EXPERIMENTAL STUDIES OF HICKORY RECRUITMENT IN A WOODED HEDGEROW AND FOREST
Bulletin of the Torrey Botanical Club
An examination of the vegetation in and around an old-growth oak-hickory 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 differential recruitment patterns in contrasting landscape elements. To determine seed discovery efficiency by small vertebrates, I planted seeds of mockernut hickory (C. tomentosa (Poir.) Nutt.) with and without their aromatic husk in both forest and hedgerow. Regardless of diaspore type or habitat, seed discovery by herbivores was found to be 85-100% after only 5 days. Gray squirrels (Sciurus carolinensis), the principal predator-disperser, were determined to be equally abundant in both landscape elements. To assess the effects of diffuse competition and predation on seedling establishment and survival, I constructed split-plot shade/exclosure cages into which 576 seedlings were explanted and subsequently monitored (survival and mortality agent) for three years. Browsing by deer and rabbits resulted in considerable mortality after one year, particularly in the forest (64% mortality) compared to the 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. By the end of the third year few seedlings remained alive (ca. 1% in forest, 10% in hedgerow). Over the 3-yr period, a small percentage of seedlings were lost due to other factors such as root grubbing, whole plant removal, and litterfall. Shading (50%), to emulate diffuse competition 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 majority of seedlings in both habitats in each field season. I conclude that certain stages of recruitment may be significantly influenced by the presiding landscape element.
Author(s): MCCARTHY, BC
Journal: Bulletin of the Torrey Botanical Club