Consequences of broadscale timber plantations for biodiversity in cleared rainforest landscapes of tropical and subtropical Australia

Abstract

In Australia, as in many countries, there has been a shift in timber production from native forests to plantations. While plantations are primarily considered an efficient means of producing timber, there is increasing interest in their potential contribution to biodiversity conservation. Plantations may have both positive and negative consequences for biodiversity, at a range of scales. We compiled a list of these consequences from the literature, and used them to assess plantation scenarios proposed for cleared rainforest landscapes in tropical and subtropical Australia. The scenarios were monocultures of: (i) hooppine, (ii) exotic pine and (iii) eucalypts; (iv) mixed species plantations; (v) a mosaic of monoculture plantations; and (vi) a mosaic of plantations and ecological restoration plantings. Of these scenarios, plantations of eucalypts and exotic pines have the least positive consequences for biodiversity: they have little or no intrinsic value in rainforest landscapes, provide poor quality habitat for rainforest biota, and (particularly eucalypts) are characterised by a relatively open canopy which in cleared landscapes favours the recruitment of grasses and other weeds.The three scenarios based on plantations of rainforest trees have similar, moderately positive consequences for biodiversity, while a mosaic of plantations and restoration plantings has the most positive consequences for biodiversity in cleared rainforest landscapes. All scenarios may have negative impacts on biodiversity conservation if plantations replace remnant forest, provide habitat for weeds, or the tree species used in plantations or their genes escape into native forests. In practice, the relative importance of positive and negative impacts, and hence the ranking of scenarios may vary with landscape forest cover. Scenarios with strongly positive consequences for biodiversity would be favoured for the reforestation of heavily cleared landscapes, whereas scenarios with few negative consequences for biodiversity would be favoured in well-forested landscapes. Consequently, any plantation of rainforest trees may have acceptable consequences for biodiversity in well-forested landscapes, provided the trees are not invasive or carrying exotic genotypes, and plantations are managed to control weeds and feral animals. With the same caveats, plantations of exotic pines may also be acceptable from a biodiversity conservation perspective in well-forested landscapes. At present, our capacity to design and manage rainforest plantations for both timber and biodiversity objectives is limited by a lack of information on factors affecting timber production, biodiversity values and trade-offs or synergies between these objectives. Obtaining this information will require the integration of large-scale, long-term biodiversity research in broadscale plantation projects.