A set of standard chronologies for tree-ring width(TRW),earlywood width(EWW)and latewood width(LWW)in Pinus tabuliformis Carr.along an altitudi-nal gradient(1450,1400,and 1350 m a.s.l.)on Baiyunshan Mountain,Central C...A set of standard chronologies for tree-ring width(TRW),earlywood width(EWW)and latewood width(LWW)in Pinus tabuliformis Carr.along an altitudi-nal gradient(1450,1400,and 1350 m a.s.l.)on Baiyunshan Mountain,Central China to analyze the effect of varying temperature and precipitation on growth along the gradi-ent.Correlation analyses showed that at all three altitudes and the TRW and EWW chronologies generally had signifi-cant negative correlations with mean and maximum tem-peratures in the current April and May and with minimum temperatures in the prior July and August,but significant positive correlations with precipitation in the current May.Correlations were generally significantly negative between LWW chronologies and all temperatures in the prior July and August,indicating that the prior summer temperature had a strong lag effect on the growth of P.tabuliformis that increased with altitude.The correlation with the standard-ized precipitation evapotranspiration index(SPEI)confirmed that wet conditions in the current May promoted growth of TR and EW at all altitudes.Significant altitudinal differences were also found;at 1400 m,there were significant positive correlations between EWW chronologies and SPEI in the current April and significant negative correlations between LWW chronologies and SPEI in the current September,but these correlations were not significant at 1450 m.At 1350 m,there were also significant negative correlations between the TRW and the EWW chronologies and SPEI in the prior October and the current July and between LWW chronology and SPEI in the current August,but these cor-relations were not significant at 1400 m.Moving correlation results showed a stable response of EWW in relation to the SPEI in the current May at all three altitudes and of LWW to maximum temperature in the prior July-August at 1400 m from 2002 to 2018.The EWW chronology at 1400 m and the LWW chronology at 1450 m were identified as more suitable for climate reconstruction.These results provide a strong scientific basis for forest management decisions and climate reconstructions in Central China.展开更多
Kigezi highlands currently experiences changes in precipitation and temperature which modify the evaporation and soil moisture storage leading to alterations in runoff and other components of hydrological systems. Ext...Kigezi highlands currently experiences changes in precipitation and temperature which modify the evaporation and soil moisture storage leading to alterations in runoff and other components of hydrological systems. Extreme events, like floods and droughts, are more intense and frequent. Furthermore heavy unpredictable rainfall has become frequent in the area, causing soil erosion and floods that destroy crops. Soil erosion is particularly a pressing challenge due to steep-sided hills leading to deterioration of soil nutrients including soil fertility. The unpredictable rains and droughts are attributed to climate change and variability. Consequently, climate change and variability have caused a significant impact on soil nutrients which have affected the agricultural productivity in the area. This paper presents findings of empirical study which explored the climate variability and soil nutrient status along altitudinal gradient. The paper particularly addresses key questions of: land management practices in the study area, nutrient availability and their effects on productivity of selected crops along altitudinal gradient in changing climate and variability. Independent variables such as topographic sequence along altitudinal gradient were evaluated against dependent variables such as yield harvests of selected grown crops and soil nutrients. Samples for crop yields were collected along transect of 0.5 kilometer using a quadrant of 4 × 4 m<sup>2</sup> along attitudinal gradient. Soil samples were taken from selected plots at 0-20cm soil depth for nutrient analysis. Analysis of physical and chemical soil parameters was carried out on soil samples and these include: soil pH, soil organic content, total nitrogen, available soil phosphorous and exchangeable bases (Ca, Mg, K and Na). The study showed that middle parts of the transects had the highest concentration of most soil nutrients, probably because the middle parts could have been a deposition centre for some organic matter from the upper parts of the hills, and lower lying areas were being affected by floods that affects the decomposition of organic matter which is the main source of nutrients. Similarly, the middle parts of the study were the most fertile due to the high concentration of soil nutrient compositions. This indicates that crop yields were significantly affected by availability of soil nutrients along same gradient, attributable to the severity in soil erosion, nutrients leaching and farming practices.展开更多
Regeneration status of tree species along elevation gradient in temperate hill forest was not understood greatly.Present research examined the tree diversity and its regeneration patterns along an elevation gradient i...Regeneration status of tree species along elevation gradient in temperate hill forest was not understood greatly.Present research examined the tree diversity and its regeneration patterns along an elevation gradient in temperate hill forest,central Nepal.Data were collected from 300 sample plots within vertical elevation bands of 10,ranging from 1365 to 2450 m asl.A random sampling method was used for data collection in three seasons,winter,pre-monsoon and post monsoon seasons.Diameter at breast height(DBH)was used to broadly categorize the plant individual into trees,saplings and seedlings.The tree species richness ranged from 12 to 25 with density of 350 to 1200 individuals per hectare.Species richness of tree and sapling showed statistically significant unimodal pattern,which peaked at mid-elevation.Elevation showed a strong and positive linear correlation with the seedling density(Deviance=0.99,p<0.001)and a significant hump-shaped relationship with sapling density(Deviance=0.95,p<0.001).Similarly,elevations showed a statistically significant negative hump-shaped relationship with all trees,saplings and seedling stages(Deviances=0.89,0.87 and 0.57).The highest values of the Shannon-Wiener index and the lowest value of the Simpson index were found at mid-elevation for all growth forms.Nearly 92%of tree species were found at regenerating stage;49%in a good renewal regeneration status,32%in fair renewal regeneration,and 11%at a poor regenerating condition.Nevertheless,4%of tree species were reported as non-regenerating stages and 4%were newly introduced species.Hence,the regeneration status of the study area was considered fairly well since sapling(78.5%)>seedling(10.6%)≤mature(10.9%).Among tested environmental variables,elevation and annual mean rainfall were the most influential factors in the regeneration of tree species.展开更多
Aims Process-based models are basic tools for predicting the response of forest carbon to future climate change.The models have commonly been tested for their predictions of spatial variation in forest produc-tivity,b...Aims Process-based models are basic tools for predicting the response of forest carbon to future climate change.The models have commonly been tested for their predictions of spatial variation in forest produc-tivity,but much less for their ability to predict temporal variation.Here,we explored methods to test the models with tree rings,using BIOME-BGC as an example.Methods We used net primary productivity(NPP)data and tree rings col-lected from five major forest types along the altitudinal gradient of Mt.Changbai,northeast China,to test local-parameterized BIOME-BGC model.We first test the model’s predictions of both spatial(Test 1)and temporal changes(Test 2)in productivity.Then we test if the model can detect the climatic factors limiting forest productiv-ity during historical climate change,as revealed by dendroclimatic analyses(Test 3).Important Findings Our results showed that BIOME-BGC could well simulate NPP of five forest types on Mt.Changbai,with an r^(2) of 0.69 between mod-eled and observed NPP for 17 plots along the altitudinal gradient(Test 1).Meanwhile,modeled NPP and ring-width indices were cor-related and showed similar temporal trends for each forest type(Test 2).While these tests suggest that the model’s predictions on spatial and temporal variation of NPP were acceptable,a further test that relate the correlations of modeled NPP with climate variables to the correlations of ring widths with climate(Test 3)showed that the model did not well identify the climatic factors limiting historical productivity dynamics for some forest types,and thus cannot reli-ably predict their future.Both dendrochronology and BIOME-BGC showed that forest types differed markedly in the climate factors limiting productivity because of differences in tree species and cli-mate condition,and thus differed in responses to climate change.Our results showed that a successful prediction of spatial NPP pat-terns cannot assure that BIOME-BGC can well simulate histori-cal NPP dynamics.Further,a correlation between modeled NPP and tree-ring series cannot assure that the limiting climatic factors for productivity have been correctly identified by the model.Our results suggest the necessity to test the temporal predictions of pro-cess-based models in a more robust way,and further integration of dendrochronology and biogeochemistry modeling may be helpful for this purpose.展开更多
