Landscape boundaries are always indicated by the vegetation boundaries. As an ecotone between closed forest and treeline, alpine timberline may respond to global climate changes sensitively. The stability of timberlin...Landscape boundaries are always indicated by the vegetation boundaries. As an ecotone between closed forest and treeline, alpine timberline may respond to global climate changes sensitively. The stability of timberline and treeline depend not only on climate change, but also on the interaction of both sides of the ecosystems. Three natural boundaries existing in the timberline transitional zone are recognized: (1) timberline (upper limit of closed forest zone); (2) treeline (upper limit of tree islands zone); (3) tree species line (upper limit of individual tree growth). Paleobotanical and sedimentary evidences suggest that there were several times of climate fluctuation during the Holocene period in this area. The timberline of Taibai Mountain must have moved for four times on the millennium scale. Being a stochastic oscillation boundary, treeline appears in a semi stable condition on the century scale. The tree species line is even more unstable, which appears in an unstable status on the decades scale. The comparison of the stability within several landscape boundaries, shed light on the sensibility of these communities to various perturbation and environmental heterogeneity, i.e., herb community is the most sensitive one, which is followed by shrubs, and forest is the most stable one. Trees and shrubs can adapt to rocky and poor soils. On the contrary, alpine herbs are able to adapt to wetter and cooler soils. Finally, under a scenario of a temperature of 1.5 4.5℃ increase, the present timberline will be relatively stable but treeline and tree species line will move upward.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
As an important ecotone,the alpine timberline is the boundary between closed-canopy montane forest and alpine vegetation,and is highly sensitive to global and regional climate changes.We provided a way to identify and...As an important ecotone,the alpine timberline is the boundary between closed-canopy montane forest and alpine vegetation,and is highly sensitive to global and regional climate changes.We provided a way to identify and extract the alpine timberline in Yarlung Zangpo Grand Canyon Nature Reserve by using remote sensing data and spatial analysis based on land use/land cover classification and NDVI distribution characteristics.Combining DEM data,the influence of slope and aspect on the distribution of alpine timberline was explored.The results showed that the alpine timberline in Yarlung Zangpo Grand Canyon is transitional timberline,with the upper boundary approximately distributed at the elevation of 3422-4373 m,the lower boundary at approximately 3270-4164 m,with a width of about 110-280 m.Alpine timberline was mainly distributed on steep and very steep slopes ranging from 25°to 45°.The maximum elevation of both the upper and lower boundaries occurred on steep slopes.The distribution of alpine timberline varies with aspects,with sunny slopes having a higher boundary than shady slopes.展开更多
Himalayan region represents the highest and most diverse treeline over the world.As one of the most conspicuous boundaries between montane forests and alpine vegetation,the alpine timberline attracted the interest of ...Himalayan region represents the highest and most diverse treeline over the world.As one of the most conspicuous boundaries between montane forests and alpine vegetation,the alpine timberline attracted the interest of researchers for many decades.However,timberline in the Himalayas is understudied compared with European counterparts due to remoteness.Here we review the distribution pattern of timberline and its climatic condition,the carbon and nutrient supply mechanism for treeline formation,and treeline shift and treeline tree recruitment under climate change scenarios.Growth limitation,rather than carbon source limitation is the physiological cause of timberline under the low temperature condition.Nutrient limitation and water stress are not the direct cause of timberline formation.However,more clear local limitation factors are need to integrate in order to enable us to predict the potential impacts and changes caused by human activity and related global change in this sensitive region.展开更多
Alpine timberline, as the ＂ecologica tion of scientists in many fields, especially in transition zone,＂ has long attracted the atten- recent years. Many unitary and dibasic fitting models have been developed to expl...Alpine timberline, as the ＂ecologica tion of scientists in many fields, especially in transition zone,＂ has long attracted the atten- recent years. Many unitary and dibasic fitting models have been developed to explore the relationship between timberline elevation and latitude or temperature. However, these models are usually on regional scale and could not be applied to other regions; on the other hand, hemispherical-scale and continental-scale models are usually based on about 100 timberline data and are necessarily low in precision. The present article collects 516 data sites of timberline, and takes latitude, continentality and mass elevation effect （MEE） as independent variables and timberline elevation as dependent variable to develop a ternary linear regression meteorological data released by WorldClim and model. Continentality is calculated using the mountain base elevation （as a proxy of mass elevation effect） is extracted on the basis of SRTM 90-meter resolution elevation data. The results show that the coefficient of determination （R2） of the linear model is as high as 0.904, and that the contribution rate of latitude, continentality and MEE to timberline elevation is 45.02% （p=0.000）, 6.04% （p=0.000） and 48.94% （p=0.000）, respectively. This means that MEE is simply the primary factor contributing to the elevation distribution of timberline on the continental and hemispherical scales. The contribution rate of MEE to timberline altitude dif- fers in different regions, e.g., 50.49% （p=0.000） in North America, 48.73% （p=0.000） in the eastern Eurasia, and 43.6% （p=0.000） in the western Eurasia, but it is usually very high.展开更多
