Tuesday, 11 June 2013

Remote sensing in reintroduction planning: oryx recovery in Chad

I was really pleased when I discovered the paper by Terri Freemantle and co-authors featured in this post, as I've been thinking about the potential for remote sensing to contribute to reintroduction programmes for a while now. One reason for this is the increasing frequency with which authors call for adequate assessments of habitat which recognise that due to global environmental change, the habitat may have altered since the species was extirpated. However, from the literature I've read, satellite-derived data is more readily used in predictive studies concerned with the potential for range shift and the feasibility of assisted colonisation. To me, it seems imperitive that reintroductions are just as careful to assess habitat suitability and the recent improvement in data that is available on global climate, vegetation and human impact should enable this to happen.

The paper concerns the scimitar-horned oryx (Oryx dammah) and its potential reintroduction to a Sahelian/sub-Saharan region of Chad. As a herbivore, a major aspect of habitat suitability is the availability of forage and this can be detected as photosynthetically active vegetation in other words, green plants. The study identified a 'greening' of the Ouadi Rimé-Ouadi Achim Game Reserve which the authors attribute to an overall increase in precipitation since the 1970s. They were also able to rule out hypotheses presented in previous studies that the increase in plant cover was due to human land use changes. They did this using a Human Footprint Index comprising data on transport, night-time lights, urban areas, land cover and population density to a resolution of 1 km. Whilst human disturbance has been relatively low and is not thought to be the driver behind greening, Freemantle et al indicate that the Reserve boundaries need to be enforced to prevent human encroachment onto now favourable pasture. The spatial variation in where greening has occured means that the oryx habitat may become squeezed as their preferred environment, the ecotone between desert and grassland, becomes narrower.

The authors admit that remote sensing techniques might be a crude tool for habitat evaluation but I agree with them that at landscape-scale, these methods offer a valuable source of information prior to undertaking any conservation translocation.  I would go further to point out that I know of few other studies that have incorporated human impact on this scale into a reintroduction planning exercise.  The data is there and available for anyone who wants to use it and I suggest that more people copy this example.

Freemantle, T. P., Wacher, T., Newby, J., & Pettorelli, N. (2013). Earth observation: overlooked potential to support species reintroduction programmes. African Journal of Ecology, n/a–n/a. doi:10.1111/aje.12060

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