Predicting the Environmental Interactions of Eucalypt Plantations Using a Process-Based Forest Model

摘要

Avoidance of possible negative impacts of eucalypt plantations on soil fertility, water resources, salinity and other environmental factors requires sound management based on a quantitative knowledge of the interactions of forest growth and environment. Process-based growth models may provide this knowledge in part, because to validly predict the influence of environmental factors on growth over a rotation, they must also predict the changes in those factors which result from the presence of the growing plantation. The 3-PG forest model provides a suitable basis for development of a management-oriented utility for predicting key environmental impacts of plantation establishment, silviculture and harvesting options. Functional extensions to 3-PG are described which allow an analysis of the interactions of eucalypt plantations with groundwater recharge, soil nutritional status and root zone salinity. Fitting 3-PG to plantation growth and biomass data from southern China reveals a need for modification of the model's response to fertility, and data sets from low rainfall areas of southeastern Australia suggest further enhancements to its ability to reflect species differences in drought tolerance. With these in place it is possible to draw conclusions about the rate of fertility decline in existing plantations, and potential growth rates and water consumption by trees if fertility decline is avoided. Within the limits of a simple root-zone hydrological and salt-balance model, it is also possible to predict the results of forest management options and salinisation or fertility decline on water output as stream flow and groundwater recharge from plantation catchments. 3-PG based modelling at the stand scale is suggested as a useful tool for forest planning, and could also form one component of a multi-part model for more comprehensive analysis of ecosystem or catchment-scale impacts.