Climate-driven changes in the thermal and moisture regimes may variously influence different tree species growth and ranges.We hypothesize that drought resistant Siberian larch(Larix sibirica Ledeb.)and precipitation-...Climate-driven changes in the thermal and moisture regimes may variously influence different tree species growth and ranges.We hypothesize that drought resistant Siberian larch(Larix sibirica Ledeb.)and precipitation-sensitive Siberian pine(Pinus sibirica Du Tour)responded differently to climate change along the elevational thermal and precipitation gradients.We studied the influence of air temperature,precipitation,soil moisture,and atmospheric drought(indicated by the drought index SPEI)on larch and pine growth along the southward megaslope of the West Sayan Ridge.We found that since 2000 climate change resulted in increasing larch and pine radial growth index(GI)(c.1.5–3times)within treeline(2000–2300 m)and timberline(1900–2000 m)ecotones,i.e.within high precipitation zones.Within the forest-steppe ecotone(1100–1200 m)in which L.sibirica is the only species,larch GI stagnated or even decreased.The total forested area increased since 2000 up to+50%in the high elevations,whereas in the low elevations(<1400 m)area changes were negligible.Within treeline and timberline,trees’GI was stimulated by summer temperature.Meanwhile,temperature increase in early spring reduces GI due to living tissue activation followed by tissue damage by desiccation.Within forest-steppe,larch radial growth was mostly dependent on soil moisture.Warming shifted dependence on moisture to the early dates of the growing period.Acute droughts decreased GI within forest-steppe as well as within treeline,whereas the drought influence on both species within highlands was insignificant.Within forest-steppe seedlings establishment was poor,whereas it was successful within treeline and timberline.Current climate change leads to stagnation or even decrease in Larix sibirica growth in the southern lowland habitat.In combination with poor seedlings establishment,reduced growth threatens the transformation of open lowland forests into forest-steppe and steppe communities.Meanwhile,in the highlands warming facilitated the growth of Siberian larch and pine and the increase of forested area.展开更多
Larix olgensis is a dominant tree species in the forest ecosystems of the Changbai Mountains of northeast China.To assess the growth response of this species to global climate change,we developed three tree-ring width...Larix olgensis is a dominant tree species in the forest ecosystems of the Changbai Mountains of northeast China.To assess the growth response of this species to global climate change,we developed three tree-ring width and biomass chronologies across a range of elevations in the subalpine forests on the eastern slope of the Changbai Mountains.We used dendroclimatic analyses to study key factors limiting radial growth in L.olgensis and its variation with elevation.The statistical characteristics of chronologies suggested that elevation is a determinant of tree growth patterns in the study area.Response function analysis of chronologies with climate factors indicated that climate–growth relationships changed with increasing elevation:tree growth at high elevation was strongly limited by June temperatures of the previous year,and as elevation decreases,the importance of temperature decreased;tree radial growth at mid-elevation was mainly controlled by precipitation towards the end of the growing season of the current year.Biomass chronologies reflected a stronger climatic signal than tree-ring width chronologies.Spatial correlation with gridded climate data revealed that our chronologies contained a strong regional temperature signal for northeast China.Trees growing below timberline appeared to be more sensitive to climate,thus optimal sites for examining growth trends as a function of climate variation are considered to be just below timberline.Our study objective was to provide information for more accurate prediction of the growth response of L.olgensis to future climate change on the eastern slope of the Changbai Mountains,and to provide information for future climate reconstructions using this tree species in humid and semi humid regions.展开更多
It is over 110 years since the term Mass Elevation Effect(MEE) was proposed by A. D. Quervain in 1904. The quantitative study of MEE has been explored in the Tibetan Plateau in recent years; however, the spatial distr...It is over 110 years since the term Mass Elevation Effect(MEE) was proposed by A. D. Quervain in 1904. The quantitative study of MEE has been explored in the Tibetan Plateau in recent years; however, the spatial distribution of MEE and its impact on the ecological pattern of the plateau are seldom known. In this study, we used a new method to estimate MEE in different regions of the plateau, and, then analyzed the distribution pattern of MEE, and the relationships among MEE, climate, and the altitudinal distribution of timberlines and snowlines in the Plateau. The main results are as follows:(1) The spatial distribution of MEE in the Tibetan Plateau roughly takes on an eccentric ellipse in northwestsoutheast trend. The Chang Tang Plateau and the middle part of the Kunlun Mountains are the core area of MEE, where occurs the highest MEE of above 11℃; and MEE tends to decreases from this core area northwestward, northeastward and southward;(2) The distance away from the core zone of the plateau is also a very important factor for MEE magnitude, because MEE is obviously higher in the interior than in the exterior of the plateau even with similar mountain base elevation(MBE).(3) The impacts of MEE on the altitudinal distribution of timberlines and snowlines are similar, i.e., the higher the MEE, the higher timberlines and snowlines. The highest timberline(4600–4800 m) appears in the lakes and basins north of the Himalayas and in the upper and middle reach valleys of the Yarlung Zangbo River, where the estimated MEE is 10.2822℃–10.6904℃. The highest snowline(6000–6200 m) occurs in the southwest of the Chang Tang Plateau, where the estimated MEE is 11.2059°C–11.5488℃.展开更多
