黑荆和银荆的繁殖扩散与入侵潜力

Invasive Potential of Two Introduced Tree Species: Acacia mearnsii and Acacia dealbata

对2种典型亚热带外来树种黑荆和银荆林分和单株土壤种子库、幼苗扩散进行调查,依据繁殖体类型、数量和扩散距离预测黑荆和银荆的入侵性。结果表明黑荆以种子繁殖为主,繁殖体数量大,银荆以根蘖繁殖为主,繁殖成功率高。黑荆和银荆林分内土壤种子库数量都很大,分别达28882粒.m-2和1475粒.m-2;种子主要分布在枯落物中,有利于其继续传播;有活力种子比例高,室内发芽率可达85%以上,树种建群能力强。虽然黑荆和银荆都有大量的繁殖体存在于土壤中,但萌发并存活的幼苗数量相对较少,林缘幼苗数量分别为0.8株.m-2和1.0株.m-2,单株周围幼苗数量分别为1.3株.m-2和0.6株.m-2,树种向外扩散速度慢;黑荆和银荆的自然扩散主要是近距离的扩散,距离约是树高的2倍,黑荆种子扩散方式以豆荚的吸胀和失水作用、重力和风力扩散为主,下风向数量最大,传播距离最远;银荆以根萌蘖扩散为主,没有方向性。以上特点表明,2个树种都具有较高的入侵潜力,在引种栽培时要因地适宜,加强管理,谨防危害当地生态环境。

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.