As plantations supply more of Australia’s timber, how they are established and harvested will increasingly shape biodiversity. Good management can make a substantial difference.
Native forest logging is winding back across Australia, so plantations will need to carry a growing share of the nation’s wood supply. Approximately one third of global timber is sourced from timber tree plantations, even though plantations cover only approximately 3 per cent of the area of forests globally. The primary objective of timber tree plantations is to grow forest products like timber and wood derivatives such as paper pulp and woodchips. However, plantations can sometimes have important values for biodiversity.
Understanding the potential value of plantations for biodiversity is important for several reasons. First, the global area of land used for plantations is large and increasing, having expanded by 75 per cent since 1990. In 2015, plantations covered 289 million ha of the earth’s surface – an area about 40 per cent the size of the entire Australian continent.
Second, plantations are often located in high-productivity areas which can also be important for biodiversity, such as for koalas (Phascolarctos cinereus) in parts of NSW and Victoria.
Third, the effects of plantations on biota can extend beyond areas directly under tree establishment and management to the broader landscape. For example, plantations can be a source of ‘wildlings’ that escape from plantation-managed areas, leading to invasive plant problems elsewhere.
Finally, plantations can alter key ecological and disturbance processes such as fire regimes and hydrological regimes, with subsequent impacts on biodiversity.
I recently led a major review of the factors which influence the value of plantations for biodiversity. The review was based not only on my experience from working in plantations in Australia since 1994, but also on a detailed assessment of the vast literature on plantations globally. The review revealed that many factors can influence how biodiversity responds to the establishment and management of plantations. A small subset of the more important ones is outlined below and includes:
1) The type of environment and land use that existed prior to plantation establishment (e.g. an intact native forest versus an already cleared pasture).
2) The completeness of the land-cover conversion to a plantation, and whether any biological legacies remain such as patches of remnant vegetation, large old native trees, rocky outcrops, wetlands, and even farm dams that were established on previous farmland (and before it was converted to a plantation).
3) The proximity of a plantation to native vegetation and the presence and location of plantations as part of a mosaic of different kinds of exotic and native vegetation in a landscape.
4) The mix of tree species being established in a plantation – such as monocultures of exotic conifers like radiata pine or combinations of native and exotic tree species.
5) The harvesting practices used to manage a plantation such as thinning, coppicing, or clearcutting.
6) How plantations modify key ecological processes that can affect biodiversity, such as altered fire regimes and hydrological regimes.
This broad range of factors means that the response of biodiversity to plantations will often be highly context dependent. That is, how biodiversity responds to plantation establishment will vary considerably from location to location and at a range of scales – from an individual stand of plantation trees, to the compartment scale, and the broader landscape where plantations are part of the suite of vegetation types.
Based on the expanded understanding of the six factors summarised above, there are a number of key strategies for plantation establishment and subsequent plantation management that can enhance biodiversity conservation in plantations. The extent to which these factors are embraced will be highly context specific and vary, for example, on whether plantation management is more closely allied with a land-sharing versus a land-sparing model.
In simple terms, the land-sharing/land-sparing paradigm refers to the two extremes of land use. Land sharing entails integration of production and conservation in the same general area, such as through retention harvest forestry (where substantial parts of stands of trees are retained at the time of harvesting), and the maintenance of all natural species and ecosystem processes in that location; sometimes termed ‘ecological forestry’.
Conversely, land sparing involves intensive wood production, such as frequently occurs in plantations, with other naturally forested land elsewhere in the landscape then ‘spared’ for conservation outcomes.
Greater consideration of approaches to maintain biodiversity in tree plantations will typically be required in a land-sharing model for plantations. Some of these considerations are set out below.
1) Complete detailed land assessments and plantation planning prior to plantation establishment. A key part of such assessments would be to ensure that no extensive areas of native vegetation are cleared or planted over (in the case of remnant native grassland) in the initial process of plantation establishment.
2) Related to approach 1, retain key biological legacies from the previous land-cover type within plantations. This includes patches of remnant vegetation, large old trees, rocky outcrops, and wetlands.
3) Consider the mix of timber tree species that comprise plantations, including whether they are a monoculture (of a single tree species) or a polyculture of a range of tree species.
4) Manage interventions like thinning or clearfelling in plantation areas. As an illustration, work on bird biodiversity in plantations in the Tumut region of NSW showed that staggering clearfelling operations meant far more native bird species persisted when only part of the plantation surrounding patches of remnant vegetation was logged, relative to when all of an area was cut. This shows how much difference the timing and pattern of harvest can make, without reducing the amount of timber produced overall.
5) Ensure that landscapes where plantations occur support not just stands of plantation trees, but also a range of other vegetation types, including areas of remnant vegetation. This creates what is termed landscape heterogeneity, which can benefit a range of often more mobile native animal species in landscapes.
6) Control invasive plant and animal species within plantations and more broadly across plantation-dominated landscapes. This last issue is a key consideration as plantations are often characterised by major problems with invasive plants such as blackberry or lantana and feral animals such as pigs, foxes, deer, and other pest animals. These plants and animals can be pervasive not only in plantations but also in adjacent forest and agricultural areas, making plantation-managed locations ‘very poor neighbours’.
Plantations will become an increasingly important part of wood supplies in Australia, especially as there is an increasing move away from native forest logging. There will be a need to manage them appropriately, not just for timber, but also in some cases to maintain other values. Codes of plantation practice need to be updated to ensure that the latest scientific information is included, so that the management of plantations is both evidence-based and conducted in ways that allow them to be eligible for appropriate product certification schemes.
David Lindenmayer
Professor David Lindenmayer is a distinguished Australian scientist and academic, specialising in landscape ecology, conservation, and biodiversity. His research focuses on integrating nature conservation with agricultural production, improving biodiversity conservation in forestry and plantations, and enhancing fire management practices. With over 1000 peer-reviewed papers and 50 books, David is one of the most published ecologists globally. He leads large-scale, long-term research programs in south-eastern Australia. A Fellow of the Australian Academy of Science, he has received numerous prestigious awards, including the ESA Whittaker Award, multiple Eureka Prizes, and the Australian Natural History Medal.