Native trees and shrubs have regenerated across a number of traditional farming areas near where we live. Is this ‘good’ or ‘bad’? Can passive regeneration deliver useful outcomes for biodiversity?
Much of the attention given to native plant regrowth in Australia has been in semi-arid rangelands in western New South Wales and Queensland. Management of regeneration of native woody plant species (i.e. ‘regrowth’) in these regions can have considerable impacts on agricultural opportunities, as well as landscape functionality and biodiversity conservation. But woody plant regeneration also occurs in many agricultural regions in south-eastern Australia. In particular, regrowth is becoming increasingly abundant in regions experiencing rapid changes in land-use demographics, such as agricultural areas close to regional cities and towns.
The extent of these regions is not trifling. Barr (2005) classified most of central, north-eastern and parts of eastern Victoria as a “rural amenity landscape” zone, in which traditional agriculture was being actively replaced by rural lifestyle development; other areas of the state were in “transition” towards this “amenity landscape” stage.
Similar demographic changes are occurring in many regions of NSW and the ACT. In Victoria, many of these regions have witnessed extensive regeneration by a wide variety of native trees and shrubs (Lunt et al. 2010a), including many eucalypts and shrubs such as Burgan (Kunzea ericoides) and Drooping Cassinia (Cassinia arcuata). Coast Tea-tree (Leptospermum laevigatum) and Coast Wattle (Acacia sophorae) are responding in similar ways in coastal areas (e.g. Costello et al. 2000; Geddes 2009).
It’s possible that a complex socio-ecological dynamic exists in these regions. Initial land-use changes appear to encourage regrowth, and while the drivers that attract amenity landscape owners to a region are complex and not fully understood, it is possible that this regrowth attracts amenity landscape owners. These new land managers then change land-use further, in turn encouraging more regrowth, either intentionally or unintentionally.
Some people in these communities appear to value this regrowth quite highly, seeing it as “healing the scars” of earlier land use. However not everyone views regrowth this rosily, as one person’s “precious regeneration” is another’s “woody weed”. For adjacent farmers implementing more traditional farm practices, regrowth may be seen as the very essence of “poor management”.
For example at a recent workshop, an extension officer told of new landholders enjoying their beautiful block of burgan-dominated “natural bush”, until accosted by a neighbor for not controlling their “@#$% weeds”. Agency staff added to the landholders’ confusion by stating that, even though it wasn’t “natural”, they were unlikely to get permission to clear it. However, the same agency representative acknowledged great uncertainty about the conservation values of this (and other) types of regrowth. What is its value for biodiversity conservation? How does it contribute to catchment targets? Does it get “more natural” as it gets older? Should they encourage landholders to try to “improve” patches of regrowth? If so, how, and what should they aim to achieve?
Unfortunately, there is little research to document how regrowth influences biodiversity patterns in many regions. Potential biodiversity values are likely to occur at the patch scale (through habitat provision) and the landscape scale (by enhancing cover and connectivity among other remnants). However, dense areas of regrowth may have detrimental effects on understorey plant diversity in some places (e.g. Costello et al. 2000). Importantly, many areas of regrowth may represent “novel ecosystems” (as described by Hobbs et al. 2009), which are maintained or influenced by human actions, and are unlikely to ever resemble the diverse “natural” ecosystems from which they were originally derived.
Of course, vegetation is valued for social as well as biophysical reasons. The concept of “ecosystem services” (i.e. “the benefits people obtain from ecosystems” (Millennium Ecosystem Assessment 2005) may provide a useful framework to integrate the social and ecological values of regrowth, as may the complementary concept of ecosystem assets. Regrowth can provide a wide range of ecosystem services and “disservices” to communities, and these services may impact at scales from local (e.g. soil protection) to global (e.g. carbon sequestration).
A short list of relevant ecosystem services includes landscape aesthetics, catchment hydrology, livestock health, biodiversity conservation, soil amelioration, fodder provision, carbon sequestration, rural amenity, spirituality, fire fuel loads, rural land property values, salinity control, recreational opportunities and erosion protection. Many readers may know of other topical issues. Importantly, however, few studies from Australian agricultural regions (out of the rangelands) have attempted to determine which ecosystem services or assets associated with regrowth are valued by regional communities, and whether communities assign different values to particular types of regrowth. Understanding how the community views regrowth will be pivotal in developing ways to enhance the ecosystem services that regrowth can provide.
