Conservationists are always looking for ways to halt the pace of deforestation in tropical rainforests and one approach involves re-cultivating abandoned agricultural land.

An international team investigating this concept has just published its findings in Nature Communications. Working in the mountainous regions of Ecuador, the researchers found afforestation and intense pasturing to be particularly effective, clearly increasing the environmental and economic value of abandoned farmlands.

Every year, 130,000 sq. km of rainforest disappear from the face of the Earth — an area equivalent to the size of Greece. The majority of this land is cleared for agricultural development — even in tropical mountain areas. However, these fields are quickly overgrown with weeds and bracken is particularly tenacious. It cannot be permanently eliminated using herbicides or by burning the land. As a result, farmers often abandon the land after a few years and start clearing new areas of forest.

"This cycle has to be broken," said professor Thomas Knoke from the Institute of Forest Management at Technische Universitat Munchen (TUM) in Germany. Knoke is lead author of the study that has just been published. "We've been investigating whether this abandoned pasture land can be recultivated, and if so, how."

The team did not just look at economic benefit when evaluating the different concepts. For the first time, this study also took environmental and socio-cultural criteria into consideration, factoring in issues such as the amount of carbon dioxide and nitrogen assimilated by plants and soil, biomass production, soil quality, impact on climate, water management and acceptance among farmers.

Sustainable land use

The area under investigation (around 150 hectares) is located in the Ecuadorian Andes at an altitude of between 1,800 and 2,100 m. The researchers looked at five different concepts:

1. No land use — abandoned land is left to nature;

2. Afforestation — planting a native species of alder;

3. Afforestation — introduction of a non-native pine species;

4. Extensive pasturing — mechanical weed control followed by initial fertilization and land use, and

5. Intense pasturing — chemical weed control and land use with regular fertilization.

Afforestation with alder and pine species proved particularly sustainable. In addition, forested regions offer the best protection against erosion in the long term, according to the announcement from TUM.

"Our study also showed that afforestation with the native Andean alder had a much more positive impact on the climate and water balance than the other land use options," added professor Jorg Bendix from Phillips-Universitat Marburg.

Engaging farmers

Typical rainforest flora and fauna are also able to gradually recolonize afforested regions. Intense pasturing scored much higher on the ecological scale than extensive pasturing. Economic benefits stemmed from the sale of wood (afforestation) or the sale of meat and milk (pasturing). Alder plantations achieved the greatest financial returns.

A survey conducted among land users showed that the majority of livestock farmers also viewed afforestation as the best land use option due to the positive ecological balance and greater long-term earnings potential.

"If we want recultivation concepts to be a success, the people using the land have to be engaged," Bendix explained.

The sustainable land use concepts all come at a cost, however. Over a period of 20 years, farmers who do not use slash-and-burn techniques are exposed to an annual loss of earnings. This amounts to $87 per hectare for afforestation and $100 per hectare for intense pasturing. The researchers regard compensation for recultivation as an important incentive for encouraging famers to replant abandoned grazing land. In the long term, trade with carbon dioxide certificates could also provide an additional source of income.

The researchers also believe that their study could be used as a reference for evaluating recultivation concepts in other tropical mountain forests, for example in Brazil or Africa.

"Abandoned agricultural land is a huge resource that is not being harnessed," Knoke suggested.

"The German Research Foundation is currently funding a number of projects that are working with farmers in Ecuador to implement the findings of the study," concluded Erwin Beck, a professor at the University of Bayreuth who started the project in Ecuador 17 years ago.