Masters Theses

Date of Award

5-1994

Degree Type

Thesis

Degree Name

Master of Science

Major

Botany

Major Professor

J. Frank McCormick

Committee Members

Cliff Amundsen, Bob Meunchen

Abstract

Two riparian forest communities were compared on the basis of community structure and composition. Parameters included species dominance, diversity, and richness, and community similarity, biomass, and plant density. These communities are close to each other and are similar in topography, elevation, aspect, soil types, and land use practices. The major abiotic difference between the communities is the level of nutrient inputs from nonpoint agricultural runoff; one community has high input levels (experimental community) and the other has relatively low levels (control community). It was hypothesized that community structure and composition would differ due to nutrient loading. The purpose of this study was to determine if differences exist, and, if so, to evaluate the differences and develop management options which would optimize forest removal of nutrients from water sources. Canopy, subcanopy, shrub, herb, and groundcover strata were analyzed.

Most differences between communities were not statistically significant. The canopy stratum of the control community was more diverse than that of the experimental community, but species richness and density were not significantly different. Subcanopy species richness was significantly higher in the control community, but plant density did not differ significantly. Woody biomass of canopy and subcanopy strata taxa was significantly higher in the control community. Species diversity was higher in the experimental community, but species richness of shrubs and herbs was quite similar in the two communities. Densities of shrubs and herbs were significantly higher in the experimental community. Groundcover species richness was higher but percent coverage was lower in the experimental community. Highest community similarity of species composition was between the canopy strata (75%) with progressively less similarity between the subcanopy, shrub, groundcover, and herb strata. Overall coefficient of community similarity was 44%.

The experimental community is less nutrient limited, is less light limited (more open canopy) than the control community, and favors faster growing, shade intolerant species. Highest species diversity occurred in upper strata of the control community where light was not limiting but nutrients were probably limiting. Significantly greater biomass in the canopy and subcanopy of the control community was probably due to less recent logging and fewer treefalls. Higher species diversity and the presence of shade intolerant species in lower strata reflect the influence of intermediate levels of disturbance in the experimental community. Higher plant density in two of three lower strata of the experimental community are consistent with expectations of increased plant growth under conditions of relatively greater light and nutrient availability.

Based upon results of this study, the preferred management practice for riparian forest communities of Herrings Marsh Run is to:1. maintain a riparian forest at least 24 m wide along all stream banks2. maintain an economically productive agroforestry zone between riparian forest and contiguous land used for traditional purposes3. on a 40 to 50 year rotation, harvest timber from 24 x 21m plots in the riparian forest according to strip shelter belt procedure.

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