Watch Phil Gibbon's presentation on the EIANZ Ecology YouTube Channel.
Biodiversity loss has already led to catastrophic impacts on critical ecosystem services - the natural capital on which the human economy depends. Diamond in his book "Collapse" (video presentation), links land-clearing to the collapse of society in western cultures. Australia is in the top "G8" land-clearing nations of the world. Biodiversity offsetting is one tool available to help control and potentially reverse this. Land-clearing already exceeds afforestation by a ratio of 2:1 and is a hazard to important ecosystem services such as rainfall propagation (McAlpine et al. 2008).
Even though the cost to reverse habitat loss - one of the more tangible externalities of land-clearing - exceeds the value gained from deforestation (PMSEIC Report, 2002), the rate of loss is simply coupled to economic demand and the drivers for this are still increasing. Biodiversity loss is not a problem that is going away, it is set to get worse as Australia's population doubles in the next 60 years, and agricultural output doubles in 30 years. As a philosophy, offsetting in some form or another, appears to be the only alternative to the current situation.
The principle of biodiversity offsets is that habitat loss can be evaluated and 'offset' within an area (usually larger area) of equivalent value. There are a number of potential pitfalls which were the subject of a recent paper in Ecological Management and Restoration. This sought to consider whether offsets could be done in practice, despite common and quite valid criticisms, summarised into four categories:
- Insufficient gain - the amount of land apportioned for offset is simply insufficient.
- Equivalence - what is like for like? Can it ever be achieved to replace what has been lost?
- Time lag - the offset might not mature and provide resources for centuries, by which time it could be too late.
- Compliance - we have a very poor record of compliance in Australia. There is evidence of poor compliance with offset schemes overseas.
EQUIVALENCE is a problem if the planted vegetation offset is very different to native vegetation. Planted or restored vegetation is never as biodiversity-rich as natural vegetation (see study by Deakin University). In a paper for the online journal, Ecology and Society, scientists further argued that you can't shoehorn restoration into a desired trajectory as there are inherent uncertainties in environmental management outcomes. We know that there are ecological barriers to restoration when habitat has been denuded to a very great degree. For offsets to work, requires a fungible metric and management adaptation, where the environment controls some of the direction of ecological succession. We also need to accept some substitution between impacts and offsets. Whether we like it or not, "like for like" is rarely, if ever, achievable and is perhaps inappropriate terminology. The desired outcome is a balance between the area being removed and the ability of offset habitat to support representative communities of species, even if it is 'modified'.
TIME LAGS are a problem if offsets are only short term. Many ecosystem features can only be restored over long time-frames e.g. tree hollows only begin to form in Eucalypts 120-220 years old. In most offset policies to date, clearing can begin before tree hollows start to develop.
COMPLIANCE is an ongoing problem and does not just mean enforcement of approvals, although one study in Canada found only a 14% compliance rate. Management is also constrained by a lack of overall biodiversity monitoring. For example, in New South Wales in 2004, 220,00 ha of clearing was formally recorded and approved but there was about 700,000 clearing in total.
Despite the pitfalls, this did not stop the Wentworth Group in 2003, under "A New Model for Landscape Conservation in NSW", recommending some type of offset mechanism for NSW. Since then, research and development of the current policy for offsets in NSW has shown that it can work but only under a strict set of circumstances, which are:
- The values lost from clearing can be feasibly restored elsewhere. i.e the lost site is already quite simple.
- Vegetation proposed for clearing is unlikely to persist in situ e.g. small paddock trees among cultivation or 'postage-stamp' areas of habitat.
- Offsets must be in place for long enough to allow habitat to recover, restoring key ecosystem processes (not just species composition).
- Management MUST deal with inherent risk and uncertainty about the values of restoration. Creation of offsets is not a process, it is an outcome. To create an outcome in the face of uncertainty, management must be adaptive; offsets must be guaranteed in perpetuity; and there must be adequate compliance on all offsets sites.
Gibbons, P. and Lindenmayer, D.B. (2007). Offsets for land clearing: no net loss or the tail wagging the dog? Environmental Management and Restoration, 8, 26-31.
McAlpine CA et al (2007) Modeling the impact of historical land cover change on Australia's regional climate Geophysical Research Letters, VOL. 34
Google Scholar search - impact of land cover on climate
PMSEIC Report "Setting Biodiversity Priorities"