Bioclimatic Gradient Research Articles

Plant functional indicators of vegetation response to climate change, past present and future: II. Modal plant functional types as response indicators for present and future climates

An assessment of plant functional indicators of vegetation response to climate change requires a science-based evaluation of functional linkages between plants and climate. This paper addresses the hypotheses outlined in the preceding paper: 1) A whole-plant system of modal plant functional types (PFTs) based on a core set of functional traits can provide an improved alternative to PFTs and traits used so far in models of vegetation response to climate change; 2) Modal PFTs are more efficient indicators of vegetation response to climate change than individual traits; 3) Improved plant functional selection criteria can lead to improved parameters in Earth System and Dynamic Global Vegetation Models. Present-day (1975 centred) plant–climate relationships were analyzed within a global climatic framework of 1327 (200 m2) sample sites covering all major biomes. Five regions were selected for their range of bioclimatic gradients (arctic-boreal; cool temperate-subtropical; humid equatorial; hot, cold deserts). Biophysical site data were recorded along gradient oriented transects (gradsects) using a standard protocol that included all vascular plant taxa and modal PFTs. Regression, ordination and species distribution modeling were used to assess plant–climate indicator values against ten bioclimatic variables including extremes of contemporary thermal, light (energy) and moisture availability and estimates for ‘present’ (1975) and year 2100 climate scenarios. Modal PFTs and individual traits were highly correlated in differing patterns with bioclimate in each of the five regions in both climate scenarios with PFTs being the best predictors. Each of the three hypotheses is supported by these results, indicating that preference should be given to modal assemblages rather than individual traits as response parameters in predictive vegetation models. The indicators identified here are but one element of the highly complex array of other factors that influence vegetation response to terrestrial environmental change such as resource use, species acclimation, invasive species and human population pressure.

A floristic-ecological classification of the shrublands of the dry Bolivian Altiplano

Aims: To identify shrubland types of the Bolivian Altiplano based on their floristic composition and on ecological factors. Location: Central and southern Bolivian Altiplano (Bolivia, central-western South America). Methods: Vascular plants were recorded in a field survey of 101 releves (10 m2). Releves were subjected to hierarchical agglomerative classification to define numerical vegetation groups. Classification techniques were based on the β-flexible linkage method (β = -0.25) with Sorensen distance. The highest crispness values defined the level of the main number of clusters identified. Diagnostic species were identified by means of the phi coefficient of fidelity. Canonical Correspondence Analysis, the Kruskal-Wallis test and a Z test were performed to assess the key ecological drivers of diversity in the Altiplano shrubland vegetation. Results: Based on numerical analyses of phytosociological releves, our work proposes four vegetation types of shrublands in the dry central and southern Bolivian Altiplano. They correspond to the following: tolillares – thickets of Fabiana densa – of the central-southern Altiplano with Junellia seriphioides; tolillares of the central-northern Altiplano with Lobivia pentlandii; lampayares – thickets of Lampayo castellani – with Parastrephia quadrangularis; and tolares – thickets of Parastrephia sp. pl. – with Parastrephia lepidophylla and Junellia minima. The bioclimatic variables were the ones best explaining the distribution patterns of the shrubland vegetation in the dry Bolivian Altiplano. Specifically, they separate the tolillares of the central-northern Altiplano with Lobivia pentlandii – at localities with a higher annual precipitation, annual ombrothermic index, and ombrothermic index of the wettest quarter – from the tolillares of the central-southern Altiplano with Junellia seriphioides. These bioclimatic gradients also position lampayares at localities with a lower than average value of annual precipitation, annual ombrothermic index, and ombrothermic index of the wettest quarter. Significant differences were found when comparing the topographic position, the degree of soil drainage and the frequency of flooding between the vegetation of tolillares on the one hand, and the vegetation of lampayares and tolares, on the other. Lampayares were exclusively related to sandy soils. Conclusions: Our four groups characterize variation within the habitat and elucidate bioclimatic gradients and soil features with related habitats. This knowledge could provide basic information on the vulnerability of different Altiplano shrubland habitats to climatic fluctuations, as this area is highly vulnerable to extreme periods of drought associated with the regional effects of climate change as well as to anthropogenic factors. Taxonomic reference: Bolivia Catalogue (2014; http://www.tropicos.org/Project/BC). Syntaxonomic reference: Navarro (1993, 2002, 2011). Abbreviations: CCA = Canonical correspondence analysis; Io = annual ombrothermic index; Iod = ombrothermic index of the driest quarter; Iow = ombrothermic index of the wettest quarter; Tw = mean temperature of the wettest quarter.

