MORRIS, LORNA L.* and JEFFREY L. WALCK. Department of Biology, Middle Tennessee State University, Murfreesboro, TN 37132. - Growth and reproduction of the nonnative Ligustrum sinense and native Forestiera ligustrina (Oleaceae): implications for invasibility of exotic shrubs.
Ligustrum sinense Lour. is a shrub native primarily to China,
and has been introduced into several areas of the world. In
southeastern United States, it grows with the native shrub
Forestiera ligustrina (Michx.) Pour. The present study compared
the branch architecture, leaf characteristics, reproduction, and
phenology of the two species to identify aspects that might influence
the invasiveness of L. sinense. Both species were sampled along
the woodland edges of cedar (limestone) glades (1362 ± 79 mmol m-2 s-1, clear day at
noon in August) and in the (mostly) redcedar forest (112 ± 13 mmol m-2 s-1) in middle
Tennessee between March 2000 and February 2001. Multivariate analyses
of variances (MANOVAs, P £ 0.05)
indicated significant differences between the species. Regardless of
the habitat, L. sinense had higher stem elongation rate, leaf
weight ratio, leaf area ratio, and number of fruits per branch, had
lower leaf abscission rate and percentage of insect-damaged leaves,
and a more tree-like growth form than F. ligustrina. Leaf area
expansion rate, leaf area, and height of L. sinense growing in
the woods were greater than those of L. sinense growing along
the glade and greater than those of F. ligustrina in both
habitats. Branch architecture based on branch length and orientation
and on bifurcation ratio was similar between the species. However,
leaves of L. sinense in both habitats and those of F.
ligustrina in the woods were oriented at 98-107° from vertical but
those of F. ligustrina along the glade were at 132°. The
results suggest that L. sinense has a competitive advantage
over F. ligustrina due to its greater ability to spatially and
temporally capture light, particularly in response to the light
environment, and its higher fruit production.
Key words: exotic species, Forestiera, invasibility, Ligustrum, Oleaceae