Mass elevation effect （MEE） refers to the thermal effect of huge mountains or plateaus, which causes the tendency for tem- perature-related montane landscape limits to occur at higher elevations in the inner massifs...Mass elevation effect （MEE） refers to the thermal effect of huge mountains or plateaus, which causes the tendency for tem- perature-related montane landscape limits to occur at higher elevations in the inner massifs than on their outer margins. MEE has been widely identified in all large mountains, but how it could be measured and what its main forming-factors are still remain open. This paper, supposing that the local mountain base elevation （MBE） is the main factor of MEE, takes the Qinghai-Tibet Plateau （QTP） as the study area, defines MEE as the temperature difference （AT） between the inner and outer parts of mountain massifs, identifies the main forming factors, and analyzes their contributions to MEE. A total of 73 mountain bases were identified, ranging from 708 m to 5081 m and increasing from the edges to the central parts of the plateau. Climate data （1981-2010） from 134 meteorological stations were used to acquire ATby comparing near-surface air temperature on the main plateau with the free-air temperature at the same altitude and simi- lar latitude outside of the plateau. The AT for the warmest month is averagely 6.15 ~C, over 12~C at Lhatse and Baxoi. A multivariate linear regression model was developed to simulate MEE based on three variables （latitude, annual mean precipitation and MBE）, which are all significantly correlated to AT. The model could explain 67.3% of MEE variation, and the contribution rates of three independent variables to MEE are 35.29%, 22.69% and 42.02%, respectively. This confirms that MBE is the main factor of MEE. The intensive MEE of the QTP pushes the 10~C isotherm of the warmest month mean temperature 1300-2000 m higher in the main plateau than in the outer regions, leading the occurrence of the highest timberline （4900 m） and the highest snowline （6200 m） of the Northern Hemisphere in the southeast and southwest of the plateau, respectively.展开更多
Background: Treeline dynamics have inevitable impacts on the forest treeline structure and composition. The present research sought to estimate treeline movement and structural shifts in response to recent warming in ...Background: Treeline dynamics have inevitable impacts on the forest treeline structure and composition. The present research sought to estimate treeline movement and structural shifts in response to recent warming in Cehennemdere, Turkey. After implementing an atmospheric correction, the geo-shifting of images was performed to match images together for a per pixel trend analysis. We developed a new approach based on the NDVI, LST(land surface temperature) data, air temperature data, and forest stand maps for a 43-year period. The forest treeline border was mapped on the forest stand maps for 1970, 1992, 2002, and 2013 to identify shifts in the treeline altitudes, and then profile statistics were calculated for each period. Twenty sample plots(10 × 10 pixels) were selected to estimatethe NDVI and LST shifts across the forest timberline using per-pixel trend analysis and non-parametric Spearman’s correlation analysis. In addition, the spatial and temporal shifts in treeline tree species were computed within the selected plots for four time periods on the forest stand maps to determine the pioneer tree species.Results: A statistically significant increasing trend in all climate variables was observed, with the highest slopein the monthly average mean July temperature(tau = 0.62, ρ < 0.00). The resultant forest stand maps showed a geographical expansion of the treeline in both the highest altitudes(22 m–45 m) and the lowest altitudes(20 m–105 m) from 1970 to 2013. The per pixel trend analysis indicated an increasing trend in the NDVI and LST values within the selected plots. Moreover, increases in the LST were highly correlated with increases in the NDVIbetween 1984 and 2017(r = 0.75, ρ < 0.05). Cedrus libani and Juniperus communis app. were two pioneer tree species that expanded and grew consistently on open lands, primarily on rocks and soil-covered areas, from 1970 to 2013.Conclusion: The present study il ustrated that forest treeline dynamics and treeline structural changes can be detected using two data sources. Additionally, the results will have a significant contribution to and implication for treeline movement studies and forest landscape change investigations attempting to project climate change impacts on tree species in response to climate warming. The results will assist forest managers in establishing some developmentaladaptation strategies for forest treeline ecotones.展开更多
We hypothesize that in mountain windy habitat trees formed clusters(hedges)as adaptive structures for seedlings’rooting,survival,and tress’upslope migration.We studied hedges formed by Siberian pine(Pinus sibirica d...We hypothesize that in mountain windy habitat trees formed clusters(hedges)as adaptive structures for seedlings’rooting,survival,and tress’upslope migration.We studied hedges formed by Siberian pine(Pinus sibirica du Tour)and larch(Larix sibirica Ledeb.)within the treeline ecotone in southern Siberian Mountains,investigated hedges formation,evolution,habitat amelioration,and analyzed tree’s growth index(GI)dependence on the eco-climate variables(air temperature,precipitation,soil moisture,wind speed)and relief features(elevation,aspect,slope steepness,and terrain curvature).We conducted a ground survey,measured biometrical parameters of trees and hedges,determined species composition and tree physiognomy,soil types and nutrient contents,and sampled wood cores and applied dendrochronology for trees’GI analysis.With high-resolution satellite scenes for hedge detection and upslope migration,we found that winter winds and soil moisture are the main constraints of trees’settlement and growth.Hedge formation always links with wind-sheltered microtopography features(boulders,local depressions or felled trees).Once the first tree is established,a positive feedback is aroused that facilitates seedling rooting and in-hedge habitat amelioration.Trees form a streamlined dense“common crown”that mitigates adverse winter wind influence.Hedges always orient along the prevailing winds,and trees’uphill migration occurs by seedlings establishment within the leeward hedge side.Hedge growth facilitates soil formation and fertilization.The concentration of nutrients(K,P,N and S)within hedges exceeds the background by 1.5-5.5 times.Hedge extension leads to increased snow accumulation that mitigates the influence of desiccation and snow abrasion and mitigates seasonal water stress.In the extremely harsh windy habitat,inhedge trees present in mat,prostrate or krummholz forms.With warming,tree stems and even twigs turn upright.Notably that GI dependence on the wind speed is insignificant until prostrated trees get turning upright.Since that,the negative correlation between GI and wind speed is arisen with subsequent decrease since hedges form streamlined crown.Hedge growth also leads to a“phytofield”formation(i.e.,grasses,lichen,moss and small bushes growth)around the hedges that,in its turn,encourages seedling rooting which is about triple more efficient than outside the phytofield.Larch,in comparison with Siberian pine,is less often formed hedges.GI of both species is stimulated by warmer air temperature in the beginning of the growth season.Meanwhile,larch GI has stronger response to elevated temperatures and less dependent on soil moisture.This indicates larch is a potential substitute of Siberian pine in a warmer and dryer climate.Hedges in warming climate evolve into closed stands due to both in-hedge tree growth and filling gaps between hedges by different tree species.展开更多
