Physiological mechanism of invasion success of trees in the Bonin islands in Japan

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The flora of Bonin islands in Japan has a high degree of endemism (70% among tree species), especially in the ridge sites with shallow soils. The dwarf evergreen forests characterized by the co-existence of a magnitude of tree species are generally found at the ridge sites. The interspecific variability of sunlit leaf characteristics was investigated among the dwarf evergreens. LMA (dry mass per unit leaf area) was positively correlated to leaf lifespan, wood (stem) density, nitrogen per unit leaf mass, lamina thickness, δC, and negatively correlated to leaf osmotic potentials and water contents at full turgor, leaf-mass based photosynthetic rates (P_n), leaf area-based P_n, and leaf nitrogen-based P_n. The values of δC were positively correlated to LAM, wood (stem) density, and leaf thickness. Nitrogen re-absorption rates at leaf shedding were 50% in the average, and were not correlated to any leaf characteristics.Bishofia javanica is an alien tree species that has successfully invaded to the Bonin islands. Because the invasion of the species was frequently found following canopy-gap formation in the islands, we hypothesized that B.javanica has greater acclimation capacity than native tree species to fluctuations in understory light. Following the shade-to-sun and sun-to-shade transfers, pioneer tree species had high new-leaf production rates but low acclimation capacity of old leaves, whereas late-successional tree species had low new-leaf production rates but high acclimation capacity of old leaves. In contrast, B.javanica had high new-leaf production rates, high acclimation capacity of old leaves, and the highest growth rates among the tree species. B.javanica seedlings had relatively high survival rates under shaded understory in the Bonin islands. We conclude that high stress-tolerance under resource conditions and high resource-use under fluctuating environment conditions are a physiological key factor of invasion success.