Abstract not found

Canonical correspondence analysis (CCA) is introduced as a multivariate extension of weighted averaging ordination, which is a simple method for arranging species along environmental variables. CCA constructs those linear combinations of environmental variables, along which the distributions of the species are max-imally separated. The eigenvalues produced by CCA measure this separation. As its name suggests, CCA is also a correspondence analysis technique, but one in which the ordination axes are constrained to be linear combinations of environmental variables. The ordination diagram generated by CCA visualizes not only a pattern of community variation (as in standard ordination) but also the main features of the distributions of species along the environmental variables. Applications demonstrate that CCA can be used both for detecting species-environment relations, and for investigating specific questions about the response of species to environmental variables. Questions in community ecology that have typically been studied by 'indirect ' gradient analysis (i.e. ordination followed by external interpretation of the axes) can now be answered more directly by CCA.

A common problem in community ecology and ecotoxicology is to discover how a multitude of species respond to external factors such as environmental variables, pollutants and management regime. Data are collected on species composition and the external variables at a number of points in space and time. Statistical methods available so far to analyze such data either assumed linear relationships or were restricted to regression analysis of the response of each species separately. To analyze the generally non-linear, non-monotone response of a community of species, one had to resort to the data-analytic methods of ordination and cluster analysis-'indirect ' methods that are generally less powerful

OF THE DISSERTATION A Markov Chain Monte Carlo Method for Approximating 2-Way Contingency Tables with Applications in the Stability Analysis of Ecological Ordination by Stanley S. Bentow Doctor of Philosophy in Statistics University of California, Los Angeles, 1999 Professor N. Donald Ylvisaker, Chair This dissertation develops a Markov Chain Monte Carlo method for approximating 2-way contingency tables with an eye toward assessing the stability of ecological ordination. Ecology is a part of biology that deals with the interrelationships between populations, communities and ecosystems and their environment. It draws on knowledge from many other disciplines such as climatology, physical geography, agronomy, and pedology [52]. Odum [75] prefers the de nition \ Ecology is the study of structure and function of nature," and stresses the role of ecosystem research in relation to the use of nature by man. Krebs [58] prefers to think of Ecology as the scienti c study of the interactions t...

Lillybridge,T.R.; Kovalchik, B.L.; Williams C.K.; Smith, B.G. 1995. Field guide for forested plant associations of the Wenatchee National Forest. Gen. Tech. Rep. PNW-GTR359. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 335 p. In cooperation with: Pacific Northwest Region, Wenatchee National Forest.

This paper describes a model which links four levels in an ecologicalhierarchy using a series of matrices. The four levels are landscape, land cover type, community and species. Each matrix quantifies the probabilistic associations between entities in two adjacent levels in the hierarchy. A landscape classification (1 km resolu- tion) provides a spatial element to the model enabling the distributions of species to be predicted and pre- sented as maps within a geographical information system Implementation of the model in Northern England is described. The distributions of 579 species of plants were predicted and compared with data from independent field surveys. The predicted distributions were found tobe accurate for 59% of species. The dis- tributions of rare and non-native (introduced) species of plant were relatively poorly predicted. The potential of this approach to model plant species distributions is discussed. 1.

This study examined the impact of logs and stumps on the understory composition of 28-yearold aspen-dominated boreal forests. Suitable logs covered more than five times the area of stumps in both harvest and wildfire stands. Logs and stumps were colonized by a significantly different assemblage of vascular plants than the forest floor. Initial colonization patterns on dead wood in both wildfire and harvest stands were similar. However, as dead wood decayed, assemblages of vascular plants diverged and became more similar to their respective forest floor assemblages. Regenerating trees and shade tolerant forbs were disproportionately more abundant on logs and stumps, while grasses, shrubs, and shade intolerant forbs were disproportionately more abundant on the forest floor.

An ecological classification system has been developed for the Pacific Southwest Region

degrees in wildland resource science (Ph.D. 1980), range management (M.S. 1978), and anthropology (A.B. 1975). At the time this report was written, she was

This paper describes the oak woodland plant communities of Northwest California and their ecological status using data from 446 ecology plots collected on federal lands in Humboldt, Trinity, Siskiyou, Mendocino, Tehama, Glenn, Colusa and Lake Counties. Geographically, oak woodlands lie between the coastal mixed evergreen forests and the valley grasslands of the Central Valley. They were found in small patches nested within a mosaic of annual grasslands and conifer forests, and hence contain species common to both of these vegetation types. The oak woodlands of northwest California were primarily included in three vegetation series: Oregon white oak (Quercus garryana), black oak (Quercus kelloggii) and blue oak (Quercus douglasii). Valley oak (Quercus lobata) was also found in the study area, but because of its limited extent and insufficient samples, it will not be described here. Due to their history of grazing and their proximity to annual grasslands, many of the Northwest California oak woodlands contained high cover of non-native species. In some types, nonnative grass and/or forb cover far exceeded that of native species. The forb and grass layers differed from one another based on the general shift of moderate overall cover of non-native grasses to native forbs. Species diversity in these oak woodland systems is a controversial subject because of perceived losses of biological diversity. After the introduction of invasive non-native, annual, Mediterranean species, many of the native species were displaced. Species composition of oak woodlands and annual grasslands will be compared with special attention paid to the cover of non-native species. The ecological status of oak woodlands in Northwest California will be discussed from several perspectives. These include species composition of grasses and forbs, comparisons of cover, species counts, annual and perennial species and native and non-native species. The long-term successional status of these systems will be described using assigned seral species status. Noxious and invasive weeds found in these oak woodlands will also be described and compared to annual grasslands.