Environmental variations and ontogeny may affect plant morphological traits and biomass allocation patterns that are related to the adjustments of plant ecological strategies. We selected 2-, 3-and 4-year-old Fritilla...Environmental variations and ontogeny may affect plant morphological traits and biomass allocation patterns that are related to the adjustments of plant ecological strategies. We selected 2-, 3-and 4-year-old Fritillaria unibracteata plants to explore the ontogenetic and altitudinal changes that impact their morphological traits(i.e., plant height, single leaf area,and specific leaf area) and biomass allocations [i.e.,biomass allocations of roots, bulbs, leaves, stems, and flowers] at relatively low altitudinal ranges(3400 m to 3600 m asl) and high altitudinal ranges(3600 m to4000 m asl). Our results indicated that plant height,root biomass allocation, and stem biomass allocation significantly increased during the process of individual growth and development, but single leaf area, specific leaf area, bulb biomass allocation, and leaf biomass allocation showed opposite trends.Furthermore, the impacts of altitudinal changes on morphological traits and biomass allocations had no significant differences at low altitude, except for single leaf area of 2-year-old plants. At high altitude,significantly reduced plant height, single leaf area and leaf biomass allocation for the 2-year-old plants,specific leaf area for the 2-and 4-year-old plants, and stem biomass allocation were found along altitudinal gradients. Significantly increased sexual reproductive allocation and relatively stable single leaf area and leaf biomass allocation were also observed for the 3-and 4-year-old plants. In addition, stable specific leaf area for the 3-year-old plants and root biomass allocation were recorded. These results suggested that the adaptive adjustments of alpine plants, in particular F. unibracteata were simultaneously influenced by altitudinal gradients and ontogeny.展开更多
In order to investigate ecological adaptation mechanism of bryophyte,two dominant mosses Thuidium cymbifolium and Mnium immarginatum in Baotianman Nature Reserve were measured the content of C,N,P and their ratio in b...In order to investigate ecological adaptation mechanism of bryophyte,two dominant mosses Thuidium cymbifolium and Mnium immarginatum in Baotianman Nature Reserve were measured the content of C,N,P and their ratio in bryophyte and soil,and analyzed the relationships of plant and soil ecological stoichiometric characteristics along altitudinal gradients.Results indicate that the content of C,N and P in green tissues of T.cymbifolium and M.immarginatum in Baotianman Nature Reserve was 46.81%-49.09%,0.21%-0.25%,and0.02%-0.08%.Among the different altitudinal gradients,C,N and P displayed significant differences: the significantly different content of C and N were showed in T.cymbifolium,and the content of N and P differed significantly in M.immarginatum.However,only N declined obviously as increasing altitude.In soil,the C,N,N/P and C/P showed an increasing trend with increasing elevation,while the P and C/N along altitudinal gradients exhibited no unified trend.With the increasing in the content C,N of soil,the content C and N of T.cymbifolium raised,while the content C and N of M.immarginatum declined.With the rise in P element of soil,N/P showed different trends between two bryophyte species,the N/P in T.cymbifolium significantly decreased,while N/P in M.immarginatum significantly increased.In addition,mean value of leaf N/P was 8.51,ranking 14-16.These results suggested that the growth of the bryophyte plants in Baotianman Nature Reserve were restricted by N element,and different utilization strategies in soil P element in different bryophyte plants led to differences in ecological stoichiometric characteristics.展开更多
This study evaluates the structure and regeneration status of woody species in the Munessa Forest,a dry Afromontane forest in southern Ethiopia.Vegetation data were collected using a systematic sampling method.Density...This study evaluates the structure and regeneration status of woody species in the Munessa Forest,a dry Afromontane forest in southern Ethiopia.Vegetation data were collected using a systematic sampling method.Density and distribution of seedlings,saplings and mature trees were assessed along an altitudinal gradient using quadrats of different sizes.The number of individuals,frequencies,heights and DBH of species>1 m and DBH>2.5 cm were recorded in altitudinal bands of 100 m.Analysis of the vegetation structure shows that the density of woody species decreases as DBH and height class increases.Basal area of stems with DBH>2.5 cm was 53.4 m^(2)ha^(−1).Population structure and regeneration patterns indicate a significant degradation of the forest due to anthropogenic disturbances.Regeneration was better for less valuable woody species than for species with economic and ecological value.This suggests a discontinuous recruitment of these species due to selective cutting of middle and higher diameter classes.Therefore,enrichment planting of high value,endangered species is necessary to maintain them as part of this forest.There is a need to develop and implement an effective forest management plan for sustainable use of these forest resources.展开更多
Environmental changes along an altitudinal gradient can facilitate the differentiation of life-history features in ectothermic species,but little attention has been devoted to the reciprocal influence of altitude and ...Environmental changes along an altitudinal gradient can facilitate the differentiation of life-history features in ectothermic species,but little attention has been devoted to the reciprocal influence of altitude and alpine slope directionality on life-history variation.According to life-history theory,increased environmental stress causes a change in reproductive allocation from number to quality of offspring,as well as a stronger trade-off between size and number of offspring.To clarify the influence of environmental pressures on the life-history features of the Qinghai toad-headed lizard Phrynocephalus vlangalii along an altitudinal cline,we surveyed late pregnant females from 3 populations of low(2,600 m),middle(3,400 m),and high(3,600 m)elevations in the Dangjin Mountain of Gansu,China from July to October 2019,and compared their inter-population differences in maternal body size,reproductive characteristics,offspring growth,and locomotor performance.Because of lower temperatures,higher humidity,and lower light intensity caused by slope aspect and altitude,the middle-altitude region experienced stronger environmental stress than the high-and low-altitude regions.Our results showed that females were larger at middle-and high-altitude sites and smaller at the low-altitude site,following Bergmann’s rule.We also found that females from low-altitude population gave birth earlier than those from the middle and high altitudes.Our results showed a shift in the offspring size-number trade-off of P.vlangalii in response to colder and harsher environments,with lizards from the alpine steppe(i.e.the middle-and high-altitude habitats)producing fewer but larger offspring than those from the warm steppe(i.e.the low-altitude habitat).Low-altitude juveniles grew faster than high-altitude ones,but at the same rates as middle-altitude juveniles.This result demonstrates that the growth of P.vlangalii was associated with temperature and light intensity.Our findings contribute to enhancing our understanding of the altitudinal variation in life-history features of plateau ectotherms and their phenotypic plasticity or local adaptation.展开更多
