enhance the existing understanding that temperature is the limiting factor at upper treelines on the northeastern Tibetan Plateau, and will be useful in the reconstruction of past temperature in future studies.展开更多
【Title】【Author】【Addresses】1 The control mechanisms of topography on alpine treeline pattern are critical to understanding treeline dynamics and future changes. These mechanisms have not been understood quite wel...【Title】【Author】【Addresses】1 The control mechanisms of topography on alpine treeline pattern are critical to understanding treeline dynamics and future changes. These mechanisms have not been understood quite well enough because of increasing human disturbance and low data resolution. In this study, the relationship between the treeline pattern and topography was analyzed based on high spatial resolution remote sensing data and a digital elevation model in an area in Changbai Mountain with little human disturbance. Future treeline patterns were also predicted. The results showed that （a） aspects with high solar radiation and low snow cover have a high coverage rate of trees, （b） the peak coverage rate of trees switches from low slopes （〈5°） to medium slopes （5°~25°） as the elevation rises because of the extreme environment, （c） the coverage rate of trees is a function that depends on environmental factors controlled by topography, （d） the future treeline pattern is controlled by new temperature mechanisms, new environmental factors and the reallocation effect of topography. Our research implies that topography controls the treeline pattern and changes in the treeline pattern associated with global warming, due to the effect of global warming on environmental factors. This study may well explain the causes of heterogeneous changes in the treeline pattern in the horizontal direction as well as differences in treeline response to climate warming.展开更多
Understanding of treeline ecotone ecophysiological adaptation to climate warming is still very limited. Furthermore, it is difficult to predict which plant species could dominate in the future. For this reason, a stud...Understanding of treeline ecotone ecophysiological adaptation to climate warming is still very limited. Furthermore, it is difficult to predict which plant species could dominate in the future. For this reason, a study was conducted in the treeline ecotone, East Tibetan Plateau to detect the adaptation of the dwarf willow(Salix eriostachya) to experimental warming. Compared to ambient conditions, the experimental warming advanced the bud break by 12 days, delayed the leaf abscission by20 days, and prolonged the growing period by 28 days.It also increased photosynthesis(47%), number of leaves(333%), leaf area(310%), and carbon sequestration of the dwarf willow. Experimental warming did not affect carbon use efficiency, but decreased water use efficiency significantly.Experimental warming enhanced the clonal ramets of Salix eriostachya(+ 3.7 shrubs m-2). The frequent air temperature fluctuations had minor effect on Salix eriostachya. Based on these findings, we highlighted that Salix eriostachya could dominate in the community treeline ecotone of east Tibetan Plateau in the future climate warming scenario.展开更多
At a global scale, tree growth in alpine treeline ecotones is limited by low temperatures. At a local scale, however, tree growth at its upper limit depends on multiple interactions of influencing factors and mechanis...At a global scale, tree growth in alpine treeline ecotones is limited by low temperatures. At a local scale, however, tree growth at its upper limit depends on multiple interactions of influencing factors and mechanisms. The aim of our research was to understand local scale effects of soil properties and nutrient cycling on tree growth limitation, and their interactions with other abiotic and biotic factors in a near-natural Himalayan treeline ecotone. Soil samples of different soil horizons, litter, decomposition layers, and foliage samples of standing biomass were collected in four altitudinal zones along three slopes, and were analysed for exchangeable cations and nutrient concentrations, respectively. Additionally, soil and air temperature, soil moisture, precipitation, and tree physiognomy patterns were evaluated. Both soil nutrients and foliar macronutrient concentrations of nitrogen(N), magnesium(Mg), potassium(K), and foliar phosphorus(P) decrease significantly with elevation. Foliar manganese(Mn) concentrations, bycontrast, are extraordinarily high at high elevation sites. Potential constraining factors on tree growth were identified using multivariate statistical approaches. We propose that tree growth, treeline position and vegetation composition are affected by nutrient limitation, which in turn, is governed by low soil temperatures and influenced by soil moisture conditions.展开更多
Background:Recent warming is affecting species composition and species areal distribution of many regions.However,although most treeline studies have estimated the rates of forest expansion into tundra,still little is...Background:Recent warming is affecting species composition and species areal distribution of many regions.However,although most treeline studies have estimated the rates of forest expansion into tundra,still little is known about the long-term dynamic of stand productivity at the forest-tundra intersection.Here,we make use of tree-ring data from 350 larch(Larix sibirica Ledeb.)and spruce(Picea obovata Ledeb.)sampled along the singular altitudinal treeline ecotone at the Polar Urals to assess the dynamic of stand establishment and productivity,and link the results with meteorological observations to identify the main environmental drivers.Results:The analysis of stand instalment indicated that more than 90%of the living trees appeared after 1900.During this period,the stand became denser and moved 50m upward,while in recent decades the trees of both species grew faster.The maximum afforestation occurred in the last decades of the twentieth century,and the large number of encountered saplings indicates that the forest is still expanding.The upward shift coincided with a slight increase of May-August and nearly doubling of September-April precipitation while the increase in growth matched with an early growth season warming(June+0.27°C per decade since 1901).This increase in radial growth combined with the stand densification led to a 6-90 times increase of biomass since 1950.Conclusion:Tree-ring based twentieth century reconstruction at the treeline ecotone shows an ongoing forest densification and expansion accompanied by an increased growth.These changes are driven by climate change mechanism,whereby the leading factors are the significant increase in May-June temperatures and precipitation during the dormant period.Exploring of phytomass accumulation mechanisms within treeline ecotone is valuable for improving our understanding of carbon dynamics and the overall climate balance in current treeline ecosystems and for predicting how these will be altered by global change.展开更多
A dendroclimatic study was conducted in the treeline ecotone of Barun Valley, eastern Nepal, to determine the tree-ring climate response and ring width trend of Abies spectabilis. A 160-year-old chronology, from 1850 ...A dendroclimatic study was conducted in the treeline ecotone of Barun Valley, eastern Nepal, to determine the tree-ring climate response and ring width trend of Abies spectabilis. A 160-year-old chronology, from 1850 to 2010, was developed from 38 tree-ring samples. No higher growth in recent decades was observed in tree-ring width in this area. The mean temperature of the current year in February and in the combined winter months of December, January, and February showed significant positive correlation with tree-ring width, although no significant correlation was found between tree-ring width and the precipitation pattern of the region. This tree-ring climate response result is different from that in other studies in Nepal, which could be attributed to location and elevation.展开更多
