PARENT SESSION
Poster Session #4: Invasions.
Monday, August 6, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall
60
Effects of removing an invasive understory shrub on growth of canopy trees in northeastern Illinois.
Kasmer, John1, Shefferson, Rich1,2, 1 2
ABSTRACT- Because common buckthorn (Rhamnus cathartica) can be present in high densities in forest understories in northeastern Illinois, we hypothesized that the shrub layer in these forests might have negative competitive effects on canopy trees. To test this hypothesis, we sampled paired areas (managed areas in which buckthorn has been removed recently, and adjacent unmanipulated areas) within five forest preserves in Lake County, IL. Within each area, we took tree cores of 16 canopy trees to look at past incremental growth, and measured soil moisture and the density of buckthorn and other shrubs within a radius of 1.7m of target trees. Although managed sites had lower densities of shrubs (p<.0005), there was no significant effect of treatment on soil moisture or on the average ring-width of canopy individuals in the last 3 years (ANCOVA, using average ring-width 5-10 years ago as a covariate), indicating that removal of buckthorn neither increased availability of soil-moisture availability nor released canopy trees from competition. However, a significant interaction term (p=0.045) indicated non-oak species showed a different response to management (decreased growth following management) than did oaks (no response). These results suggest that while buckthorn does not generally have a strong negative effect on canopy trees, some canopy species may actually be negatively affected by management, and that future research should focus on the effects of different management techniques on the managed forests.
KEY WORDS: Rhamnus cathartica, management techniques, invasive species, competition