Aims Increasing evidence worldwide indicates that high mountain regions are not immune to invasion by alien plants.Here,we aimed to address whether three major woody invaders of low-mountain areas are constrained to l...Aims Increasing evidence worldwide indicates that high mountain regions are not immune to invasion by alien plants.Here,we aimed to address whether three major woody invaders of low-mountain areas are constrained to lower altitudes due to climatic restrictions or just by low propagule pressure.We hypothesize that the increasing climatic harshness towards higher altitudes restricts seedling establishment and survival of these woody invaders and thus their potential for altitudinal expansion.Methods The study was carried out in the Sierras Grandes Mountains,Córdoba,central Argentina(32°50′S,64°90′W).We addressed the hypothesis with an experimental approach,dissociating the effect of the environmental gradient from that of propagule pressure,by discarding the influence of seed sources.We translocated seeds of Gleditsia triacanthos L.,Ligustrum lucidum W.T.Aiton.and Pyracantha angustifolia(Franch.)C.K.Schneid.along the altitudinal gradient(from 900 to 2700 m asl).Seven sites were selected along the altitudinal gradient,spaced every 200-400 m.Three plots(4×4 m)were selected within each altitudinal site and excluded from livestock;100 seeds of each species were sown within each plot(6300 seeds in total).Seedling emergence and survival was monitored during two growing seasons and soil temperature and moisture was recorded as well.The field experiment was complemented with lab assays.Important Findings Climate along this altitudinal gradient might be least restrictive at mid elevations,as a result of the intersection between opposite soil temperature and moisture gradients.Sown seeds germinated along the whole altitudinal gradient and seedlings successfully established and over-wintered well above their current altitudinal distribution(up to 2200 m for Ligustrum and 2400 m for Gleditsia and Pyracantha).Additional lab assays confirmed field patterns and gave some insights into contrasting regeneration strategies between these invaders that might help to overcome stochastic environmental constraints in the germination stage.Overall,seedlings of three major woody invaders of low-mountain woodlands can establish and survive at higher elevations than their current distribution.In contrast to natives,they seem to be broad climate tolerators,rather than specialized stress tolerators,capable of germinating and growing across a wide elevational range.While long-term experiments might be necessary to fully address the potentials for altitudinal expansion,out results on early lifecycle stage suggest that the invaders studied here would have mostly a dispersal barrier rather than a climate barrier to establish in the upper belt of the Sierras Grandes.展开更多
Aims The tropical conservatism hypothesis(TCH)links environmental tolerance,diversification,dispersal and evolutionary history in explaining why warm,wet tropical regions harbor more species than colder,drier regions....Aims The tropical conservatism hypothesis(TCH)links environmental tolerance,diversification,dispersal and evolutionary history in explaining why warm,wet tropical regions harbor more species than colder,drier regions.The TCH is considered as a dominant explanation for broad-scale patterns of species richness across the globe,such as the latitudinal diversity gradient.At its core,the TCH predicts a positive relationship between clade age and tempera-ture.Here,I test this prediction using a data set of angiosperm tree assemblages from Malesia.Methods I assembled an altitudinal gradient of 15 communities of angio-sperm trees.I calculated the mean family age(MFA)of tree species for each community.I used ordinary regression analysis and spatial autoregression analysis to determine the relationships of species richness and MFA with elevation,temperature and precipitation.I used correlation analysis to assess relationships between paired variables.Important Findings MFA is negatively correlated with tree species richness,and increases with elevation and decreases with temperature for the alti-tudinal gradient.MFA remains significantly increasing with decreas-ing temperature along the altitudinal gradient after accounting for spatial autocorrelation in a species-ordination space.The negative relationship between clade age and temperature along the altitudi-nal gradient in Malesia is contrary to the TCH.展开更多
Understanding the radial growth trends of trees and their response to recent warming along elevation gradients is crucial for assessing how forests will be impacted by future climate change.Here,we collected 242 tree-...Understanding the radial growth trends of trees and their response to recent warming along elevation gradients is crucial for assessing how forests will be impacted by future climate change.Here,we collected 242 tree-ring cores from five plots across the Qinghai spruce(Picea crassifolia Kom.)forest belt(2600–3350 m a.s.l.)in the central Qilian Mountains,Northwest China,to study trends in the radial growth of trees and their response to climate factors with variable elevation.All the sampled P.crassifolia chronologies showed an increasing trend in the radial growth of trees at higher altitudes(3000–3350 m),whereas the radial growth of trees at lower altitudes(2600–2800 m)has decreased in recent decades.The radial growth of trees was limited by precipitation at lower elevations(L,ML),but mainly by temperature at higher elevation sites(MH,H,TL).Climate warming has caused an unprecedented increase in the radial growth of P.crassifolia at higher elevations.Our results suggest that ongoing climate warming is beneficial to forest ecosystems at high elevations but restricts the growth of forest ecosystems at low elevations.展开更多
Aims In perennial species,the allocation of resources to reproduction results in a reduction of allocation to vegetative growth and,therefore,impacts future reproductive success.As a consequence,variation in this trad...Aims In perennial species,the allocation of resources to reproduction results in a reduction of allocation to vegetative growth and,therefore,impacts future reproductive success.As a consequence,variation in this trade-off is among the most important driving forces in the life-history evolution of perennial plants and can lead to locally adapted genotypes.In addition to genetic variation,phenotypic plasticity might also contribute to local adaptation of plants to local conditions by mediating changes in reproductive allocation.Knowledge on the importance of genetic and environmental effects on the tradeoff between reproduction and vegetative growth is therefore essential to understand how plants may respond to environmental changes.Methods We conducted a transplant experiment along an altitudinal gradient from 425to1921 min the frontrange of the Western Alps of Switzerland to assess the influence of both altitudinal origin of populations and altitude of growing site on growth,reproductive investment and local adaptation in Poa alpina.Important findings In our study,the investment in reproduction increased with plant size.Plant growth and the relative importance of reproductive investment decreased in populations originating from higher altitudes compared to populations originating from lower altitudes.The changes in reproductive investment were mainly explained by differences in plant size.In contrast to genetic effects,phenotypic plasticity of all traits measured was low and not related to altitude.As a result,the population from the lowest altitude of origin performed best at all sites.Our results indicate that in P.alpina genetic differences in growth and reproductive investment are related to local conditions affecting growth,i.e.interspecific competition and soil moisture content.展开更多
To describe the biodiversity patterns of plants along an altitudinal gradient on the Qinghai-Tibetan Plateau and to clarify the bias in plant specimen records at high altitude.Methods We conducted a large-scale invest...To describe the biodiversity patterns of plants along an altitudinal gradient on the Qinghai-Tibetan Plateau and to clarify the bias in plant specimen records at high altitude.Methods We conducted a large-scale investigation of vegetation at a wide range of altitudes,focusing on a high-altitudinal range(3200-5200 m)at different locations on the Qinghai-Tibetan Plateau.We then compared the altitudinal distribution of plant species obtained from our field investigation with that in plant specimen records from published sources and an online database.Important Findings Our data provide evidence that altitude plays a large role in regulating species composition on the Qinghai-Tibetan Plateau.We could not,however,detect a clear relationship between altitude and species richness,although a weak monotonically increasing trend of richness was detected with increasing altitude.According to specimen records,most species have been sampled at a wide range of altitudes,and the average range of 145 species is>2000 m.Despite this wide range,more than half of the species we observed were at higher altitudes than the specimen records indicate.High-altitude areas have probably been so poorly sampled that only a small fraction of the resident species has been recorded.This study clearly shows the regional bias of specimen records in the Qinghai-Tibetan Plateau.展开更多