The Changbai Mountains,located in the temperate monsoon climate zone of East Asia,is an ideal loca-tion for the research on timberline response to global changes.In this study,the topsoils were collected from differen...The Changbai Mountains,located in the temperate monsoon climate zone of East Asia,is an ideal loca-tion for the research on timberline response to global changes.In this study,the topsoils were collected from different vertical vegetation zones on the northern slope of the Changbai Mountains,Northeast China in August 2009,and phytoliths in the soil samples were extracted by using wet oxidation method and identified with Motic 2.0 microscope in laboratory.The results show that phytoliths are abundant in the topsoils of the study area.The herbal phytoliths are primarily composed of elongated,tooth-shaped,point-shaped and hat-shaped phytoliths,as well as a small amount of fan-shaped and square-shaped ones.The elongated,tooth-shaped,point-shaped and hat-shaped phytoliths are representative of cold climate,while fan-shaped and square-shaped ones are representative of warm and humid climate.In the conifer broadleaved mixed forest zone,coniferous forest zone and broadleaf forest zone,there are close correlations between vegetation and woody phytoliths in the topsoils,indicating that the woody plants of a region can be reconstructed from the woody phytolith assemblages in the topsoils.Meanwhile,the topsoil phytolith assemblages can also be used to reconstruct the understory herbs effectively.The phytolith assemblages in the topsoils of the forest community and herbal community differ significantly,which can help indicate the historical location of the timberline.展开更多
Physiological and ecological mechanisms that define treelines are still debated. It has been suggested that the absence of trees above the treeline is caused by low temperatures that limit growth. Thus, we hypothesize...Physiological and ecological mechanisms that define treelines are still debated. It has been suggested that the absence of trees above the treeline is caused by low temperatures that limit growth. Thus, we hypothesized that there is a critical minimum temperature （CTmin） preventing xylogenesis at treeline. We tested this hypothesis by examining weekly xylogenesis across three and four growing seasons in two natural Smith fir （Abies georgei var. srnithii） treeline sites on the southeastern Tibetan Plateau. Despite differences in the timing of cell differentiation among years, minimum air temperature was the dominant climatic variable associated with xylem growth; the critical minimum temperature （CTmin） for the onset and end of xylogenesis occurred at 0.7 ±0.4 ℃. A process-based modelling chronology of tree-ring formation using this CTmin was consistent with actual tree-ring data. This extremely low CTmin permits Smith fir growing at treeline to complete annual xylem production and maturation and provides both support and a mechanism for treeline formation.展开更多
Aims Forest growth and recruitment and their relationships to climate are complex.The aims of our study are(i)to examine the patterns in tree radial growth and recruitment along an altitudinal gradient in Mt.Everest r...Aims Forest growth and recruitment and their relationships to climate are complex.The aims of our study are(i)to examine the patterns in tree radial growth and recruitment along an altitudinal gradient in Mt.Everest region and(ii)to identify the climatic factors that are responsible to the observed patterns in tree growth and recruitment.Methods Four plots,each 30360 m in size,were established from the lower to upper limits of the eastern Himalayan fir forest in Dingjie County of the Mt.Everest Nature Reserve,China.Dendrochronological techniques were applied to obtain information about the radial growth and age of the trees in the plots.Correlation analysis was used to identify the relationships between radial growth and recruitment of trees and climatic variables,i.e.monthly mean temperature and Palmer Drought Severity Index(PDSI).The population age structure was analyzed to investigate the recruitment history.Important Findings The timberline plot was characterized by significant tree recruitments in the recent three decades and sporadic recruitments in earlier periods.The other three plots showed recruitment pulses during 1880–1910 in Plot 3700 m,during 1870–80 and 1920–30 in Plot 3520 m and during 1900–40 in Plot 3410 m.The recruitment of fir trees in the timberline was sensitive to summer(June–September)temperatures,but it was mainly controlled by episodic disturbances in lower altitudes.Fir radial growth in the upper two plots was positively correlated with previous winter and current August temperature.Fir radial growth at the two lower plots was positively correlated with PDSI from previous September to current September.展开更多
Aims How species respond to climate change at local scales will depend on how edaphic and biological characteristics interact with species physiological limits and traits such as dispersal.Obligate seeders,those speci...Aims How species respond to climate change at local scales will depend on how edaphic and biological characteristics interact with species physiological limits and traits such as dispersal.Obligate seeders,those species that depend on fire for recruitment,have few and epi-sodic opportunities to track a changing climate envelope.in such cases,long-distance seed dispersal will be necessary to take advan-tage of rare recruitment opportunities.We examine recruitment patterns and seedling growth below,at and above the timberline of an obligate-seeding Australian montane forest tree(Eucalyptus delegatensis)after stand-replacing fire,and place these changes in the context of regional warming.Methods We use two methods to detect whether E.delegatensis can estab-lish and persist above the timberline after stand-replacing wildfire in montane forests in south-east Australia.First,we examine estab-lishment patterns by using belt transects at six sites to quantify how changes in post-fire recruit density with increasing distance above the timberline seven years post-fire.Second,to determine whether dispersal or physiological constraints determine post-fire establish-ment patterns,we transplanted seedlings and saplings into bare ground above(100 m elevation),at,and below(50 m elevation)timberline 18-months after fire.We monitored seedling growth and survival for one growing season.Important Findings There was minimal upslope migration of the species after fire with most saplings observed near seed-bearing timberline trees,with only occasional outpost saplings.Transplanted seedlings and saplings sur-vived equally well across one growing season when planted above existing timberlines,relative to saplings at or below the timberline.Seedling and sapling growth rates also did not differ across these location,although seedlings grew at much faster rates than saplings.These findings suggest that upslope growing season conditions are unlikely to limit initial range expansion of trees after fire.instead,it is more likely that seed traits governing dispersal modulate responses to environmental gradients,and global change more generally.展开更多