Different types of vegetation patches are alternately and randomly distributed in a timberline ecotone where the upper limit is the treeline and the lower limit is the timberline.However,most studies on timberline/tre...Different types of vegetation patches are alternately and randomly distributed in a timberline ecotone where the upper limit is the treeline and the lower limit is the timberline.However,most studies on timberline/treeline altitudinal distributions have simplified timberline or treeline as continuous curves and disregarded the fuzziness of timberline/treeline and the randomness of different vegetation patch distributions in a timberline ecotone.To study the altitudinal distribution characteristics of timberline and treeline from the perspective of uncertainty theory,we constructed the timberline and treeline elevation cloud models in Mt.Namjagbarwa in east Himalayas.Subsequently,we established multiple linear regression models by using nine influencing factors,namely,aspect,slope,topographic relief,dryness index,average temperature in January and July,latitude,summit syndrome(represented by the vertical distance from the peak),and snow effect(represented by the nearest distance from the snow)as independent variables,and the elevations of timberline/treeline as dependent variables.Then we compared the contributions of the nine factors in timberline,treeline,and the core and peripheral areas of timberline and treeline.The results show that 1)the timberline/treeline elevation cloud model can represent the overall characteristics(especially the uncertainty)of the altitudinal distributions of the timberline/treeline well.The uncertainty of treeline’s altitudinal distribution is higher than that of timberline(entropy and hyper entropy:207.59 m and 70.36 m for treeline elevation cloud;entropy and hyper entropy:191.17 m and 50.13 m for timberline elevation cloud).2)The influence of climate and topography on timberline and treeline are similar.The average temperature in July has a significant negative correlation with the timberline/treeline elevation in Mt.Namjagbarwa,which is the most critical factor that affects timberline and treeline elevation,explaining the altitudinal distribution of 44.01%timberline and 46.74%treeline.However,the contributions of the nine factors in core and peripheral areas of timberline and treeline area are evidently different.展开更多
Under conditions of a warmer climate,the advance of the alpine treeline into alpine tundra has implications for carbon dynamics in mountain ecosystems.However,the above- and below-ground live biomass allocations among...Under conditions of a warmer climate,the advance of the alpine treeline into alpine tundra has implications for carbon dynamics in mountain ecosystems.However,the above- and below-ground live biomass allocations among different vegetation types within the treeline ecotones are not well investigated.To determine the altitudinal patterns of above-/below-ground carbon allocation,we measured the root biomass and estimated the above-ground biomass(AGB) in a subalpine forest,treeline forest,alpine shrub,and alpine grassland along two elevational transects towards the alpine tundra in southeast Tibet.The AGB strongly declined with increasing elevation,which was associated with a decrease in the leaf area index and a consequent reduction in carbon gain.The fine root biomass(FRB) increased significantly more in the alpine shrub and grassland than in the treeline forest,whereas the coarse root biomass changed little with increasing altitudes,which led to a stable below-ground biomass(BGB) value across altitudes.Warm and infertile soil conditions might explain the large amount of FRB in alpine shrub and grassland.Consequently,the root toshoot biomass ratio increased sharply with altitude,which suggested a remarkable shift of biomass allocation to root systems near the alpine tundra.Our findings demonstrate contrasting changes in AGB and BGB allocations across treeline ecotones,which should be considered when estimating carbon dynamics with shifting treelines.展开更多
Alpine treeline ecotones are highly sensitive to climate warming.The low temperature-determined alpine treeline is expected to shift upwards in response to global warming.However,little is known about how temperature ...Alpine treeline ecotones are highly sensitive to climate warming.The low temperature-determined alpine treeline is expected to shift upwards in response to global warming.However,little is known about how temperature interacts with other important factors to influence the distribution range of tree species within and beyond the alpine treeline ecotone.Hence,we used a GF-2 satellite image,along with bioclimatic and topographic variables,to develop an ensemble suitable habitat model based on the species distribution modeling algorithms in Biomod2.We investigated the distribution of suitable habitats for B.ermanii under three climate change scenarios(i.e.,low(SSP126),moderate(SSP370)and extreme(SSP585)future emission trajectories)between two consecutive time periods(i.e.,current-2055,and 2055-2085).By 2055,the potential distribution range of B.ermanii will expand under all three climate scenarios.The medium and high suitable areas will decline under SSP370 and SSP585scenarios from 2055 to 2085.Moreover,under the three climate scenarios,the uppermost altitudes of low suitable habitat will rise to 2,329 m a.s.l.,while the altitudes of medium and high suitable habitats will fall to 2,201 and2,051 m a.s.l.by 2085,respectively.Warming promotes the expansion of B.ermanii distribution range in Changbai Mountain,and this expansion will be modified by precipitation as climate warming continues.This interaction between temperature and precipitation plays a significant role in shaping the potential distribution range of B.ermanii in the alpine treeline ecotone.This study reveals the link between environmental factors,habitat distribution,and species distribution in the alpine treeline ecotone,providing valuable insights into the impacts of climate change on high-elevation vegetation,and contributing to mountain biodiversity conservation and sustainable development.展开更多
We performed a meta-analysis on over 100 studies applying remote sensing(RS)and geographic information systems(GIS)to understand treeline dynamics.A literature search was performed in multiple online databases,includi...We performed a meta-analysis on over 100 studies applying remote sensing(RS)and geographic information systems(GIS)to understand treeline dynamics.A literature search was performed in multiple online databases,including Web of Knowledge(Thomson Reuters),Scopus(Elsevier),BASE(Bielefeld Academic Search Engine),CAB Direct,and Google Scholar using treeline-related queries.We found that RS and GIS use has steadily increased in treeline studies since 2000.Spatialresolution RS and satellite imaging techniques varied from low-resolution MODIS,moderate-resolution Landsat,to high-resolution WorldView and aerial orthophotos.Most papers published in the 1990s used low to moderate resolution sensors such as Landsat Multispectral Scanner and Thematic Mapper,or SPOT PAN(Panchromatic)and MX(Multispectral)RS images.Subsequently,we observed a rise in high-resolution satellite sensors such as ALOS,GeoEye,IKONOS,and WorldView for mapping current and potential treelines.Furthermore,we noticed a shift in emphasis of treeline studies over time:earlier reports focused on mapping treeline positions,whereas RS and GIS are now used to determine the factors that control treeline variation.展开更多
