Eucalypts and groundwater: managing plantations to avoid resource depletion and environmental detriment in China and Australia

China

Dr Jim Morris
Phone: 03 9450 8722
Fax: 03 9450 8644
Email: jim.morris@nre.vic.gov.au

• CSIRO Land and Water, Australia
• China Eucalypt Research Centre, China
• University of Melbourne, Australia
• South China Institute of Botany, China
• Research Institute of Tropical Forestry, China

$999,235

01/07/1999 - 30/06/2003

Dr John Fryer

In southern China, eucalypt plantations have become a major source of hardwood pulp and timber products. About 1 million hectares are planted, and the area continues to grow by about 10% per year. However, despite the introduction of more suitable tree genotypes and selective tree breeding, the productivity of plantations in southern China appeared to be falling after two or more rotations, and there was evidence of a decline in the soil fertility of the sites. As well, plantations appeared to increase soil erosion and deplete the groundwater needed for dry season irrigation of rice and sugar cane.
Practices such as removing litter and understorey vegetation in the plantations, and harvesting the root systems along with the rest of the tree, were thought to be the main causes for some of these problems. However, there was little information on water use and water balance of eucalypt plantations in southern China. Research was therefore needed to understand how silvicultural choices, including site preparation, tree spacing and rotation length, affected plantation water balance. Australia's eucalypt plantation industry would also benefit.

The main aim of the project was to address the problems of falling yields, soil erosion and suspected groundwater depletion in eucalypt plantations on Leizhou Peninsula in southern China.

The project comprised four sub-projects. The first involved investigation of the social and economic factors that affect forest utilisation. Scientists examined management practices such as litter and understorey removal, and harvesting of whole trees, with emphasis on the social and economic factors that gave rise to these practices. The team established a long-term demonstration of better plantation management, and used analysis and models to derive recommendations for plantation management that could work in combination with other land uses and harmonise with catchment management.
The second sub-project quantified plantation water use at different sites with different species and management factors. Surface runoff, infiltration, evapotranspiration, and groundwater recharge or discharge were measured in relation to soil and climate. As part of this work the team also recorded water and nutrient balance of eucalypt forest and pine plantations in northeastern Victoria during thinning and fertilising operations, and applied the results to develop criteria for plantation sustainability.
In the third sub-project the team modelled the productivity and hydrological impacts of plantations. The scientists employed a simple, large-scale model capable of rudimentary representation of the interactions between surface land-use and shallow groundwater hydrology, and applied it to the hydrological relationship between plantations and other land uses.
The fourth sub-project was devoted to technology transfer and extension of results.

The socio-economic investigation of the extent of, reasons for and alternatives to whole-tree and litter harvesting in China identified that local populations received substantial economic and environmental benefits from eucalypt plantations. Issues of land security and taxation were found to limit plantation establishment. Smaller plantations established by private growers often suffered from poor management practices. Nutrient depletion and soil degradation due to litter collection and whole tree harvesting were problems in many plantations.

Derivation of soundly-based estimates of plantation water use showed that eucalypt plantations established in southern China do not use more water than other plantation species and crops, although different soil types show a substantial range of water holding capacities.

The project focused on raising awareness with forest managers and researchers, to convince them that appropriate modelling could help allay landholder concerns about adverse effects of plantations on water yields and assist in improving plantation yields. Substantial efforts also went into explaining the project and its potential to improve stand productivity to managers from areas outside the Leizhou study area.

Models of stand growth (3PG) and local hydrological processes (Topog) developed in Australia were parameterised and validated for the Leizhou Peninsula. The scientists used data collected in the project and from other sources including existing technical literature and plantation management records. A Chinese language interface to the 3PG growth model was developed to assist Chinese researchers and forest managers to use the 3PG model.

Successful parameterization of the process-based 3PG model to predict growth of the eucalypt stands on the Leizhou Peninsula has encouraged acceptance of 3PG and of modelling in general as a tool for forest management. The TOPOG hydrological model is more difficult to parameterise and use than 3PG and is therefore best considered a research tool for investigating catchment processes rather than a management tool.

A regional-scale catchment model describing vegetation growth and water use with a resolution of 1 km2 over areas of 1000-10,000 km2 was developed to an advanced stage. Initially the model will incorporate available information on climate, vegetation water use, groundwater recharge and subsurface flows for the Leizhou Peninsula and for one or more Australian catchments.