・The decrease in the number of gravel bars, which were formerly extensive in rivers, as a result of dam and dike construction is a matter of concern.

・The group analyzed past and present aerial photographs and satellite images, and found that gravel bars had decreased and woodland expanded in two out of four rivers in which dams had been constructed.

・Bird species that are specialized for life on gravel bars (such as plovers) were abundant in the area with extensive gravel bars.

・Woodland expansion was predicted to reduce the abundance of birds specialized for life on gravel bars.

The effect of the flow regulation by dam construction on organisms has been studied mainly in terms of the instream environment from the short-term perspective. This study used aerial photographs and satellite images of rivers with and without dam construction to compare the terrestrial environment around these rivers between several decades ago and today.

The results showed that although there had been no great changes to the terrestrial environment around rivers without dams, for two out of four rivers in which dams had been constructed, trees had encroached onto gravel bars, which had become covered with vegetation in the process of woodland expansion.

Bird surveys showed that bird species specialized for life on the gravel bars were abundant in the areas with extensive gravel bars. Woodland expansion was predicted to increase the populations of woodland birds, but to decrease those of gravel bar birds.

The flow regulation by dam construction worldwide is suggested to have a major effect on the terrestrial environment around rivers via processes including woodland expansion.

Futoshi Nakamura, Professor, Graduate School of Agriculture, Hokkaido University

TEL/FAX: +81-11-706-3842

E-mail: nakaf@for.agr.hokudai.ac.jp

Forest Ecosystem Management Group