A QUANTITY AND PERIOD CHANGES ON WILLOW SEEDS IN THE RIVERS OF HOKKAIDO

Abstract

To monitor the quantity and period changes in willow seed of river, we investigated the flowing willow seed in water. The survey sites were the Toyohira river, Tyubetsu river, Teshio river and Tokachi river. The survey was conducted three points on every river between snowmelt flood season that occur in willow seeds dispersal and ordinary water-level season. Plankton net was used to catch the willow seeds.

In early June, it was just starting to catch seeds on trap at every river. The volume peak of flowing willow seeds were; Toyohira river was in early June, Tyubetsu river was not, Teshio river was in early June and early July and Tokachi river was in early July. There are little seeds collected at the Tyubetsu river.

The results also show that the quantity vary in all sorts of seeds according to the season. These results can be basic information for willow management in the river channel.