Vanishing rainforests, disappearing species

    
Loss of biodiversity is widely noted as one of the most important negative effects of deforestation. In this post I will briefly explain how tropical deforestation effects biodiversity and why we should be worried about it. I will do so mainly through summarizing a great article by Bradshaw et al. (2009) ‘Tropical turmoil: a biodiversity tragedy in progress’. 

One of the most imporant drivers of biodiversity loss in tropical regions is loss of habitat through the distruction of rainforests. Bradshaw et al (2009) predicts this driver to exceed the effects of climate change, invasive species, and overexploitation even in their worst case scenarios. Even thought tropical forests only represent 7% of Earth’s land surface, they provide habitat for 60% of all know species of our planet. 20 of the 34 global biodiversity hotspots are found in the tropics.  

While the loss of one or a few species may not seem such a huge problem for some, extinctions can have cascading effects leading to subsequent co-extinctions and disturbance of ecological balance. Most flowering plants in tropical rainforests are pollinated by animals. Bradshaw et al. (2009) explains that the number of bird species is predicted to decline by 13% by 2100 with a devastating effect on seed dispersal in many regions. An estimated one-third of the human diet in tropical countries comes from insect pollinated plants and the loss of pollinators may also have an effect outside of forests, on neighboring agricultural lands and can potentially cause decline in yields. In addition, some rainforest predator species play important roles in pest control on farms adjacent to forested areas. 

Compared to extinctions from “natural” causes such as gradual environmental change, newly established competitive interactions, or occasional catastrophic events, human action is implicated in a 100- to 10000-fold increase in extinction rates (Bradshaw et al, 2009). According to Pimm and Raven (2000) an estimated 10000 to 10 million species now become extinct each decade. In addition, they estimate that 40% of the species in Myers’ 25 biodiversity hotspots may go extinct as a result of tropical deforestation alone, with 0.1 to 0.3% of all tropical forest species disappearing annually. This, some scientists argue, could mean the arrival of the sixth known mass extinction event in Earth’s history.