文摘Landscape boundaries are always indicated by the vegetation boundaries. As an ecotone between closed forest and treeline, alpine timberline may respond to global climate changes sensitively. The stability of timberline and treeline depend not only on climate change, but also on the interaction of both sides of the ecosystems. Three natural boundaries existing in the timberline transitional zone are recognized: (1) timberline (upper limit of closed forest zone); (2) treeline (upper limit of tree islands zone); (3) tree species line (upper limit of individual tree growth). Paleobotanical and sedimentary evidences suggest that there were several times of climate fluctuation during the Holocene period in this area. The timberline of Taibai Mountain must have moved for four times on the millennium scale. Being a stochastic oscillation boundary, treeline appears in a semi stable condition on the century scale. The tree species line is even more unstable, which appears in an unstable status on the decades scale. The comparison of the stability within several landscape boundaries, shed light on the sensibility of these communities to various perturbation and environmental heterogeneity, i.e., herb community is the most sensitive one, which is followed by shrubs, and forest is the most stable one. Trees and shrubs can adapt to rocky and poor soils. On the contrary, alpine herbs are able to adapt to wetter and cooler soils. Finally, under a scenario of a temperature of 1.5 4.5℃ increase, the present timberline will be relatively stable but treeline and tree species line will move upward.
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(Grant No.91647212)IWHR Research&Development Support Program(WE0163A052018)the Open Research Fund of Guangxi Key Laboratory of Water Engineering Materials and Structures,Guangxi Institute of Water Resources Research(Grant No.GXHRI-WEMS-2020-13)。
文摘As an important ecotone,the alpine timberline is the boundary between closed-canopy montane forest and alpine vegetation,and is highly sensitive to global and regional climate changes.We provided a way to identify and extract the alpine timberline in Yarlung Zangpo Grand Canyon Nature Reserve by using remote sensing data and spatial analysis based on land use/land cover classification and NDVI distribution characteristics.Combining DEM data,the influence of slope and aspect on the distribution of alpine timberline was explored.The results showed that the alpine timberline in Yarlung Zangpo Grand Canyon is transitional timberline,with the upper boundary approximately distributed at the elevation of 3422-4373 m,the lower boundary at approximately 3270-4164 m,with a width of about 110-280 m.Alpine timberline was mainly distributed on steep and very steep slopes ranging from 25°to 45°.The maximum elevation of both the upper and lower boundaries occurred on steep slopes.The distribution of alpine timberline varies with aspects,with sunny slopes having a higher boundary than shady slopes.
基金The National Natural Science Foundation of China and ICIMOD Joint Research Project(41661144045)。
文摘Himalayan region represents the highest and most diverse treeline over the world.As one of the most conspicuous boundaries between montane forests and alpine vegetation,the alpine timberline attracted the interest of researchers for many decades.However,timberline in the Himalayas is understudied compared with European counterparts due to remoteness.Here we review the distribution pattern of timberline and its climatic condition,the carbon and nutrient supply mechanism for treeline formation,and treeline shift and treeline tree recruitment under climate change scenarios.Growth limitation,rather than carbon source limitation is the physiological cause of timberline under the low temperature condition.Nutrient limitation and water stress are not the direct cause of timberline formation.However,more clear local limitation factors are need to integrate in order to enable us to predict the potential impacts and changes caused by human activity and related global change in this sensitive region.
基金National Natural Science Foundation of China,No.41030528No.40971064
文摘Alpine timberline, as the ＂ecologica tion of scientists in many fields, especially in transition zone,＂ has long attracted the atten- recent years. Many unitary and dibasic fitting models have been developed to explore the relationship between timberline elevation and latitude or temperature. However, these models are usually on regional scale and could not be applied to other regions; on the other hand, hemispherical-scale and continental-scale models are usually based on about 100 timberline data and are necessarily low in precision. The present article collects 516 data sites of timberline, and takes latitude, continentality and mass elevation effect （MEE） as independent variables and timberline elevation as dependent variable to develop a ternary linear regression meteorological data released by WorldClim and model. Continentality is calculated using the mountain base elevation （as a proxy of mass elevation effect） is extracted on the basis of SRTM 90-meter resolution elevation data. The results show that the coefficient of determination （R2） of the linear model is as high as 0.904, and that the contribution rate of latitude, continentality and MEE to timberline elevation is 45.02% （p=0.000）, 6.04% （p=0.000） and 48.94% （p=0.000）, respectively. This means that MEE is simply the primary factor contributing to the elevation distribution of timberline on the continental and hemispherical scales. The contribution rate of MEE to timberline altitude dif- fers in different regions, e.g., 50.49% （p=0.000） in North America, 48.73% （p=0.000） in the eastern Eurasia, and 43.6% （p=0.000） in the western Eurasia, but it is usually very high.
