Constraints on Plant Establishment and Community Composition

M. Hester

Project Overview

Our primary objective is to achieve a better understanding of the environmental constraints (both abiotic and biotic) on plant establishment and community composition in the Manchac-area wetlands.

Our primary focus is on herbaceous (non-woody) plant communities. Additionally, constraints on baldcypress seed germination and seedling establishment is also investigated. Preliminary data collection and analysis for the reciprocal transplant study indicate that the edaphic (soil) conditions differ significantly between the two sites. The interstitial sulfide concentration at the North Pass site was higher than the Tobe Canal site during the first two measurement periods. Although North Pass was initially more acidic in the summer it became less acidic than Tobe Canal by the fall of 2001. Soil redox potentials between the sites differed at both 1 cm and 15 cm. At both depths and times Tobe Canal had higher redox potential readings.

Plant species richness differed between the two sites at the spring and fall sampling, with Tobe Canal having higher species richness.

The plant species richness at Tobe Canal decreased during the summer, while plant species richness at North Pass increased. The plant species percent cover of Sagittaria lancifolia decreased over time, regardless of disturbance, at Tobe Canal, but not at North Pass. Conversely, the percent cover of Spartina patens decreased at North Pass, while it remained unchanged at Tobe Canal. Fertilization reduced the decline of S. patens percent cover at North Pass, but has not yet had a significant effect at Tobe Canal. Both species tended to have higher percent cover when transplanted into plots where the neighboring vegetation was either removed or killed.