Some findings on vegetative and sexual reproduction of koa

Abstract

Some environmental factors which influence the reproductive behavior of Acacia koa var. hawaiiensis (Rock) were studied on the east flank of Mauna Loa, Hawaii. Additionally, some factors were tested under controlled conditions. It was found that soil moisture as well as soil temperature in terms of day-degrees are limiting factors for koa germination. Variability among individual seeds in regard to their germination requirements is very great. This results in a functional relationship between germination rates and time. Another important factor appears to be soil aeration as indicated by the stimulating effect of soil cultivation. Dry periods limit survival of germinated seeds. Vegetative suckering is a compensative reproductive behavior in drier and/or cooler areas. But suckering does not occur when the soil is covered by a dense and tall grass sward. Scalping the sward, and to a smaller degree, clipping of the vegetation, stimulates koa suckering. Initial growth in suckers and seedlings depends on temperature, soil moisture and light intensity. It was possible to show some relationships quantitatively.