As conservation is all about the economy these days, people are wondering whether nature reserves and similar protected areas are actually helping or harming the people living in the area. They might harm by stopping people from exploiting natural resources, but they may also help by offering opportunities in eco-tourism and benefits from ecosystem services.
If one wants to know which way the overall balance turns out, there appears to be very little hard data to go on, but now K. Andam et al. have published a "controlled study" in PNAS trying to eliminate error by comparing the economic development of sites with a nature reserve to that of sites similar in all aspects except that they are lacking such a protected area.
Carrying out this kind of analysis on various sites in Costa Rica and in Thailand, the authors come to a cautiously optimistic conclusion, namely that the "treated" samples (i.e. with a protected area) have done somewhat better than the control samples.
So now if your conservation project runs up against local nimbyism, you can always throw a copy of that article at the opposition.
Kwaw S. Andam, Paul J. Ferraro, Katharine R. E. Sims, Andrew Healy, and Margaret B. Holland
Protected areas reduced poverty in Costa Rica and Thailand
PNAS published ahead of print May 24, 2010, doi:10.1073/pnas.0914177107
Abstract and free access to PDF file.