Pattern of scorpion diversity across a bioclimatic dry-wet gradient in Neotropical forests

Understanding large-scale patterns of biological diversity is one of the most important issues in ecology. Parameters of scorpion assemblages may serve as a proxy to understand how arthropods respond to bioclimatic changes by adjusting their spatially structured distribution. We analysed how scorpion species richness, abundance, and composition respond to climatic variations found along a longitudinal gradient between wet (Atlantic Forest) and dry (Caatinga hypo and hyperxerophilic) forests in Brazil. A total of 20 sites were sampled four times along a 712 km longitudinal wet-dry bioclimatic gradient in north-eastern Brazil. We recorded 2653 scorpions from 12 species, belonging to five genera and two families. Environmental variables associated with precipitation and temperature had a strong effect on scorpion distribution, resulting in a distinct faunal composition at both extremes of the gradient. Species composition presented a turnover along the bioclimatic gradient, with beta diversity increasing towards the drier sites. The increase of dryness coincide with increases in temperature, moisture reduction, and a general environmental harshness. Our study, therefore, indicates that species sensitivity to climatic variation determines scorpion distribution in Neotropical forests.

Consistent sorting but contrasting transition zones in plant communities along bioclimatic gradients

Correlations between plant species occurrences and climate are used as evidence of ecological sorting and climate sensitivity. However, because observed patterns may be spatially and historically contingent, interpretations of compositional responses to spatial differences in climate should ideally consider past climatic fluctuations, edaphic factors, nonlinear turnover rates and transition zones (ecotones) in environmental and geographic space. We tested whether drivers of plant community compositional turnover and transition zones are consistent, rather than spatially contingent, across spatially isolated and biologically contrasting (independent) ecosystems. We used four broad-scale transects in Australia, which are spatially isolated and climatically and ecologically diverse: NATT (Northern Territory); BATS (New South Wales); SWATT (Western Australia) and TREND (South Australia). We used Generalised Dissimilarity Modelling to ascertain the relative contributions of space (geographic distance) and environmental variables to compositional turnover. We mapped transition zones using modelled nonlinear responses. Purely spatial contributions were estimated using variance partitioning. Models explained 26–52% of deviance in compositional dissimilarity. Mean annual rainfall and geographic distance were the most important explanatory variables, although topographic relief outranked rainfall for the topographically complex BATS transect. Purely spatial structure accounted for only 7–12% of explained deviance, pointing to the shared prevalence of species sorting along spatially structured rainfall gradients. Zones of rapid compositional turnover across bioclimatic gradients were evident across the contrasting ecosystems. These transitions zones tended to occur at the arid extremes of rainfall gradients and as plains transitioned into complex topography. Responses to other variables were inconsistent among transects. Transition zones were spatially contingent, influenced by local topography, and generally occurred within different subintervals (value ranges) along gradients. The somewhat idiosyncratic compositional responses suggest that assessment of broadscale compositional drivers including climate change should incorporate regional variation. However, the consistently strong species sorting along rainfall gradients demonstrates a common key response to moisture limitation.

Biotic predictors complement models of bat and bird responses to climate and tree diversity in European forests.

Bats and birds are key providers of ecosystem services in forests. How climate and habitat jointly shape their communities is well studied, but whether biotic predictors from other trophic levels may improve bird and bat diversity models is less known, especially across large bioclimatic gradients. Here, we achieved multi-taxa surveys in 209 mature forests replicated in six European countries from Spain to Finland, to investigate the importance of biotic predictors (i.e. the abundance or activity of defoliating insects, spiders, earthworms and wild ungulates) for bat and bird taxonomic and functional diversity. We found that nine out of 12 bird and bat diversity metrics were best explained when biotic factors were added to models including climate and habitat variables, with a mean gain in explained variance of 38% for birds and 15% for bats. Tree functional diversity was the most important habitat predictor for birds, while bats responded more to understorey structure. The best biotic predictors for birds were spider abundance and defoliating insect activity, while only bat functional evenness responded positively to insect herbivory. Accounting for potential biotic interactions between bats, birds and other taxa of lower trophic levels will help to understand how environmental changes along large biogeographical gradients affect higher-level predator diversity in forest ecosystems.