Climate constitutes the main limiting factor for tree-ring growth in high-elevation forests, and the relationship between tree-ring growth and climate is complex. Based on tree-ring chronology and meteorological data,...Climate constitutes the main limiting factor for tree-ring growth in high-elevation forests, and the relationship between tree-ring growth and climate is complex. Based on tree-ring chronology and meteorological data, the influence of precipitation, mean temperature and mean minimum temperature at yearly, seasonal and monthly scales on the tree-ring growth of Picea crossifolia was studied at treeline ecotones in the Qilian Mountains, northwestern China. The results show that growing season temperatures of previous and current years are important limiting factors on tree-ring growth, particularly June mean temperature and mean minimum temperature of current year. The precipitations in the previous winter and current spring have a positive correlation, and in the current fall has a negative correlation with tree-ring growth, but these correlations are not significant. Our results suggest that temperature controls tree-ring growth more strongly than precipitation at treeline ecotones in the Qilian Mountains.展开更多
Unprecedented modern rates of warming are expected to advance alpine treelines to higher elevations,but global evidence suggests that current treeline dynamics are influenced by a variety of factors.Seasonal snow cove...Unprecedented modern rates of warming are expected to advance alpine treelines to higher elevations,but global evidence suggests that current treeline dynamics are influenced by a variety of factors.Seasonal snow cover has an essential impact on tree recruitment and growth in alpine regions,which may in turn influence current treeline elevation;however,little research has been conducted on its role in regional treeline formation.Based on 11,804treeline locations in the eastern Himalayas,we extracted elevation,climate,and topographic data for treeline and snowline.Specifically,we used linear and structural equation modelling to assess the relationship between these environmental factors and treeline elevation,and the climate-snow-treeline interaction mechanism.The results showed that the treeline elevation increased with summer temperature and permanent or seasonal snowline elevation,but decreased with snow cover days and spring temperature at the treeline positions(P<0.001).Importantly,spring snowline elevation(33.4%)and seasonal snow cover days(21.1%)contributed the most to treeline elevation,outperforming the permanent snowline,temperature,precipitation,and light.Our results support the assertion that the temperature-moisture interaction affects treeline elevation in the eastern Himalayas,but we also found that the effects were strongly mediated by seasonal snow cover patterns.The increasing tendency of snow cover governed by climate humidification observed in the eastern Himalayas,is likely to limit future treeline advancement and may even cause treeline decline due to the mortality of the remaining old trees.Together,our findings highlight the role of seasonal snow cover patterns in determining treeline elevation in the eastern Himalayas,which should be considered when assessing the potential for treeline ascent in snow-mediated alpine systems elsewhere.展开更多
The alpine treeline ecotone is an important component of mountain ecosystems of the Nepal Himalaya; it plays a vital role in the livelihood of indigenous people,and provides ecosystem services. However,the region face...The alpine treeline ecotone is an important component of mountain ecosystems of the Nepal Himalaya; it plays a vital role in the livelihood of indigenous people,and provides ecosystem services. However,the region faces a problem of paucity of data on treeline characteristics at the regional and landscape scales. Therefore,we used Remote Sensing(RS),and Geographic Information Science(GIS) approaches to investigate cross-scale interactions in the treeline ecotone. Additionally,European Space Agency land cover map,International Center for Integrated Mountain Development(ICIMOD) land cover map,ecological map of Nepal,and United States Geological Survey Shuttle Radar Topography Mission-Digital Elevation Model were used to analyze treeline pattern at the regional scale. Digital Globe high-resolution satellite imagery of Barun(eastern Nepal) and Manang(central Nepal) were used to study treeline patterns at the landscape scale. Treeline elevation ranges from 3300-4300 m above sea level. Abies spectabilis,Betula utilis,and Pinus wallichiana are the main treeline-forming species in the Nepal Himalaya. There is an east to west treeline elevationgradient at the regional scale. No slope exposure is observed at the regional scale; however,at the landscape scale,slope exposure is present only in a disturbed area(Manang). Topography and human disturbance are the main treeline controlling factor in Barun and Manang respectively.展开更多
Stand structure dynamics are considered as major happenings in any forest as a response to environmental changes.However,this important topic is underrepresented in the treeline studies in the Nepal Himalayas.We aimed...Stand structure dynamics are considered as major happenings in any forest as a response to environmental changes.However,this important topic is underrepresented in the treeline studies in the Nepal Himalayas.We aimed to investigate site-as well as species-specific changes in morphometric features(basal diameter,crown cover,density,and height)along the elevational gradient across treeline ecotones in response to recent environmental changes.The stand structure characteristics of Abies spectabilis,Pinus wallichiana,and Betula utilis across the treeline ecotone of three study sites in Eastern(Barun),Central(Manang),and Western(Dhorpatan)Nepal were analyzed to elucidate structural heterogeneities.Altogether,eight transects(20 m×(60–250 m))across the treeline ecotone were established.Trees of all life forms,trees(>2 m),saplings(0.5–2 m),and seedlings(<0.5 m),within each transect were enumerated and sampled for the morphometric features and age.Site-specific and species-specific stand structure dynamics were found.The rate of basal area increment was higher in Barun,but the Manang treeline,despite profound regeneration in recent years,had a low annual basal area increment.Moreover,the altitudinal distribution of age and morphometry were not consistent among those ecotones.Furthermore,intra-specific competition was not significant.The site-specific stand structure dynamics explain why treelines do not respond uniformly to increasing temperature.It invokes,in further studies,the incorporation of the tree’s morphometric adaptation traits,phenotypic plasticity,and interactions between species genotype and the environment.展开更多
