ROOT DEVELOPMENT AND GROWTH OF MIXED STANDS OF Eucalyptus urograndis AND Acacia mangium UNDER DIFFERENT TYPES OF SOIL TILLAGE

Atmospheric nitrogen (N)-fixing tree species provide numerous benefits for the soil. The objective of this study was to evaluate the effect of soil management on root development and growth of trees in mixed stands of Eucalyptus urograndis (Eucalyptus urophylla S. T. Blak and Eucalyptus grandis W. Hill ex Maiden) and Acacia mangium Willd. These species were established in a randomized block design with split plots, subjected to minimum tillage and intensive tillage, monospecific stand of Eucalyptus urograndis (1) and Acacia mangium (2), in addition to the intercropping of these species with 50% of the density of the compound compartment of each species (3). Increments in diameter and height were measured up to 49 months after installation of the experiment and fine roots (<2 mm in diameter) were sampled at five different points in two sets of trees per plot up to 1.0 m depth (0-0.1, 0.1-0.3, 0.3-0.5, 0.5-1.0 m) using a steel probe with 0.045 m internal diameter. After 49 months, E. urograndis trees showed greater increments in height and diameter. Treatment 2 showed a higher fine root density (FRD) in all layers. The implementation of mixed stands intensified the FRD of E. urograndis in the 0-0.1 m layer. Effect on root development was observed only in the 0.1-0.3 m layer, where intensive tillage increased FRD in treatment 2. Thus, mixed stands can be an excellent alternative for forest production in areas subjected to soil degradation.

Dugong distribution, the seagrass Halophila spinulosa, and thermal environment in winter indeeper waters of eastern Shark Bay, WA

Five aerial survey transects in eastern Shark Bay, along which dugongs (Dugong dugon) had been reported in deep water in July 1989, were flown on 3 and 14 July 1992. As in 1989, dugong sightings were concentrated between 9- and 15-m depth contours. Thermal patterns shown on images obtained from NOAA satellites, and direct measurement of temperatures in the water column, confirmed that temperatures were at least 19�C where dugongs were concentrated. Although no seagrass had previously been reported in this zone, examination of benthic communities using a remotely controlled underwater video system revealed an apparently monospecific stand of Halophila spinulosa. Dugong behaviour, observed from a 10-m catamaran, indicated that the animals were diving to the bottom. Long, deep dives may be more costly in time and energy than the shorter dives characteristic of feeding in shallow water. H. spinulosa has large fleshy rhizomes similar to those known to contain abundant starch in other members of the genus and it is suggested that carbohydrate-rich rhizomes might compensate for the higher costs of foraging in deep water. Previously known stands of preferred forage species appeared inadequate to support the large dugong population of Shark Bay, but if temperatures are favourable throughout the winter and if the H. spinulosu observed in this study is available throughout the year, this H. spinulosa community may be an important resource for the Shark Bay dugong population.

The abundance of native insects on the introduced weed Mimosa pigra in Northern Australia

ABSTRACTA monospecific stand of the alien shrub Mimosa pigra (Mimosaceae) was examined weekly for 14 months from March 1984. A total of 44 phytophagous insect species were found on M. pigra. The five most abundant of these made up 74% of the total community. This insect community in general showed a distinct seasonal cycle of abundance with maximum numbers during the wet season. However, a few species had a completely different pattern.Two species, Mictis profana (Hemiptera: Coreidae) and Platymopsis humeralis (Coleoptera: Cerambycidae), were observed to cause substantial damage to M. pigra. When compared with the fauna of M. pigra from its native region, Central America, that of the Northern Territory is low in leaf and flower-feeding insects. It is suggested that these types of insects be sought as future biocontrol agents to complement those native insects causing damage and those biocontrol agents already released.