Vegetation on mesic loamy and sandy soils along a 1700-km maritime Eurasia Arctic Transect.

QuestionsHow do plant communities on zonal loamy vs. sandy soils vary across the full maritime Arctic bioclimate gradient? How are plant communities of these areas related to existing vegetation units of the European Vegetation Classification? What are the main environmental factors controlling transitions of vegetation along the bioclimate gradient?Location1700‐km Eurasia Arctic Transect (EAT), Yamal Peninsula and Franz Josef Land (FJL), Russia.MethodsThe Braun‐Blanquet approach was used to sample mesic loamy and sandy plots on 14 total study sites at six locations, one in each of the five Arctic bioclimate subzones and the forest–tundra transition. Trends in soil factors, cover of plant growth forms (PGFs) and species diversity were examined along the summer warmth index (SWI) gradient and on loamy and sandy soils. Classification and ordination were used to group the plots and to test relationships between vegetation and environmental factors.ResultsClear, mostly non‐linear, trends occurred for soil factors, vegetation structure and species diversity along the climate gradient. Cluster analysis revealed seven groups with clear relationships to subzone and soil texture. Clusters at the ends of the bioclimate gradient (forest–tundra and polar desert) had many highly diagnostic taxa, whereas clusters from the Yamal Peninsula had only a few. Axis 1 of a DCA was strongly correlated with latitude and summer warmth; Axis 2 was strongly correlated with soil moisture, percentage sand and landscape age.ConclusionsSummer temperature and soil texture have clear effects on tundra canopy structure and species composition, with consequences for ecosystem properties. Each layer of the plant canopy has a distinct region of peak abundance along the bioclimate gradient. The major vegetation types are weakly aligned with described classes of the European Vegetation Checklist, indicating a continuous floristic gradient rather than distinct subzone regions. The study provides ground‐based vegetation data for satellite‐based interpretations of the western maritime Eurasian Arctic, and the first vegetation data from Hayes Island, Franz Josef Land, which is strongly separated geographically and floristically from the rest of the gradient and most susceptible to on‐going climate change.

How much is enough? Influence of number of presence observations on the performance of species distribution models

Abstract Species distribution modeling (SDM) can be useful for many applied purposes, e.g., mapping and monitoring of rare and endangered species. Sparse presence data are a recurrent, major obstacle to precise modeling of species distributions. Thus, knowing the minimum number of presences required to obtain reliable distribution models is of fundamental importance for applied use of SDM. This study uses a novel approach to assess the critical sample size (CSS) sufficient for an accurate prediction of species distributions with Maximum Entropy Modeling (MaxEnt). Large presence datasets for thirty insect species, ranging from generalists to specialists regarding their responses to main bioclimatic gradients, were used to produce reference distribution models. Models based on replicated subsamples of different size drawn randomly from the full dataset were compared to the reference model using the index of vector similarity distribution models. Models based on replicated subsamples of different size drawn randomly from the full dataset were compared to the reference model using the index of vector similarity (IVS). Two thresholds for IVS were determined based on comparison of nine reference models to random null models. The threshold values correspond to 0.95 and 0.99 probability that a model outperforms a random null model in terms of similarity to the reference dataset. For 90% of the species, clearly nonrandom models were obtained with less than 10 presence observations, and for 97% of the species with less than 15 presence observations. We conclude that the number of presence observations required to produce nonrandom models is generally low and, accordingly, that even sparse datasets may be useful for distribution modelling.