As one of the main non-zonal factors,the mass elevation effect(MEE)has significant impacts on both regional climates and mountain ecological patterns.In recent years,with the development of quantitative techniques and...As one of the main non-zonal factors,the mass elevation effect(MEE)has significant impacts on both regional climates and mountain ecological patterns.In recent years,with the development of quantitative techniques and methods,quantitative studies on the MEE and its implication on mountain altitudinal belts have developed rapidly.However,some issues have not been solved yet,such as high errors in spatial temperature estimations and difficulties in the definition and extraction of intramountain base elevation.Moreover,there is still a lack of comparative studies on the MEE and its influence on treelines and snowlines as most studies were conducted on specific mountains or plateaus.To compare the MEE magnitudes of the Tibetan Plateau(TP)and the Bolivian Plateau(BP),we estimated the correspondent air temperatures and simulated the solar radiations based on MODIS surface temperature,station observation,and treeline data.Then,we analyzed the elevation of the 10℃isotherms on the two plateaus,the temperatures at the same elevation,and the solar radiations.According to the mechanism of the MEE and the relationship of solar radiation and treeline,we constructed treeline models for the two plateaus through a stepwise regression analysis by considering several influencing factors of the MEE(e.g.,air temperature and precipitation)and using solar radiation as its proxy.The results showed that:(1)the MEE magnitude on the TP is equivalent to that on the BP although the former is slightly higher than the latter;(2)the MEE strongly influences the highest treelines in the northern and southern hemispheres,which both occur on the two plateaus.Notably,the treeline distribution models based on solar radiation had higher accuracies than those models with parameters of temperature and precipitation(the adjusted R^(2)values were 0.76 for the TP and 0.936 for the BP),indicating that solar radiation can be used to quantify the MEE and its implications on treelines.Overall,the results of this study can serve as a basis for subsequent analyses on the MEE’s impact factors.展开更多
基金support of the German Research Council(DFG)since 1976 and the cooperation with Sichuan University,Yunnan University,and the Institutes of the Chinese Academy of Sciences(CAS)in Kunming,Chengdu,Lanzhou,Xining,and Beijing.Udo Schickhoff is also grateful to the DFG for funding treeline-related research(SCHI 436/14e1)the National Natural Science Foundation of China(grant numbers U20A2080 and 31622015)Sichuan University(Institutional Research Fund,2021SCUNL102,Fundamental Research Funds for the Central Universities,SCU 2022D003)。
文摘The conversion of forests to pastures is the most important human intervention that has shaped the natural landscape into the Anthropocene environment.The Qinghai-Tibet Plateau(QTP),which has both forest drought-lines and alpine treelines with specific ecotone structures,including isolated trees in treeless plant-covers that represent ever existed forest cover according to‘Lonely Tooth Hypothesis’,offers an excellent model in which to examine the extent and timing of human activity on the conversion of forest to pasture.The objectives of this paper are to review(1)palaeo-environmental records of the Early Holocene that indicate when forests were first converted to‘alpine meadows’,and(2)current records of the changing treeline ecotone in the region.‘Alpine meadows’of the QTP are part of the largest conversion of mountain forests into pastures worldwide.This change in forest cover is possibly a consequence of the agro-pastoral transition and the dawn of the Anthropocene on the QTP.To date,however,there is an interdisciplinary gap in knowledge of 5000 years between the palaeo-ecological and the archaeolocical and zoo-archaeological records.Rapid changes of the rural economy and the exodus from remote highland villages to down-country cities have diminished the age-old impacts of summer grazing and pasture management by fire;reforestation is obvious,but often seen exclusively as an effect of Anthropocene global warming.We believe that more interdisciplinary collaborations on the QTP are necessary to increase our understanding of the treelines of the Anthropocene in High Asia.
基金the Ministry of Environment Forest and Climate Change and GB Pant National Institute of Himalayan Environment for providing financial assistance through the National Mission on Himalayan Studies (GAP-0199)
文摘Treelines are ecologically unique,fragile,and rich in natural resources.They harbour high species diversity and at the same time are under threat due to anthropogenic activities.Recognizing this,the present study has been framed to document the patterns of species richness and diversity in the state of Himachal Pradesh,western Himalaya.A total of six treeline sites(three disturbed and three undisturbed)were identified for vegetation sampling.Trees,shrubs,and herbs were sampled at each site using nested plots of 10 m^(2),5 m^(2),and 1 m^(2),respectively.The study exhibits the rich diversity of treeline communities,the patterns of which varied between treeline sites.Altogether,221 species of vascular plants belonging to 47 families and 140 genera were recorded from the area.Amongst families,Asteraceae was the dominant family followed by Apiaceae and Ranunculaceae.The study also revealed the presence of threatened species like Aconitum heterophyllum,Angelica glauca,Bergenia stracheyi,Dactylorhiza hatagirea,Picrorhiza kurroa,and Trillium govanianum etc.at treeline.Moreover,species composition revealed high densities of Betula utilis followed by the under canopy of Rhododendron campanulatum and R.anthopogon at treeline sites.Overall,species richness of herbs,shrubs,and trees were higher at undisturbed site as compared to disturbed one.The diversity indices of herbs and shrubs varied significantly between treeline sites while that of trees was non-significant.At the same time,soil properties showed distinct patterns wherein pH and available nitrogen significantly varied between treeline sites.Present study provides detailed insights into the floristic and ecological aspects of treeline communities from the unexplored ecoregion of western Himalaya.The treelines in the area are anthropogenically depressed and continued land-use activities might result in habitat fragmentation and displacement of plant communities in the near future.
文摘Treeline ecotone dynamics of Abies spectabilis （D. Don） Mirb. in the Barun valley, Makalu Barun National Park, eastern Nepal Himalaya were studied by establishing seven plots （20 m x variable length） from the foresfline to the tree species limit： three plots on the south- and north-facing slopes each （S1-S3, N1-N3）, and one plot on the east- facing slope （E） in the relatively undisturbed forests. A dendroecological method was used to study treeline advance rate and recruitment pattern. In all the plots, most trees established in the early 20th century, and establishment in the second half of the 20th century was confined to the foresfline area. Treeline position has not advanced substantially in the Barun valley, with 0nly 22 m average elevational shift in the last 13o years, and with average current shifting rate of 14 cm/yr. Moreover, no significant relationship was found between tree age and elevation on the south-, north-, and east-facing slopes. The number of seedlings and saplings in near the treeline area was negligible compared to that near the foresfline area. Therefore, A. spectabilis treeline response to the temperature change was slow, despite the increasing temperature trend in the region. Beside the temperature change, factors such as high inter-annual variability in temperature, dense shrub cover, and local topography also play an important role in treeline advance and controlling recruitment pattern above the treeline.
