Agroforestry plot in restored area, Cultivando Água Boa restoration program, Itaipu Binacional, Brazil CIFOR/Yoly Guterrez

Forests are full of surprises.

Parts of the Amazon, Panama’s Darien and many other places we think of as home to pristine primary forests are actually the outcome of centuries-old natural forest regeneration. Much of this regrowth in the Americas happened when Amerindians, around the time of European colonization, abandoned their fields and dramatically reduced their farming activities, while at the same time the need for forest conversion by early colonists was insignificant.

One of the key messages of this year’s International Day of Forests is that forests can come back.

Unfortunately, this may not be as true as it once was, especially where deforestation and forest degradation remain unabated and soil erosion is severe.  And many of the countries that pledged to restore millions of hectares of degraded land as part of the Bonn Challenge, a global effort to restore 350 million hectares of land by 2030, show high deforestation rates.

So how can forest restoration support biodiversity in the 21st century?

Naturally or “passively” restored forests certainly do a better job at bringing back biodiversity than monoculture plantations. But it’s slow. It can take centuries of regeneration before the original assemblage of species return in numbers. Climate change, habitat fragmentation, loss of animal seed dispersers and fires can act together to slow biodiversity recovery. Still, this shouldn’t discourage us from naturally restoring forests to protect biodiversity.

Recent studies suggest that relying on passive forest restoration may end up being cheaper and more socially acceptable than tree-planting schemes.  However, to make the right decisions and to be cost efficient, it’s crucial to be able to predict where passive forest restoration is more likely to occur and where it is more likely to persist over time once farmland is abandoned. Another critical element is knowing how much biodiversity is needed for both people and nature during the process of forest restoration to supply essential services such as insect pollination, hydrological regulation, erosion and pest control.

Planning for forest restoration and biodiversity recovery also requires consideration of the impacts on local livelihoods, which may be affected far beyond the actual restoration projects. For example, given the importance of Amazon moisture for Brazilian agriculture, it has been argued that much of Brazil´s national target to restore 12 million hectares of degraded land by 2030 should take place in southern and eastern Amazonia.

Forest biodiversity has slowly made a comeback in several locations across Latin America through passive restoration over the last decade, covering not less than 2 million hectares—including parts of the tropical Andes.  And natural reforestation in montane areas has important implications in watersheds affected by deforestation.

With limited funding and a sometimes short-term mindset to restoration projects, the world needs both natural and active forest regeneration to speed the recovery of forest biodiversity—or in some cases a mix of the two. Local conditions differ and restoration efforts require approaches tailored to those conditions. These include changing aspirations and goals by stakeholders, legal and legislative changes, natural cycles like fires and droughts. Setbacks will also happen, due to lack of technical knowledge, or lack of access to it, particularly in developing countries.

Despite the hurdles, protecting and enhancing biodiversity via forest restoration, while maintaining other forest values, is a challenge we must confront. Forest restoration can reverse biodiversity loss, yet it requires careful decision making and prioritization.  And most importantly, to effectively restore forest biodiversity, we need to conserve the remaining tracts of intact forests at all costs.