Community structure of woody plants on islands along a bioclimatic gradient

Understanding patterns of community structure and the causes for their variation can be furthered by comparative biogeographic analyses of island biotas. We used woody plant data at the local scale to investigate variations in species rarity, alpha, beta, and gamma diversity within and between three islands from the oceanic archipelagoes of Azores, Canaries and Mascarene. We used standardized protocols to sample ten 50 m × 50 m forest plots in each of the three islands with contrasting climate and regional species pools: Terceira (Azores), Tenerife (Canaries), and Reunion (Mascarene Islands). Occupancy frequency distributions and species abundance distributions were used to investigate rarity. The partitioning of beta diversity in a distance-decay framework was used to test for spatial patterns of community composition. Rarity was much more pronounced in the highly diverse islands of Tenerife and Reunion than in the regionally poorer island of Terceira. The number of species rose faster with increasing sample area in both Tenerife and Reunion. The slope of the species rank abundance curve was steeper in Terceira whereas the richer island assemblages approached a lognormal model. Compositional changes according to spatial distance were mostly due to replacement of species in Terceira and Reunion. Our results point to important differences in the community structure of Terceira, which is the less diverse and temperate region in comparison to Tenerife and Reunion which are highly diverse.

Plant and ant assemblages predicted to decouple under climate change

AbstractAimMarked differences in plant and animal responses to climate change could have a profound impact on community composition and function, with implications for habitat structure and resource availability for fauna, and the provision of faunal‐mediated ecological services for flora. We examine the comparative sensitivity of plant and ant assemblages to climatic change, and determine if we should expect community breakdown and a loss of ecosystem function under climate change.LocationA bioclimatic gradient from the temperate to arid zone in South Australia.MethodsWe sampled plant and ant assemblages along the gradient to establish assemblage‐level responses to spatial climatic change using ordinations, and then projected assemblage responses to future climate change scenarios.ResultsWe recorded totals of 363 plant and 227 ant species. Alignment between plant and ant communities was high, suggesting a high degree of similarity in the structuring of plant and ant communities in relation to environmental variation. However, our modelling suggested that ant assemblages were up to 7.5 times more sensitive to projected climate change than were plant assemblages, forecasting a very substantial decoupling of these assemblages under a future climate.Main conclusionsOur results indicate that a high degree of community reorganization and change in ecosystem function should be expected under climate change.

A novel Brassica rapa L. genetic diversity found in Algeria

To gain new insights into the complex evolutionary history of Brassica rapa, we investigated the genetic diversity of wild and domesticated populations from an unexplored area in its center of origin (Mediterranean basin). These populations were collected in Algeria, which presents a wide ecogeographic range and an exceptional bioclimatic gradient. We wanted to answer the following questions: (1) Were the local landraces domesticated from the local wild forms? (2) Do these populations offer a new diversity never described? (3) How is this diversity related to B. napus? Morphological traits and SSR markers were analysed to explore the genetic diversity among 18 Algerian B. rapa accessions that were compared to those previously analysed in this species and to B. napus varieties. Among worldwide B. rapa diversity, the wild and cultivated Algerian groups showed the highest allelic richness, suggesting that breeding has not significantly eroded genetic diversity in Algerian local landraces. Wild and cultivated B. rapa accessions from Algeria formed two clusters regardless of their local geographic origin and were distinct from all the B. rapa groups already described. Surprisingly, B. napus accessions clustered either with wild Algerian group or with the group containing mainly Asian accessions. This new diversity will be of high interest for B. rapa and B. napus breeding.

Sampling bias in presence-only data used for species distribution modelling: theory and methods for detecting sample bias and its effects on models

Abstract This paper provides a theoretical understanding of sampling bias in presence-only data in the context of species distribution modelling. This understanding forms the basis for two integrated frameworks, one for detecting sampling bias of different kinds in presence-only data (the bias assessment framework) and one for assessing potential effects of sampling bias on species distribution models (the bias effects framework). We exemplify the use of these frameworks to museum data for nine insect species in Norway, for which the distribution along the two main bioclimatic gradients (related to oceanicity and temperatures) are modelled using the MaxEnt method. Models of different complexity (achieved by use of two different model selection procedures that represent spatial prediction or ecological response modelling purposes, respectively) were generated with different types of background data (uninformed and background-target-group [BTG]). The bias assessment framework made use of comparisons between observed and theoretical frequency-of-presence (FoP) curves, obtained separately for each combination of species and bioclimatic predictor, to identify potential sampling bias. The bias effects framework made use of comparisons between modelled response curves (predicted relative FoP curves) and the corresponding observed FoP curves for each combination of species and predictor. The extent to which the observed FoP curves deviated from the expected, smooth and unimodal theoretical FoP curve, varied considerably among the nine insect species. Among-curve differences were, in most cases, interpreted as indications of sampling bias. Using BTG-type background data in many cases introduced strong sampling bias. The predicted relative FoP curves from MaxEnt were, in general, similar to the corresponding observed FoP curves. This indicates that the main structure of the data-sets were adequately summarised by the MaxEnt models (with the options and settings used), in turn suggesting that shortcomings of input data such as sampling bias or omission of important predictors may overshadow the effect of modelling method on the predictive performance of distribution models. The examples indicate that the two proposed frameworks are useful for identification of sampling bias in presence-only data and for choosing settings for distribution modelling options such as the method for extraction of background data points and determining the appropriate level of model complexity.