基金The Tomsk State University Development Program《Priority-2030》supported this study。
文摘Climate-driven changes in the thermal and moisture regimes may variously influence different tree species growth and ranges.We hypothesize that drought resistant Siberian larch(Larix sibirica Ledeb.)and precipitation-sensitive Siberian pine(Pinus sibirica Du Tour)responded differently to climate change along the elevational thermal and precipitation gradients.We studied the influence of air temperature,precipitation,soil moisture,and atmospheric drought(indicated by the drought index SPEI)on larch and pine growth along the southward megaslope of the West Sayan Ridge.We found that since 2000 climate change resulted in increasing larch and pine radial growth index(GI)(c.1.5–3times)within treeline(2000–2300 m)and timberline(1900–2000 m)ecotones,i.e.within high precipitation zones.Within the forest-steppe ecotone(1100–1200 m)in which L.sibirica is the only species,larch GI stagnated or even decreased.The total forested area increased since 2000 up to+50%in the high elevations,whereas in the low elevations(<1400 m)area changes were negligible.Within treeline and timberline,trees’GI was stimulated by summer temperature.Meanwhile,temperature increase in early spring reduces GI due to living tissue activation followed by tissue damage by desiccation.Within forest-steppe,larch radial growth was mostly dependent on soil moisture.Warming shifted dependence on moisture to the early dates of the growing period.Acute droughts decreased GI within forest-steppe as well as within treeline,whereas the drought influence on both species within highlands was insignificant.Within forest-steppe seedlings establishment was poor,whereas it was successful within treeline and timberline.Current climate change leads to stagnation or even decrease in Larix sibirica growth in the southern lowland habitat.In combination with poor seedlings establishment,reduced growth threatens the transformation of open lowland forests into forest-steppe and steppe communities.Meanwhile,in the highlands warming facilitated the growth of Siberian larch and pine and the increase of forested area.
基金supported by the China Public Welfare Forest Project(No.200804001)
文摘Larix olgensis is a dominant tree species in the forest ecosystems of the Changbai Mountains of northeast China.To assess the growth response of this species to global climate change,we developed three tree-ring width and biomass chronologies across a range of elevations in the subalpine forests on the eastern slope of the Changbai Mountains.We used dendroclimatic analyses to study key factors limiting radial growth in L.olgensis and its variation with elevation.The statistical characteristics of chronologies suggested that elevation is a determinant of tree growth patterns in the study area.Response function analysis of chronologies with climate factors indicated that climate–growth relationships changed with increasing elevation:tree growth at high elevation was strongly limited by June temperatures of the previous year,and as elevation decreases,the importance of temperature decreased;tree radial growth at mid-elevation was mainly controlled by precipitation towards the end of the growing season of the current year.Biomass chronologies reflected a stronger climatic signal than tree-ring width chronologies.Spatial correlation with gridded climate data revealed that our chronologies contained a strong regional temperature signal for northeast China.Trees growing below timberline appeared to be more sensitive to climate,thus optimal sites for examining growth trends as a function of climate variation are considered to be just below timberline.Our study objective was to provide information for more accurate prediction of the growth response of L.olgensis to future climate change on the eastern slope of the Changbai Mountains,and to provide information for future climate reconstructions using this tree species in humid and semi humid regions.
基金supported by the Natural Science Foundation of China (Grant Nos. 41401111 and 41601091)National Key R&D Program of China (2017FY100900)
文摘It is over 110 years since the term Mass Elevation Effect(MEE) was proposed by A. D. Quervain in 1904. The quantitative study of MEE has been explored in the Tibetan Plateau in recent years; however, the spatial distribution of MEE and its impact on the ecological pattern of the plateau are seldom known. In this study, we used a new method to estimate MEE in different regions of the plateau, and, then analyzed the distribution pattern of MEE, and the relationships among MEE, climate, and the altitudinal distribution of timberlines and snowlines in the Plateau. The main results are as follows:(1) The spatial distribution of MEE in the Tibetan Plateau roughly takes on an eccentric ellipse in northwestsoutheast trend. The Chang Tang Plateau and the middle part of the Kunlun Mountains are the core area of MEE, where occurs the highest MEE of above 11℃; and MEE tends to decreases from this core area northwestward, northeastward and southward;(2) The distance away from the core zone of the plateau is also a very important factor for MEE magnitude, because MEE is obviously higher in the interior than in the exterior of the plateau even with similar mountain base elevation(MBE).(3) The impacts of MEE on the altitudinal distribution of timberlines and snowlines are similar, i.e., the higher the MEE, the higher timberlines and snowlines. The highest timberline(4600–4800 m) appears in the lakes and basins north of the Himalayas and in the upper and middle reach valleys of the Yarlung Zangbo River, where the estimated MEE is 10.2822℃–10.6904℃. The highest snowline(6000–6200 m) occurs in the southwest of the Chang Tang Plateau, where the estimated MEE is 11.2059°C–11.5488℃.
基金National Natural Science Foundation of China(No.41571099,41030528)
文摘Mass elevation effect （MEE） refers to the thermal effect of huge mountains or plateaus, which causes the tendency for tem- perature-related montane landscape limits to occur at higher elevations in the inner massifs than on their outer margins. MEE has been widely identified in all large mountains, but how it could be measured and what its main forming-factors are still remain open. This paper, supposing that the local mountain base elevation （MBE） is the main factor of MEE, takes the Qinghai-Tibet Plateau （QTP） as the study area, defines MEE as the temperature difference （AT） between the inner and outer parts of mountain massifs, identifies the main forming factors, and analyzes their contributions to MEE. A total of 73 mountain bases were identified, ranging from 708 m to 5081 m and increasing from the edges to the central parts of the plateau. Climate data （1981-2010） from 134 meteorological stations were used to acquire ATby comparing near-surface air temperature on the main plateau with the free-air temperature at the same altitude and simi- lar latitude outside of the plateau. The AT for the warmest month is averagely 6.15 ~C, over 12~C at Lhatse and Baxoi. A multivariate linear regression model was developed to simulate MEE based on three variables （latitude, annual mean precipitation and MBE）, which are all significantly correlated to AT. The model could explain 67.3% of MEE variation, and the contribution rates of three independent variables to MEE are 35.29%, 22.69% and 42.02%, respectively. This confirms that MBE is the main factor of MEE. The intensive MEE of the QTP pushes the 10~C isotherm of the warmest month mean temperature 1300-2000 m higher in the main plateau than in the outer regions, leading the occurrence of the highest timberline （4900 m） and the highest snowline （6200 m） of the Northern Hemisphere in the southeast and southwest of the plateau, respectively.
