A 19-Year Study of the Dynamics of an Invasive Alien Tree, Bischofia javanica, on a Subtropical Oceanic Island

A 19-yr study of the dynamics of an invasive alien species, Bischofia javanica Blume, in a secondary forest was conducted in the Bonin Islands, Japan. The study was begun in 1984 when another alien species, Pinus luchuensis Mayer, had begun to die because of infection by a pine nematode as well as typhoon damage in 1983. Diameters at breast height (DBHs) of all trees in a 20 by 20 m plot and heights of all saplings (<1.3 m, ≥0.3 m in height) were measured almost every 3 yr. The total basal area of P. luchuensis decreased over time, and all trees had fallen over by 1998. The total basal area of B. javanica increased more than 10-fold over 19 yr without changes in tree or sapling density. Up to 1990, growth rates of trees of B. javanica were higher than those of two native canopy trees (Pouteria obovata and Machilus kobu), but a third native canopy tree (Schima mertensiana) had growth rates comparable with those of B. javanica. After 1990, there were few differences between growth rates of B. javanica and native species. However, mortality and recruitment of B. javanica were lower than those of native species of canopy trees during the survey period. The higher growth rate, lower mortality, and lower recruitment led to a shift from a skewed size distribution of the individuals of B. javanica toward a more bellshaped size distribution. Our results suggest that regeneration and maintenance of B. javanica populations in the secondary forests depend on canopy gaps occasionally created by disturbances.