Background:The relationship between climate and radial growth of trees exhibits spatial variation due to environ-mental changes.Therefore,elucidation of how the growth–climate responses of trees vary in space is esse...Background:The relationship between climate and radial growth of trees exhibits spatial variation due to environ-mental changes.Therefore,elucidation of how the growth–climate responses of trees vary in space is essential for understanding forest growth dynamics to facilitate scientific management with the ongoing global climate warming.To explore the altitudinal and slope variations of these interactions,tree-ring width chronologies of Larix olgensis A.Henry were analyzed in the southern Lesser Khingan Mountains,Northeast China.Results:The radial growth of L.olgensis exhibited significant 5-to 10-year periodic changes at three altitudes and two slopes,and the frequency change occurred mainly during the early growth stage and after 2000.The radial growth of L.olgensis was significantly negatively correlated with September precipitation only at low altitudes,but also with the mean temperature in July–August and the mean maximum temperature in June–August at high altitudes.The radial growth of L.olgensis at low and middle altitudes as well as on the sunny slope led to a higher demand for moisture,while temperature was the key limiting factor at high altitudes and on the shady slope.Conclusions:The climate–radial growth relationship of L.olgensis exhibits altitudinal and slope variability.This study quantitatively describes the spatially varying growth–climate responses of L.olgensis in the southern Lesser Khingan Mountains,which provides basic data for the management of L.olgensis forests and the prediction of future climate impacts on forest ecosystems.展开更多
Aims Several mechanistic hypotheses have been developed to explain the existence of alpine treelines worldwide.The reproduction limita-tion hypothesis(RLH)postulates that reproductive processes such as seed production...Aims Several mechanistic hypotheses have been developed to explain the existence of alpine treelines worldwide.The reproduction limita-tion hypothesis(RLH)postulates that reproductive processes such as seed production and dispersal are restricted in treeline envi-ronments,thereby limiting the establishment of new individuals in advance of extant treelines.Despite its popularity,no study has tested this hypothesis in a comprehensive fashion.In this experi-ment,we attempted to answer whether there are enough viable seeds being dispersed beyond treeline for sexually mediated tree-line advance,and what the implications of climate change might be on these processes.Methods We established 30 plots across two aspects(north vs.south)and three elevational habitats(forest,treeline and tundra)in a white spruce(Picea glauca)boreal forest-alpine tundra ecotone in south-west Yukon,Canada.In each plot,tree characteristics,seed produc-tion and predispersal damage were measured.Additionally,eight dispersal trays were positioned in each plot to measure seed rain,and germination trials with and without predation exclosures were constructed in a subset of plots to quantify dispersal and germina-tion success.Important Findings Results were highly variable both temporally and spatially.In 2014,a mast year,69%of adult trees produced cones compared to 0.4%in the following year.Higher density of trees in forest plots compared to treeline and tundra resulted in greater seed production at lower elevations.Across all plots,88%of seeds were damaged before dispersal or were not viable.Treeline plots had significantly greater predispersal damage.Seed rain was greater in south-facing plots than north-facing plots.Less than 2%of seeds produced on the landscape were dispersed into Tundra plots,located 50 m above treeline.There was a net movement of seeds from the north-facing slope to the south at our study site,likely due to prevailing winds during the dispersal period.Germination counts were more than double on north-facing slopes and one-third higher inside exclo-sures.Cumulatively,the results provide some evidence for the RLH.Collectively,the high amount of predispersal damage and non-viable seeds,variability associated with dispersal and significant seed predation can functionally influence treeline dynamics.These findings suggest that global treeline distribution models,which rely largely on temperature,may not be entirely accurate for predicting treeline advance-at least at finer temporal scales.Many stochas-tic factors need to align temporally for successful advance,which is likely to result in a lag of many decades between the period of temperature amelioration and an increased number of trees beyond extant treelines.展开更多
ndividuals that inhabit broad elevational ranges may experience unique environmental challenges.Because temperature decreases with increased elevation,the ectotherms living at high elevations have to manage limited ac...ndividuals that inhabit broad elevational ranges may experience unique environmental challenges.Because temperature decreases with increased elevation,the ectotherms living at high elevations have to manage limited activity time and high thermoregulatory effort.The resting metabolic rate(RMR)of a postabsorptive animal is related to its total energy requirements as well as many other fitness traits.Mesquite lizards(Sceloporus grammicus)living on La Malinche Volcano,Mexico,inhabit a wide elevational range with some populations apparently thriving above the tree line.We measured the RMR of lizards from different elevations(i.e.,2,600,3,200,and 4,100 m)at four ecologically relevant temperatures(i.e.,15,25,30,and 35°C)and found that RMR of mesquite lizards increased with temperature and body mass.More importantly,lizards from the high-elevation population had mass specific RMR that was higher at all temperatures.While the higher RMRs of high-elevation populations imply higher metabolic costs at a given temperature these lizards were also smaller.Both of these traits may allow these high elevation populations to thrive in the face of the thermal challenges imposed by their environment.展开更多
Sceloporus lizards depend on external heat to achieve their preferred temperature(Tsel)for performing physiological processes.Evidence both in the field and laboratory indicates that pregnant females of this Genus sel...Sceloporus lizards depend on external heat to achieve their preferred temperature(Tsel)for performing physiological processes.Evidence both in the field and laboratory indicates that pregnant females of this Genus select body temperatures(Tb)lower than 34℃ as higher temperatures may be lethal to embryos.Therefore,thermoregulation is crucial for successful embryo development.Given the increase in global air temperature,it is expected that the first compensatory response of species that inhabit tropical climates will be behavioral thermoregulation.We tested whether viviparous Sceloporus formosus group lizards in the wild exhibited differences in thermoregulatory behavior to achieve the known Tsel for developing embryos regardless of local thermal conditions.We quantified field active body temperature,thermoregulatory behavior mechanisms(time of sighting,microhabitat used and basking time)and available microhabitat thermal conditions(i.e.operative temperature)for 10 lizard species during gestation,distributed along an altitudinal gradient.We applied both conventional and phylogenic analyses to explore whether Tb or behavioral thermoregulation could be regulated in response to different thermal conditions.These species showed no significant differences in field Tb during gestation regardless of local thermal conditions.In contrast,they exhibited significant differences in their behavioral thermoregulation associated with local environmental conditions.Based on these observations,the differences in thermoregulatory behavior identified are interpreted as compensatory adjustments to local thermal conditions.We conclude that these species may deal with higher temperatures predicted for the tropics by modulating their thermoregulatory behavior.展开更多
基金This research was funded by National Key Research and Development Program of China(No.2018YFA0605601)National Natural Science Foundation of China(No.42077417,41671042).
