Short-rotation tree plantations are recognised as a fast way to grow timber, whether softwood or hardwood. Trees may be planted into areas of felled forest as well as planted or sown into pasture lands. In Australia, both kinds of plantation are productive, with annual growth rates of eucalypts up to 30 m3/ha in southwest Australian pastures. In India, however, despite experience with eucalypt plantations over the last 150 years, growth rates are poor (5-10 m3/ha/yr) and declining. Nutrition is seen as the key to maintaining or improving growth.
Natural forests do not appear to be nutrient deficient; native tree species and their associated understorey vegetation and soil micro-organisms use and recycle the inherent soil fertility efficiently. When trees are harvested, however, the tree-soil cycle is broken and nutrients are removed, depleting the soil reserves unless there is continuing re-supply, from added fertilisers, or from microbial breakdown of surface and soil organic matter.
The project is working with researchers at India's Kerala Forest Research Institute and at the CSIRO Centre for Mediterranean Agriculture to measure and model the growth, development, nutritional status and physiology of young eucalypts in response to management treatments and climate. In addition to the work on eucalypts, scientists will analyse changes in soil nutrient and organic matter to depths of one metre, and measure soil water storage above the watertable.
Near Kerala (3000 mm/year average rainfall) in south-west India, Eucalyptus grandis will be planted at two sites at high altitude on the slopes of the Western Ghats and E. tereticorni will be planted at two sites on the coastal plains. Western Australian sites will grow E. globulus near the upper and lower limits of its rainfall range (approx. 1100 mm/year and 650 mm/year) and at high and low soil fertility.
At all sites, established plantations will be sampled and then partially harvested. The harvest residues known as slash - leaves, branches, bark, understorey plants and tree litter will be partly or wholly removed or burnt, or left and spread over the site. After eucalypts are replanted, various legume crops will be grown and assessed. Six applications of phosphorus, or nitrogen fertiliser with basal nutrients will be applied. Pot trials will compare soil from the unharvested established plantations and from adjacent pasture or forest.
Weed control will feature in the experiments in India, as will trenching on the contour to improve water recharge. In India it is important that plantations do not lower the watertable, in contrast to the situation in Western Australia.
A cost/benefit analysis will be based on the resulting data.
The overall objective of this project, located in Kerala, India and in Western Australia, was to identify and develop practices for manipulating soil organic matter, and soil and tree nutrient and water status. This forms the basis for implementing silvicultural regimes that optimise conservation and use of site resources and enable sustainable wood production from eucalypt plantations.
A final review of the project found that it had been successful within the limitation of a five-year time frame. Improved establishment techniques resulted in stimulating early growth to mid rotations. Initial economic analyses indicate an internal rate of return of 20% from best treatments. Strategic process-related research on stand and soil nutrient economy has provided sound insights into the operation of these processes and their dynamics. However data are needed from a full rotation (7 years) to enable simulation with a degree of confidence.
The project has gathered much practical information on the use of fertilisers, weed control and ground cover planting with eucalypt plantations, and demonstrated the differential responses of species over different sites. In particular it has been able to quantify responses to treatments, which allow economic analyses that can inform management decisions. At this stage of the rotation there appeared to be no response to retention of slash from the previous rotation, and to nitrogen-fixing groundcovers, contrary to expectation from research elsewhere, although this may change further into the rotation. The research has produced a better scientific understanding of the dynamics of fertiliser response in this climate and on these soils, including the role of soil organic matter in the nutrient cycling.
The training/capacity building component of the project has been particularly successful with an obvious increase in the skills of the KFRI team in field experimentation and laboratory techniques.
Links:
[1] http://www.aciar.gov.au/country/India
[2] http://www.aciar.gov.au/programarea/Forestry