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

"This poses a great risk in times of climate change," the scientist said during a lecture at the Climate change and biodiversity scientific cooperation day event held on October 20 at the Institute of Technological Research (IPT), FAPESP and the Consulates General of France and Germany in São Paulo.

"Most eucalyptus clones in use today in Brazil are great for rapid growth, as long as there is sufficient water availability. In severe drought events, increasingly frequent with climate change, eucalyptus and other commercial species can dry up and die, as well as reduce the supply of water to people. That's why we need to look for ways to make forest plantations more resilient to drought and economic in water use," he said.

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

This strategy of promoting mixed forest plantations, where various genetic materials or even tree species are mixed, has also been pointed out as one of the most promising solutions based on nature to be implemented in forest restoration programs, in order to potentiate CO2 sequestration by trees and, at the same time, make planted forests more resistant to drought. It is not yet clear, however, how tree diversity influences the functioning of the forest and at the same time favors mitigation and adaptation to climate change, the researcher said.

"The expectation is that the more species a forest has, the better its functioning and resilience to climate change, because it will more efficiently use environmental resources such as water," 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), from France, is conducting a large-scale experiment unprecedented in Brazil. The project, supported by FAPESP, is being conducted in an area of 6 hectares of the Experimental Station of Forest Sciences of Esalq-USP in Itatinga, in the interior of São Paulo.

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 forestry or forest restoration and widely distributed throughout the Atlantic Forest and the Cerrado.

The various forest compositions are also being submitted to different treatments of nutrient and water availability, obtained from the addition or not of fertilizers and the use of plastic canvases to intercept rainwater.

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

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

Drought resistance

One of the study lines of the project is on how to increase carbon absorption 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 such as 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 peak growth phases. Therefore, if eucalyptus plantations are not well planned, some of the most important problems presented by climate change, which are droughts, can be amplified," Brancalion said.

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

Commercial eucalyptus clones have been developed to maximize productivity, which is only possible when there is good water availability. With climate change, however, periods of large 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've seen hundreds of hectares of plantations with trees totally dead from lack of water," he said.

International collaboration

The project conducted 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 covers 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 of the forestry sector.

The project is complemented by interviews conducted in Brazil and 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 address 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," Brancalion said.

This type of international collaboration in research will be even more important in the post-pandemic moment of COVID-19, 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 to speak seriously and forge strong collaboration to avoid and address new global challenges and threats, such as those caused by global climate change and biodiversity loss," he said.

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

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

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

"We have cooperated in many areas, but we can move to other fields in the future, such as green hydrogen," he said.

Source: Um só Planeta