An Understory Comparison of the Exotic Phellodendron amurense Rupr. (Rutaceae) and Adjacent Native Canopy species in an Urban and Suburban Woodland

An understory comparison of the invasive tree species Phellodendron amurense Rupr. and surrounding native tree species at two locations in the greater New York metropolitan region is examined. The understory of canopies consisting of P. amurense was compared with adjacent canopies consisting of native tree species based upon their species density, richness and native understory composition. To determine if differences can be accounted for by shade cast by the canopy, leaf area indices were compared between the two canopy types at both locations.

At both locations there was a significantly lower number of individual plants per m2 quadrat under P. amurense than under native canopy (p < .0032; p < .0088) When looking at only native understory species, there was also a highly significant difference with P. amurense canopies having lower numbers of native individuals present per quadrat (p < .0009, p < .0001). There was also a significant difference between the invaded versus native sites in the mean number of total species per m2 quadrat at one site (p < .0001), while the second site showed a non significant difference (p < .0059).

Canopy Analysis revealed no significant differences in leaf area index between canopy types at either site although leaf area index was higher under native species at both locations indicating that shading is not likely to play a role in the lower density of understory individuals under P. amurense.