Abstract:

Regimes of regeneration and dispersal distance of two typical exotic tree species in the subtropics of China,Black Wattle,Acacia mearnsii,and Silver Wattle,Acacia dealbata,were studied through investigating soil seed bank to predict their invasive potential. The results showed that Black Wattle is prolific in seed production and mainly reproduced sexually,while Silver Wattle sprouts heavily with high survival rate. Soil seed bank density of Black Wattle and Silver Wattle was 28 882 seeds·m^-2 and 1 475 seeds·m^-2 ,respectively. Most seeds fell on the ground or into litter,revealing potential for further dispersal. Seeds in soil seed bank were viable with germination rate over 85%. Although these two tree species had plenty of seeds in their soil seed banks,emerged seedlings were much fewer. At the stand edge,there were 0.8 seedlings·m^-2 and 1.0 seedlings·m^-2 ,respectively,and around mother trees respectively 1.3 seedlings·m ^-2 and 0.6 seedlings·m^-2. The above data indicated that the actual expansion of the two species was not significant. Seed dispersal distance was short,approximately twice as the height of the mother trees. The dispersal of Black Wattle seeds was affected by moisture condition of pod,weight of seeds and wind. Along with the wind direction seeds were much more and dispersed farther than those at other directions. Silver Wattle colonized site by sprouting and no significant directional difference was found. The results indicated that the potential risk in biological invasion of the two species is high,so they should be properly introduced and planted in the places where are uneasy to be invaded.

Key words: Acacia mearnsii, Acacia dealbata, seed dispersal, biological invasion