文摘Numerous studies have reported that treelines are moving to higher elevations and higher latitudes.Most treelines are temperature limited and warmer climate expands the area in which trees are capable of growing.Hence,climate change has been assumed to be the main driver behind this treeline movement.The latest review of treeline studies was published in 2009 by Harsch et al.Since then,a plethora of papers have been published studying local treeline migration.Here we bring together this knowledge through a review of 142 treeline related publications,including 477 study locations.We summarize the information known about factors limiting tree-growth at and near treelines.Treeline migration is not only dependent on favorable growing conditions but also requires seedling establishment and survival above the current treeline.These conditions appear to have become favorable at many locations,particularly so in recent years.The review revealed that at 66%of these treeline sites forest cover had increased in elevational or latitudinal extent.The physical form of treelines influences how likely they are to migrate and can be used as an indicator when predicting future treeline movements.Our analysis also revealed that while a greater percentage of elevational treelines are moving,the latitudinal treelines are capable of moving at greater horizontal speed.This can potentially have substantial impacts on ecosystem carbon storage.To conclude the review,we present the three main hypotheses as to whether ecosystem carbon budgets will be reduced,increased or remain the same due to treeline migration.While the answer still remains under debate,we believe that all three hypotheses are likely to apply depending on the encroached ecosystem.Concerningly,evidence is emerging on how treeline migration may turn tundra landscapes from net sinks to net sources of carbon dioxide in the future.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41030528 and No. 40971064)
文摘Alpine treeline, as a prominent ecological boundary between forested mountain slopes and alpine meadow/shrub, is highly complex in altitudinal distribution and sensitive to warming climate. Great efforts have been made to explore their distribution patterns and ecological mechanisms that determine these patterns for more than 100 years, and quite a number of geographical and ecophysiological models have been developed to correlate treeline altitude with latitude or a latitude related temperature. However,on a global scale, all of these models have great difficulties to accurately predict treeline elevation due to the extreme diversity of treeline site conditions.One of the major reasons is that "mass elevation effect"(MEE) has not been quantified globally and related with global treeline elevations although it has been observed and its effect on treeline elevations in the Eurasian continent and Northern Hemisphere recognized. In this study, we collected and compiled a total of 594 treeline sites all over the world from literatures, and explored how MEE affects globaltreeline elevation by developing a ternary linear regression model with intra-mountain base elevation(IMBE, as a proxy of MEE), latitude and continentality as independent variables. The results indicated that IMBE, latitude and continentality together could explain 92% of global treeline elevation variability, and that IMBE contributes the most(52.2%), latitude the second(40%) and continentality the least(7.8%) to the altitudinal distribution of global treelines. In the Northern Hemisphere, the three factors' contributions amount to 50.4%, 45.9% and 3.7% respectively; in the south hemisphere, their contributions are 38.3%, 53%, and 8.7%, respectively. This indicates that MEE, virtually the heating effect of macro-landforms, is actually the most significant factor for the altitudinal distribution of treelines across the globe, and that latitude is relatively more significant for treeline elevation in the Southern Hemisphere probably due to fewer macro-landforms there.
基金The Strategic Priority Research Program from the Chinese Academy of Sciences No.XDA05080201 National Natural Science Foundation of China, No.41071061
文摘There are differing views regarding the climatic factors that limit radial growth of Qilian juniper （Juniperus przewalskii Kom.） at the upper treelines on the northeastern Tibetan Plateau. In this study, trees from an upper tree northeastern Tibetan Plateau were selected to limits the radial growth of Qilian juniper. Using ine site in the Anyemaqen Mountains of the present new evidence that low temperature a signal-free regional curve standardization （SF-RCS） method, a ring-width chronology for Qilian juniper was developed extending from AD 1082 to 2010. The results of correlation analysis between tree-ring index and instrumental climatic variables showed that both winter （December in the previous year and January in the current year） and summer （July and August in the current year） temperatures were signifi- cantly and positively correlated with the tree-ring index. Precipitation in June was also significantly and positively correlated with the tree-ring index, but was not as important as low temperature in controlling tree growth. To test the key limiting climatic factor for tree radial growth at different altitudes, an indicator termed the ＂relative distance to upper treeline＂ （RDUT） was developed to quantify the representativeness of collected samples for the forest＇s upper treeline. The RDUT showed that the upper 20% of the forest belt may be an important boundary in terms of capturing the temperature signal from tree-ring width at the upper treelines on the northeastern Tibetan Plateau. Our findings enhance the existing understanding that temperature is the limiting factor at upper treelines on the northeastern Tibetan Plateau, and will be useful in the reconstruction of past temperature in future studies.
基金supported by the Special Fund of National Seismological Bureau, China (Grant No. 201208005)the National Natural Science Foundation of China (Grant No. 41171072)the National Grand Fundamental Research 973 Program of China (Grant No. 2009CB426305)
文摘【Title】【Author】【Addresses】1 The control mechanisms of topography on alpine treeline pattern are critical to understanding treeline dynamics and future changes. These mechanisms have not been understood quite well enough because of increasing human disturbance and low data resolution. In this study, the relationship between the treeline pattern and topography was analyzed based on high spatial resolution remote sensing data and a digital elevation model in an area in Changbai Mountain with little human disturbance. Future treeline patterns were also predicted. The results showed that （a） aspects with high solar radiation and low snow cover have a high coverage rate of trees, （b） the peak coverage rate of trees switches from low slopes （〈5°） to medium slopes （5°~25°） as the elevation rises because of the extreme environment, （c） the coverage rate of trees is a function that depends on environmental factors controlled by topography, （d） the future treeline pattern is controlled by new temperature mechanisms, new environmental factors and the reallocation effect of topography. Our research implies that topography controls the treeline pattern and changes in the treeline pattern associated with global warming, due to the effect of global warming on environmental factors. This study may well explain the causes of heterogeneous changes in the treeline pattern in the horizontal direction as well as differences in treeline response to climate warming.
