Mixed forest plantations tend to be more resilient to climate change

In Brazil, there are about 10 million hectares of commercial wood plantations, of which approximately 80% are composed of eucalyptus, mainly destined to the production of paper and cellulose. More than half of the plantations of this tree in the country use a single clone (plants with the same genetic makeup), said Pedro Brancalion, a professor at the Luiz de Queiroz Higher School of Agriculture at the University of São Paulo (Esalq-USP).

“This represents a great risk in times of climate change”, evaluated the scientist during a lecture at the Climate change and biodiversity scientific cooperation day, held on October 20, at the Technological Research Institute (IPT), by Fapesp and the general consulates of France and Germany in São Paulo.

“Most of the eucalyptus clones in use today in Brazil are great for fast growth, as long as sufficient water is available. In severe drought events, increasingly frequent with climate change, eucalyptus and other commercial species can dry up and die, as well as reducing the supply of water to people. Therefore, it is necessary to seek ways to make forest plantations more resilient to drought and economical in the use of water”, he pointed out.

One of the solutions to achieve these goals is to increase the biological complexity of commercial plantations, mixing clones or adding new species to the system, evaluated Brancalion.

This strategy of promoting mixed forest plantations, where several genetic materials or even tree species are mixed, has also been identified as one of the most promising nature-based solutions to be implemented in forest restoration programs, in order to enhance the sequestration of CO2 from trees while making planted forests more drought resistant.

It is still not clear, however, how the diversity of trees influences the functioning of the forest and at the same time favors the mitigation and adaptation to climate change, pondered the researcher.

“The expectation is that the more species a forest has, the better its functioning and its resilience to climate change, as it will use environmental resources such as water more efficiently,” he explained.

In order to test this ecological theory and expand the knowledge base to promote mixed forest plantations, the researcher, in collaboration with colleagues from Esalq-USP and the Center for International Cooperation in Agronomic Research for Development (Cirad), in France, is carrying out an unprecedented large-scale experiment in Brazil.

The project, supported by Fapesp, is being carried out in an area of ​​6 hectares of the Experimental Station of Forest Sciences of Esalq-USP in Itatinga, in the interior of São Paulo.

A total of 150 experimental plots with different levels of tree diversity were planted in the area, ranging from one to six native species of great interest for silviculture or forest restoration and widely distributed throughout the Atlantic Forest and the Cerrado.

The different forest compositions are still being subjected to different treatments for the availability of nutrients and water, obtained from the addition or not of fertilizers and the use of plastic sheets to intercept rainwater.

By comparing mixed forest plantations with monocultures, it will be possible to assess not only the impacts of tree diversity on the functioning of an ecosystem, but also to develop guidelines for restoration programs, said Brancalion.

“The idea is to use biodiversity as a fundamental strategy to adapt timber plantations to the 21st century, in times of climate change,” he said.

drought resistance

One of the project’s lines of study is on how to increase carbon uptake by these mixed forest plantations. Another aspect of the research is how to make them more resistant to drought, a critical problem for very fast-growing trees like eucalyptus, which require a lot of water during development.

“Fast-growing forest plantations can consume almost the same volume of water that rain brings to some basins in the peak growth phases. Therefore, if eucalyptus plantations are not well planned, some of the most important problems presented by climate change , which are droughts, could be amplified”, pondered Brancalion.

The researcher also underlined that the new frontier for eucalyptus plantations in Brazil is Mato Grosso do Sul, a region known for having a seasonally dry climate.

Commercial eucalyptus clones were developed to maximize productivity, which is only possible when there is good water availability. With climate change, however, periods of high water deficit tend to become more common and restrict forest productivity.

“Eucalyptus plantations require a lot of water and when there are extreme droughts the trees die. I have seen plantations of hundreds of hectares with trees completely dead due to lack of water”, he said.

international collaboration

The project led by Brazilian and French researchers is part of a network of experiments aimed at understanding the impacts of tree diversity on the functioning of ecosystems, called TreeDivNet.

The network encompasses other experiments established in Austria, Sweden, Belgium, Germany and France. In addition, it has the participation not only of universities and research institutions, but also of coalitions in the forestry sector.

The project is complemented by interviews carried out in Brazil and in some of these countries to understand the challenges and opportunities for the expansion of mixed forest plantations.

“The existence of these controlled experiments in different regions of the world will allow us to have a global view of how biodiversity can help us to face some of the most important challenges brought by climate change in different ecosystems, such as tropical and temperate forests. This is important because we know that the climate will not change in the same way everywhere in the world,” said Brancalion.

This type of international collaboration in research will be even more important in the post-Covid-19 pandemic period, said Marco Antonio Zago, president of Fapesp, at the opening of the event.

“When society recovers from the most significant global disaster of the century, which was the Covid-19 pandemic, it will be the right time for us to get serious and forge strong collaboration to avoid and face new global challenges and threats, such as those caused by global climate change and the loss of biodiversity”, he evaluated.

The French Consul General in São Paulo, Christophe Alamelama, stressed that in order to respond to the challenges posed by climate change and the loss of global biodiversity, governments must base themselves on science and that international cooperation in this area is vital.

“We look forward to increasing Franco-Brazilian cooperation in research on biodiversity and climate change,” he said.

The consul general of Germany in São Paulo, Martina Hackelberg, said that Brazil is a particularly important partner for the European country and has a key role in the fight against climate change.

“We have already cooperated in many areas, but we can advance to other fields in the future, such as green hydrogen”, he evaluated.