The importance of small patches of habitat for conservation

In this post Associate Editor Akira Mori discusses a paper he recently handled by Ayesha Tulloch and colleagues ‘Understanding the importance of small patches of habitat for conservation’

Landscape perspectives are important for land management in human-modified ecosystems, and the related development of land-clearing policy. Informed by a large body of macroecological theory and field research, scientists as well as practitioners have long discussed and struggled to find solutions to allocating land areas between human development and biological conservation. As seen in the land-sharing versus land-sparing or the SLOSS (single large or several small) reserve debate, no single solution has been found due to many conflicts and constraints. This difficulty exists especially in regions with high levels of land-use intensification or habitat fragmentation. In this regard, a recent paper by Tulloch et al. (2015) is intriguing. Here, the first author (Ayesha Tulloch) and I (Akira Mori) introduce the main findings in this exciting paper.

More than 80% of native vegetation has been lost worldwide. In Australia, clearing of remnant vegetation nearly doubled from about 52,000 hectares in 2012–13 to about 95,000 hectares in 2013–14, and has nearly quadrupled since 2009–10 (WWF 2015). In of the face of this increasing trend of land clearing and fragmentation, conservation activities have largely focused on keeping remaining large patches intact. This means that the increasingly important roles of smaller patches in the conservation of remaining vegetation have been largely disregarded.

Tulloch et al. present the first study to compare historical and current patch size distributions to evaluate how important small patches are to different ecosystems. Using data on vegetation clearing in Australia, they calculated the historical change in the contribution of patches below different size thresholds to overall extent, and a new patch metric based on the Gini coefficient that indicates how unequal the distribution of patch sizes is relative to historical distributions.

Tulloch et al. found that many vegetation communities in Australia now occur disproportionately in small patches. They estimated that at least 22% of major vegetation communities in Australia have more than 50% of their remaining extent in patches smaller than 1000 hectares. In particular, they found that many vegetation communities have been exposed to the double jeopardy of high loss and high fragmentation, such as Brigalow and Mulga communities in central Queensland. These communities are currently undergoing increased clearing and fragmentation as a result of changes to clearing laws that allow areas of high agricultural value to be cleared in Queensland.

Clearing of Mulga habitat in central Australia. Photo attribution: Michelle Venter ©

Importantly, “the long-term consequence of not accounting for the role of all vegetation patches in terms of their benefit to biodiversity conservation outcomes is the continuous erosion of small patches in highly fragmented vegetation communities and the slow, inevitable decline of vegetation communities and the species dependent on them for their persistence: a death by a thousand cuts.” says Tulloch.

Brigalow scaly-foot (Paradelma orientalis), a legless lizard threatened by habitat loss due to land clearing and thinning operations. This species is endemic to Queensland and occurs mostly in the Brigalow vegetation community (one of the most vulnerable communities to loss of small patches in their analysis). Its distribution is highly fragmented due to large proportions of potential habitat being cleared throughout the species’ range. Photo attribution: Jeremy Ringma ©

According to Tulloch et al., their simple multi-pronged metric for assessing ecosystem vulnerability can potentially improve current methods of ecosystem assessment (e.g. the IUCN Red List of Ecosystems) by considering the size and configuration of remaining patches as well as overall loss. They claim that their approach is the first to explore the consequences of small-scale vegetation clearing due to the failure of current policies to protect vegetation patches smaller than a given threshold.

I believe that such policy failure is not only the case in Australia, but is also true in many other developed countries around the globe. Considering the novelty as well as the applicability to various regions, the measures demonstrated in Tulloch et al.’s study are important to test in other regions. Tulloch et al. conclude that their measures allow different stakeholders to assess how dependent ecosystems are on patches of different sizes, and enable policymakers to make more informed decisions about where and if vegetation protection or clearing should be permitted.