Wind pollination and insect pollination of two temperate willow species, Salix miyabeana and Salix sachalinensis

Pollination systems of Salix miyabeana and Salix sachalinensis were studied at a riverside in northern Japan in order to measure the balance of wind p ollination and insect pollination. In 1996, 19 clones of each species were selected, and seed-set success by a net-bagging (to exclude insect visitati on) and an artificial pollination (to remove pollen limitation) were compar ed to by natural pollination. For S. miyabeana, the same experiment was rep eated in two populations in 1997. Proportion of seed set through wind polli nation dominated in both species in this study. Pollen limitation was commo n under natural conditions, and S. sachalinensis relied more on insect poll ination for seed production than S. miyabeana. Meteorological factors such as precipitation and hours of sunshine during the flowering season influenc ed the potential reproductive activity of the willow between years. In the wet and cloudy spring of 1996, clones which obtained high seed set depended more on insect pollination for both species, whereas in the dry and sunny spring of 1997, such clones depended more on wind pollination for S. miyabe ana. Because the efficiency of wind pollination seemed to be more sensitive to fluctuating weather conditions than insect pollination, insect pollinat ion was considered to play an assurance role for seed production in these w illows.