Mathematical model can help conservationists choose.
Are we causing a sixth great mass-extinction? I don’t pretend to know the answer. But while the causes and extent of current extinctions aren’t always easy to identify, it does seem that since we arrived, and certainly since the Industrial Revolution, species appear to be disappearing at an alarming rate. For many of these events, habitat loss or degradation is one of the main culprits. Take away an organism’s place to live and, quite logically, it shall live no more.
Restore or Protect?
Unsurprisingly then, an often proposed measure is to stop habitat loss. There are two major strategies. The first one aims to restore habitats that have already been lost. Think tree planting in reforestation efforts, for example. The second one seeks to protect whatever more or less pristine habitat that is left. The establishment of national parks is a good example of this.
Protection is frequently prioritized. After all, that’s the one that likely yields the fastest, most direct benefits and in many cases of habitat decline or disappearance we really don’t have any time to lose. However, is protection really always the best choice? And if not, when should we use which strategy?
To answer these questions, researchers from Australia and the UK teamed up to beef up the matter with some science. One of their many interesting findings: we have to make a choice.
Cost, speed and time
They began by developing a mathematical model that took into account the rate at which the restoration proceeds, the details of how many and which species are lost or about to go extinct, and the ecosystem services the habitat provides. Working through the maths, they arrived at a relatively straightforward rule of thumb to decide when to do what.
The optimal decision depends on the ratio of the costs of both strategies, the speed at which habitats can be restored and how fast non-restored land degrades. Put simply, the higher costs of restoration are justified when they’re offset by the speed at which land can regain its pre-restoration qualities.
They applied the model to two real-world situations: coastal defence in northern Borneo, and bird conservation in the Atlantic forests of Paraguay. The results suggest that the former would benefit more from restoration while the latter should focus on protection.
Make a choice
The authors caution that habitat loss and degradation are complex processes which are difficult to completely encapsulate in a model. Therefore, they urge to see their rule of thumb as a guideline rather than an immutable rule. They do, however, point out one final interesting feature: splitting the available budget to pursue both protection and restoration simultaneously never emerged as best option for preventing biodiversity loss. It can work when you do one after the other, but never both at the same time, which is sometimes advocated as compromise.
Restore or protect, to save biodiversity we’ll need both (just not at the same time).
Possingham, H., Bode, M., & Klein, C. (2015). Optimal Conservation Outcomes Require Both Restoration and Protection PLOS Biology, 13 (1) DOI: 10.1371/journal.pbio.1002052