When planting trees threatens the forest


Campaigns to plant huge numbers of trees could backfire, according to a new study by researchers of several universities including UCLouvain1 that is the first to rigorously analyze potential effects of subsidies in such schemes.

The analysis, published in Nature Sustainability, reveals how efforts such as the global Trillion Trees campaign, could lead to more biodiversity loss and little, if any, additional carbon sequestration. The researchers emphasize, however, that these efforts could have significant benefits if they include strong subsidy restrictions, such as prohibitions against replacing native forests with tree plantations.

If policies to incentivize tree plantations are poorly designed or poorly enforced, there is a high risk of not only wasting public money but also losing both terrestrial carbon and biodiversity,” said study co-author Eric Lambin, Professor in University of Louvain (UCLouvain). “That’s the exact opposite of what these policies are aiming for.”

The experience of Chile

The researchers involved with the new study wanted to zero in on the role of subsidies designed to encourage private landowners to plant trees because such payments are widely proposed as a promising solution to a variety of environmental challenges. So, the scientists looked at one of the world’s longest running and most influential afforestation subsidy policies, Chile’s Decree Law 701. The law, in effect from 1974 to 2012 and currently being considered for reintroduction, has served as the model for similar policies in a number of South American countries and international development projects.

The researchers set out to quantify the full impact of the afforestation subsidies and calculate their effects on net carbon and biodiversity changes across the entire country. They compared the area of Chilean forests under three scenarios: actual observed subsidy patterns, no subsidies and subsidies combined with fully enforced restrictions on the conversion of native forests to plantations. They found that, relative to a scenario of no subsidies, afforestation payments expanded the area covered by trees, but decreased the area of native forests. Since Chile’s native forests are more carbon dense and biodiverse than plantations, the subsidies failed to increase carbon storage, and accelerated biodiversity losses. However, strict enforcement of restrictions on native forest conversion would have improved the policy’s carbon and biodiversity outcomes.

Nations should design and enforce their forest subsidy policies to avoid the undesirable ecological impacts that resulted from Chile’s program,” said study coauthor Cristian Echeverría, a professor at the University of Concepción in Chile. “Future subsidies should seek to promote the recovery of the many carbon- and biodiversity-rich natural ecosystems that have been lost.”

1.Stanford University, University of Louvain, University of California at Santa Barbara,University of Concepción in Chile.

Published on June 22, 2020