基金National Natural Science Foundation of China(NSFC)(Grant Nos.31170423,31200375)
文摘Understanding of treeline ecotone ecophysiological adaptation to climate warming is still very limited. Furthermore, it is difficult to predict which plant species could dominate in the future. For this reason, a study was conducted in the treeline ecotone, East Tibetan Plateau to detect the adaptation of the dwarf willow(Salix eriostachya) to experimental warming. Compared to ambient conditions, the experimental warming advanced the bud break by 12 days, delayed the leaf abscission by20 days, and prolonged the growing period by 28 days.It also increased photosynthesis(47%), number of leaves(333%), leaf area(310%), and carbon sequestration of the dwarf willow. Experimental warming did not affect carbon use efficiency, but decreased water use efficiency significantly.Experimental warming enhanced the clonal ramets of Salix eriostachya(+ 3.7 shrubs m-2). The frequent air temperature fluctuations had minor effect on Salix eriostachya. Based on these findings, we highlighted that Salix eriostachya could dominate in the community treeline ecotone of east Tibetan Plateau in the future climate warming scenario.
文摘At a global scale, tree growth in alpine treeline ecotones is limited by low temperatures. At a local scale, however, tree growth at its upper limit depends on multiple interactions of influencing factors and mechanisms. The aim of our research was to understand local scale effects of soil properties and nutrient cycling on tree growth limitation, and their interactions with other abiotic and biotic factors in a near-natural Himalayan treeline ecotone. Soil samples of different soil horizons, litter, decomposition layers, and foliage samples of standing biomass were collected in four altitudinal zones along three slopes, and were analysed for exchangeable cations and nutrient concentrations, respectively. Additionally, soil and air temperature, soil moisture, precipitation, and tree physiognomy patterns were evaluated. Both soil nutrients and foliar macronutrient concentrations of nitrogen(N), magnesium(Mg), potassium(K), and foliar phosphorus(P) decrease significantly with elevation. Foliar manganese(Mn) concentrations, bycontrast, are extraordinarily high at high elevation sites. Potential constraining factors on tree growth were identified using multivariate statistical approaches. We propose that tree growth, treeline position and vegetation composition are affected by nutrient limitation, which in turn, is governed by low soil temperatures and influenced by soil moisture conditions.
基金N.D.,V.K.,A.G.,and A.G.were supported by the Russian Science Foundation(Grant No.17-14-01112)V.M.was supported by the Russian Foundation of Basic Research(Grant No.19-05-00756)Data collection was partly performed within the frameworks of a state contract with the Institute of Plant and Animal Ecology,Ural Branch,Russian Academy of Sciences.
文摘Background:Recent warming is affecting species composition and species areal distribution of many regions.However,although most treeline studies have estimated the rates of forest expansion into tundra,still little is known about the long-term dynamic of stand productivity at the forest-tundra intersection.Here,we make use of tree-ring data from 350 larch(Larix sibirica Ledeb.)and spruce(Picea obovata Ledeb.)sampled along the singular altitudinal treeline ecotone at the Polar Urals to assess the dynamic of stand establishment and productivity,and link the results with meteorological observations to identify the main environmental drivers.Results:The analysis of stand instalment indicated that more than 90%of the living trees appeared after 1900.During this period,the stand became denser and moved 50m upward,while in recent decades the trees of both species grew faster.The maximum afforestation occurred in the last decades of the twentieth century,and the large number of encountered saplings indicates that the forest is still expanding.The upward shift coincided with a slight increase of May-August and nearly doubling of September-April precipitation while the increase in growth matched with an early growth season warming(June+0.27°C per decade since 1901).This increase in radial growth combined with the stand densification led to a 6-90 times increase of biomass since 1950.Conclusion:Tree-ring based twentieth century reconstruction at the treeline ecotone shows an ongoing forest densification and expansion accompanied by an increased growth.These changes are driven by climate change mechanism,whereby the leading factors are the significant increase in May-June temperatures and precipitation during the dormant period.Exploring of phytomass accumulation mechanisms within treeline ecotone is valuable for improving our understanding of carbon dynamics and the overall climate balance in current treeline ecosystems and for predicting how these will be altered by global change.
文摘A dendroclimatic study was conducted in the treeline ecotone of Barun Valley, eastern Nepal, to determine the tree-ring climate response and ring width trend of Abies spectabilis. A 160-year-old chronology, from 1850 to 2010, was developed from 38 tree-ring samples. No higher growth in recent decades was observed in tree-ring width in this area. The mean temperature of the current year in February and in the combined winter months of December, January, and February showed significant positive correlation with tree-ring width, although no significant correlation was found between tree-ring width and the precipitation pattern of the region. This tree-ring climate response result is different from that in other studies in Nepal, which could be attributed to location and elevation.
基金supported by the National Natural Science Foundation of China(Grant No.41401111)the Natural Science Foundation of Shandong Province(Grant No.ZR2021MD080 and Grant No.ZR2014DQ017)the Shandong Agricultural Science and Technology Fund Project(Grant No.2019LY006)。
文摘Different types of vegetation patches are alternately and randomly distributed in a timberline ecotone where the upper limit is the treeline and the lower limit is the timberline.However,most studies on timberline/treeline altitudinal distributions have simplified timberline or treeline as continuous curves and disregarded the fuzziness of timberline/treeline and the randomness of different vegetation patch distributions in a timberline ecotone.To study the altitudinal distribution characteristics of timberline and treeline from the perspective of uncertainty theory,we constructed the timberline and treeline elevation cloud models in Mt.Namjagbarwa in east Himalayas.Subsequently,we established multiple linear regression models by using nine influencing factors,namely,aspect,slope,topographic relief,dryness index,average temperature in January and July,latitude,summit syndrome(represented by the vertical distance from the peak),and snow effect(represented by the nearest distance from the snow)as independent variables,and the elevations of timberline/treeline as dependent variables.Then we compared the contributions of the nine factors in timberline,treeline,and the core and peripheral areas of timberline and treeline.The results show that 1)the timberline/treeline elevation cloud model can represent the overall characteristics(especially the uncertainty)of the altitudinal distributions of the timberline/treeline well.The uncertainty of treeline’s altitudinal distribution is higher than that of timberline(entropy and hyper entropy:207.59 m and 70.36 m for treeline elevation cloud;entropy and hyper entropy:191.17 m and 50.13 m for timberline elevation cloud).2)The influence of climate and topography on timberline and treeline are similar.The average temperature in July has a significant negative correlation with the timberline/treeline elevation in Mt.Namjagbarwa,which is the most critical factor that affects timberline and treeline elevation,explaining the altitudinal distribution of 44.01%timberline and 46.74%treeline.However,the contributions of the nine factors in core and peripheral areas of timberline and treeline area are evidently different.