文摘A set of standard chronologies for tree-ring width(TRW),earlywood width(EWW)and latewood width(LWW)in Pinus tabuliformis Carr.along an altitudi-nal gradient(1450,1400,and 1350 m a.s.l.)on Baiyunshan Mountain,Central China to analyze the effect of varying temperature and precipitation on growth along the gradi-ent.Correlation analyses showed that at all three altitudes and the TRW and EWW chronologies generally had signifi-cant negative correlations with mean and maximum tem-peratures in the current April and May and with minimum temperatures in the prior July and August,but significant positive correlations with precipitation in the current May.Correlations were generally significantly negative between LWW chronologies and all temperatures in the prior July and August,indicating that the prior summer temperature had a strong lag effect on the growth of P.tabuliformis that increased with altitude.The correlation with the standard-ized precipitation evapotranspiration index(SPEI)confirmed that wet conditions in the current May promoted growth of TR and EW at all altitudes.Significant altitudinal differences were also found;at 1400 m,there were significant positive correlations between EWW chronologies and SPEI in the current April and significant negative correlations between LWW chronologies and SPEI in the current September,but these correlations were not significant at 1450 m.At 1350 m,there were also significant negative correlations between the TRW and the EWW chronologies and SPEI in the prior October and the current July and between LWW chronology and SPEI in the current August,but these cor-relations were not significant at 1400 m.Moving correlation results showed a stable response of EWW in relation to the SPEI in the current May at all three altitudes and of LWW to maximum temperature in the prior July-August at 1400 m from 2002 to 2018.The EWW chronology at 1400 m and the LWW chronology at 1450 m were identified as more suitable for climate reconstruction.These results provide a strong scientific basis for forest management decisions and climate reconstructions in Central China.
文摘Kigezi highlands currently experiences changes in precipitation and temperature which modify the evaporation and soil moisture storage leading to alterations in runoff and other components of hydrological systems. Extreme events, like floods and droughts, are more intense and frequent. Furthermore heavy unpredictable rainfall has become frequent in the area, causing soil erosion and floods that destroy crops. Soil erosion is particularly a pressing challenge due to steep-sided hills leading to deterioration of soil nutrients including soil fertility. The unpredictable rains and droughts are attributed to climate change and variability. Consequently, climate change and variability have caused a significant impact on soil nutrients which have affected the agricultural productivity in the area. This paper presents findings of empirical study which explored the climate variability and soil nutrient status along altitudinal gradient. The paper particularly addresses key questions of: land management practices in the study area, nutrient availability and their effects on productivity of selected crops along altitudinal gradient in changing climate and variability. Independent variables such as topographic sequence along altitudinal gradient were evaluated against dependent variables such as yield harvests of selected grown crops and soil nutrients. Samples for crop yields were collected along transect of 0.5 kilometer using a quadrant of 4 × 4 m<sup>2</sup> along attitudinal gradient. Soil samples were taken from selected plots at 0-20cm soil depth for nutrient analysis. Analysis of physical and chemical soil parameters was carried out on soil samples and these include: soil pH, soil organic content, total nitrogen, available soil phosphorous and exchangeable bases (Ca, Mg, K and Na). The study showed that middle parts of the transects had the highest concentration of most soil nutrients, probably because the middle parts could have been a deposition centre for some organic matter from the upper parts of the hills, and lower lying areas were being affected by floods that affects the decomposition of organic matter which is the main source of nutrients. Similarly, the middle parts of the study were the most fertile due to the high concentration of soil nutrient compositions. This indicates that crop yields were significantly affected by availability of soil nutrients along same gradient, attributable to the severity in soil erosion, nutrients leaching and farming practices.
基金the University grant Commission, Kathmandu Nepal for partial financial assistance (Sand T 23-2076/77)
文摘Regeneration status of tree species along elevation gradient in temperate hill forest was not understood greatly.Present research examined the tree diversity and its regeneration patterns along an elevation gradient in temperate hill forest,central Nepal.Data were collected from 300 sample plots within vertical elevation bands of 10,ranging from 1365 to 2450 m asl.A random sampling method was used for data collection in three seasons,winter,pre-monsoon and post monsoon seasons.Diameter at breast height(DBH)was used to broadly categorize the plant individual into trees,saplings and seedlings.The tree species richness ranged from 12 to 25 with density of 350 to 1200 individuals per hectare.Species richness of tree and sapling showed statistically significant unimodal pattern,which peaked at mid-elevation.Elevation showed a strong and positive linear correlation with the seedling density(Deviance=0.99,p<0.001)and a significant hump-shaped relationship with sapling density(Deviance=0.95,p<0.001).Similarly,elevations showed a statistically significant negative hump-shaped relationship with all trees,saplings and seedling stages(Deviances=0.89,0.87 and 0.57).The highest values of the Shannon-Wiener index and the lowest value of the Simpson index were found at mid-elevation for all growth forms.Nearly 92%of tree species were found at regenerating stage;49%in a good renewal regeneration status,32%in fair renewal regeneration,and 11%at a poor regenerating condition.Nevertheless,4%of tree species were reported as non-regenerating stages and 4%were newly introduced species.Hence,the regeneration status of the study area was considered fairly well since sapling(78.5%)>seedling(10.6%)≤mature(10.9%).Among tested environmental variables,elevation and annual mean rainfall were the most influential factors in the regeneration of tree species.
基金This work was supported by the National Natural Science Foundation of China(31370620 and 31321061)the State Scholarship Fund of China(2011811457).
文摘Aims Process-based models are basic tools for predicting the response of forest carbon to future climate change.The models have commonly been tested for their predictions of spatial variation in forest produc-tivity,but much less for their ability to predict temporal variation.Here,we explored methods to test the models with tree rings,using BIOME-BGC as an example.Methods We used net primary productivity(NPP)data and tree rings col-lected from five major forest types along the altitudinal gradient of Mt.Changbai,northeast China,to test local-parameterized BIOME-BGC model.We first test the model’s predictions of both spatial(Test 1)and temporal changes(Test 2)in productivity.Then we test if the model can detect the climatic factors limiting forest productiv-ity during historical climate change,as revealed by dendroclimatic analyses(Test 3).Important Findings Our results showed that BIOME-BGC could well simulate NPP of five forest types on Mt.Changbai,with an r^(2) of 0.69 between mod-eled and observed NPP for 17 plots along the altitudinal gradient(Test 1).Meanwhile,modeled NPP and ring-width indices were cor-related and showed similar temporal trends for each forest type(Test 2).While these tests suggest that the model’s predictions on spatial and temporal variation of NPP were acceptable,a further test that relate the correlations of modeled NPP with climate variables to the correlations of ring widths with climate(Test 3)showed that the model did not well identify the climatic factors limiting historical productivity dynamics for some forest types,and thus cannot reli-ably predict their future.Both dendrochronology and BIOME-BGC showed that forest types differed markedly in the climate factors limiting productivity because of differences in tree species and cli-mate condition,and thus differed in responses to climate change.Our results showed that a successful prediction of spatial NPP pat-terns cannot assure that BIOME-BGC can well simulate histori-cal NPP dynamics.Further,a correlation between modeled NPP and tree-ring series cannot assure that the limiting climatic factors for productivity have been correctly identified by the model.Our results suggest the necessity to test the temporal predictions of pro-cess-based models in a more robust way,and further integration of dendrochronology and biogeochemistry modeling may be helpful for this purpose.
