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  • Soil nitrogen availability  (1)
  • Spatial analysis  (1)
  • 1
    ISSN: 1432-1939
    Keywords: Key words Coastal dune ecosystems ; Ion exchange membrane spikes ; Soil nitrogen availability ; Soil resource heterogeneity ; Spatial statistics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract There are few studies in natural ecosystems on how spatial maps of soil attributes change within a growing season. In part, this is due to methodological difficulties associated with sampling the same spatial locations repeatedly over time. We describe the use of ion exchange membrane spikes, a relatively nondestructive way to measure how soil resources at a given point in space fluctuate over time. We used this method to examine spatial patterns of soil ammonium (NH+ 4) and nitrate (NO− 3) availability in a mid-successional coastal dune for four periods of time during the growing season. For a single point in time, we also measured soil NH+ 4 and NO− 3 concentrations from soil cores collected from the mid-successional dune and from an early and a late successional dune. Soil nitrogen concentrations were low and highly variable in dunes of all ages. Mean NH+ 4 and NO− 3 concentrations increased with the age of the dune, whereas coefficients of variation for NH+ 4 and NO− 3 concentrations decreased with the age of the dune. Soil NO− 3 concentration showed strong spatial structure, but soil NH+ 4 concentration was not spatially structured. Plant-available NH+ 4 and NO− 3 showed relatively little spatial structure: only NO− 3 availability in the second sampling period had significant patch structure. Spatial maps of NH+ 4 and NO− 3 availability changed greatly over time, and there were few significant correlations among soil nitrogen availability at different points in time. NO− 3 availability in the second sampling period was highly correlated (r = 0.90) with the initial soil NO− 3 concentrations, providing some evidence that patches of plant-available NO− 3 may reappear at the same spatial locations at irregular points in time.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Plant ecology 80 (1989), S. 107-138 
    ISSN: 1573-5052
    Keywords: Ecological theory ; Mantel test ; Mapping ; Model ; Spatial analysis ; Spatial autocorrelation ; Vegetation map
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The spatial heterogeneity of populations and communities plays a central role in many ecological theories, for instance the theories of succession, adaptation, maintenance of species diversity, community stability, competition, predator-prey interactions, parasitism, epidemics and other natural catastrophes, ergoclines, and so on. This paper will review how the spatial structure of biological populations and communities can be studied. We first demonstrate that many of the basic statistical methods used in ecological studies are impaired by autocorrelated data. Most if not all environmental data fall in this category. We will look briefly at ways of performing valid statistical tests in the presence of spatial autocorrelation. Methods now available for analysing the spatial structure of biological populations are described, and illustrated by vegetation data. These include various methods to test for the presence of spatial autocorrelation in the data: univariate methods (all-directional and two-dimensional spatial correlograms, and two-dimensional spectral analysis), and the multivariate Mantel test and Mantel correlogram; other descriptive methods of spatial structure: the univariate variogram, and the multivariate methods of clustering with spatial contiguity constraint; the partial Mantel test, presented here as a way of studying causal models that include space as an explanatory variable; and finally, various methods for mapping ecological variables and producing either univariate maps (interpolation, trend surface analysis, kriging) or maps of truly multivariate data (produced by constrained clustering). A table shows the methods classified in terms of the ecological questions they allow to resolve. Reference is made to available computer programs.
    Type of Medium: Electronic Resource
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