Factors limiting regeneration of Quercus alba and Cornus florida in formerly cultivated coastal plain sites, South Carolina

Abstract

To determine the extent that resources, conditions and herbivory limit regeneration of Quercus alba L. and Cornus florida L. in formerly cultivated coastal plain uplands, we planted seedlings of the two species in two pine and one pine–hardwood forest understory and three adjacent clearcuts. Soil carbon and moisture, available nitrogen and phosphorus, and gap light index (GLI) were measured next to each seedling. Over two growing seasons, stem and leaf herbivory were estimated and survival was recorded. At the end of 2 years, all surviving stems were harvested to determine total leaf area and 2-year biomass growth. Survival to the end of the study was not significantly different between clearcuts (62.9%) and understories (64.6%). However, clearcuts led to significantly greater biomass growth and leaf area (ANOVA; P<0.05) for both Q. alba and C. florida. Soil moisture and available nutrients were also greater in the clearcuts ( P<0.05). Using separate multiple linear (growth) or logistic (survival) regressions for each combination of three sites, two cutting treatments and two species, we found that soil moisture significantly affected survival in 12.5% and biomass growth in 8.3% of the regressions. Light availability significantly impacted biomass growth in 16.7% of the regressions. Stem and leaf herbivory had very little impact on survival (8.3%), but when combined, these two factors significantly impacted leaf area or biomass growth in 33.3% of the regressions. Seedling responses were highly variable, and no regression model accounted for more than 70.0% of this variation. In our study, stand-scale variation in seedling responses (especially the difference between clearcut and understory) was much greater than within-stand variation. Of the within-stand factors measured, herbivory was clearly the most important. To establish these species in mesic upland coastal plain sites, we recommend planting immediately after clearcutting.