Long-term impacts of harvest residue management on nutrition, growth and productivity of an exotic pine plantation of sub-tropical Australia

Residue retention is an important issue in evaluating the sustainability of production forestry. However, its long-term impacts have not been studied extensively, especially in sub-tropical environments. This study investigated the long-term impact of harvest residue retention on tree nutrition, growth and productivity of a F1 hybrid (Pinus elliottii var. elliottii × Pinus caribaea var. hondurensis) exotic pine plantation in sub-tropical Australia, under three harvest residue management regimes: (1) residue removal, RR0; (2) single residue retention, RR1; and (3) double residue retention, RR2. The experiment, established in 1996, is a randomised complete block design with 4 replicates. Tree growth measurements in this study were carried out at ages 2, 4, 6, 8 and 10 years, while foliar nutrient analyses were carried out at ages 2, 4, 6 and 10 years. Litter production and litter nitrogen (N) and phosphorus (P) measurements were carried out quarterly over a 15-month period between ages 9 and 10 years. Results showed that total tree growth was still greater in residue-retained treatments compared to the RR0 treatment. However, mean annual increments of diameter at breast height (MAID) and basal area (MAIB) declined significantly after age 4 years to about 68-78% at age 10 years. Declining foliar N and P concentrations accounted for 62% (p < 0.05) of the variation of growth rates after age 4 years, and foliar N and P concentrations were either marginal or below critical concentrations. In addition, litter production, and litter N and P contents were not significantly different among the treatments. This study suggests that the impact of residue retention on tree nutrition and growth rates might be limited over a longer period, and that the integration of alternative forest management practices is necessary to sustain the benefits of harvest residues until the end of the rotation.

An annotated check list of Ramularia species in Australia

An annotated check list of Ramularia species in Australia, based on re-examinations of collections deposited at BRIP, DAR and VPRI, is presented. Twenty-eight species are reported in Australia, most of them on introduced host plants. The new species Cladosporium myrtacearum, Ramularia craspediicola and R. muehlenbeckiae are described. Collections of Cladosporium uredinicola, Neoramularia karelii, Passalora perfoliati and Pseudocercospora pongamiae-pinnatae, previously deposited in Australian herbaria under 'Ramularia sp.', are newly recognised for Australia.