Although there is a general consensus on the distribution and ecological features of terrestrial biomes, the allocation of alpine ecosystems in the global biogeographic system is still unclear. Here, ...we delineate a global map of alpine areas above the treeline by modelling regional treeline elevation at 30 m resolution, using global forest cover data and quantile regression. We then used global datasets to 1) assess the climatic characteristics of alpine ecosystems using principal component analysis, 2) define bioclimatic groups by an optimized cluster analysis and 3) evaluate patterns of primary productivity based on the normalized difference vegetation index. As defined here, alpine biomes cover 3.56 Mkm2 or 2.64% of land outside Antarctica. Despite temperature differences across latitude, these ecosystems converge below a sharp threshold of 5.9°C and towards the colder end of the global climatic space. Below that temperature threshold, alpine ecosystems are influenced by a latitudinal gradient of mean annual temperature and they are climatically differentiated by seasonality and continentality. This gradient delineates a climatic envelope of global alpine biomes around temperate, boreal and tundra biomes as defined in Whittaker's scheme. Although alpine biomes are similarly dominated by poorly vegetated areas, world ecoregions show strong differences in the productivity of their alpine belt irrespectively of major climate zones. These results suggest that vegetation structure and function of alpine ecosystems are driven by regional and local contingencies in addition to macroclimatic factors.
Understanding and explaining the use of green spaces and forests is challenging for sustainable urban planning. In recent years there has been increasing demand for novel approaches to investigate ...urban green infrastructure by capitalizing on large databases from existing citizen science tools. In this study, we analyzed iNaturalist data to perform an assessment of the intentional use of these urban spaces for their value and to understand the main drivers. We retrieved the total number of observations obtained across a set of 672 European cities and focused on reporting from mapped green areas and forests. We used two separate multivariate explanatory models to investigate which factors explained variations in the number of observations for green areas and forests. We found a relatively heterogeneous use of these two urban green spaces. Gross domestic product was important in explaining the number of visits. Availability and accessibility also had positive relationships with the use of green areas and forests in cities, respectively. This study paves the way for better integration of citizen science data in assessing cultural services provided by urban green infrastructure and therefore in supporting the evaluation of spatial planning policies for the sustainable development of urban areas.
Refugia will be important to the response of alpine vegetation to climate change. Potential refugia exist at multiple scales, including a range-wide mesoscale. The climates of alpine grasslands of 23 ...mountain ranges of southern and central Europe were evaluated to assess whether each range would support potential refugia in projected future climates. The mean temperature the warmest month and quarter with the precipitation of the warmest quarter, derived from gridded global climate data at ~ 1 km resolution, were examined range-wide and for areas identified as alpine grassland to identify limits within each range. The overlap of current grassland climate and future range-wide climates, the latter calculated using regional projections from three global models with three socioeconomic driving scenarios, were assessed as potential refugia. Among the nine projections, three had none of the current grassland climates in any of the 23 ranges by 2100, while two retained more than 20% in more than half of the ranges. Most of the potential mesoscale refugia were in the Alps. Micro-refugia and warmer and drier fundamental climatic niches for alpine grassland species could mitigate these bleak results, but otherwise they are extremely threatened.
Introduction
Whether the distribution and assembly of plant species are adapted to current climates or legacy effects poses a problem for their conservation during ongoing climate change. The alpine ...regions of southern and central Europe are compared to those of the western United States and Canada because they differ in their geographies and histories.
Methods
Individual-based simulation experiments disentangled the role of geography in species adaptations and legacy effects in four combinations: approximations of observed alpine geographies vs. regular lattices with the same number of regions (realistic and null representations), and virtual species with responses to either climatic or simple spatial gradients (adaptations or legacy effects). Additionally, dispersal distances were varied using five Gaussian kernels. Because the similarity of pairs of regional species pools indicated the processes of assembly at extensive spatiotemporal scales and is a measure of beta diversity, this output of the simulations was correlated to observed similarity for Europe and North America.
Results
In North America, correlations were highest for simulations with approximated geography and location-adapted species; those in Europe had their highest correlation with the lattice pattern and climate-adapted species. Only SACEU correlations were sensitive to dispersal limitation.
Discussion
The southern and central European alpine areas are more isolated and with more distinct climates to which species are adapted. In the western United States and Canada, less isolation and more mixing of species from refugia has caused location to mask climate adaptation. Among continents, the balance of explanatory factors for the assembly of regional species pools will vary with their unique historical biogeographies, with isolation lessening disequilibria.
•A novel application to assess the spatialvariability of tree cover and density.•Spatial variability in Savanna ecosystem is influenced by environmental factors.•Management regime has an influence ...within the boundaries of the environmental template.
