摘要 : Twenty-two plots were established at 4 sites in a Eucalyptus nitens plantation and measured over 3 yr to investigate the effects of competition from naturally regenerated Acacia dealbata (a woody weed) on productivity. Three of th... 展开 Twenty-two plots were established at 4 sites in a Eucalyptus nitens plantation and measured over 3 yr to investigate the effects of competition from naturally regenerated Acacia dealbata (a woody weed) on productivity. Three of the sites had been planted in 1988, and the plots were established in 1994, and the fourth site had been planted in 1992, with plots established in 1994 and 1995. Under favourable moisture conditions, A. dealbata grew at a rate close to (and sometimes exceeding) that of E. nitens, bringing about canopy closure by 2 yr old where A. dealbata stem densities were high. Competition peaked at age 2-6 yr before declining as the A. dealbata canopy was suppressed, in part by intra-specific Acacia competition. E. nitens basal area was highly significantly inversely correlated with A. dealbata stem density from ages 2-8 yr. However, a simple correlation between E. nitens and A. dealbata basal areas was significant only in young stands (age 2-4 yr). The effects of early-age competition by A. dealbata on E. nitens productivity were substantial, reducing standing volume in comparison with Acacia-free plots by almost 25% by age 8 yr. Soil nitrogen status was positively correlated with A. dealbata presence at both ages sampled (4 and 8 yr) and negatively correlated with E. nitens basal area. A. dealbata was, therefore, considered to be a net contributor of nitrogen during this period, but competition for other resources negated any positive effect of this contribution. 收起