Gender dimorphism in Corema album across its biogeographical area and implications under a scenario of extreme drought events

In dioecious species, traits may have evolved because of significantly different resource demands associated with male versus female sexual reproduction. It is generally assumed that females have higher reproductive costs, thereafter in long-lived species, males often exceed females in vigour and suffer lower physiological limitations under stress. However, large-scale studies of gender dimorphism and the link between survival and physiological responses and compensation mechanisms are still lacking. In this study, we compared canopy performance, photochemical efficiency, leaf water potential, Δ13C, leaf nitrogen content and δ15N in both genders of the dioecious species Corema album (Ericaceae) across all the species’ biogeographical distribution. This area corresponds to a wide climatic gradient, from temperate and humid to Mediterranean, across the Atlantic coast of the Iberian Peninsula.Our results evidenced that the species responds to the bioclimatic gradient, and most variables were significantly correlated with annual rainfall and bioclimatic indices, although gender dimorphism was only manifested in Δ13C and in leaf water potential at the peak of the drought season. Female plants have significantly higher values of Δ13C, which could be attributed to lower water use efficiency; however, male plants presented more negative leaf water potentials than females, especially in the populations with the warmest and most arid climate.We concluded that C. album populations adjust to the climatic gradient at different hierarchical scales, from physiological instantaneous to time-integrated traits, with gender dimorphism only occurring in sub-optimal environments The absence of morphological differences between genders and the maintenance of a less negative water potential in females in the dry period in southern more arid populations, suggests the existence of compensatory mechanisms at underground level.

The role of tolerance variation in vulnerability forecasting of insects.

Quantifying the amount of climatic change organisms can withstand before exceeding their physiological tolerance is a cornerstone of vulnerability forecasting. Yet most work in this area treats tolerance as a fixed trait. We review recent work that quantifies variation in high temperature tolerance across bioclimatic gradients, and we explore the implications for vulnerability to climate change. For some sources of variation, including differences in the evolutionary potential of heat tolerance across latitude, the typical biogeographic pattern of high vulnerability in the tropics is exacerbated. For other sources of variation, including certain types of plastic variation in heat tolerance, the biogeographic pattern of high tropical vulnerability is diminished. As a consequence, thermal tolerance variation should not be ignored in vulnerability forecasting.

Autosuccession in alpine vegetation: Testing the concept on an altitudinal bioclimatic gradient, Jotunheimen, southern Norway

Specific tests of autosuccession (equivalent to non-replacement change in species composition) are made, in which pioneer communities on roadside verges and areas of patterned ground disturbed by cryoturbation are compared with mature communities on a bioclimatic gradient from sub-alpine woodland (850 m a.s.l) to high-alpine fjellfield (2200 m a.s.l). Autosuccession is quantified for the first time using community similarity coefficients and indices of pioneer persistence and importance, which measure nominal- or ordinal-scale differences in species composition between 65 paired pioneer and mature communities. Linear relationships to altitude, with coefficient and index values of ~90–100% in the upper part of the high-alpine belt to ~10–20% in the sub-alpine zone, indicate a continuum from autosuccession to relay succession (the latter characterised by high species turnover and replacement change). Values based on ordinal-scale data are generally ~10% lower than those based on nominal-scale data and use of pioneer sites from roadside verges result in a ~20% offset relative to pioneer sites from sorted circles (the latter comparison reflecting the effect of substrate differences). Autosuccession appears to be characteristic only at altitudes >2000 m a.s.l. in the upper high-alpine belt. Replacement change increases in importance as a constituent of mixed-mode succession through the conventional mid- and low-alpine belts. Spatial variation in the nature of primary succession along the bioclimatic gradient supports a geo-ecological model of succession with predominantly allogenic controls (climatic stress and high levels of substrate disturbance by cryoturbation) at high altitudes and increasing autogenic controls (biological interactions and substrate stability) at lower altitudes.

