Last year I wrote what has become a highly viewed post here at ConservationBytes.com about the plight of the world’s freshwater biodiversity. In a word, it’s ‘buggered’.
But there are steps we can take to avoid losing even more of that precious freshwater biodiversity. The first, of course, is to stop sucking all the water out of our streams and wetlands. With a global population of 7.5 billion people and climbing, the competition for freshwater will usually mean that non-human life forms lose that race. However, the more people (and those making the decisions, in particular) realize that intact wetlands do us more good as wetlands rather than carparks, housing developments, or farmland (via freshwater filtering, species protection, carbon storage, etc.), the more we have a chance to save them.
My former MSc student, the very clever David Deane1, has been working tireless to examine different scenarios of wetland plant biodiversity change in South Australia, and is now the proud lead author of a corker of a new paper in Biological Conservation. Having already published one paper about how wetland plant biodiversity patterns are driven by rare terrestrial plants, his latest is a very important contribution about how to manage our precious wetlands.
You can imagine different future scenarios of water loss or development that could further compromise wetland-network integrity. One is that rainfall declines over time as a result of climate change or dodgy water-allocation politics, thus stressing some of the shallower or smaller wetlands more heavily than others, or just reducing the size of each wetland in the network as the water volume declines. Another is the selective destruction of particular wetlands in the network to make way for more farmland or housing estates.
Of course, there are many plausible scenarios, but one might be tempted to predict that losing a few wetlands at the expense of keeping the entire network would be a better biodiversity outcome than each wetland shrinking slightly. Further, an intelligent conservation biologists could be forgiven for assuming that sacrificing big wetlands instead of small ones would do less overall harm, mainly because the species-area relationship predicts bigger patches to have more species.
Unfortunately, you’d be wrong.
First, it turns out that all wetlands aren’t the same, and that just because a wetland is big, it doesn’t mean that it contains more endemic species (a certain lack of nestedness, in other words). This means that losing a single wetland versus the equivalent area taken from all the wetlands in the network would result in a higher loss of endemic plant species on average.
Further, and perhaps more interestingly, smaller wetlands tended to accumulate rarer, endemic species faster than larger wetlands, so these little guys tend to be more valuable then their big cousins in terms of irreplaceable plant diversity.
So perhaps counterintuitively, the most important wetlands to protect in the network are the little ones!
This has huge implications for how we manage our wetland complexes in Australia, and especially as the competition for water increases. We need to make sure that we keep as many of the small wetlands intact and safe as possible, while simultaneously ensuring that the entire networks have enough water to persist.
CJA Bradshaw
1David is a former employee of the South Australia Department of Environment, Water and Natural Resources (DEWNR), so he had access to a wonderful database of wetland plant surveys on which to base his MSc thesis. He is now pursing a PhD at the University of Alberta (Canada) under the supervision of ecological-modelling guru, Fangliang He. We wish him all the best in his latest endeavour.
