Effects of site management in pine plantations on the coastal lowlands of subtropical Queensland, Australia.

Biomass and nutrient distribution in a 30-year-old slash pine (Pinus elliottii) plantation in Queensland, Australia, were estimated following clear-felling in November 1995, to provide a basis for interpreting changes in the nutrient pools and tree responses to harvest residue management practices applied at the establishment of the second rotation. Total biomass at clearfall of a typical slash pine stand was 316 t ha-1, of which 206 t ha-1 was removed in logs. Nitrogen and P removed in logs accounted for 7.6 and 3.4% of total N and P, respectively, in the ecosystem. Residues remaining after logging contained 12% of the total N and 5.2% of the total P. Proper management of these residues is therefore critical for sustaining site productivity. Following clear felling, a long-term experiment was established to assess the impacts of harvesting residues and litter management regimes on soil fertility and productivity of the second crop F1 hybrid between slash pine and Honduras Caribbean pine (P. caribaea var. hondurensis). Early results from this experiment showed that tree stem volume and above ground biomass production increased by 31 and 29%, respectively, at age 39 months by retaining litter and logging residues, compared with the treatment in which logging residues and litter were removed. Further improvements in tree growth have been achieved by doubling the quantity of residues retained and by controlling weed competition. Foliar nutrient concentrations indicated that N may play an important role in the maintenance of long-term site productivity. Differences exist in the growth and foliar nutrient concentrations between the different hybrid families tested but all families responded similarly to the residue treatments. The presence of the residues increased soil moisture levels in the surface soil during a dry season. There was a marked reduction in the quantity of residue, especially the finer fraction, after 39 months. This study has contributed to an improved understanding of the soil and plant factors controlling productivity and provided a basis for more detailed studies on processes underpinning plantation sustainability.