A Generalized Lidar-Based Model for Predicting the Merchantable Volume of Balsam Fir of Sites Located along a Bioclimatic Gradient in Quebec, Canada

Lidar-based models rely on an optimal relationship between the field and the lidar data for accurate predictions of forest attributes. This relationship may be altered by the variability in the stand growth conditions or by the temporal discrepancy between the field inventory and the lidar survey. In this study, we used lidar data to predict the timber merchantable volume (MV) of five sites located along a bioclimatic gradient of temperature and elevation. The temporal discrepancies were up to three years. We adjusted a random canopy height coefficient (accounting for the variability amongst sites), and a growth function (accounting for the growth during the temporal discrepancy), to the predictive model. The MV could be predicted with a pseudo-R2 of 0.86 and a residual standard deviation of 24.3 m3 ha−1. The average biases between the field-measured and the predicted MVs were small. The variability of MV predictions was related to the bioclimatic gradient. Fixed-effect models that included a bioclimatic variable provided similar prediction accuracies. This study suggests that the variability amongst sites, the occurrence of a bioclimatic gradient and temporal discrepancies are essential in building a generalized lidar-based model for timber volume.

When macroecological transitions are a fiction of sampling: comparing herbarium records to plot‐based species inventory data

Natural history collections are alternative data sources to plot‐based species inventories for analysing macroecological species turnover. Herbarium records sample diversity well at regional level and are taxonomically validated. However, they are ad hoc from a sampling perspective, generating spatial and taxonomic biases. The implications of biased sampling on beta diversity (β) estimation, and use of herbarium data to identify macroecological transitions, remain unexplored. We tested sampling influences by comparing herbarium data with systematically collected inventory data from the Mount Lofty–Flinders Ranges region of Australia. We calculated β within moving windows across bioclimatic gradients using metrics varying in sensitivity to richness differences (pairwise/multi‐site Sørensen β; Simpson β; Harrison et al. β‐2), and correlated β to species sampling and between herbarium and plot data. We tested whether generalised dissimilarity modelling (GDM) revealed the same compositional transitions in herbarium and plot data along environmental gradients. Sørensen, Simpson and multi‐site Sørensen β had strong negative correlations with richness (indicating sampling bias) for herbarium data (Pearson's r = –0.85, –0.80, –0.81, respectively) but not plots (r = –0.27, –0.28, –0.11). Harrison et al. β‐2 correlated poorly with richness (herbarium: r = –0.16; plots: r = –0.14) but herbarium and plot data were only weakly correlated (r = 0.18). All other metrics correlated poorly (–0.03 < r < 0.16) between datasets, suggesting biases. GDMs differed in variable importance but revealed similar transition zones for key gradients. We conclude that untransformed herbarium data are unsuitable for detecting macroecological transitions because turnover is linearly related to sampling intensity and correlates poorly with systematic surveys. Herbarium data should be used cautiously for β, even with methods insensitive to richness differences. However, herbarium data can robustly reproduce transition zones when modelled along environment gradients. We recommend this approach for detecting macroecological transitions using natural history data in the absence of plot data.

New data on distribution and ecology of rare in the Khanty-Mansi Autonomous District (Western Siberia) moss species (Bryophyta)

New locations of 25 rare species of mosses, known earlier in the Khanty-Mansi Autonomous District from one or a few locations, are provided. Their ecology, phytocenotic affinity and peculiarities of the distribution on the territory of the autonomous district and taiga zone of the Western Siberia as a whole are discussed. A high proportion of rare species in the moss flora of the central part of the taiga zone of Western Siberia resulted from limited distribution or absence of suitable habitats associated with stony substrates and outcrops of groundwater rich in mineral nutrition elements, as well as from intermediate (ecotone) position of the flora on the latitudinal bioclimatic gradient from south to north.

Assessment of MODIS-derived indices (2001-2013) to drought across Taiwan's forests.

