Deforestation And Its Effects On Bird Communities
Forest degradation is arguably the greatest threat to biodiversity, ecosystem services, and rural livelihoods worldwide. It’s an issue that is very apparent in Mexico—a diverse, developing country with a somewhat limited regulatory and management framework. Between 1970 and 2005, the lack of effective land management policies contributed to extensive deforestation, often at a rate of more than 5000 km2/year (about 1930 miles2/year). This equates to an area bigger than that of the Great Salt Lake in Utah.
Previous research has shown that such widespread degradation of forests reduces the range size of many vertebrates and can result in local extinctions. Naturally, low income communities depend on forest resources, but there are cases when resource extraction rates exceed those of regeneration. This conflicts with conservation goals and is a recurring phenomenon in several regions of Mexico. In community-owned areas, degradation is mainly caused by logging. National park (NP) forests also experience this issue with illegal livestock grazing and firewood harvesting often being the cause.
In this study, a group of researchers from the U.S. and Switzerland compared bird communities in managed and unmanaged forests in the Sierra Tarahumara region of Mexico, which covers about 15% of the country’s total forest biomass. The scientists used mathematical models and data from a two-year breeding bird survey to increase our understanding of how forest birds respond to the habitat degradation that timber harvesting can cause.
According to the authors, species richness—the number of species in a given area—is the measure of biodiversity that most researchers use. It can provide vital information about how an ecosystem changes with time. The researchers estimated species richness from detection data with a statistical model, while accounting for the imperfect detection of species. During the observational period (2008–2009), the researchers recorded 73 bird species across the sampling locations despite the model having estimated that 125 species should be present. Based on this, the scientists hypothesized that they failed to detect 52 species, which highlights the importance of accounting for imperfect detection.
The results will not surprise many of us: the researchers found the highest bird occupancy and richness estimates on NP sites and community land not subjected to recent logging. The logged locations contained, on average, just 1/4 of the species found on NP sites. These findings support previous studies that have shown that current forestry practices in the region have resulted in widespread degradation and loss of forest productivity. The researchers found that we can use such findings to reach reliable conclusions about the status of bird communities and the states of forest systems in both intact and degraded sites. Researchers could apply similar models to other species (of both animals and plants) to evaluate the current status of ecosystem structure and function.
It is perhaps unsurprising that bird diversity, and likely biodiversity in general, was greater in less disturbed, mixed-age forest sites. Mature trees and their structures provide unique habitats for species. To maximize biodiversity, the researchers recommend establishing more national parks, restoring degraded habitats, and curbing the harvesting of large trees. Using such a model as that outlined in this paper could enable forest managers to predict how specific interventions would affect a given site’s biodiversity.
Animal advocates will benefit from learning about this study: the successful establishment of such a model would allow forest managers to test how a planned forestry activity may affect certain forests, which could help guide forest practices in advance. What’s more, we can apply such a methodology not only to bird species, but also to a wider range of animal species in subsequent studies.