EXPERIMENTAL STUDIES OF HICKORY RECRUITMENT IN A WOODED HEDGEROW AND FOREST

An examination of the vegetation in and around an old-growth oak-hicko ry forest in Central New Jersey suggested that hickories (Carya spp., Juglandaceae) were not regenerating in the forest at the same rate as in adjacent wooded hedgerows (5-7 m wide corridors dominated by trees and shrubs). The goal of this study was to experimentally examine how factors affecting seed and seedling survival might account for these d ifferential recruitment patterns in contrasting landscape elements. To determine seed discovery efficiency by small vertebrates, I planted s eeds of mockernut hickory (C. tomentosa (Poir.) Nutt.) with and withou t their aromatic husk in both forest and hedgerow. Regardless of diasp ore type or habitat, seed discovery by herbivores was found to be 85-1 00% after only 5 days. Gray squirrels (Sciurus carolinensis), the prin cipal predator-disperser, were determined to be equally abundant in bo th landscape elements. To assess the effects of diffuse competition an d predation on seedling establishment and survival, I constructed spli t-plot shade/exclosure cages into which 576 seedlings were explanted a nd subsequently monitored (survival and mortality agent) for three yea rs. Browsing by deer and rabbits resulted in considerable mortality af ter one year, particularly in the forest (64% mortality) compared to t he hedgerow (21% mortality). During the second year, the major source of mortality switched to physiological stress resulting from drought. Mortality due to drought stress was more noticeable in the hedgerow. B y the end of the third year few seedlings remained alive (ca. 1% in fo rest, 10% in hedgerow). Over the 3-yr period, a small percentage of se edlings were lost due to other factors such as root grubbing, whole pl ant removal, and litterfall. Shading (50%), to emulate diffuse competi tion by overstory, was not found to affect survival to any significant extent in either habitat. Phytophagous insects did not result in any observable mortality but did remove 1-10% of the leaf area of the majo rity of seedlings in both habitats in each field season. I conclude th at certain stages of recruitment may be significantly influenced by th e presiding landscape element.