文摘Background: Treeline dynamics have inevitable impacts on the forest treeline structure and composition. The present research sought to estimate treeline movement and structural shifts in response to recent warming in Cehennemdere, Turkey. After implementing an atmospheric correction, the geo-shifting of images was performed to match images together for a per pixel trend analysis. We developed a new approach based on the NDVI, LST(land surface temperature) data, air temperature data, and forest stand maps for a 43-year period. The forest treeline border was mapped on the forest stand maps for 1970, 1992, 2002, and 2013 to identify shifts in the treeline altitudes, and then profile statistics were calculated for each period. Twenty sample plots(10 × 10 pixels) were selected to estimatethe NDVI and LST shifts across the forest timberline using per-pixel trend analysis and non-parametric Spearman’s correlation analysis. In addition, the spatial and temporal shifts in treeline tree species were computed within the selected plots for four time periods on the forest stand maps to determine the pioneer tree species.Results: A statistically significant increasing trend in all climate variables was observed, with the highest slopein the monthly average mean July temperature(tau = 0.62, ρ < 0.00). The resultant forest stand maps showed a geographical expansion of the treeline in both the highest altitudes(22 m–45 m) and the lowest altitudes(20 m–105 m) from 1970 to 2013. The per pixel trend analysis indicated an increasing trend in the NDVI and LST values within the selected plots. Moreover, increases in the LST were highly correlated with increases in the NDVIbetween 1984 and 2017(r = 0.75, ρ < 0.05). Cedrus libani and Juniperus communis app. were two pioneer tree species that expanded and grew consistently on open lands, primarily on rocks and soil-covered areas, from 1970 to 2013.Conclusion: The present study il ustrated that forest treeline dynamics and treeline structural changes can be detected using two data sources. Additionally, the results will have a significant contribution to and implication for treeline movement studies and forest landscape change investigations attempting to project climate change impacts on tree species in response to climate warming. The results will assist forest managers in establishing some developmentaladaptation strategies for forest treeline ecotones.
基金The Tomsk State University Development Program(《Priority-2030》)。
文摘We hypothesize that in mountain windy habitat trees formed clusters(hedges)as adaptive structures for seedlings’rooting,survival,and tress’upslope migration.We studied hedges formed by Siberian pine(Pinus sibirica du Tour)and larch(Larix sibirica Ledeb.)within the treeline ecotone in southern Siberian Mountains,investigated hedges formation,evolution,habitat amelioration,and analyzed tree’s growth index(GI)dependence on the eco-climate variables(air temperature,precipitation,soil moisture,wind speed)and relief features(elevation,aspect,slope steepness,and terrain curvature).We conducted a ground survey,measured biometrical parameters of trees and hedges,determined species composition and tree physiognomy,soil types and nutrient contents,and sampled wood cores and applied dendrochronology for trees’GI analysis.With high-resolution satellite scenes for hedge detection and upslope migration,we found that winter winds and soil moisture are the main constraints of trees’settlement and growth.Hedge formation always links with wind-sheltered microtopography features(boulders,local depressions or felled trees).Once the first tree is established,a positive feedback is aroused that facilitates seedling rooting and in-hedge habitat amelioration.Trees form a streamlined dense“common crown”that mitigates adverse winter wind influence.Hedges always orient along the prevailing winds,and trees’uphill migration occurs by seedlings establishment within the leeward hedge side.Hedge growth facilitates soil formation and fertilization.The concentration of nutrients(K,P,N and S)within hedges exceeds the background by 1.5-5.5 times.Hedge extension leads to increased snow accumulation that mitigates the influence of desiccation and snow abrasion and mitigates seasonal water stress.In the extremely harsh windy habitat,inhedge trees present in mat,prostrate or krummholz forms.With warming,tree stems and even twigs turn upright.Notably that GI dependence on the wind speed is insignificant until prostrated trees get turning upright.Since that,the negative correlation between GI and wind speed is arisen with subsequent decrease since hedges form streamlined crown.Hedge growth also leads to a“phytofield”formation(i.e.,grasses,lichen,moss and small bushes growth)around the hedges that,in its turn,encourages seedling rooting which is about triple more efficient than outside the phytofield.Larch,in comparison with Siberian pine,is less often formed hedges.GI of both species is stimulated by warmer air temperature in the beginning of the growth season.Meanwhile,larch GI has stronger response to elevated temperatures and less dependent on soil moisture.This indicates larch is a potential substitute of Siberian pine in a warmer and dryer climate.Hedges in warming climate evolve into closed stands due to both in-hedge tree growth and filling gaps between hedges by different tree species.
