The herbaceous layer (vascular plants ≤1 in in height) is an important component of forest ecosystems and a potentially sensitive vegetation stratum in response to acid deposition. This study tested several hypotheses concerning soil and herbaceous layer response to experimental acidification at the Fernow Experimental Forest in north-central West Virginia. Fifteen circular sample plots (0.04 ha) were established in each of three watersheds: WS3 (an ≈ 20-yr-old watershed receiving acidification treatment with (NH4)2SO4), WS4 (>80-yr-old control), and WS7 (≈ 20-yr-old control). The herb layer was sampled intensively in 10 1-m2 subplots within each sample plot, including determination of species composition, cover, and random biomass harvests. Harvested plant material was separated by species and analyzed for macronutrients, micronutrients, and Al. Soft was sampled from harvest subplots and analyzed for texture, pH, organic matter, and macro- and micronutrients. Few differences among watersheds for virtually all measured soil variables indicated minimal response of soil fertility to the acidification treatment. The herbaceous layer was also quite similar among watersheds with respect to cover-biomass and species diversity; WS7, however, had ≈ 70% higher herb layer cover that both Ws3 and WS4, a result of the predominance of a few high-cover fern species and attributable to the north-facing aspect of WS7 vs. south-facing aspects of WS3/WS4. There was a high degree of species similarity among watersheds, suggesting no shift in species composition in response to acidification. There was also minimal response of element concentrations to acidification, although Fe and Al exhibited evidence of increased uptake in WS3. We conclude that, contrary to our expectations, there has been little substantive response of the soil and herb layer to acidification, but hypothesize that herbaceous layer species may experience toxicity problems with increased mobility of Al and micronutrients in the future.
This research was funded by USDA-FS Cooperative Grant no. 23-590 through NE-4301, Fernow Experimental Forest, Parsons, WV. The use of trade, firm, or corporation names in this paper is for the information and convenience of the user. Such use does not constitute an official endorsement or approval by the U.S. Department of Agriculture or the Forest Service of any product or service to the exclusion of others that may be suitable. We are indebted to Steve Horsley for helpful discussion of fern data.