基金funded by the Natural Science Foundation Project of Sichuan Science and Technology Department (2018JY0305)Key Projects of the Natural Science Foundation of Sichuan Education Department (18ZA0002)
文摘Environmental variations and ontogeny may affect plant morphological traits and biomass allocation patterns that are related to the adjustments of plant ecological strategies. We selected 2-, 3-and 4-year-old Fritillaria unibracteata plants to explore the ontogenetic and altitudinal changes that impact their morphological traits(i.e., plant height, single leaf area,and specific leaf area) and biomass allocations [i.e.,biomass allocations of roots, bulbs, leaves, stems, and flowers] at relatively low altitudinal ranges(3400 m to 3600 m asl) and high altitudinal ranges(3600 m to4000 m asl). Our results indicated that plant height,root biomass allocation, and stem biomass allocation significantly increased during the process of individual growth and development, but single leaf area, specific leaf area, bulb biomass allocation, and leaf biomass allocation showed opposite trends.Furthermore, the impacts of altitudinal changes on morphological traits and biomass allocations had no significant differences at low altitude, except for single leaf area of 2-year-old plants. At high altitude,significantly reduced plant height, single leaf area and leaf biomass allocation for the 2-year-old plants,specific leaf area for the 2-and 4-year-old plants, and stem biomass allocation were found along altitudinal gradients. Significantly increased sexual reproductive allocation and relatively stable single leaf area and leaf biomass allocation were also observed for the 3-and 4-year-old plants. In addition, stable specific leaf area for the 3-year-old plants and root biomass allocation were recorded. These results suggested that the adaptive adjustments of alpine plants, in particular F. unibracteata were simultaneously influenced by altitudinal gradients and ontogeny.
基金Supported by Supported by Scientific research foundation of Nanyang Normal University(zx2012015)Foundation of Henan Educational Committee(13A180817)Foundation and Advanced Technology Research Program of Henan Province(142300410453)
文摘In order to investigate ecological adaptation mechanism of bryophyte,two dominant mosses Thuidium cymbifolium and Mnium immarginatum in Baotianman Nature Reserve were measured the content of C,N,P and their ratio in bryophyte and soil,and analyzed the relationships of plant and soil ecological stoichiometric characteristics along altitudinal gradients.Results indicate that the content of C,N and P in green tissues of T.cymbifolium and M.immarginatum in Baotianman Nature Reserve was 46.81%-49.09%,0.21%-0.25%,and0.02%-0.08%.Among the different altitudinal gradients,C,N and P displayed significant differences: the significantly different content of C and N were showed in T.cymbifolium,and the content of N and P differed significantly in M.immarginatum.However,only N declined obviously as increasing altitude.In soil,the C,N,N/P and C/P showed an increasing trend with increasing elevation,while the P and C/N along altitudinal gradients exhibited no unified trend.With the increasing in the content C,N of soil,the content C and N of T.cymbifolium raised,while the content C and N of M.immarginatum declined.With the rise in P element of soil,N/P showed different trends between two bryophyte species,the N/P in T.cymbifolium significantly decreased,while N/P in M.immarginatum significantly increased.In addition,mean value of leaf N/P was 8.51,ranking 14-16.These results suggested that the growth of the bryophyte plants in Baotianman Nature Reserve were restricted by N element,and different utilization strategies in soil P element in different bryophyte plants led to differences in ecological stoichiometric characteristics.
基金supported by the National Key R&D Program of China(2017YFD0600600).
文摘This study evaluates the structure and regeneration status of woody species in the Munessa Forest,a dry Afromontane forest in southern Ethiopia.Vegetation data were collected using a systematic sampling method.Density and distribution of seedlings,saplings and mature trees were assessed along an altitudinal gradient using quadrats of different sizes.The number of individuals,frequencies,heights and DBH of species>1 m and DBH>2.5 cm were recorded in altitudinal bands of 100 m.Analysis of the vegetation structure shows that the density of woody species decreases as DBH and height class increases.Basal area of stems with DBH>2.5 cm was 53.4 m^(2)ha^(−1).Population structure and regeneration patterns indicate a significant degradation of the forest due to anthropogenic disturbances.Regeneration was better for less valuable woody species than for species with economic and ecological value.This suggests a discontinuous recruitment of these species due to selective cutting of middle and higher diameter classes.Therefore,enrichment planting of high value,endangered species is necessary to maintain them as part of this forest.There is a need to develop and implement an effective forest management plan for sustainable use of these forest resources.
基金Thiswork was supported,by the Strategic Priority Research Program of the Chinese Academy of Sciences(XDA20050201)the National Natural Science Fund of China(31861143023).
文摘Environmental changes along an altitudinal gradient can facilitate the differentiation of life-history features in ectothermic species,but little attention has been devoted to the reciprocal influence of altitude and alpine slope directionality on life-history variation.According to life-history theory,increased environmental stress causes a change in reproductive allocation from number to quality of offspring,as well as a stronger trade-off between size and number of offspring.To clarify the influence of environmental pressures on the life-history features of the Qinghai toad-headed lizard Phrynocephalus vlangalii along an altitudinal cline,we surveyed late pregnant females from 3 populations of low(2,600 m),middle(3,400 m),and high(3,600 m)elevations in the Dangjin Mountain of Gansu,China from July to October 2019,and compared their inter-population differences in maternal body size,reproductive characteristics,offspring growth,and locomotor performance.Because of lower temperatures,higher humidity,and lower light intensity caused by slope aspect and altitude,the middle-altitude region experienced stronger environmental stress than the high-and low-altitude regions.Our results showed that females were larger at middle-and high-altitude sites and smaller at the low-altitude site,following Bergmann’s rule.We also found that females from low-altitude population gave birth earlier than those from the middle and high altitudes.Our results showed a shift in the offspring size-number trade-off of P.vlangalii in response to colder and harsher environments,with lizards from the alpine steppe(i.e.the middle-and high-altitude habitats)producing fewer but larger offspring than those from the warm steppe(i.e.the low-altitude habitat).Low-altitude juveniles grew faster than high-altitude ones,but at the same rates as middle-altitude juveniles.This result demonstrates that the growth of P.vlangalii was associated with temperature and light intensity.Our findings contribute to enhancing our understanding of the altitudinal variation in life-history features of plateau ectotherms and their phenotypic plasticity or local adaptation.
基金Fondo para la Investigación Científica y Tecnológica FONCyT(BID PICT 953)Consejo Nacional de Investigaciones Científicas y Técnicas(CONiCET)(PIP 1286)+2 种基金the Inter-American Institute for Global Change Research(CRN II 2005supported by the US National Science Foundation Inter-American Institute for Global Change Research(IAI)Grant GEO-0452325)Secretaría de Ciencia y Tecnología-Universidad Nacional de Córdoba(Secyt)(Universidad Nacional de Córdoba).
