25 October 2010
The vast number of landslides triggered by the May 2008 Wenchuan earthquake, and in its aftermath has been extensively described, not least on this blog. One of the documented impacts of these landslides was the well-documented loss of habitat of the giant panda (A. melanoleuca) due to extensive forest loss. However, there is a great deal more to that story than meets the eye, as a newly-published paper by Vina et al (2010) describes. The research is very interesting, and has some quite substantial implications for landslide management in earthquake-prone areas.
The study examines forested areas affected by the earthquake in Wenchuan County, in the main area affected by the earthquake. Wenchuan County includes Wolong, the famous giant Panda conservation area. The context for the study is important though – that is that contrary to popular understanding, the forested area of China has been increasing, not decreasing over the last decade or so. There are two key reasons for this:
- Economic growth has led to a huge migration of people to urban areas, reducing the pressure on rural resources;
- In the aftermath of the devastating floods in 1998, China started a huge programme of forest conservation and restoration, most notably incentivising farmers to return hillside croplands to forest.
So, the key question that this research has addressed is how the dynamics of forests in Wenchuan County. The research team mapped forest cover using Landsat TM satellite images acquired in 1994 and 2001 (i.e. before the conservation effort) and 2007. Augmented with higher resolution IKONOS and Quickbird images from 2000 and 2007. These images were used to map forest cover.
The results are fascinating. Between 1994 and 1991 the forest cover declined from just under 44% in 1994 to about 39.5% in 2001. However, by 2007 the forest cover was back to about 44%, showing that the conservation programmes had generated real results.
The earthquake of course reversed this trend. In the aftermath of the seismic event the forest cover was again mapped using Landsat TM images. The results suggest that 192.6 square kilometres of forest were lost in Wenchuan County, representing just under 11% of the forest cover in 2007. The consequence was that forest cover declined to about 39%. However, the authors estimate that without the conservation programmes this would have been as low 33.5%. Thus, although the occurrence of landslides in the earthquake was truly dreadful, the ecological picture would have been far worse if it hadn’t been for the forestry programmes. One aspect that the paper does not cover though is that the loss of forestry increasing seismic landslide susceptibility, and thus the loss might have been greater again
The authors finish by speculating on the long term recovery of the forest resources in the aftermath of the earthquake. They note that the construction of new housing, such as that shown to the left (from my recent trip to the area), is likely to have the effect of moving people away from the more remote rural areas, which may well result in the abandonment of more farmland, and thus increased forest recovery. This may well have substantial benefits for conservation efforts, albeit at potentially high cost to those people most affected by the earthquake.
Viña, A., Chen, X., McConnell, W., Liu, W., Xu, W., Ouyang, Z., Zhang, H., & Liu, J. (2010). Effects of Natural Disasters on Conservation Policies: The Case of the 2008 Wenchuan Earthquake, China. AMBIO DOI: 10.1007/s13280-010-0098-0