Search Results
How are bryophyte alpha and beta diversities distributed across spatial scales along an elevational gradient in an oceanic island? Which mechanisms and drivers operate to shape them? Starting from a multiscale hierarchical sampling approach along an 1000 m elevational transect, we used additive diversity partitioning and null modeling to evaluate the contributions of the alpha and beta diversity components to overall bryophyte diversity in Terceira Island, Azores. Substrate-level diversity patterns were explored by means of the Sørensen Similarity Index and the Lloyd Index of Patchiness. Elevation-level beta diversity was decomposed into its replacement and richness differences components, with several environmental variables being evaluated as diversity predictors. Bryophyte diversity proved to be primarily due to beta diversity between elevation sites, followed by diversity among substrates. Compositional differences between neighboring sites decreased with elevation, being mainly caused by species replacement and correlating with differences in relative humidity and disturbance. At the substrate level, we found a great homogeneity in terms of species composition, coupled with a low substrate specialization rate. We conclude that, in Terceira’s native vegetation patches, regional processes, such as environmental gradients associated with elevation, play a greater role in shaping bryophyte diversity than local processes. Moister and less disturbed areas at mid-high elevation harbor a richer bryoflora, consistently more similar and stable between neighbouring sites. Simultaneously, the different substrates available are somewhat ecologically redundant, supporting few specialized species, pointing to these areas providing optimal habitat conditions for bryophytes. Our findings provide a better understanding of how bryophyte diversity is generated in Terceira Island, indicating that management and conservation measures should focus on island-level approaches, aiming to protect and rehabilitate additional natural vegetation patches at different elevations, especially in the severely disturbed lowlands.
Abstract
The International Atomic Energy Agency (IAEA), in cooperation with World Meteorological Organization (WMO) initiated in 1960 a world-wide survey of the isotope composition of monthly precipitation. The paper reviews the global distribution patterns of tritium and stable isotopes in precipitation and their relation to meteorological and climatic variables.
The climatology of soil respiration in Hungary is presented. Soil respiration is estimated by a Thornthwaite-based biogeochemical model using soil hydrophysical data and climatological fields of precipitation and air temperature. Soil respiration fields are analyzed for different soil textures (sand, sandy loam, loam, clay loam and clay) and time periods (year, growing season and months). Strong linear relationships were found between soil respiration and the actual evapotranspiration for annual and growing season time periods. In winter months soil respiration is well correlated with air temperature, while in summer months there is a quite variable relationship with water balance components. The strength of linear relationship between soil respiration and climatic variables is much better for coarser than for finer soil texture.
Two-year seasonal monitoring of the flight of Phthorimaea operculella by means of pheromone traps was organized at four sites in three districts in Bulgaria: Sofia, Kyustendil and Plovdiv. Comparison between sticky traps and dry funnel traps has shown that sticky traps were much more effective in capturing of males of this pest than the dry ones. The results of our investigations showed that the pest could appear in the field as early as the end of March and also intensive flight could be observed up to the end of November. Single catches were registered even in January. However, because of overlapping of the generations, their number and periods of moth emergence was not possible to be distinguished by the catches in pheromone traps. Analyses of climatic data (mean air temperature and mean rainfall) indicated that none of the climatic variables investigated strongly affected P. operculella trap catches.
The acceleration of grassland loss on the global scale has been reported in many studies, which is often attributed to the combination of land use change and increased variability of climatic processes. Extensive steppe national parks serve as an ideal study site for grassland conservation, especially wilderness areas where the natural effects of grazing on wildlife can still be tracked. In our study we aim to investigate the effects of habitat structure, grazing type and intensity as well as climatic variables on species abundance, species richness and abundance of functional groups of ground-breeding bird species in the largest compact alkali grassland area of central Europe. We applied the information theoretic approach estimating the importance of ecological predictors according models of substantial support. The main result of our study shows that ground-breeding bird communities in steppe areas exhibit highly species-specific responses to the species of grazers, grazing intensity, habitat composition and climatic predictors. Across the most supported models, species-specific habitat composition values were the most supported predictors. Our findings show that although the response of ground-breeding birds to vegetation, grazing and climatic predictors is highly species-specific, consistent patterns of responsiveness to grazing and climatic patterns emerge, which calls for long-term studies on the combined effects of climatic variability and management of grazing systems.