文摘Aims Increasing evidence worldwide indicates that high mountain regions are not immune to invasion by alien plants.Here,we aimed to address whether three major woody invaders of low-mountain areas are constrained to lower altitudes due to climatic restrictions or just by low propagule pressure.We hypothesize that the increasing climatic harshness towards higher altitudes restricts seedling establishment and survival of these woody invaders and thus their potential for altitudinal expansion.Methods The study was carried out in the Sierras Grandes Mountains,Córdoba,central Argentina(32°50′S,64°90′W).We addressed the hypothesis with an experimental approach,dissociating the effect of the environmental gradient from that of propagule pressure,by discarding the influence of seed sources.We translocated seeds of Gleditsia triacanthos L.,Ligustrum lucidum W.T.Aiton.and Pyracantha angustifolia(Franch.)C.K.Schneid.along the altitudinal gradient(from 900 to 2700 m asl).Seven sites were selected along the altitudinal gradient,spaced every 200-400 m.Three plots(4×4 m)were selected within each altitudinal site and excluded from livestock;100 seeds of each species were sown within each plot(6300 seeds in total).Seedling emergence and survival was monitored during two growing seasons and soil temperature and moisture was recorded as well.The field experiment was complemented with lab assays.Important Findings Climate along this altitudinal gradient might be least restrictive at mid elevations,as a result of the intersection between opposite soil temperature and moisture gradients.Sown seeds germinated along the whole altitudinal gradient and seedlings successfully established and over-wintered well above their current altitudinal distribution(up to 2200 m for Ligustrum and 2400 m for Gleditsia and Pyracantha).Additional lab assays confirmed field patterns and gave some insights into contrasting regeneration strategies between these invaders that might help to overcome stochastic environmental constraints in the germination stage.Overall,seedlings of three major woody invaders of low-mountain woodlands can establish and survive at higher elevations than their current distribution.In contrast to natives,they seem to be broad climate tolerators,rather than specialized stress tolerators,capable of germinating and growing across a wide elevational range.While long-term experiments might be necessary to fully address the potentials for altitudinal expansion,out results on early lifecycle stage suggest that the invaders studied here would have mostly a dispersal barrier rather than a climate barrier to establish in the upper belt of the Sierras Grandes.
文摘Aims The tropical conservatism hypothesis(TCH)links environmental tolerance,diversification,dispersal and evolutionary history in explaining why warm,wet tropical regions harbor more species than colder,drier regions.The TCH is considered as a dominant explanation for broad-scale patterns of species richness across the globe,such as the latitudinal diversity gradient.At its core,the TCH predicts a positive relationship between clade age and tempera-ture.Here,I test this prediction using a data set of angiosperm tree assemblages from Malesia.Methods I assembled an altitudinal gradient of 15 communities of angio-sperm trees.I calculated the mean family age(MFA)of tree species for each community.I used ordinary regression analysis and spatial autoregression analysis to determine the relationships of species richness and MFA with elevation,temperature and precipitation.I used correlation analysis to assess relationships between paired variables.Important Findings MFA is negatively correlated with tree species richness,and increases with elevation and decreases with temperature for the alti-tudinal gradient.MFA remains significantly increasing with decreas-ing temperature along the altitudinal gradient after accounting for spatial autocorrelation in a species-ordination space.The negative relationship between clade age and temperature along the altitudi-nal gradient in Malesia is contrary to the TCH.
基金National Natural Science Foundation of China,No.41790422The Second Tibetan Plateau Scientific Expedition and Research Program(STEP),No.2019QZKK0301+3 种基金The National Key Research&Development(R&D)Program of China,No.2019YFC0507401National Natural Science Foundation of China,No.41801018The 111 Project,No.BP0618001The Foundation for Excellent Youth Scholars of“Northwest Institute of Eco-Environment and Resources”,CAS,No.FEYS2019004。
文摘Understanding the radial growth trends of trees and their response to recent warming along elevation gradients is crucial for assessing how forests will be impacted by future climate change.Here,we collected 242 tree-ring cores from five plots across the Qinghai spruce(Picea crassifolia Kom.)forest belt(2600–3350 m a.s.l.)in the central Qilian Mountains,Northwest China,to study trends in the radial growth of trees and their response to climate factors with variable elevation.All the sampled P.crassifolia chronologies showed an increasing trend in the radial growth of trees at higher altitudes(3000–3350 m),whereas the radial growth of trees at lower altitudes(2600–2800 m)has decreased in recent decades.The radial growth of trees was limited by precipitation at lower elevations(L,ML),but mainly by temperature at higher elevation sites(MH,H,TL).Climate warming has caused an unprecedented increase in the radial growth of P.crassifolia at higher elevations.Our results suggest that ongoing climate warming is beneficial to forest ecosystems at high elevations but restricts the growth of forest ecosystems at low elevations.
基金Swiss National Science Foundation(grant 110000 to A.G.)the European Commission(FP6 projects MACIS and ECOCHANGE).
文摘Aims In perennial species,the allocation of resources to reproduction results in a reduction of allocation to vegetative growth and,therefore,impacts future reproductive success.As a consequence,variation in this trade-off is among the most important driving forces in the life-history evolution of perennial plants and can lead to locally adapted genotypes.In addition to genetic variation,phenotypic plasticity might also contribute to local adaptation of plants to local conditions by mediating changes in reproductive allocation.Knowledge on the importance of genetic and environmental effects on the tradeoff between reproduction and vegetative growth is therefore essential to understand how plants may respond to environmental changes.Methods We conducted a transplant experiment along an altitudinal gradient from 425to1921 min the frontrange of the Western Alps of Switzerland to assess the influence of both altitudinal origin of populations and altitude of growing site on growth,reproductive investment and local adaptation in Poa alpina.Important findings In our study,the investment in reproduction increased with plant size.Plant growth and the relative importance of reproductive investment decreased in populations originating from higher altitudes compared to populations originating from lower altitudes.The changes in reproductive investment were mainly explained by differences in plant size.In contrast to genetic effects,phenotypic plasticity of all traits measured was low and not related to altitude.As a result,the population from the lowest altitude of origin performed best at all sites.Our results indicate that in P.alpina genetic differences in growth and reproductive investment are related to local conditions affecting growth,i.e.interspecific competition and soil moisture content.
文摘To describe the biodiversity patterns of plants along an altitudinal gradient on the Qinghai-Tibetan Plateau and to clarify the bias in plant specimen records at high altitude.Methods We conducted a large-scale investigation of vegetation at a wide range of altitudes,focusing on a high-altitudinal range(3200-5200 m)at different locations on the Qinghai-Tibetan Plateau.We then compared the altitudinal distribution of plant species obtained from our field investigation with that in plant specimen records from published sources and an online database.Important Findings Our data provide evidence that altitude plays a large role in regulating species composition on the Qinghai-Tibetan Plateau.We could not,however,detect a clear relationship between altitude and species richness,although a weak monotonically increasing trend of richness was detected with increasing altitude.According to specimen records,most species have been sampled at a wide range of altitudes,and the average range of 145 species is>2000 m.Despite this wide range,more than half of the species we observed were at higher altitudes than the specimen records indicate.High-altitude areas have probably been so poorly sampled that only a small fraction of the resident species has been recorded.This study clearly shows the regional bias of specimen records in the Qinghai-Tibetan Plateau.
