Understanding the importance of small patches of habitat for conservation

Tulloch, A.I.T., Barnes, M., Ringma, J., Fuller, R.A. and J. E.M. Watson (2015). Understanding the importance of small patches of habitat for conservation. Journal of Applied Ecology, 53: 418-429.

We demonstrate a simple multi-pronged metric for assessing ecosystem vulnerability, which 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. Our 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.The main findings of our research:

* More than 80% of native vegetation has been lost worldwide. Conservation activities in heavily cleared landscapes focus on keeping remaining large patches intact, often disregarding the increasingly important role of smaller patches in conserving remaining vegetation.

* We examine historical and current patch size distributions to evaluate how important small patches are to different ecosystems. Using data on vegetation clearing in Australian, we calculate the historical change in the contribution of patches below different size thresholds to overall extent.

* We find that many vegetation communities in Australia now occur disproportionately in small patches – at least 22% of major vegetation communities have >50% of their remaining extent in patches smaller than 1000 hectares.

* For some communities the loss of patches as small as 1 ha would be catastrophic – for others it would make very little difference to persistence at all.

* Many vegetation communities are exposed to the double jeopardy of high loss and high fragmentation, such as Brigalow and Mulga in Queensland. These communities are currently undergoing increased clearing as a result of changes to clearing laws that allow high agricultural value land to be cleared.

* 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.

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