EARLY TREE AND PASTURE GROWTH IN AN AGROFORESTRY SYSTEM EVALUATING ALBIZIA-LEBBECK, CASUARINA-CUNNINGHAMIANA AND EUCALYPTUS-MACULATA IN SOUTH-EAST QUEENSLAND

An experiment evaluating Albizia lebbeck, Casuarina cunninghamiana and Eucalyptus maculata at 5 densities amongst a pasture containing Chlor is gayana cv. Callide (rhodes grass), Chamaecrista rotundifolia cv. Wy nn (Wynn cassia), Stylosanthes scabra cv. Seca (stylo), Lotononis bain esii cv. Miles (lotononis) and Trifolium repens cv. Haifa (white clove r) was established in south-east Queensland in 1990. The 5 planting de nsities (78, 182, 343, 771 and 1189 stems/ha) were replicated on lower , mid- and upper slope positions. Over the first 3 years, C. cunningha miana (mean height 5.5 m) grew significantly (P < 0.05) faster than E. maculata (4.3 m), which, in turn, grew significantly faster than A. l ebbeck (2.6 m). Due to its poor growth and a mortality rate of 12.3%, A. lebbeck was considered poorly suited to the site. The heights of th e 3 species were not significantly affected by planting density or pos ition on the slope. Stem diameter at 1.3 m (DBH), measured for 3-year- old C. cunninghamiana only, peaked at 343 stems/ha. The DBHs of mid- a nd lower slope trees were similar and significantly (P < 0.05) greater , by 17.4%, than those of upper slope trees. During the third year aft er establishment, median pasture yield (measured midway between trees at all spacings) was significantly (P < 0.05) increased under the high est 2 density treatments of A. lebbeck (by 17.7% and 39.6%) and E. mac ulata (by 25.5% and 17.2%) when compared with the other density treatm ents. The proportion of pasture in each plot killed by the application of herbicide around the base of establishing trees increased with inc reasing density, from 1.4% (78 stems/ha) to 21% (1189 stems/ha). Thus, although median pasture yield was significantly higher under the high est densities, yields adjusted for these sprayed areas were similar an d unaffected by tree density, averaging 7.4 t/ha. At this early stage, pasture yields were also unaffected by tree species or slope position .