Abstract. Geostatistics brings to ecology novel tools for the interpretation of spatial patterns of organisms, of the numerous environmental components with which they interact, and of the joint spatial dependence between organisms and their environment. The purpose of this paper is to use data from the ecological literature as well as from original research to provide a comprehensive and easily understood analysis ofgeostatistics' manner of modeling and methods. The traditional geostatistical tool, the variogram, a tool that is beginning to be used in ecology, is shown to provide an incomplete and misleading summary of spatial pattern when local means and variances change. Use of the non-ergodic covariance and correlogram provides a more effective description of lag-to-lag spatial dependence because the changing local means and variances are accounted for. Indicator transformations capture the spatial patterns of nominal ecological variables like gene frequencies and the presence/absence of an organism and of subgroups of a population like large or small individuals. Robust variogram measures are shown to be useful in data sets that contain many data outliers. Appropriate removal of outliers reveals latent spatial dependence and patterns. Cross-variograms, cross-covariances, and cross-correlograms define the joint spatial dependence between co-occurring organisms. The results of all of these analyses bring new insights into the spatial relations of organisms in their environment.

No abstract

This study was initiated to develop a model for predicting the relative impacts of alternative reservoir designs on vegetation in the backwater zone. The result is a probabilistic model based on niche differentiation in the floodplain forest. Existing methodologies provided estimates of the flooding regime modifications produced by variable backwater conditions during reservoir operation. The model is exercised, with hydrolic modifications as input, to simulate shifts in species distribution. The model has been applied to evaluate the impact of a proposed reservoir on the vegetation of Robert Allerton Part, a 607 km2 natural area in east—central Illinois. Comparison of simulations for three alternative plans for the reservoir provides a basis for distinguishing among them, and suggests that the impact of one would be substantially less than the other two.

We measured the timing and magnitude of nitrogenase activity and N2 fixation by lupines colonizing early successional volcanic sites at Mount St. Helens. Nitrogenase activity (measured by acetylene reduction) in Lupinus lepidus growing at a pyroclastic site exhibited significant diurnal trends, with lowest ethylene evolution rates at night. Nitrogenase activity also followed seasonal trends, with high rates in June, very low levels in August, the dry warm part of the season, and a partial recovery of nitrogenase activity in September after precipitation resumed. A comparison of typical nitrogenase activities measured at several sites suggested that rates of N2 fixation were highest in L. lepidus growing at disturbed low N sites. Adult lupine C and N composition also varied during the growing season, with trends correlated with seasonal patterns of nitrogenase activity. Seasonal N2 fixation in L. lepidus and L. Latifolius was measured using 15N isotope. Both species fixed °60% of their N during the first season of growth with some evidence of preferential allocation to aboveground biomass. N fixation by Lupinus lepidus individuals was ° 18.1 mg/g biomass or an average of 15.4 mg per plant, while L. latifolius fixed an average of 16.3 mg/g biomass, equivalent to 22.9 mg per plant. Average net C fixation during the same period was 355 and 589 mg per plant for L. lepidus and L. latifolius, respectively. Despite these rates, the current distribution of L. lepidus into a few, small patches that occupy <1% of the surface area indicates that annual N inputs by lupines are <0.05 kg/ha and thus probably not the primary source of N input into developing Mount St. Helens pyroclastic sites except at a local scale.

Lupine influence on soil C, N, and microbial activity was estimated by comparing root-zone soil (LR) to nonroot-zone soil (NR) collected at Mount St. Helens. Samples were collected from 5 sites forming a gradient of C and N levels as a reflection of different locations and varying volcanic disturbance by the 1980 eruption. In volcanic substrates undergoing primary ecosystem development, C and N levels were low, as would be expected, but higher in LR soil than NR soil. At the least disturbed sites, N was only slightly greater in LR soil whereas significantly less C was observed in LR soil than in surrounding NR soil. Inorganic-N concentrations were small at all sites but comprised a significant proportion of the total amount of soil N in volcanic substrates. In general, LR zone soil contained significantly more NH -N. The addition of glucose increased respiration in soils from all sites with the greatest relative response in volcanic soil from the low end of the C and N gradient. Active soil microbial biomass-C and cumulative respiration were correlated with C and N and were significantly greater in LR soil than in NR soil for all sites. These results are consistent with some expected trends in ecosystem development and demonstrate the significance of resource dynamics and lupines in determining patterns of ecosystem response to disturbance at Mount St. Helens. They also suggest that processes leading to soil heterogeneity can be related to either development or to degradation depending on the context of the specific ecosystem or resource under consideration.