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Achieving good ecological outcomes in aggregated retention coupes

Aggregated retention (ARN) is designed to retain matureforest elements within harvested coupes, leading to production forest landscapes with greater ecological integrity and function than were clearfelling alone used. Aggregated retention coupes need to be carefully designed to maximise the benefits of retained mature forest for biodiversity. A series of criteria has been developed to guide the design of aggregated retention coupes, with metrics to assess whether individual aggregated retention coupes meet the ecological goals of aggregated retention.

The proposed system of coupe-level metrics for assessing biodiversity outcomes for ARN coupes is based on Forestry Tasmania’s Goals and Guidelines for Variable Retention (VR), which can be simplified as: Objective 1: facilitating rapid re-establishment of mature forest biodiversity into the harvested area, by ensuring forest influence on the majority of the harvested area.













Objective 2: ensuring retention of biological legacies after harvesting

Objective 3: ensuring suitable conditions for plant regeneration and animal habitat in the harvested area, with connectivity between retained forest edges and the regenerating stand

Many aspects of coupe design contribute towards ecological outcomes through providing current and future habitat suitable for the various components of forest biodiversity. Further, variability both within coupes and among different coupes is central to the variable retention approach. The performance measures are thus designed to allow room for flexibility, and to allow trade-offs between competing ecological objectives, whilst setting limits within which a coupe design must lie to successfully meet the stated goals. These metrics have been tested on coupes harvested to date using aggregated retention, and demonstrate that most coupes are achieving good ecological outcomes.

The results also illustrate how adaptive management with changing coupe designs has resulted in improved outcomes for biodiversity. For example, compared to early aggregated retention coupes, current coupes contain larger aggregates and these are more often located on coupe edges, thereby reducing edge-effects and improving connectivity for animal movement. A lower proportion of retained forest has been impacted by regeneration burns, and less harvested area has been negatively impacted by creation of firebreaks.