Global study reveals vast potential for natural forest regeneration

Led by Dr Brooke Williams, a conservation ecologist in the QUT School of Biology and Environmental Science, and Dr Hawthorne Beyer, Head of Geospatial Science at carbon removal startup Mombak, the study found that the current biophysical conditions of more than 215 million hectares could support the natural regeneration of tropical forest.

The work, published in the renowned journal Nature, was conducted while both researchers were working for the Institute for Capacity Exchange in Environmental Decisions (ICEED).

Forest restoration is a key strategy needed to meet nature-based sustainable development goals.

The identified area could sequester 23.4 gigatonnes of carbon over 30 years.

"We need broad scale forest restoration to mitigate the biodiversity and climate crises," Dr Williams said.

"Tree planting in degraded landscapes can be costly but by leveraging natural regeneration techniques, nations can meet their restoration goals cost effectively."

Tres Barras, Brazil. Photo by Dr Brooke Williams.

Of the model's total estimated potential, 98 million hectares were identified in the Neotropics, 90 million in the Indomalayan tropics, and 25.5 million in the Afrotropics.

The study highlights that five countries - Brazil, Indonesia, China, Mexico and Colombia - account for 52 per cent of the regeneration potential, underscoring the need for targeted restoration efforts.

QUT Professor Jonathan Rhodes, a co-author of the study, explained these countries with high potential for national regeneration also represent important social and economic opportunities.

"It is important that the implications for local people are considered to ensure that they also benefit from restoration activities," he said.

Additionally, natural regeneration techniques often result in more biodiverse forests when compared to tree planting, senior author Dr Renato Crouzeilles, Director of Science at Mombak, said.

"Where ecological conditions are such that forests can grow back on their own or with low-cost assistance, natural regeneration can be more effective than full tree-planting in terms of biodiversity outcomes," he said.

Tropical forested regions are particularly important due to their unparalleled biodiversity, rapid growth rates and because large areas have already been cleared and degraded.

This research is based on a dataset created by a team of international experts, including Associate Professor Matthew Fagan from the University of Maryland, Baltimore County, who analysed historical natural regrowth patches and categorised forest regrowth across tropical regions.

"In a previous study, we used satellite images to identify millions of small areas where tree cover increased over time," Professor Fagan said.

"We then used machine learning to exclude the areas planted by humans, focusing on natural regrowth. Those natural patches were the input data for this novel study, the first to predict where future forest regrowth will occur, given observed past regrowth."

Copey de Dota, Costa Rica. Photo by Associate Professor Matthew Fagan.

Professor Robin Chazdon from the University of the Sunshine Coast noted that while identifying suitable biological conditions was crucial, soil and socioeconomic factors also play a role in determining forest quality.

"By partnering with nature, we can reach the scale and benefits that are needed to replenish the value of lost forest ecosystems," she said.

Dr Starry Sprenkle-Hyppolite, Restoration Science Senior Director at Conservation International, highlighted the model's value for implementing targeted, scalable and cost-effective restoration strategies.

"We are already using this dataset to explore and ground truth 'hotspots' for natural climate solutions based on assisted natural regeneration, working with local communities and land managers who may be interested in allowing some of the forest to recover on their land. This strategy can help encourage more investments in nature so that forests stay healthy and continue to provide the food, water and economic opportunity that humanity needs to survive," she said.

To support and advance tropical forest restoration, the authors have made the dataset publicly available and free to use.

"As we are increasingly faced with the impacts of climate change, the team urges governments to recognise the importance of leveraging natural regeneration potential as a powerful nature-based solution," Dr Williams said.

"We must restore vast areas of these important ecosystems that deliver multiple benefits to nature and people."

Read the full paper, The global potential for natural regeneration in deforested tropical regions, published in the journal Nature online.

The study is funded by Conservation International and the Walton Family Foundation.

Main image (left to right): Professor Jonathan Rhodes and Dr Brooke Williams

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