You are here
Harvard Forest Symposium Abstract 2005
- Title: Ecosystem effects and legacies of the introduced N-fixing tree, Robinia pseudoacacia, in the upland coastal forests of Cape Cod, MA.
- Primary Author: Betsy Von Holle (Harvard Forest)
- Abstract:
Robinia pseudoacacia, a nitrogen-fixing, clonal tree species native to the central Appalachian and Ozark Mountains, is considered to be one of the top 100 worldwide woody plant invaders. In a previous study, we demonstrated that this species had an average of ten times the number and cover of nonnative species under its canopy, compared to native-canopied forest (primarily Pinus rigida and Quercus alba/velutina) located 20 m from the sampled locust stand in Cape Cod, MA. However, we also found that the total land cover of Robinia pseudoacacia, or black locust, in the outer Cape has significantly declined over the past three decades. Aerial photographs taken immediately following Hurricane Hugo, which occurred in 1989, revealed that windthrow from this event was the cause of the loss of many of these locust canopies. To understand the legacy effects of this species on this upland coastal ecosystem, we established field plots within areas that were formerly locust stands (as revealed by aerial photography and field identification) where we identified plant species composition and cover in addition to rates of soil nitrogen cycling. This field study was conducted during the peak months of nitrogen cycling for Cape Cod: July-August. Preliminary analyses have revealed that the areas that were formerly locust stands are intermediate between native pine-oak and nonnative locust stands in levels of nitrate (Figure 1A) and nonnative species richness (Figure 2A). Soil ammonium levels of former locust stands remained elevated (Figure 1B) at the levels of current locust stands. However, native species diversity levels are highest within these former locust stands (Figure 2B). The native black cherry, Prunus serotina, dominates the overstory canopy of these former locust stands. Thus, levels of soil nitrate, and especially soil ammonium, in formerly locust stands continue to be elevated relative to those under native pine-oak stands. Other legacy effects of locust are altering the successional trajectory and continuing to serve as ‘islands of invasion’ within this resistant system. Competition and soil nutrient experiments in the field and greenhouse are in progress to understand the mechanism for the understory dominance of locust stands by nonnative species.
- Research Category:
