Fatin Chowdhury ’20

Forests are stratified in sections such as the herbaceous layer, which includes tracheophytes (plants with vasculature) over 1 meter in height and can be extremely ecologically significant. Potential factors influencing forest dynamics in this context include top layer (overstory) characteristics and soil quality. A researcher at the University of West Florida, Frank S. Gilliam, recently conducted work at the Fernow Experimental Forest in West Virginia in order to explore this matter. Specifically, he tested the hypothesis that elevated availability of nitrogen would cause the species dynamics of the herbaceous layer to change from being primarily influenced by soil nitrogen fertility to instead being mainly influenced by forest stand structure. 

Nitrogen levels were determined via colorimetric measurements of ammonia and nitrate. The overall extent of mineralization and nitrification were also measured. In addition, a distance meter was used in determining the structure of the forest canopy in terms of measured values. Measurement fields such as canopy area index (CAI) and others considered aspects of the environment such as canopy surface area. The study’s conclusion was in contrast to the hypothesis, and observations key to this finding were tied to Rubus allegheniensis (common blackberry) plants and its tendency to increase in cover alongside increasing nitrogen and light levels. While herbaceous cover as a whole was mostly connected with nitrogen levels, individual plant species were influenced notably by not only soil dynamics but also canopy dynamics. 

Gilliam also put forth in his paper that other considerations such as temperature and precipitation conditions are relevant in exploring this issue. Building on previous studies, he was able to collect evidence indicating that nitrogen in large amounts does not lead to forest structure becoming the predominant influence on the composition of Fernow forest’s herbaceous layer. 

Sources

1. Gilliam, F. (2019). Response of herbaceous layer species to canopy and soil variables in a central Appalachian hardwood forest ecosystem. Plant Ecology, 220(12), 1131–1138. https://doi.org/10.1007/s11258-019-00984-3
2. Image retrieved from: https://unsplash.com/photos/dkzlTpMYYMQ