2000 BES Abstracts


A comparison of exotic and non-exotic plant populations in the Gwynns Falls riparian corridor

Grace S. Brush, Wayne C. Zipperer


Of 147 plant species sampled in the Gwynns Falls riparian corridor, 55 are exotics. Of those 55 exotics, 10 are trees and 45 herbs. Diversity is similar throughout the corridor for trees and herbs, but higher for herbs.

Size distributions of trees and percent cover of herbs show that species have discrete distributions throughout the watershed with small trees of some species occurring in the upper and middle sections and large trees occurring in the lower watershed, and vice versa. Among native species, Fraxinus pennsylvanica is restricted almost entirely to the middle and lower watershed, while Acer negundo and Juglans nigra occur predominantly in the upper and middle sections. Non-North American exotic trees are concentrated in the lower watershed. Except for 3 species, herbaceous exotics with >0.5% cover are concentrated in the upper, middle or lower watershed.

The watershed is characterized by a geologic, soils and hydrologic gradient, ranging from schist that weathers into a well-drained soil in the upper watershed to saprolitic soils weathered primarily from gneiss in the lower section. Flooding is much less frequent in the lower watershed, where streams are more deeply incised. Superimposed on this gradient is a history of human activity that has altered local riparian habitats. Some of the vegetation distributions can be explained by specific human alterations of the natural gradients.