Bc. Mccarthy, EXPERIMENTAL STUDIES OF HICKORY RECRUITMENT IN A WOODED HEDGEROW AND FOREST, Bulletin of the Torrey Botanical Club, 121(3), 1994, pp. 240-250
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.