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Plant Effects on Soils in Drylands: Implications for Community Dynamics and Ecosystem Restoration

DOI: 10.1007/1-4020-3447-4_6
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    ABSTRACT: Aims Studies of species distribution patterns traditionally have been conducted at a single scale, often overlooking species–environ-ment relationships operating at finer or coarser scales. Testing diversity-related hypotheses at multiple scales requires a robust sampling design that is nested across scales. Our chief motivation in this study was to quantify the contributions of different predictors of herbaceous species richness at a range of local scales. Methods Here, we develop a hierarchically nested sampling design that is balanced across scales, in order to study the role of several envi-ronmental factors in determining herbaceous species distribution at various scales simultaneously. We focus on the impact of woody vegetation, a relatively unexplored factor, as well as that of soil and topography. Light detection and ranging (LiDAR) imaging enabled precise characterization of the 3D structure of the woody veg-etation, while acoustic spectrophotometry allowed a particularly high-resolution mapping of soil CaCO 3 and organic matter contents. ImportantFindings We found that woody vegetation was the dominant explanatory variable at all three scales (10, 100 and 1 000 m 2), accounting for more than 60% of the total explained variance. In addition, we found that the species richness–environment relationship was scale dependent. Many studies that explicitly address the issue of scale do so by comparing local and regional scales. Our results show that efforts to conserve plant communities should take into account scale dependence when analyzing species richness–envi-ronment relationships, even at much finer resolutions than local vs. regional. In addition, conserving heterogeneity in woody veg-etation structure at multiple scales is a key to conserving diverse herbaceous communities.
    Journal of Plant Ecology 01/2012; · 1.36 Impact Factor
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    ABSTRACT: The study of species coexistence and community assembly has been a hot topic in ecology for decades. Disentangling the hierarchical role of abiotic and biotic filters is crucial to understand community assembly processes. The most critical environmental factor in semi-arid environments is known to be water availability, and perennials are usually described as nurses that create milder local conditions and expand the niche range of several species. We aimed to broaden this view by jointly evaluating how biological soil crusts (BSCs), water availability, perennial species (presence/absence of Stipa tenacissima) and plant-plant interactions shape a semi-arid annual plant community. The presence and cover of annual species was monitored during three years of contrasting climate. Water stress acted as the primary filter determining the species pool available for plant community assembly. Stipa and BSCs acted as secondary filters by modulating the effects of water availability. At extremely harsh environmental conditions, Stipa exerted a negative effect on the annual plant community, while at more benign conditions it increased annual community richness. Biological soil crusts exerted a contradictory effect depending on climate and on the presence of Stipa, favoring annuals in the most adverse conditions but showing repulsion at higher water availability conditions. Finally, interactions among co-occurring annuals shaped species richness and diversity of the final annual plant assembly. This study sheds light on the processes determining the assembly of annual communities and highlights the importance of Biological Soil Crusts and of interactions among annual plants on the final outcome of the species assembly.
    PLoS ONE 01/2012; 7(7):e41270. · 3.53 Impact Factor
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    ABSTRACT: Water relations are essential in plant–plant interactions, particularly in Mediterranean coastal sand dunes, owing to marked drought periods and the possibility of groundwater (GW) salinization. In this study, seasonal water use dynamics were explored in the interaction between a native–invasive species, Retama monosperma, and the endangered Thymus carnosus, in south-western Spain. The following variables were measured: xylem water isotopic composition to determine water sources, predawn and midday stem water potential and free leaf proline content as stress indicator. GW electrical conductivity and stable isotopes were also analysed to assess water table salinity. In late summer and spring, the warmest seasons, Thymus beneath Retama displayed significantly lower water potential and higher leaf proline content than isolated Thymus, whereas Retama showed the highest proline content in autumn and winter. Water sources showed different patterns depending on the Thymus situation: Isolated ones always matched the brackish GW, as well as Retama plants, whereas Thymus beneath Retama switched among rainfall, soil and water table, showing a seasonal change in the water-harvesting strategy. Overall, competition for water sources between both species was discovered, which led to a shift in water use and water uptake strategies of understorey Thymus. The results also demonstrate the importance and potential use of species interaction studies in the development of threatened species management strategies. Copyright © 2013 John Wiley & Sons, Ltd.
    Ecohydrology 05/2013; · 2.78 Impact Factor

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