基金supported by the National Natural Science Foundation of China(Grant No.31870620)the Fundamental Research Funds for the Central Universities(Grant No.PTYX202107).
文摘Background:The relationship between climate and radial growth of trees exhibits spatial variation due to environ-mental changes.Therefore,elucidation of how the growth–climate responses of trees vary in space is essential for understanding forest growth dynamics to facilitate scientific management with the ongoing global climate warming.To explore the altitudinal and slope variations of these interactions,tree-ring width chronologies of Larix olgensis A.Henry were analyzed in the southern Lesser Khingan Mountains,Northeast China.Results:The radial growth of L.olgensis exhibited significant 5-to 10-year periodic changes at three altitudes and two slopes,and the frequency change occurred mainly during the early growth stage and after 2000.The radial growth of L.olgensis was significantly negatively correlated with September precipitation only at low altitudes,but also with the mean temperature in July–August and the mean maximum temperature in June–August at high altitudes.The radial growth of L.olgensis at low and middle altitudes as well as on the sunny slope led to a higher demand for moisture,while temperature was the key limiting factor at high altitudes and on the shady slope.Conclusions:The climate–radial growth relationship of L.olgensis exhibits altitudinal and slope variability.This study quantitatively describes the spatially varying growth–climate responses of L.olgensis in the southern Lesser Khingan Mountains,which provides basic data for the management of L.olgensis forests and the prediction of future climate impacts on forest ecosystems.
文摘Aims Several mechanistic hypotheses have been developed to explain the existence of alpine treelines worldwide.The reproduction limita-tion hypothesis(RLH)postulates that reproductive processes such as seed production and dispersal are restricted in treeline envi-ronments,thereby limiting the establishment of new individuals in advance of extant treelines.Despite its popularity,no study has tested this hypothesis in a comprehensive fashion.In this experi-ment,we attempted to answer whether there are enough viable seeds being dispersed beyond treeline for sexually mediated tree-line advance,and what the implications of climate change might be on these processes.Methods We established 30 plots across two aspects(north vs.south)and three elevational habitats(forest,treeline and tundra)in a white spruce(Picea glauca)boreal forest-alpine tundra ecotone in south-west Yukon,Canada.In each plot,tree characteristics,seed produc-tion and predispersal damage were measured.Additionally,eight dispersal trays were positioned in each plot to measure seed rain,and germination trials with and without predation exclosures were constructed in a subset of plots to quantify dispersal and germina-tion success.Important Findings Results were highly variable both temporally and spatially.In 2014,a mast year,69%of adult trees produced cones compared to 0.4%in the following year.Higher density of trees in forest plots compared to treeline and tundra resulted in greater seed production at lower elevations.Across all plots,88%of seeds were damaged before dispersal or were not viable.Treeline plots had significantly greater predispersal damage.Seed rain was greater in south-facing plots than north-facing plots.Less than 2%of seeds produced on the landscape were dispersed into Tundra plots,located 50 m above treeline.There was a net movement of seeds from the north-facing slope to the south at our study site,likely due to prevailing winds during the dispersal period.Germination counts were more than double on north-facing slopes and one-third higher inside exclo-sures.Cumulatively,the results provide some evidence for the RLH.Collectively,the high amount of predispersal damage and non-viable seeds,variability associated with dispersal and significant seed predation can functionally influence treeline dynamics.These findings suggest that global treeline distribution models,which rely largely on temperature,may not be entirely accurate for predicting treeline advance-at least at finer temporal scales.Many stochas-tic factors need to align temporally for successful advance,which is likely to result in a lag of many decades between the period of temperature amelioration and an increased number of trees beyond extant treelines.
基金from CONACyT(MP)and the Catedras CONA-CyT program(ADP,883)the Secretaría de Medio Ambiente y Recursos Naturales for providing the collecting permits(SGPA/DGVS/15396/15 and SGPA/DGVS/007736/18).
文摘ndividuals that inhabit broad elevational ranges may experience unique environmental challenges.Because temperature decreases with increased elevation,the ectotherms living at high elevations have to manage limited activity time and high thermoregulatory effort.The resting metabolic rate(RMR)of a postabsorptive animal is related to its total energy requirements as well as many other fitness traits.Mesquite lizards(Sceloporus grammicus)living on La Malinche Volcano,Mexico,inhabit a wide elevational range with some populations apparently thriving above the tree line.We measured the RMR of lizards from different elevations(i.e.,2,600,3,200,and 4,100 m)at four ecologically relevant temperatures(i.e.,15,25,30,and 35°C)and found that RMR of mesquite lizards increased with temperature and body mass.More importantly,lizards from the high-elevation population had mass specific RMR that was higher at all temperatures.While the higher RMRs of high-elevation populations imply higher metabolic costs at a given temperature these lizards were also smaller.Both of these traits may allow these high elevation populations to thrive in the face of the thermal challenges imposed by their environment.
基金supported by the Programa de Apoyo a Proyectos de Investigación e Innovación Tecnológica(PAPIIT)of the Universidad Nacional Autónoma de México(Project number:IN221208)the Consejo Nacional para la Ciencia y la Tecnología(CONACYT)and also partially supported by a National Science Foundation grant(DEB-0416160[ENS])An Instituto Bioclon(ENS)Permit for field work in all locations was issued by Secretaria de Medio Ambiente y Recursos Naturales(SEMARNAT GPA/DGVS/04949).
文摘Sceloporus lizards depend on external heat to achieve their preferred temperature(Tsel)for performing physiological processes.Evidence both in the field and laboratory indicates that pregnant females of this Genus select body temperatures(Tb)lower than 34℃ as higher temperatures may be lethal to embryos.Therefore,thermoregulation is crucial for successful embryo development.Given the increase in global air temperature,it is expected that the first compensatory response of species that inhabit tropical climates will be behavioral thermoregulation.We tested whether viviparous Sceloporus formosus group lizards in the wild exhibited differences in thermoregulatory behavior to achieve the known Tsel for developing embryos regardless of local thermal conditions.We quantified field active body temperature,thermoregulatory behavior mechanisms(time of sighting,microhabitat used and basking time)and available microhabitat thermal conditions(i.e.operative temperature)for 10 lizard species during gestation,distributed along an altitudinal gradient.We applied both conventional and phylogenic analyses to explore whether Tb or behavioral thermoregulation could be regulated in response to different thermal conditions.These species showed no significant differences in field Tb during gestation regardless of local thermal conditions.In contrast,they exhibited significant differences in their behavioral thermoregulation associated with local environmental conditions.Based on these observations,the differences in thermoregulatory behavior identified are interpreted as compensatory adjustments to local thermal conditions.We conclude that these species may deal with higher temperatures predicted for the tropics by modulating their thermoregulatory behavior.
