P. J. Polglase

Change in soil carbon following afforestation

Abstract Quantifying changes in soil C may be an important consideration under large-scale afforestation or reforestation. We reviewed global data on changes in soil C following afforestation, available from 43 published or unpublished studies, encompassing 204 sites. Data were highly variable, with soil C either increasing or decreasing, particularly in young ( 10 and The most important factors affecting change in soil C were previous land use, climate and the type of forest established. Results suggest that most soil C was lost when softwoods, particularly Pinus radiata plantations, were established on ex-improved pastoral land in temperate regions. Accumulation of soil C was greatest when deciduous hardwoods, or N2-fixing species (either as an understorey or as a plantation), were established on ex-cropped land in tropical or subtropical regions. Long-term management regimes (e.g. stocking, weed control, thinning, fertiliser application and fire management) may also influence accumulation of soil C. Accumulation is maximised by maintaining longer (20–50 years) forest rotations. Furthermore, inclusion of litter in calculations reversed the observed average decrease in soil C, so that amount of C in soil and litter layer was greater than under preceding pasture.

Soil water under forests (SWUF): a model of water flow and soil water content under a range of forest types

A new model (soil water under forest, SWUF) is suitable for predicting the daily water content within both surface soil layers and the sub-soil under a range of forest types, and is suitable for use in models of mineralisation of soil organic matter as well as models of forest production. This empirical cascading bucket-type model was largely derived by combining algorithms from well-tested models for prediction of soil water under agriculture. However, it extends these to predict the water content of the litter layer, and the influence of the litter layer, weeds and understorey, and site mounding, on SWUFs. Measurements of soil water content under native forest, and pine and eucalypt plantations, were available for 59 sites across southern Australia. The model was parameterised to about half (27) of these datasets, while the remainder (32) were used for validation, for which the model explained 86% of the variation in observed water content. Sensitivity analysis indicated that important input data required were the observed upper limit of water content, bulk density, and climatic data, particularly solar radiation. The estimated area of ground that was covered by litter and canopy were also important inputs.

Predicting Growth, Carbon Sequestration and Salinity Impacts of Forestry Plantations

Farm forestry is an increasingly important form of diversifying farm income and helping to deal with environmental issues including dryland salinity, global warming and climate variability. Here we briefly describe the development, use and spatial application of improved versions of the plantation growth model, 3-PG, to provide estimates of productivity and carbon sequestration as well as salinity impacts. Several forestry scenarios using eucalypt species and Pinus radiata were tested with application to the Corangamite Catchment in south western Victoria, Australia.