If we wish to maintain or enhance the ecosystem services that regrowth can provide, we will need to actively engage with communities to understand the social-economic drivers of present land-use decisions, how these communities perceive and value regrowth, and how this will affect their landuse options and decisions, and future biodiversity patterns.
To this end, our research institute recently initiated a new research program with the (very long) title of, “ecological and social responses to native plant regeneration in dynamic rural landscapes”. This multi-disciplinary research program aims to enhance environmental sustainability in rural Australia by improving our ability to manage regrowth for a broad range of social and environmental values.
Occurrences of native regrowth provide an enormous opportunity to achieve many of our desired regional conservation goals, and protection of vital ecosystem services in agricultural regions - at very low cost. However it also presents a threat to viable land-uses in some areas.
To manage regrowth well, we need a much better handle on what it delivers, what trade-offs exist, and how these are perceived and valued by different members of the community.
I co-wrote this article with my colleagues, Catherine Allan, Peter Spooner, Rik Thwaites and John Morgan. The article was first published in Australasian Plant Conservation – the fantastic journal of the Australian Network for Plant Conservation. If you’d like to refer to this article, please use the reference to the ANPC’s journal (as below), to attract readers to this valuable magazine.
Barr, N. (2005). Understanding Rural Victoria. Department of Primary Industries, Victoria, Melbourne.
Costello, D.A., Lunt, I.D. & Williams, J.E. (2000) Effects of invasion by the indigenous shrub Acacia sophorae on plant composition of coastal grasslands in south-eastern Australia. Biological Conservation 96, 113-121.
Geddes, L.S. (2009) Plant community changes associated with Leptospermum laevigatum invasion and senescence on the Yanakie Isthmus, Wilsons Promontory. Honours thesis. School of Botany, La Trobe University, Bundoora Melbourne.
Hobbs, R.J., Higgs, E. & Harris, J.A. (2009). Novel ecosystems: implications for conservation and restoration. Trends in Ecology & Evolution 24, 599-605.
Lunt, I.D., Allan, C., Spooner, P., Thwaites, R. & Morgan, J. (2010). Managing regrowth in Australia’s changing rural landscape: a social phenomenon. Australasian Plant Conservation 19(1), 5-6.
Lunt, I.D., Winsemius, L.M., McDonald, S.P., Morgan, J.W. and Dehaan, R.L. (2010). How widespread is woody plant encroachment in temperate Australia? Changes in woody vegetation cover in lowland woodland and coastal ecosystems in Victoria from 1989 to 2005. Journal of Biogeography 37, 722-732.
I’m really glad this issue is getting some attention. The social aspect of regrowth is intense and cannot be ignored (as much as I’ve tried). The assumption that dense regeneration in unnatural and a threat to biodiversity is just that, an assumption. We need more data! I think it’s tempting to lump regrowth in with woody plant encroachment, but eucalypt regrowth, in particular, is very distinct from shrub encroachment in terms of changes to the understorey environment, recruitment patterns and subsequent trajectory. Regrowth may actually be very ‘natural’; tree clearing may be a recent phenomenon, but mass mortality of trees is not. Anyway, great article!
Hi Meg, thanks for your comment – my very first! You’ve highlighted lots of complexities that are wrapped up in the regrowth / encroachment issue – social vs ecological impacts, threats to biodiversity, naturalness, trees vs shrubs, impacts on understoreys (and hence other species and processes), long term trends and trajectories, and more. We really need lots more work on all of these issues – not just ecological work, but social studies too, as you say. My guess is that there’ll be very different phenomena in different regions – with different drivers, impacts and trajectories – but at the moment we don’t have many good frameworks to help people to work past the ‘woody weed’ perspective. I reckon this is a really exciting area to work in – the fact that its complicated may be one of the reasons why it has fallen through the cracks, and been neglected, up to now. Best wishes Ian