The current loss of biodiversity requires long-term monitoring of the distribution of living organisms, particularly in regions, such as mountains, which are highly sensitive to climatic and environmental changes. In 2007, three alpine parks in N-W Italy started a field program to determine the factors which influence animal biodiversity and identify the most appropriate methods for periodically repeatable monitoring. Twelve altitudinal transects (from montane to alpine belt) were chosen, each composed of 4–7 sampling units, for a total of 69 monitored plots. In each station, five taxonomic groups (carabids, butterflies, spiders, staphylinids, birds) were systematically sampled and topographic, environmental and micro-climatic variables were recorded. The aim was to assess the distribution of different taxa along altitudinal gradients and the relative influence of geographical, environmental and climatic factors. The data showed that species richness and community composition of invertebrates are mainly determined by altitude and microclimatic conditions, whereas birds are more sensitive to habitat structure. For invertebrates, the strong relationship with temperature suggests their potential sensitivity to climatic variations. The analysis of biodiversity patterns across vegetation belts indicated that the alpine belt hosts few species but a high percentage of endemic and vulnerable species, highlighting its importance for conservation purposes. This work offers a representative sample of the northwestern Italian Alps and it is a first step of a monitoring effort that will be repeated every five years to highlight the response of alpine biodiversity to climate and land-use changes.
Spatial distribution modelling can be a useful tool for elaborating conservation strategies for tree species characterized by fragmented and sparse populations. We tested five statistical models—Support Vector Regression (SVR), Multivariate Adaptive Regression Splines (MARS), Gaussian processes with radial basis kernel functions (GP), Regression Tree Analysis (RTA) and Random Forests (RF)—for their predictive performances. To perform the evaluation, we applied these techniques to three tree species for which conservation measures should be elaborated and implemented: one Mediterranean species ( Quercus suber ) and two temperate species ( Ilex aquifolium and Taxus baccata ). Model evaluation was measured by MSE, Goodman-Kruskal and sensitivity statistics and map outputs based on the minimal predicted area criterion. All the models performed well, confirming the validity of this approach when dealing with species characterized by narrow and specialized niches and when adequate data (more than 40–50 samples) and environmental and climatic variables, recognized as important determinants of plant distribution patterns, are available. Based on the evaluation processes, RF resulted the most accurate algorithm thanks to bootstrap-resampling, trees averaging, randomization of predictors and smoother response surface.
Our aim was to describe vegetation heterogeneity at a regional scale in northeastern Patagonia and to identify the environmental variables associated to it. The study area encompasses 13 144 km2 and is characterized by a mixture of species typical of Patagonian steppes and Monte Desert. We performed 48 vegetation relevés, which were randomly assigned to a training set and to a validation set (32 and 16 relevés, respectively). Training set was subjected to cluster analysis, which allowed the identification of two plant communities one related to Patagonian steppes and another to the Monte desert. We derived 3 attributes of the seasonal curve of the NDVI as indicators of ecosystem function: the seasonal amplitude (SA), the date of the maximum (DOM), and the large seasonal integral (LSI). We explored the relationship between NDVI attributes and communities by classification tree analysis. LSI was the strongest predictor among NDVI attributes, separating both communities without misclassification errors. Patagonian steppes occupy areas with higher LSI. The partial RDA analysis explained 38.1% of total data variation, of which 16.5% was ascribed to environment, 7.9% to space, and 13.7% to spatial component of environment. Patagonian steppes are closer to the coast, in areas exhibiting higher annual precipitation and lower annual temperature range than Monte deserts. Our results indicate the occurrence of two plant communities in the study area and highlight the significance of climatic variables to explain their spatial distribution. As most scenarios of future climate predict greater annual thermal amplitude in the study area, the limit between both communities could be displaced eastward.
–43. Wu, D., Yu, Q., Wang, E., Hengsdijk, H. (2008): Impact of spatial-temporal variations of climatic variables on summer maize yield in North China Plain. International J. Plant Production , 2 , 71
, D., Royo, C., Martos-Nunez, V., Garcia del Moral, L.F. 2003a. Durum wheat quality in Mediterranean environments. II. Influence of climatic variables and relationships between quality parameters. Field Crops Res. 80 :133
