Development of spatial heterogeneity in vegetation and soil properties after land abandonment in a semi-arid ecosystem
ABSTRACT To mitigate erosion on abandoned fields in semi-arid ecosystems, it is important to understand how vegetation and soil properties and patterns develop after land abandonment. Our objective was to investigate the development of spatial heterogeneity in vegetation and soil properties after land abandonment. We described the vegetation composition, collected soil samples and made detailed aerial photographs for two series of abandoned fields on marl and calcrete in Southeast Spain. The images were classified into bare and vegetated patches, and spatial metrics were calculated for each site. Our results showed that recovery of vegetation and change in soil properties after land abandonment are slow and take at least 40 years in such a semi-arid environment. Succession on calcrete appeared to be faster than on marl, probably because more water is available due to the higher rock fragment cover. Organic matter, aggregate stability and electrical conductivity were all significantly higher under vegetated patches. We found a clear linear relationship between vegetation cover and most spatial metrics, which offers the possibility of upscaling spotted vegetation patterns. The results of our integrated approach to study spatial heterogeneity in vegetation and soil properties can be used to improve predictions of runoff and erosion.
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ABSTRACT: Dry subtropical regions (DST), originally hosting woodlands and savannas, are subject to contrasting human pressures and land uses and different degrees of water limitation. We quantified how this variable context influences landscape pattern and vegetation functioning, by exploring the associations between three groups of variables describing (i) human pressures (population density, poverty, and market isolation) and climate (water availability), (ii) landscape pattern (woody cover, infrastructure, paddock size, etc.), and (iii) vegetation functioning (magnitude and stability of primary productivity), in regions of Asia, Africa, Australia, and America. We collected data from global socioeconomic databases and remote sensing products for 4525 samples (representing uncultivated and cultivated conditions), located along 35 transects spanning semiarid to subhumid conditions. A Reciprocal Averaging ordination of uncultivated samples revealed a dominant gradient of declining woody cover accompanied by lower and less stable productivity. This gradient, likely capturing increasing vegetation degradation, had a negative relationship with poverty (characterized by infant mortality) and with market isolation (measured by travel time to large cities). With partial overlaps, regions displayed an increasing degradation ranking from Africa to South America, to Australia, to North America, and to Asia. A similar analysis of cultivated samples, showed a dominant gradient of increasing paddock size accompanied by decreasing primary productivity stability, which included all regions except Asia. This gradient was negatively associated with poverty and population density. A unique combination of small paddocks and high infrastructure differentiated Asian cultivated samples. While water availability gradients were related to productivity trends, they were unrelated to landscape pattern. Our comparative approach suggests that, in DST, human pressures have an overwhelming role driving landscape patterns and one shared with water availability shaping vegetation functioning.Global Change Biology 02/2013; 19(2):441-58. · 8.22 Impact Factor
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ABSTRACT: The typical patchy structure of dryland vegetation is a result of soil–plant feedbacks occurring in water-limited areas. The resilience of dryland ecosystems depends largely on the persistence of fertility islands associated with vegetated patches, which determines the efficiency of the vegetation regarding recolonising the gaps that result from disturbances. In this study, we investigated the mechanisms underlying soil–plant interactions throughout the process of the growth and senescence of alpha grass (Macrochloa tenacissima) and the subsequent disintegration of islands of fertility and microtopography formed during the process at two nearby alpha grass communities exhibiting different degrees of development. The life cycle of alpha grass and the rise and disintegration of the underlying microrelief were accompanied by feedback changes in the content of soil C fractions presenting different times of cycling and incorporation to the soil, the collection of particles from splash erosion, redistribution phenomena related to particles of different sizes, and erosion of the most easily erodible materials. Despite their ecological and geographical proximity, the study sites differ with respect to the persistence, after plant death, of fertility islands, which almost disappear in one case, while they remain in the other, constituting a resource for the growth of new plants and resulting in greater development and resilience in the community. A subtle erodibility threshold emerges as a cause of the considerable differences in vegetation between the two sites.Journal of Arid Environments 01/2013; 89:57-66. · 1.77 Impact Factor
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ABSTRACT: Landscape metrics are used in a wide range of environmental studies such as land use change and land degradation studies, soil erosion and run-of predictions, management of hunting communities, and strategic planning for environmental management, to name just a few. Due to their utility for a variety of applications, there are many indices and software packages that have been designed to provide calculations and analysis of landscape structure patterns in categorical maps. With the purpose of making a comparison between the most used tools (Fragstats, V-Late, PA4), this paper examines their advantages and disadvantages in order to create a list of common features that need to be incorporated into this type of software. An Application Programming Interface (API) is produced without limitations on data input,that is capable of calculating vector or raster metrics and is extensible. This API should make it possible not only to build third party applications easily,but also make it possible to add new metrics and research into new paradigms related to traditional landscape metrics. Land-metrics DIY (Do It Yourself) is the library presented in this paper. It can calculate almost 40 landscape metrics from geometry provided by an ESRI Shapele.Environmental Modelling and Software - ENVSOFT. 10/2013;