Tropical and subtropical ecosystems, the largest terrestrial carbon pools, are very susceptible to the variability of seasonal precipitation. However, the assessment of drought conditions in these regions is often overlooked due to the preconceived notion of the presence of high humidity. Drought indices derived from remotely sensed imagery have been commonly used for large-scale monitoring, but feasibility of drought assessment may vary across regions due to climate regimes and local biophysical conditions. Therefore, this study aims to evaluate the feasibility of 11 commonly used MODIS-derived vegetation/drought index in the forest regions of Taiwan through comparison with the station-based standardized precipitation index with a 3-month time scale (SPI3). The drought indices were further transformed (standardized anomaly, SA) to make them better delineate the spatiotemporal variations of drought conditions. The results showed that the Normalized Difference Infrared Index utilizing the near-infrared and shortwave infrared bands (NDII6) may be more superior to other indices in delineating drought patterns. Overall, the NDII6 SA-SPI3 pair yielded the highest correlation (mean r ± standard deviation = 0.31 ± 0.13) and was most significant in central and south Taiwan (r = 0.50-0.90) during the cold, dry season (January and April). This study illustrated that the NDII6 is suitable to delineate drought conditions in a relatively humid region. The results suggested the better performance of the NDII6 SA-SPI3 across the high climate gradient, especially in the regions with dramatic interannual amplifications of rainfall. This synthesis was conducted across a wide bioclimatic gradient, and the findings could be further generalized to a much broader geographical extent.

Population genetic structure is shaped by historical, geographic, and environmental factors in the leguminous shrub Caragana microphylla on the Inner Mongolia Plateau of China

BackgroundUnderstanding how landscape factors, including suites of geographic and environmental variables, and both historical and contemporary ecological and evolutionary processes shape the distribution of genetic diversity is a primary goal of landscape and conservation genetics and may be particularly consequential for species involved in ecological restoration. In this study, we examine the factors that shape the distribution of genetic variation in a leguminous shrub (Caragana microphylla) important for restoration efforts on the Mongolian Plateau in China. This region houses several major bioclimatic gradients, and C. microphylla is an important restoration species because it stabilizes soils and prevents advancing desertification on the Inner Mongolia Plateau caused by ongoing climate change.ResultsWe assembled an expansive genomic dataset, consisting of 22 microsatellite loci, four cpDNA regions, and 5788 genome-wide SNPs from ten populations of C. microphylla. We then applied ecological niche modelling and linear and non-linear regression techniques to investigate the historical and contemporary forces that explain patterns of genetic diversity and population structure in C. microphylla on the Inner Mongolia Plateau. We found strong evidence that both geographic and environmental heterogeneity contribute to genetic differentiation and that the spatial distribution of genetic diversity in C. microphylla appears to result partly from the presence of a glacial refugium at the southwestern edge of its current range.ConclusionsThese results suggest that geographic, environmental, and historical factors have all contributed to spatial genetic variation in this ecologically important species. These results should guide restoration plans to sustain genetic diversity during plant translocations.

Relationships between vegetation, air and soil temperatures on Norwegian mountain summits

ABSTRACTGeographic variations in air and soil temperatures are dependent on several biotic and abiotic factors. Air temperature has mostly been used to characterize thermal conditions for plant life, and studies of bioclimatic gradients. From a biological point of view, it is also essential to know to what extent soil temperature is coupled with air temperature. In this study, we have quantified the deviations between soil and air temperatures along gradients in latitude, altitude, and possible effects of the vegetation. Sixteen different temperature variables were estimated from 49 vegetation plots on 19 mountain summits along the high mountain range in Norway, ranging from 230 to 1780 m a.s.l., and from 59°N to 71°N. Soil and air temperature variables were estimated from the study plots during one year. All air and soil temperature variables were significantly correlated, but the rate of explanation was mostly relatively low (37.0–60.0%), except during the growing season. Start of the growing season, determined by air or soil temperatures, could deviate by 38 days mainly due to effects of frozen soils. Vegetation composition, especially the lichen cover, had a major impact on soil temperature, Dwarf shrub cover increased significantly with increasing July temperature. Lichen abundance and degree of soil frost were strongly correlated, and explained a major part of the variation in soil temperatures. The study indicates that air temperature is generally a poor proxy for soil temperature in cold areas, except during July.