Empirical analysis of vegetation dynamics and the possibility of a catastrophic desertification transition

The process of desertification in the semi-arid climatic zone is considered by many as a catastrophic regime shift, since the positive feedback of vegetation density on growth rates yields a system that admits alternative steady states. Some support to this idea comes from the analysis of static patterns, where peaks of the vegetation density histogram were associated with these alternative states. Here we present a large-scale empirical study of vegetation dynamics, aimed at identifying and quantifying directly the effects of positive feedback. To do that, we have analyzed vegetation density across $~2.5 \times 10^6 \ \rm{km}^2$ of the African Sahel region, with spatial resolution of $30 \times 30$ meters, using three consecutive snapshots. The results are mixed. The local vegetation density (measured at a single pixel) moves towards the average of the corresponding rainfall line, indicating a purely negative feedback. On the other hand, the chance of spatial clusters (of many "green" pixels) to expand in the next census is growing with their size, suggesting some positive feedback. We show that these apparently contradicting results emerge naturally in a model with positive feedback and strong demographic stochasticity, a model that allows for a catastrophic shift only in a certain range of parameters. Static patterns, like the double peak in the histogram of vegetation density, are shown to vary between censuses, with no apparent correlation with the actual dynamical features

Multiscale Analyses of Mammal Species Composition – Environment Relationship in the Contiguous USA

Relationships between species composition and its environmental determinants are a basic objective of ecology. Such relationships are scale dependent, and predictors of species composition typically include variables such as climate, topographic, historical legacies, land uses, human population levels, and random processes. Our objective was to quantify the effect of environmental determinants on U.S. mammal composition at various spatial scales. We found that climate was the predominant factor affecting species composition, and its relative impact increased in correlation with the increase of the spatial scale. Another factor affecting species composition is land-use–land-cover. Our findings showed that its impact decreased as the spatial scale increased. We provide quantitative indication of highly significant effect of climate and land-use–land-cover variables on mammal composition at multiple scales

Mapping and assessment of vegetation types in the tropical rainforests of the Western Ghats using multispectral Sentinel-2 and SAR Sentinel-1 satellite imagery

Detailed mapping and regular monitoring of tropical rainforests is important for conservation and management of highly fragmented tropical rainforest habitats and biodiversity. Several studies have observed that it is highly challenging to map different vegetation types in tropical rainforests due to large environmental heterogeneity, high topographical variability and near constant cloud cover. In the present study, we assessed the capability of optical multispectral Sentinel-2 MSI bands, their derived NDVI and textures, and SAR Sentinel-1 bands and their textures to discriminate different vegetation types in the tropical rainforests of the Western Ghats using maximum likelihood and random forest classification. We also compared the results of our classification with previous such maps of the study area. Finally, we evaluated the magnitude of habitat fragmentation by using derived landscape metrics. Our classification had high accuracy (>75), especially compared to previous classification efforts. Our results emphasise the significance of using vegetation indices and textures for vegetation type classification in the Western Ghats. Furthermore, the results suggest that rainforest habitats and other agro-ecosystems, suitable as habitats for numerous plant and animal species, are highly fragmented and require top conservation priority. High spectral and spatial resolution, continuity, affordability and access makes Sentinel-2 one of the best options for regular monitoring of tropical rainforests

Automatic Importation of Relational Schemas in Pegasus

This paper describes a technique for importing automatically an external relational schema into Pegasus, a heterogeneous, multidatabase system. The Pegasus data model is a functional object model which supports specialization, object-identity, and nested aggregation. The import algorithm generates the definition of a Pegasus schema which captures the semantics of a relational schema containing information about primary keys and referential integrity constraints. The algorithm described can be adapted easily for other semantic and objectoriented data models

LRC and SRC for specific rainfall lines.

<p>The date for 350-400 mm/year region (panels A-C) exemplify the typical scenario, where the LRC (panel A and with error bars in panels B and E) decreases monotonously with density. On the other hands, in panel D one notices that the 1999-2002 line appears to indicate positive feedback. This is a rare exception (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0189058#pone.0189058.s004" target="_blank">S3 Fig</a>), the apparent positive feedback disappears in the 2002-2015 interval. Panel C shows a typical SRC curve, while in panel F the curve is almost flat; this flat curve is, again, an exception, as seen in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0189058#pone.0189058.s002" target="_blank">S1</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0189058#pone.0189058.s003" target="_blank">S2</a> Figs. The details of the smoothing and fitting procedures are given in the Text B in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0189058#pone.0189058.s001" target="_blank">S1 Appendix</a>.</p

The relative frequency distribution of vegetation cover is plotted here for four levels of mean annual precipitation using the data of 1999 (blue) and 2002 (red).

<p>The average vegetation cover decreased during this period, so the histograms of 2002 are shifted systematically to the left. The histograms for 650-700 mm/y (panel A) admit a clear single peak for both years, in the region 800-850 mm/y (panel B) one observes a crossover from a unimodal to bimodal distribution and for 550-600 mm/y (panel C) the histogram has a double peak in 1999 and a single peak in 2002, meaning that the modality of the histogram is <i>not</i> a robust feature of the system. The local response curve (LRC) in all cases has a negative slope (left inset). The spatial response curve (SRC) shows signs of positive feedback in most of the cases, but there are some rare exceptions, See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0189058#pone.0189058.s003" target="_blank">S2</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0189058#pone.0189058.s014" target="_blank">S13</a> Figs for more details.</p

Representative vegetation in the three vegetation belts along the elevation gradient in the Mt. Hermon study area.

<p>Photos are by Salit Kark (bottom and top) and Oded Levanoni (middle).</p

A graphic representation of the ecotones detected in the study site (for birds and butterflies in purple and orange respectively) compared with vegetation belts, as described in previous studies of Mt. Hermon (Shmida 1974).

<p>Black contours denote 100 m elevation intervals. The background color gradient represents elevation from low (in green) to high (in brown).</p

Losing its ground: a case study of fast declining populations of a ‘least-concern’ species, the bonnet macaque (Macaca radiata)

The populations of many species that are widespread and commensal with humans have been drastically declining during the past few decades, but little attention has been paid to their conservation. Here, we report the status of the bonnet macaque, a species that is considered ‘least-concern’ for conservation. We show that the widely ranging rhesus macaque is expanding its range into the distributional range of the bonnet macaque, a species endemic only to southern India. Bonnet macaques have very low abundance in forests of all types indicating that it is not a typically forest dwelling species. The traditionally preferred habitats of bonnet macaques have been Hindu temples/ tourist spots but our data reveal that nearly 50% population of bonnet macaques has disappeared from such previously occupied spots. Another preferred habitat of bonnet macaques has been roadsides with abundant Ficus trees adjoining croplands. We found that between 2003 and 2015, the roadsides have drastically changed where vegetation has been replaced with barren lands and urbanization. Consequently, the populations of bonnet macaques have declined by more than 65% over the past 25 years, and by more than 50% between 2003 and 2015 alone. We, therefore, conclude that this ‘least-concern’ species is actually facing serious conservation challenges. We also identify a few places such as small hillocks with natural vegetation and a few temples/tourist spots which are likely to remain stable and thus can serve as ‘bonnet macaque conservation reserves’. Since the bonnet macaque shares many traits with several other commensal and ‘low-risk’ species, it can serve as a model for the development of long-term conservation strategies for most such species