A POSSIBLE LINK BETWEEN RAINFALL AND HEART ROT INCIDENCE IN <em>ACACIA</em> <em>MANGIUM</em>?

Abstract

Over the last 20 years extensive plantations of Acacia mangium have been established in Sabah and Kalimantan on the island of Borneo, Peninsular Malaysia, Sumatra and Papua New Guinea. Areas under A. mangium plantations continue to expand annually in these regions. Although there are several reports of heart rot in A. mangium, figures are only available from Malaysia. In Sabah, between 10 and 50% heart rot incidence has been reported in 6- to 9-y-old trees while in Peninsular Malaysia between 49 and 98% of 2- to 8-y-old trees have been found to have heart rot. The volume of wood affected by the disease was, however, relatively low. In its natural habitat, A. mangium grows in areas with a strongly seasonally distributed mean annual rainfall of 1500-3000 mm. It is our hypothesis that the higher incidence of heart rot in A. mangium in Peninsular Malaysia compared to Sabah may be associated with the lack of a seasonal distribution of rainfall in the peninsula. The absence of a dry spell probably reduces the self-pruning ability of A. mangium branches in Peninsular Malaysia. These dying branches probably permit the development of entry points for the decay fungi. Such conditions of continuous high relative humidity are also conducive to fungal infection.