Defoliation of trees in roadside corridors and remnant vegetation in the Western Australian wheatbelt

Abstract

We compared the abundance and impact of caterpillars of the bag-shelter moth (Ochrogaster lunifer) on trees of Acacia acuminata on road verges and within a large reserve in the Western Australian wheatbelt. Caterpillars were observed to cause severe damage to roadside trees during an outbreak of the insect in 1987 and 1988. The caterpillars live communally in a bag which develops on a tree branch. Within the reserve, bags were present early in the season but failed to develop and no caterpillars reached maturity. On road verges, the number of bags per tree was significantly greater on narrow verges than on medium or wide verges. An individual colony consumed foliage estimated to be equivalent to that carried by a tree 2 m tall. Colonies were found only on trees greater than 2 m tall, and abundance increased with tree size. Caterpillars significantly affected the numbers of leaves present on tagged shoots on trees in road verges, and defoliated shoots produced a flush of new leaves. Foliar N and P were significantly hiqher in mature leaves on road verges than in the reserve, and soil N was also higher on road verges. We suggest that ecological processes are significantly modified in road verges, especially narrow verges, compared with intact vegetation, and that this has important implications for corridor management. Intensive management of narrow corridors, or widening of these corridors, is required for their long-term persistence.