Understory Plant Richness and Native Tree Invasion in Exotic Robinia pseudoacacia Stands in Hokkaido, Japan
We investigated the ecological impact of the exotic black locust (Robinia pseudoacacia) on native vegetation in Hokkaido, northern Japan. Many researchers have considered that native plant species in black locust stands are excluded because of the facilitated establishment of invasive exotic herbaceous plants in the stands. In the present study, the understory vegetation in 25 black locust plantations was compared with that in 23 white birch (Betula platyphylla var. japonica) plantations. White birch is a native deciduous pioneer tall tree species in Hokkaido. In addition, the relationship between the stand age and the maximum dbh was compared between regenerating native trees and black locust in each black locust plantation. The number of understory plant species in black locust plantations did not differ statistically from that in white birch plantations. Few exotic plants were observed in black locust plantations. Furthermore, many regenerating native tree species were found in black locust plantations. The maximum dbh of regenerating native species increased significantly with stand age, with some of them outgrowing black locust. In conclusion, we found no evidence that native plant species were being excluded because of the establishment of invasive exotic herbaceous plants in black locust stands in Hokkaido, Japan.
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