Mixed forest plantations tend to be more resilient to climate change, scientists say

To confirm this hypothesis, researchers in Brazil and France are conducting an experiment to find out how tree diversity influences carbon uptake and drought tolerance. The project was discussed by participants in an event held at IPT, the São Paulo State Technological Research Institute.

By Elton Alisson  |  Agência FAPESP – Brazil has some 10 million hectares of commercial timber plantations, about 78% of which consist of eucalyptus trees mainly used to produce pulp and paper. Seventy percent of Brazil’s eucalyptus plantations use a single clone and hence have the same genetic makeup. “This represents a major risk in times of climate change,” said Pedro Brancalion, a professor at the University of São Paulo’s Luiz de Queiroz College of Agriculture (ESALQ-USP), in his presentation to a seminar entitled “Climate change and biodiversity scientific cooperation day”, held on October 20, 2022, at the São Paulo State Technological Research Institute (IPT). The event was hosted by FAPESP and the Consulates-General of France and Germany in São Paulo.

“Most of the eucalyptus cultivars planted in Brazil today are very fast-growing if you have water. In extreme drought events, which are increasingly frequent as part of climate change, eucalypts and other commercial species dry up and die. These plantations also reduce the amount of water available to people. We must find ways to make timber plantations more drought-resilient and economical in the use of water,” Brancalion said.

One of the solutions is to increase the biological complexity of commercial timber plantations by mixing clones or adding new species. The strategy of mixed plantations containing trees with different kinds of genetic makeup and even different tree species is also considered one of the most promising nature-based forest restoration solutions, increasing carbon sequestration and making plantations more drought-resistant. However, it is not yet clear how tree diversity influences forest functioning while at the same time favoring climate change mitigation and adaptation.

“The hope is that the more species a forest has, the better it functions and the more resilient it will be to climate change since it will use water and other environmental resources more efficiently,” Brancalion said.

To test this ecological theory and extend knowledge of mixed forest plantations, Brancalion teamed up with colleagues at ESALQ-USP and France’s Agricultural Research Center for International Development (CIRAD) to conduct an experiment on an unprecedentedly large scale in Brazil. The project, which is supported by FAPESP, is located in an area of six hectares on ESALQ-USP’s Forest Science Experiment Station in Itatinga, São Paulo state.

The researchers planted 150 experimental plots with different levels of tree diversity, ranging from one to six native species of great interest to silviculture or forest restoration and widely distributed in the Atlantic Rainforest or Cerrado, Brazil’s savanna-like biome.

The different forest compositions are also being submitted to different nutrient and water regimes, obtained by adding or withholding fertilizer and using plastic tarpaulins to intercept rainwater.

Mixed plantations will be compared with monocultures to assess the impact of tree species diversity on ecosystem functioning and also to help formulate guidelines for forest restoration programs, Brancalion explained. “The idea is to use biodiversity as a fundamental strategy to adapt timber plantations to the twenty-first century at a time of climate change,” he said.

Resistance to drought

One of the project’s goals is to find out how to increase carbon absorption by mixed forest plantations. Another is to see how they can be made more drought-resistant, a key issue for fast-growing trees such as eucalypts, which require large amounts of water during their development.

“Rapid-growth forest plantations can consume almost the same amount of water as the precipitation that falls in some basins in peak growth stages. Unless eucalyptus groves are well planned, some of the most important problems posed by climate change, such as drought, could be made worse,” Brancalion said.

He also noted that the new frontier for eucalyptus planting in Brazil is Mato Grosso do Sul, a state known to have a seasonally dry climate.

Commercial eucalypt clones were developed to maximize productivity, which is possible only when there is an abundant water supply. With climate change, however, periods of acute water deficit are becoming more frequent, limiting forest productivity.

“Eucalyptus plantations require a great deal of water. The trees die in an extreme drought. I’ve seen plantations with hundreds of hectares of trees that have all died for lack of water,” Brancalion said.

International collaboration

The project conducted by Brazilian and French researchers is part of TreeDivNet, a global network of experiments designed to analyze the impact of tree diversity on ecosystem functioning.

Other experiments in the network are under way in Austria, Belgium, France, Germany and Sweden. Universities, research institutions and forestry industry coalitions are also taking part.

The project is complemented by interviews conducted in Brazil and elsewhere to understand the challenges and opportunities for expansion of mixed forest plantations. “The existence of these controlled experiments in different regions of the planet will enable us to have a global vision of how biodiversity can help us meet some of the most important challenges posed by climate change to different ecosystems, such as tropical and temperate forests. This is important because we know the climate won’t change in the same ways everywhere in the world,” Brancalion said.

This kind of international research collaboration will be even more important in the wake of the COVID-19 pandemic, according to FAPESP President Marco Antonio Zago, who opened the event.

“As society recovers from the most significant global disaster of this century, the COVID-19 pandemic, it’s the right time to talk seriously and forge strong collaborations in order to avoid and face new challenges, such as those caused by global climate change and biodiversity loss,” he said.

For Christophe Alamelama, French deputy consul in São Paulo, governments must deploy science-based solutions to address the challenges posed by climate change and biodiversity loss, and international cooperation is key in this area. “We’re eager to enhance Franco-Brazil cooperation in research on biodiversity and climate change,” he said. 

For Martina Hackelberg, German consul in São Paulo, Brazil is a particularly important partner of Germany and plays a key role in the mitigation of climate change. “In many areas, we are already cooperating very well, and we can move forward into other fields in future, such as green hydrogen,” she said.