Wood and biomass production of Leucaena in subtropical Australia

Although only Leucaena leucocephala is widely used, most members of the Leucaena genus have potential as multipurpose species for tropical agroforestry systems. To investigate the wood and biomass production potential of the Leucaena genus, 116 accessions covering the 22 species were evaluated over a two-year period at Brisbane, southeast Queensland, Australia. Trees were planted into replicated line plots 5 m long, with rows spaced 3 m apart. Trees were initially planted at 0.5 m spacings within the plots, but were thinned to 1 m spacings prior to the evaluation period. The hybrid accessions, KX2 (L. pallida x L. leucocephala) and KX3 (L. diversifolia x L. leucocephala), were the most productive, yielding over 50 kg dry matter (DM)/tree. L. trichandra OFI53/88 and L. diversifolia CPI33820 were the most productive non-hybrid accessions producing total yields of 41 and 37 kg DM/tree, respectively. Cultivar Tarramba (26 kg DM/tree) was the most productive of the 26 L. leucocephala accessions assessed in the trial but all these accessions suffered from psyllid (Heteropsylla cubana) attack at this site. A series of non-destructive growth measurements was recorded every three months over the two-year evaluation period. Root collar diameter (RCD), stem number and plant height were found to be the most useful of the measurements for non-destructive assessment of accession agronomic characteristics. A relationship between yield and a growth index (calculated as RCD(2) x Height/1000), was derived from data from all accessions and could be used as a reliable predictor of yield (r(2) = 0.94). The widespread use of the F1 hybrid leucaenas is currently limited by a lack of seed. Technologies to economically produce F1 hybrid seed on a commercial scale are required before the potential of these accessions in agroforestry systems can be fully realized.