基金supported by the National Natural Science Foundation of China (41561011)the Natural Science Foundation of Jiangxi Province, China (20151BAB213029)
文摘Under conditions of a warmer climate,the advance of the alpine treeline into alpine tundra has implications for carbon dynamics in mountain ecosystems.However,the above- and below-ground live biomass allocations among different vegetation types within the treeline ecotones are not well investigated.To determine the altitudinal patterns of above-/below-ground carbon allocation,we measured the root biomass and estimated the above-ground biomass(AGB) in a subalpine forest,treeline forest,alpine shrub,and alpine grassland along two elevational transects towards the alpine tundra in southeast Tibet.The AGB strongly declined with increasing elevation,which was associated with a decrease in the leaf area index and a consequent reduction in carbon gain.The fine root biomass(FRB) increased significantly more in the alpine shrub and grassland than in the treeline forest,whereas the coarse root biomass changed little with increasing altitudes,which led to a stable below-ground biomass(BGB) value across altitudes.Warm and infertile soil conditions might explain the large amount of FRB in alpine shrub and grassland.Consequently,the root toshoot biomass ratio increased sharply with altitude,which suggested a remarkable shift of biomass allocation to root systems near the alpine tundra.Our findings demonstrate contrasting changes in AGB and BGB allocations across treeline ecotones,which should be considered when estimating carbon dynamics with shifting treelines.
基金the National Key R&D Program of China(Grant NO.2022YFF1300904)the National Natural Science Foundation of China(Grant NO.42001106,42371075,42271119)+2 种基金the Joint Fund of National Natural Science Foundation of China(Grant NO.U19A2042,U19A2023,U20A2083)the Natural Science Foundation of Jilin Province,China(YDZJ202201ZYTS483)Youth Innovation Promotion Association,Chinese Academy of Sciences(2023238)。
文摘Alpine treeline ecotones are highly sensitive to climate warming.The low temperature-determined alpine treeline is expected to shift upwards in response to global warming.However,little is known about how temperature interacts with other important factors to influence the distribution range of tree species within and beyond the alpine treeline ecotone.Hence,we used a GF-2 satellite image,along with bioclimatic and topographic variables,to develop an ensemble suitable habitat model based on the species distribution modeling algorithms in Biomod2.We investigated the distribution of suitable habitats for B.ermanii under three climate change scenarios(i.e.,low(SSP126),moderate(SSP370)and extreme(SSP585)future emission trajectories)between two consecutive time periods(i.e.,current-2055,and 2055-2085).By 2055,the potential distribution range of B.ermanii will expand under all three climate scenarios.The medium and high suitable areas will decline under SSP370 and SSP585scenarios from 2055 to 2085.Moreover,under the three climate scenarios,the uppermost altitudes of low suitable habitat will rise to 2,329 m a.s.l.,while the altitudes of medium and high suitable habitats will fall to 2,201 and2,051 m a.s.l.by 2085,respectively.Warming promotes the expansion of B.ermanii distribution range in Changbai Mountain,and this expansion will be modified by precipitation as climate warming continues.This interaction between temperature and precipitation plays a significant role in shaping the potential distribution range of B.ermanii in the alpine treeline ecotone.This study reveals the link between environmental factors,habitat distribution,and species distribution in the alpine treeline ecotone,providing valuable insights into the impacts of climate change on high-elevation vegetation,and contributing to mountain biodiversity conservation and sustainable development.
基金supported by 2014-2019 Title V-PPOHA-#P031M1400412018/19 AY Faculty RSCA grant at CSU Dominguez Hills for summer funding
文摘We performed a meta-analysis on over 100 studies applying remote sensing(RS)and geographic information systems(GIS)to understand treeline dynamics.A literature search was performed in multiple online databases,including Web of Knowledge(Thomson Reuters),Scopus(Elsevier),BASE(Bielefeld Academic Search Engine),CAB Direct,and Google Scholar using treeline-related queries.We found that RS and GIS use has steadily increased in treeline studies since 2000.Spatialresolution RS and satellite imaging techniques varied from low-resolution MODIS,moderate-resolution Landsat,to high-resolution WorldView and aerial orthophotos.Most papers published in the 1990s used low to moderate resolution sensors such as Landsat Multispectral Scanner and Thematic Mapper,or SPOT PAN(Panchromatic)and MX(Multispectral)RS images.Subsequently,we observed a rise in high-resolution satellite sensors such as ALOS,GeoEye,IKONOS,and WorldView for mapping current and potential treelines.Furthermore,we noticed a shift in emphasis of treeline studies over time:earlier reports focused on mapping treeline positions,whereas RS and GIS are now used to determine the factors that control treeline variation.
基金supported by the Major Research Plan of National Natural Science Foundation of China (No. 91025014),the National Natural Science Foundation of China (No. 30800147)
文摘Climate constitutes the main limiting factor for tree-ring growth in high-elevation forests, and the relationship between tree-ring growth and climate is complex. Based on tree-ring chronology and meteorological data, the influence of precipitation, mean temperature and mean minimum temperature at yearly, seasonal and monthly scales on the tree-ring growth of Picea crossifolia was studied at treeline ecotones in the Qilian Mountains, northwestern China. The results show that growing season temperatures of previous and current years are important limiting factors on tree-ring growth, particularly June mean temperature and mean minimum temperature of current year. The precipitations in the previous winter and current spring have a positive correlation, and in the current fall has a negative correlation with tree-ring growth, but these correlations are not significant. Our results suggest that temperature controls tree-ring growth more strongly than precipitation at treeline ecotones in the Qilian Mountains.
