London, England (CNN) -- One of the biggest dilemmas for conservationists is that preserving the environment often conflicts with the needs of the poorest communities who live there.
In many areas, forests of outstanding biodiversity are being chopped down by poor subsistence farmers in need of firewood and land to grow the food they need to survive, ecologists say.
Enter Payments for Environmental Services, or PES, an idea gaining popularity among conservationists as a way of allowing communities to benefit from conservation of their environment.
The idea is to that local communities are paid depending on the outcome of agreed objectives, such as stopping forest clearance, poaching and wildfires.
The United Nations Environment Program is testing PES in several countries as a way of reducing deforestation. While many conservationists like the idea of PES, few have tested empirically whether it actually works.
Scientists from the University of East Anglia are carrying out a controlled experiment in Rwanda to compare how the forest is conserved in communities that receive payments compared with those who do not.
The three-year ReDirect Rwanda project, which began last year, involves eight villages around Nyungwe National Park, one of the largest mountainous forests in Africa. Four of the villages receive payments -- paid to every individual household -- if woodcutting, bamboo cutting and snaring are reduced in their areas, and four villages do not receive payments.
Nicole Gross-Camp, a researcher on the ReDirect Rwanda project, said: "In my previous ecology work, I always felt there was a disconnection between conservation and the communities, usually subsistence farmers, living on the periphery of national parks.
"I found PES an intriguing concept that could marry these two aims of development and conservation. This is an empirical study to see how well PES can do that.
"The major issue is whether conservation and development are compatible and whether we can address these issues simultaneously. That is, whether people can find alternatives to what they are currently using.
"The outcome will be far-reaching for other potential places where this could be established."
She said Rwanda was a suitable place to test PES because it is one of the most densely populated countries in Africa, mainly made up of poor subsistence farmers. The Rwandan government has made a strong commitment to conservation, and Nyungwe National Park has a high biodiversity and a number of endemic species, she added.
Some local people carry out illegal wood collection, bamboo collection, snaring of animals and honey collection in the national park in order to survive, Gross-Camp said.
Bamboo is widely used for building homes, roofs, furniture, bedding, baskets and crafts. Animals, such as Gambian rats, duikers and bush pigs, are snared for food. Honey collection harms the forest because people usually cut down trees and smoke out bees, which often starts wildfires, Gross-Camp said.
"There are alternative sources of these products, but whether they are sufficiently accessible and affordable remains a question," she said.
Gross-Camp said that so far the project seemed to be working, with all but one of the communities reducing harmful activities in the forest.
She added: "Now we need to assess how this has affected the communities' livelihoods. We don't want to make anyone worse off than they were at the start."
One of the challenges for PES is to be sustainable in the long term. The ReDirect Rwanda project has funding from the European Research Council, but if people are to make lasting lifestyle changes, their payments need to be guaranteed beyond the end of the project.
"Who will continue to pay when we finish?" said Gross-Camp.
The answer, conservationists hope, is that large businesses will make the payments to offset their environmental activities.
However, Josh Donlan, director of the U.S.-based Advanced Conservation Strategies, said it might take regulation to persuade large businesses to contribute.
"More and more countries are looking into PES programs run by governments, but I think a lot of people would like to see more payment programs with the private sector as the 'buyer', said Donlan.
"It's hard to persuade the private sector to engage in PES schemes voluntarily, so that might have to be through regulation."
Neil Burgess, Professor of Conservation Biology at the University of Copenhagen, Denmark, advises the WWF and the United Nations Environment Program on PES. He is working on several UNEP-led pilot projects in Tanzania testing forest carbon payments to local communities.
Burgess said: "These projects have the potential to work and are starting to work, in that money is moving from companies and capital cities to local people -- which has never happened before.
"That gives us hope for the future that big companies may start paying more farmers to change their land use.
"The biggest problem is actually getting the money to poor people in rural areas who do not have bank accounts or Internet banking.
"It becomes quite inefficient if you need staff to drive around in cars distributing money to individuals."
In the case of ReDirect Rwanda, the project coincides with a government campaign to increase the use of bank accounts, so all payments are being made into bank accounts.
Still, some people have a day's walk to reach their nearest bank, Gross-Camp said.