基金Under the auspices of National Natural Science Foundation of China (No 40971116)Major State Basic Research Development Program of China (No 2009CB426305)Technology Innovation Project of Northeast Normal University in Eleventh Five-Year Plan Period (No NENU-Stb07002)
文摘The Changbai Mountains,located in the temperate monsoon climate zone of East Asia,is an ideal loca-tion for the research on timberline response to global changes.In this study,the topsoils were collected from different vertical vegetation zones on the northern slope of the Changbai Mountains,Northeast China in August 2009,and phytoliths in the soil samples were extracted by using wet oxidation method and identified with Motic 2.0 microscope in laboratory.The results show that phytoliths are abundant in the topsoils of the study area.The herbal phytoliths are primarily composed of elongated,tooth-shaped,point-shaped and hat-shaped phytoliths,as well as a small amount of fan-shaped and square-shaped ones.The elongated,tooth-shaped,point-shaped and hat-shaped phytoliths are representative of cold climate,while fan-shaped and square-shaped ones are representative of warm and humid climate.In the conifer broadleaved mixed forest zone,coniferous forest zone and broadleaf forest zone,there are close correlations between vegetation and woody phytoliths in the topsoils,indicating that the woody plants of a region can be reconstructed from the woody phytolith assemblages in the topsoils.Meanwhile,the topsoil phytolith assemblages can also be used to reconstruct the understory herbs effectively.The phytolith assemblages in the topsoils of the forest community and herbal community differ significantly,which can help indicate the historical location of the timberline.
基金supported by the National Natural Science Foundations of China(41525001,41661144040,41601204)supported by the Bilateral Project between China and Slovenia(BI-CN/09–11-012)+1 种基金COST Action(FP1106,STRe ESS)supported by the Chinese Academy of Sciences President International Fellowship Initiative for Visiting Scientists(2016VBA074)
文摘Physiological and ecological mechanisms that define treelines are still debated. It has been suggested that the absence of trees above the treeline is caused by low temperatures that limit growth. Thus, we hypothesized that there is a critical minimum temperature （CTmin） preventing xylogenesis at treeline. We tested this hypothesis by examining weekly xylogenesis across three and four growing seasons in two natural Smith fir （Abies georgei var. srnithii） treeline sites on the southeastern Tibetan Plateau. Despite differences in the timing of cell differentiation among years, minimum air temperature was the dominant climatic variable associated with xylem growth; the critical minimum temperature （CTmin） for the onset and end of xylogenesis occurred at 0.7 ±0.4 ℃. A process-based modelling chronology of tree-ring formation using this CTmin was consistent with actual tree-ring data. This extremely low CTmin permits Smith fir growing at treeline to complete annual xylem production and maturation and provides both support and a mechanism for treeline formation.
基金Natural Science Foundation of China(30670365,40631002 and 30870461)the Chinese Academy of Sciences(KSCXYW-Z-1022).
文摘Aims Forest growth and recruitment and their relationships to climate are complex.The aims of our study are(i)to examine the patterns in tree radial growth and recruitment along an altitudinal gradient in Mt.Everest region and(ii)to identify the climatic factors that are responsible to the observed patterns in tree growth and recruitment.Methods Four plots,each 30360 m in size,were established from the lower to upper limits of the eastern Himalayan fir forest in Dingjie County of the Mt.Everest Nature Reserve,China.Dendrochronological techniques were applied to obtain information about the radial growth and age of the trees in the plots.Correlation analysis was used to identify the relationships between radial growth and recruitment of trees and climatic variables,i.e.monthly mean temperature and Palmer Drought Severity Index(PDSI).The population age structure was analyzed to investigate the recruitment history.Important Findings The timberline plot was characterized by significant tree recruitments in the recent three decades and sporadic recruitments in earlier periods.The other three plots showed recruitment pulses during 1880–1910 in Plot 3700 m,during 1870–80 and 1920–30 in Plot 3520 m and during 1900–40 in Plot 3410 m.The recruitment of fir trees in the timberline was sensitive to summer(June–September)temperatures,but it was mainly controlled by episodic disturbances in lower altitudes.Fir radial growth in the upper two plots was positively correlated with previous winter and current August temperature.Fir radial growth at the two lower plots was positively correlated with PDSI from previous September to current September.
文摘Aims How species respond to climate change at local scales will depend on how edaphic and biological characteristics interact with species physiological limits and traits such as dispersal.Obligate seeders,those species that depend on fire for recruitment,have few and epi-sodic opportunities to track a changing climate envelope.in such cases,long-distance seed dispersal will be necessary to take advan-tage of rare recruitment opportunities.We examine recruitment patterns and seedling growth below,at and above the timberline of an obligate-seeding Australian montane forest tree(Eucalyptus delegatensis)after stand-replacing fire,and place these changes in the context of regional warming.Methods We use two methods to detect whether E.delegatensis can estab-lish and persist above the timberline after stand-replacing wildfire in montane forests in south-east Australia.First,we examine estab-lishment patterns by using belt transects at six sites to quantify how changes in post-fire recruit density with increasing distance above the timberline seven years post-fire.Second,to determine whether dispersal or physiological constraints determine post-fire establish-ment patterns,we transplanted seedlings and saplings into bare ground above(100 m elevation),at,and below(50 m elevation)timberline 18-months after fire.We monitored seedling growth and survival for one growing season.Important Findings There was minimal upslope migration of the species after fire with most saplings observed near seed-bearing timberline trees,with only occasional outpost saplings.Transplanted seedlings and saplings sur-vived equally well across one growing season when planted above existing timberlines,relative to saplings at or below the timberline.Seedling and sapling growth rates also did not differ across these location,although seedlings grew at much faster rates than saplings.These findings suggest that upslope growing season conditions are unlikely to limit initial range expansion of trees after fire.instead,it is more likely that seed traits governing dispersal modulate responses to environmental gradients,and global change more generally.
