Abstracts

Gallardo, A. 2003, 'Spatial Variability of Soil Properties in a Floodplain Forest in Northwest Spain', Ecosystems, vol. 6, pp. 564-576.

Floodplain forests are generally areas of high plant diversity compared with upland forests. Higher environmental heterogeneity, especially variation in below ground properties may help explain this high diversity. However, there is little information available on the spatial scale and pattern of below ground resources in floodplain forests. Geostatistics and co-efficient of variation (CV) were used to describe the spatial variability of 20 soil properties ranging from essential plant nutrients, such as NH₄⁺–N or PO₄³â€“P, to nonessential elements like Ti or V. The spatial variation of Si-to-(Al + Fe) ratio, an index of soil development, was also analyzed. Semivariograms and maps of selected properties were used to discriminate between the effect of flooding (andother mechanisms that may contribute to large scale trends in data) and local heterogeneity. The hypothesis that elements mainly cycled through biological processes (such as N) show different spatial properties than elements cycled through both biological and geological processes (such as P) or elements under strict geological control (such as Ti or V) is also presented. Redox potential was the most variable property (CV = 1.35) followed by mineral N, phosphate, organic matter, and carbon. Nonessential elements for organisms such as Si, Al, Ti, Rh, or V were less variable, supporting the hypothesis that biological control on soil properties leads to higher spatial variability. The range (the average distance within which the samples correlate spatially) varied between 3.89 m for water content to 18.5 m for the Si-to-(Al + Fe) ratio. The proportion of the total variance that can be modeled as spatial dependence (structural variance) was very variable, ranging between 0.34 for Fe and 0.96 for K. The addition of the large trend had a strong influence on the CV of most soil variables and created a gradient in C accumulation and the mineral weathering rate. Our results suggest that flooding and other processes that are responsible for large spatial trends in the floodplain forest differentially affect biologically and geologically controlled variables and at different turnover rates, thus providing a heterogeneous edaphic environment.

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Grace, J.B., Allain, L., et al. 2000, 'Vegetation Associations in a Rare Community Type - Coastal Tallgrass Prairie', Plant Ecology, vol. 147, pp. 105-115.

The coastal prairie ecoregion is located along the northwestern coastal plain of the Gulf of Mexico in North America. Because of agricultural and urban development, less than 1% of the original 3.4 million ha of this ecosystem type remains in native condition, making it one of the most endangered ecosystems in North America. The objective of this study was to characterize the vegetation and environmental relationships in a relatively pristine example of lowland coastal prairie in order to provide information for use in conservation and restoration. The study area was a small, isolated prairie located near the southern boundary of the coastal prairie region. Samples were taken along three parallel transects that spanned the prairie. Parameters measured included species composition, elevation, soil characteristics, indications of recent disturbance, above-ground biomass, and light penetration through the plant canopy. Fifty-four species were found in the 107 0.25-m² plots and a total of 96 species were found at the site. Only two non-native species occurred in sample plots, both of which were uncommon. Cluster analysis was used to identify six vegetation groups, which were primarily dominated by members of the Poaceae or Asteraceae. A conspicuous, natural edaphic feature of the prairie was the presence of ‘mima’ mounds, which are raised areas approximately 0.5 to 1 m high and 5 to 10 m across. Indicator species analysis revealed a significant number of species that were largely restricted to mounds and these were predominately upland and colonizing species. Ordination was performed using nonmetric, multidimensional scaling. The dominant environmental influence on species composition was found to be elevation and a host of correlated factors including those associated with soil organic content. A secondary group of factors, consisting primarily of soil cations, was found to explain additional variance among plots. Overall, this prairie was found to contain plant associations that are now rare in the surrounding landscape. Within the prairie, plant groups were largely separated by a suite of environmental conditions associated with topography. These results suggest that conservation and restoration efforts will need to carefully consider local topographic influences in order to be successful.

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Manu, V., Blair, G., et al., The use of Mulches to Increase Yields and Improve the Sustainability of Pacific Island Cropping Systems..

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