Effects of climate changes on the water relations of endemic vegetation in the Ogasawara Islands.

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To evaluate the effects of long-term climate changes on endemic vegetation in the Ogasawara Islands, we examined the relationships between seasonal drought and the physiological properties of endemic tree species, such as water relations and growth period. The seasonal variations of sap flow and conductance showed that the transpiration rates of endemic tree species were depressed in severe drought conditions and that the endemic tree species changed their water relations to resist the seasonal drought. Moreover, the leaf water potential of endemic species was rapidly decreased with the depletion of soil water in seasonal drought periods, and the growth period was shortened compare to that in the wetter area. These results suggested that the recent drying trend would change the water relations and growth of endemic tree species, and, therefore, that the long-term climate change could be risk factors affecting the endemic vegetation of the Ogasawara Islands.