High human population density eliminates the positive effect of forest protection in a tropical biodiversity hotspot

By Patrícia Dérer

Sri Lanka and the Indian Western Ghats (also known as Sahyadri Mountain Range) make up one of 36 Biodiversity Hotspots. These areas are the Earth’s most biologically rich—yet threatened—terrestrial regions; they were designated in order to preserve the most species.

The Western Ghats belong to the eight “hottest hotspots” based on their high plant and animal endemism¹. They include a wide range of ecosystems: moist and dry deciduous forests, montane rainforests, evergreen forests and the unique Shola grasslands. The hotspot is the home of 332 globally threatened species, and holds viable populations of such endangered mammals as tiger (Panthera tigris), Asian elephant (Elephas maximus), Asiatic wild dog (Cuon alpinus) and gaur (Bos gaurus). Moreover, the hotspot contains more than 30 percent of all plant, fish, reptile, amphibian, bird and mammal species found in India.

Concurrently with its high conservational value, the region has the highest population density among all biodiversity hotspots (average 350 people/km²)². Faced with tremendous population pressure, the hotspot’s forests have been dramatically affected by the demands for timber and agricultural land. Between 1920 and 1990, 40 percent of the region’s natural vegetation was converted to coffee and tea plantations, and today only 6.3% primary vegetation remains³

In a recent study, “Parks protect forest cover in a tropical biodiversity hotspot, but high human population densities can limit success”⁴ Krishnadas et al. examine the correlates of forest loss following the region’s rapid economic expansion. Between 2000 and 2016, the Western Ghats lost approximately 750 km² of forest. Fortunately, these rates are the region’s lowest in the last 100 years, and are substantially lower than for other forested parts of India⁵. Nevertheless, the negative impact of this patchy type of small-scale deforestation on biodiversity could be substantial, and remains largely unexamined.

The authors assess the relative importance of various demographic, administrative and biophysical factors that predicted the rates of the recent forest loss. Overall, deforestation occurred primarily outside protected areas; forest protection – in the form of wildlife sanctuaries and national parks – successfully reduced forest loss by 30%.

The authors find that by every 22 km increase in mean distance to town, forest loss decreased by 16%, with a lesser impact for protected areas. Protected areas were 36% less likely to lose forest than non-protected forests when closer to towns. Similarly, with every 4 km increase in distance from roads, forest loss decreased by 21%, and decreased by 33% for protected areas.

However, the advantage of formal protection declined by 32% with every increase of 24,000 people above mean local population densities. In other words, where local human populations were higher in the Western Ghats, protected areas were 70% more likely to lose forest cover than non-protected areas. This implies that the difference in forest loss between protected and non-protected areas mostly disappears at high local population densities.

These findings indicate that even with rapid development, protected areas help retain forest cover within a global Biodiversity Hotspot. However, high human population densities and their associated road development negatively affect these benefits of protection. Consequently, strong actions to halt population growth –such as greater funding for family planning programs – are essential in order to achieve successful forest protection.

References:

1. Myers, N., Mittermeier, R. A., Mittermeier, C. G., da Fonseca, G. A. B. & Kent, J. Biodiversity hotspots for conservation priorities. Nature 403, 853–858 (2000).
2. Cincotta, R. P., Wisnewski, J. & Engleman, R. Human population in the biodiversity hotspots. Nature 404, 990–992 (2000).
3. Sloan, S., Jenkins, C. N., Joppa, L. N., Gaveau, D. L. A. & Laurance, W. F. Remaining natural vegetation in the global biodiversity hotspots. Biol. Conserv. 177, 12–24 (2014).
4. Krishnadas, M., Agarwala, M., Sridhara, S. & Eastwood, E. Parks protect forest cover in a tropical biodiversity hotspot, but high human population densities can limit success. Biol. Conserv. 223, 147–155 (2018).
5. Reddy, C. S., Jha, C. S. & Dadhwal, V. K. Assessment and monitoring of long-term forest cover changes (1920-2013) in Western Ghats biodiversity hotspot. J. Earth Syst. Sci. 125, 103–114 (2016).