Review of long-term trends in soil carbon stocks under harvested native forests in Australia

[摘要] This report provides information that will assist the Australian Government's Department of the Environment with its implementation of Forest Management activity into the National Inventory System. The work aimed to i) undertake a literature review of long term (decades) trends in soil organic carbon (SOC) stocks in harvested native forest systems; and ii) provide synthesis and analysis of the available literature to test whether there is any clear empirical evidence, or evidence from modelling, that harvestingcauses SOC stocks to deviate substantially from an equilibrium range over the long term. The review was limited to long-term (decades) trends in carbon stocks in mineral soils under harvested native forests, focussing on literature relating to Australia's harvested native forests and drawing upon relevant international meta-analyses.Literature searches were performed using the database 'ISI Web of Science'. Additional references cited within papers and reviews/meta-analyses were also identified. Only publicly-available literature (peer-reviewed publications and reports) was included. Data on changes in SOC following harvesting in native forests were compiled from relevant Australian measurement-based and modelling studies. Where relevant, information from international meta-analyses and reviews was also included.Few studies met the scope of the review, all in Eucalyptus regnans forest at a single site in Victoria. Of these, most reported a decrease in SOC associated with mechanical disturbance of the soil or no change in the first 10 years following harvesting in the surface 30 cm. Where slash was burnt post-harvest, there was no significant change in SOC 10 years after harvesting. The only empirical information available on long-term (multi-decadal) trends was from a chronosequence study which showed no difference in SOC stocksbetween harvested and unharvested E. regnans forests.Australian modelling studies showed no consistent long-term trend in SOC, with results strongly dependent on the assumptions used in the modelling and varying from no change, to decreases and increases under various scenarios and harvest systems. Where a change was reported, the intensity of the harvest system was found to be important, with the direction of the effect differing for clearfell and slash burn systems, all of which reported a decrease in SOC, versus selection systems, which reported an increase.International meta-analyses showed that:i) There are small decreases in SOC when using harvest systems that remove large amounts of biomass (such as whole tree harvesting), or on particular soil types (or site preparations);ii) There are small increases in SOC immediately following harvest where large amounts of residues are produced, and incorporated into the soil. There may be longer-term increases in SOC where sites have had fertiliser added, or where the growth of nitrogen-fixing species following burning increases biomass production. The production of charcoal may also contribute to increases in SOC following burning; andiii) At many sites, any initial decreases in SOC storage recover over time, as either residues left form harvesting decompose, or lost material is replenished by the growing forest, with recovery times ranging from 4 to 20 years. Given that most of the studies were from coniferous forests and deciduous hardwood forests growing in the Northern Hemisphere, it is uncertain how applicable these results are to harvested native forest systems in Australia.Results from the measurement-based studies suggest at least two mechanisms/pathways for impacts of harvesting and regeneration burning on SOC:i) Immediate and short-term changes resulting from mechanical disturbance to the soil due to harvesting activity, which dominate the existing measurements in Australian native forests. Disturbance potentially can cause losses through displacement or erosion, or stimulate decomposition and losses from respiration...

[发布日期] 2014-06-01 [发布机构] CSIRO

[效力级别] Environmental Management [学科分类] 地球科学(综合)