Date of Award

8-1981

Degree Type

Thesis

Degree Name

Master of Science

Major

Ecology and Evolutionary Biology

Major Professor

E. E. C. Clebsch

Committee Members

H. R. DeSelm, Edward Buckner

Abstract

The vegetation, seed rain, and seed banks were examined in a beech gap and a spruce stand in the high elevations Smoky Mountains to quantify the seed exchanges between these two plant communities. This information is of interest because these beech gaps are believed to be slowly invaded by Picea rubens along the abrupt boundary between the stands.

Five transects of seed traps were set up perpendicular to the boundary, extending into each community. Sticky and gravity traps were placed at preset intervals along the transects to collect seed rain for one year. At each seed rain sample site a soil core was collected to examine viable seeds and vegetative propagules in the soil.

The vegetation analysis showed quantitative differences rather than compositional difference between the tree canopies of the beech gap and spruce stand. The beech gap was dominated by Fagus grandifolia, whereas the spruce stand was dominated by Picea rubens and Betula lutea. The shrub layer and herbaceous vegetation differed greatly between these two plant communities. Canopy transects across the boundary demonstrated a narrow ecotonal zone rather than a distinct boundary between the communities although from a distance the boundary appeared sharp.

The seed rain data showed substantial seed dispersal of Betula lutea and Pica rubens and minimal dispersal of Cacalia rugelia into the beech gap from the spruce stand. Some seeds of Poa alsodes were able to disperse into the spruce stand from the beech gap. Evidence is presented showing that Eupatorium rugosum was dispersed from the Clingman's Dome Road into the beech gap and possibly into the spruce stand as well. The seed bank data confirmed the exchange of seeds of these species except for Cacalia rugelia.

The seed bank results agreed with other seed bank studies, in the absence of seeds of late successional woody species such as Fagus grandifolia and Picea rubens. In contrast with most seed bank studies, the seed banks in these communities had a high similarity with the overlying vegetation. multivariate and analytical techniques showed significant differences in the seed banks between these adjacent plant communities. Reciprocal averaging showed a beech gap seed bank species gradient which is highly correlated with sample core slope position. This seed bank gradient is probably in response to a moisture topographic gradient affecting the overlying herbaceous species populations.

The implications of the limited seed exchanges between these communities are discussed in terms of the possible invasion of the spruce stand vegetation into the beech gap. The potential role of seeds stored in the soil in succession and vegetation dynamics is discussed.

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