In protected areas of the African savanna tree cover, structure and species composition are influenced by a combination of many different variables. These include complex and multi-scaled interplay of environmental factors such as water and nutrient availability, fire, herbivory and, when occurring, direct human disturbance. In this study, we conducted a comprehensive and comparative analysis of the spatial variability of tree cover and density in three neighboring Southern African National Parks (Kruger, Limpopo, and Gonarezhou) characterized by similar environmental conditions but different management plans. We sampled 3382 plots of 0.5 ha across the three parks using an innovative methodology defined as augmented visual interpretation, based on a free and open source software. This software, named Collect Earth, allows access to very high spatial and temporal resolution imagery archives. Spatial variability of tree cover and density was analyzed comparing the three parks and the two bioclimatic regions (semiarid and dry subhumid) characterizing them. The effect of relevant environmental variables such as edaphic factors, precipitation and fire frequency was also assessed. Kruger National Park is characterized by the lowest values of tree cover and density among the three Parks. Contrary to what was expected and the general trend of Southern Africa, the dry subhumid zone showed lower values of tree cover and density than the semiarid zone. Such variability is hypothesized to be related to the different managements of the three parks within the general environmental template characterizing the African savanna as well as differences in tree species composition between the two climatic zones.
The importance of environmental difference among sites and dispersal limitations of species to the explanation of diversity differs among biological systems and geographical regions. We hypothesized ...that climate and then dispersal limitation will predominantly explain the similarity of alpine vegetation at increasing distances between pairs of regions at subcontinental extent. We computed the similarity of all pairs of 23 European mountain regions below 50° N after dividing the species lists of each region by calcareous or siliceous substrates. Distance decay in similarity was better fitted by a cubic polynomial than a negative exponential function, and the fit was better on calcareous than on siliceous substrate. Commonality analysis revealed that the proportion of explanation of beta diversity by climatic difference had unimodal patterns on a gradient of increasing distance between regions, while explanation by dispersal limitation had consistently rising patterns on both substrates. On siliceous substrate, dispersal limitation explained more of the variation in beta diversity only at longer distances, but it was predominant at all distances on calcareous substrate. The steeper response to distance at <1600 km and >2600 km may indicate dispersal limitation at different temporal scales, and the uptick in the response to distance at the longest distances may reflect how isolated some regions have been before and since the last glacial maximum.
Cities are considered important areas for biodiversity and host a high plant species richness. However, many factors, such as urbanisation or changes in land use, can affect the presence of ...spontaneous flora and, consequently, represent a threat for biodiversity. How species respond to these factors of change in cities over time is a relevant and current issue and spatiotemporal analyses represent an essential step forward to better understand these dynamic systems and to fill gaps of knowledge. In this paper we present a comparison between a floristic survey carried out in 1995 on a grid-cell for the city of Rome and a new survey, performed between 2015 and 2018, in order to verify if the species composition significantly changed over time and to which drivers this change was related to. For 76 grid-cells of the raster, each of which of 1.6 km
2
, we recorded all spontaneous vascular species. We analysed the differences between the two surveys by means of statistical tests on species richness, by species turnover, by generalised linear models (GLMs) and by Ellenberg indicator values. The patterns of species richness are similar between the two surveys, although an increase in the number of species per grid-cell, on average, was observed. This increase regarded both native and alien richness, with significant differences only for aliens. Many species significantly reduced or increased their frequencies, comparing the two surveys. A set of environmental variables, among which the presence of protected areas, are relevant for explaining the pattern of species’ frequencies and its change over time.
Our results suggest that the flora of the city, notwithstanding the steady human pressure and the increase in alien species, maintained a high level of heterogeneity.
Aim
Area and environmental heterogeneity together explain most patterns of species diversity but disentangling their relative importance has been difficult. Here, we empirically examined this ...relationship and parsed their relative importance, and that of the heterogeneity—effective area trade‐off, at different spatial scales and in different spatial representations in simulations.
Location
Alpine grasslands of 23 mountain ranges of southern and central Europe.
Taxon
Vascular plants.
Methods
We developed metrics of climatic and edaphic heterogeneity, using principal components analyses and the shoelace algorithm, and added elevation range. We applied commonality analysis to partition the unique and shared explanation of the observed vascular plant species richness among selected metrics. A simulation was developed to separate the relative importance of area and heterogeneity at different extents and representations of spatial nestedness, and the heterogeneity—effective area trade‐off was evaluated by altering spatial discreteness.
Results
The explanation of the observed regional richness was shared by area and heterogeneity. The simulation revealed that heterogeneity was consistently more important, but less so among smaller areas. This qualitative pattern was maintained regardless of whether and how nestedness was represented. The heterogeneity–effective area trade‐off occurred in a few simulations of more discrete habitats.
Main Conclusions
Scale dependence may account for discrepancies among past empirical studies wherein environmental heterogeneity has usually outweighed area in the explanation of species richness; and it is not affected by nestedness. The potential heterogeneity–effective area trade‐off may be limited to locations where the environmental heterogeneity is quite discrete or if the added environment is beyond the niches of any species in the potential pool. The significant importance of area per se in small territories indicates that microrefugia, even with an unlikely full range of heterogeneity, will suffer local extinctions in the face of climate change.
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