Changes in Older and Younger Woods in West-Central Ohio

Author Institution: Dept. of Biological Sciences, Wright State University, OHThis study examines changes in two forest stands in the Quercus-Acer saccharum forest region of west central Ohio: an old-growth stand changing from Quercus-dominated to Acer saccharum-dominated and a stand established following agricultural abandonment about 1950. Both stands are in the Wright State University woods. Permanent plots were sampled in 1980 (younger stand only), 1982 (older stand only), 1993, and 2000. The older stand had more small, fewer intermediate, and more large stems than the younger stand. The plot in the new stand showed a bell-shaped distribution with most stems established shortly after land abandonment. Mortality decreased and growth increased with stem size for both stands. Acer saccharum in all sizes and large Quercus dominated the older stand. The younger stand was dominated by Robinia pseudo-acacia with Acer saccharum also important. In the older plots small stems generally were clustered, intermediate-sized stems randomly distributed, and the largest stems regularly distributed. In the younger plot small stems were aggregated while larger ones were randomly distributed. Quercus regenerated well until the late 1800s, singly or in small groups, but few stems have become established since 1900. Quercus may need fires or grazing to regenerate successfully. Both stands are changing to increased dominance by Acer saccharum and other shade-tolerant species as they lose species (Robinia pseudo-acacia in the younger stand, Quercus in the older stand) more successful under past than present conditions

Comparing the Sexual Reproductive Success of Two Exotic Trees Invading Spanish Riparian Forests vs. a Native Reference

A widely accepted hypothesis in invasion ecology is that invasive species have higher survival through the early stages of establishment than do non-invasive species. In this study we explore the hypothesis that the sexual reproductive success of the invasive trees Ailanthus altissima (Mill.) Swingle and Robinia pseudoacacia L. is higher than that of the native Fraxinus angustifolia Vahl., all three species coexisting within the riparian forests of Central Spain. We compared different stages of the early life cycle, namely seed rain, seed infestation by insects, seed removal by local fauna, seed germination under optimal conditions and seedling abundance between the two invasive trees and the native, in order to assess their sexual reproductive success. The exotic species did not differ from the native reference (all three species displaying high seed rain and undergoing seed losses up to 50% due to seed removal by the local fauna). Even if the exotic R. pseudoacacia showed a high percentage of empty and insect-parasited seeds along with a low seedling emergence and the exotic A. altissima was the species with more viable seeds and of higher germinability, no differences were found regarding these variables when comparing them with the native F. angustifolia. Unsuitable conditions might have hampered either seedling emergence and survival, as seedling abundance in the field was lower than expected in all species -especially in R. pseudoacacia-. Our results rather suggest that the sexual reproductive success was not higher in the exotic trees than in the native reference, but studies focusing on long-term recruitment would help to shed light on this issue