THE POTENTIAL FOR INCREASING FOREST PRODUCTIVITY

Abstract

The short term solution to increasing forest productivity in Australia lies in rapid expansion of reforestation works: the problems involved here are in part social and economic. In the long run, biological problems may prove more important, and these are discussed with reference to (1) plant introduction and breeding, and (2) cultural measures, including fertilizing. Plant introduction trials may fail if the soil fertility factor is overlooked. This is illustrated by the introduction of hoop pine (Araucaria cunninghamii Ait.), a rainforest species, into the sclerophyll forest environment of the coastal lowlands of south Queensland. Utilization of poorly drained sites in this region would greatly increase its potential for forestry. The humic gley soils can produce high yields provided the trees can survive an intermittently high water table during the first few years. The low humic gley soils are less fertile, but should have considerable potential when planted to a suitable species and appropriately fertilized. Phosphorus is the major limiting nutrient in lateritic podzolic soils. Total soil phosphate was formerly used as an index of phosphorus status, but a more reliable index is needed. Attention is being directed to the use of plant analysis: critical levels for phosphorus in the foliage of loblolly pine (P.taeda L.) and slash pine (P.elliottii Engelm.) have been tentatively established. Loblolly pine planted on lateritic podzolic soils in southeast Queensland may become deficient in nitrogen and potassium during the establishment phase. Response to nitrogen fertilizers is ephemeral, being most pronounced in the year of planting. Evidence points to a change in the nitrogen economy of exotic pine stands once they have formed canopy. Quantitative data on all aspects of ecosystem dynamics are needed to provide a rational basis for the utilization of forest resources. Site deterioration may occur if losses from the nutrient cycle are not balanced by accession of nutrients, either by fertilizing or by natural processes. The magnitude of such losses and gains must be known in addition to the details of the nutrient cycle itself.