基金supported by the Second Tibetan Plateau Scientific Expedition and Research(STEP)program of China(No.2019QZKK0301)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDA26010101)the National Natural Science Foundation of China(Nos.31860123,31560153)。
文摘Unprecedented modern rates of warming are expected to advance alpine treelines to higher elevations,but global evidence suggests that current treeline dynamics are influenced by a variety of factors.Seasonal snow cover has an essential impact on tree recruitment and growth in alpine regions,which may in turn influence current treeline elevation;however,little research has been conducted on its role in regional treeline formation.Based on 11,804treeline locations in the eastern Himalayas,we extracted elevation,climate,and topographic data for treeline and snowline.Specifically,we used linear and structural equation modelling to assess the relationship between these environmental factors and treeline elevation,and the climate-snow-treeline interaction mechanism.The results showed that the treeline elevation increased with summer temperature and permanent or seasonal snowline elevation,but decreased with snow cover days and spring temperature at the treeline positions(P<0.001).Importantly,spring snowline elevation(33.4%)and seasonal snow cover days(21.1%)contributed the most to treeline elevation,outperforming the permanent snowline,temperature,precipitation,and light.Our results support the assertion that the temperature-moisture interaction affects treeline elevation in the eastern Himalayas,but we also found that the effects were strongly mediated by seasonal snow cover patterns.The increasing tendency of snow cover governed by climate humidification observed in the eastern Himalayas,is likely to limit future treeline advancement and may even cause treeline decline due to the mortality of the remaining old trees.Together,our findings highlight the role of seasonal snow cover patterns in determining treeline elevation in the eastern Himalayas,which should be considered when assessing the potential for treeline ascent in snow-mediated alpine systems elsewhere.
文摘The alpine treeline ecotone is an important component of mountain ecosystems of the Nepal Himalaya; it plays a vital role in the livelihood of indigenous people,and provides ecosystem services. However,the region faces a problem of paucity of data on treeline characteristics at the regional and landscape scales. Therefore,we used Remote Sensing(RS),and Geographic Information Science(GIS) approaches to investigate cross-scale interactions in the treeline ecotone. Additionally,European Space Agency land cover map,International Center for Integrated Mountain Development(ICIMOD) land cover map,ecological map of Nepal,and United States Geological Survey Shuttle Radar Topography Mission-Digital Elevation Model were used to analyze treeline pattern at the regional scale. Digital Globe high-resolution satellite imagery of Barun(eastern Nepal) and Manang(central Nepal) were used to study treeline patterns at the landscape scale. Treeline elevation ranges from 3300-4300 m above sea level. Abies spectabilis,Betula utilis,and Pinus wallichiana are the main treeline-forming species in the Nepal Himalaya. There is an east to west treeline elevationgradient at the regional scale. No slope exposure is observed at the regional scale; however,at the landscape scale,slope exposure is present only in a disturbed area(Manang). Topography and human disturbance are the main treeline controlling factor in Barun and Manang respectively.
文摘Stand structure dynamics are considered as major happenings in any forest as a response to environmental changes.However,this important topic is underrepresented in the treeline studies in the Nepal Himalayas.We aimed to investigate site-as well as species-specific changes in morphometric features(basal diameter,crown cover,density,and height)along the elevational gradient across treeline ecotones in response to recent environmental changes.The stand structure characteristics of Abies spectabilis,Pinus wallichiana,and Betula utilis across the treeline ecotone of three study sites in Eastern(Barun),Central(Manang),and Western(Dhorpatan)Nepal were analyzed to elucidate structural heterogeneities.Altogether,eight transects(20 m×(60–250 m))across the treeline ecotone were established.Trees of all life forms,trees(>2 m),saplings(0.5–2 m),and seedlings(<0.5 m),within each transect were enumerated and sampled for the morphometric features and age.Site-specific and species-specific stand structure dynamics were found.The rate of basal area increment was higher in Barun,but the Manang treeline,despite profound regeneration in recent years,had a low annual basal area increment.Moreover,the altitudinal distribution of age and morphometry were not consistent among those ecotones.Furthermore,intra-specific competition was not significant.The site-specific stand structure dynamics explain why treelines do not respond uniformly to increasing temperature.It invokes,in further studies,the incorporation of the tree’s morphometric adaptation traits,phenotypic plasticity,and interactions between species genotype and the environment.
基金supported by the National Natural Science Foundation of China(Grant Nos.41871350,41571099)the Scientific and Technological Basic Resources Survey Project(Grant No.2017FY100900)。
文摘As one of the main non-zonal factors,the mass elevation effect(MEE)has significant impacts on both regional climates and mountain ecological patterns.In recent years,with the development of quantitative techniques and methods,quantitative studies on the MEE and its implication on mountain altitudinal belts have developed rapidly.However,some issues have not been solved yet,such as high errors in spatial temperature estimations and difficulties in the definition and extraction of intramountain base elevation.Moreover,there is still a lack of comparative studies on the MEE and its influence on treelines and snowlines as most studies were conducted on specific mountains or plateaus.To compare the MEE magnitudes of the Tibetan Plateau(TP)and the Bolivian Plateau(BP),we estimated the correspondent air temperatures and simulated the solar radiations based on MODIS surface temperature,station observation,and treeline data.Then,we analyzed the elevation of the 10℃isotherms on the two plateaus,the temperatures at the same elevation,and the solar radiations.According to the mechanism of the MEE and the relationship of solar radiation and treeline,we constructed treeline models for the two plateaus through a stepwise regression analysis by considering several influencing factors of the MEE(e.g.,air temperature and precipitation)and using solar radiation as its proxy.The results showed that:(1)the MEE magnitude on the TP is equivalent to that on the BP although the former is slightly higher than the latter;(2)the MEE strongly influences the highest treelines in the northern and southern hemispheres,which both occur on the two plateaus.Notably,the treeline distribution models based on solar radiation had higher accuracies than those models with parameters of temperature and precipitation(the adjusted R^(2)values were 0.76 for the TP and 0.936 for the BP),indicating that solar radiation can be used to quantify the MEE and its implications on treelines.Overall,the results of this study can serve as a basis for subsequent analyses on the MEE’s impact factors.
