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United States Department of Agriculture

Agricultural Research Service

Title: Large-Scale Related Effects on the Determination of Plant Communities and Relationships with Environmental Variables

Authors
item Drewa, Paul
item Bradfield, Gary - UNIV OF BRITISH COLUMBIA

Submitted to: Community Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 20, 2000
Publication Date: September 20, 2000
Citation: DREWA, P.B., BRADFIELD, G.E. LARGE-SCALE RELATED EFFECTS ON THE DETERMINATION OF PLANT COMMUNITIES AND RELATIONSHIPS WITH ENVIRONMENTAL VARIABLES. COMMUNITY ECOLOGY. 2000. V. 1(2). P. 157-164.

Interpretive Summary: The influence of scale on recognizing plant community patterns was examined using vegetation-environment data collected from a subalpine wet meadow in south-coastal British Columbia. Cover of plant species was recorded in 225, 0.25m**2 quadrats located at 5m intervals within a 40m x 120m sampling grid. Environmental data were also collected from each quadrat location and dconsisted of ground-level elevation as well as measured and mathematical estimates of 5 soil characteristics (carbon content, pH, electrical conductivity, % sand and % clay). Field sampling scale was adjusted by aggregating neighboring quadrats into composite sampling units; analytical scale was altered by varying the intercept level in dendrograms from a cluster analysis of the plant cover data corresponding to the different sampling scales. The resulting classifications were evaluated for their ability to explain variation in the vegetation and environmental data. Vegetation variation was highest at the smallest sampling scale indicating complex, fine-grained plant communities occur in the subalpine wet meadow. In contrast, environmental variation was highest at the larger sampling scales indicating changes in environmental factors are not as complex and change more gradually within the study area. Broad changes in environmental factors were consistent with recognition of 3 main vegetation zones along an elevation-drainage gradient within the sampling grid--upper mixed-forb, middle heath and lower sedge. This study reaffirms the need for careful consideration of field sampling techniques as well as analytical phases of vegetation research to ensure description and interpretation of patterns adequately address study objectives and vegetation-environment relationships are more completely investigated at different scales.

Technical Abstract: The influence of scale on the discernment of plant community patterns was examined using vegetation-environment data collected from a subalpine wet meadow in south-coastal British Columbia. Species cover data were recorded in 225, 0.25m**2 quadrats systematically located at 5m intervals in a 40m x 120m sampling grid. Environmental data consisted of quadrat elevations as well as measured and Kriged estimates of 5 soil variables (carbon content, pH, electrical conductivity, percent sand, and percent clay). Sampling scale was adjusted by aggregating neighboring quadrats into composite sampling units; analytical scale was altered by varying the intercept level in dendrograms from minimum increase of sum of squares cluster analysis of the vegetation data corresponding to the different sampling scales. The resulting classifications were evaluated for their ability to explain variation in the vegetation data and in the environmental data. The vegetation variation explained by the classifications was highest at the smallest sampling scale indicating that vegetation heterogeneity is fine grained. In contrast, the environmental variation explained was higher for the classifications based on the larger composite sampling units implying a coarser scaling of abiotic conditions within the study area. These results were consistent with the recognition of 3 main zones along a drainage gradient within the sampling grid--upper mixed-forb, middle heath and lower sedge. This study reaffirms the need for consideration of alternatives both in field sampling and analytical phases of vegetation research to ensure that description and interpretation of patterns adequately address study objectives and that vegetation-environment relationships are more completely investigated from a hierarchical perspective.

Last Modified: 4/20/2014
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