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An international research team, including experts from the Ecological-Botanical Garden (ÖBG) at the University of Bayreuth, has demonstrated in a new study that native tree species in Argentina grow at a similar rate to introduced North American pine species—contrary to previous assumptions. Moreover, the exotic pines displace native trees and increase the risk of forest fires, especially in the context of climate change. The researchers their findings in Forest Ecology and Management.

Non-native plant species are often introduced and cultivated with the expectation of faster growth or higher yields. While the cultivation of exotic crops may be economically attractive, it frequently carries ecological risks: introduced species can displace native plants, alter soil chemistry, and disrupt entire ecosystems.

Studies such as the one involving the ÖBG at the University of Bayreuth help to understand the impacts of exotic cultivation, counteract past forestry mistakes, and provide recommendations for forestry authorities, forest enterprises, and private woodland owners to promote climate-resilient forests for the future.

Since the 1970s, North American pine species—believed to grow faster than native trees—have been planted in Argentina for timber production. As a result, exotic pines have displaced many native species such as the Coihue southern beech and the Chilean cedar, significantly altering the ecosystem. Until now, however, there has been a lack of research comparing the actual productivity of exotic pines with native tree species.

An international research team, including the ÖBG at the University of Bayreuth, has addressed this issue: for the first time, they systematically compared native and introduced species across multiple sites in different climate zones of Argentina. "This approach allows our study to produce findings that are not limited to a single location but can be generalized," says Dr. Robert Weigel, Executive Director of the ÖBG.

To compare the growth dynamics of introduced and native trees, the researchers analyzed tree rings using core samples, which reveal insights into climatic conditions based on their width. The first 32 years of growth were of particular interest, as they represent the so-called "stem exclusion phase"—a period marked by intense competition for sunlight, water, and nutrients, during which less competitive plants die off. The researchers also used stable isotope analysis to examine water loss and associated drought stress during this phase.

"The assumption that introduced pine species grow faster and are therefore more productive for timber could not be confirmed by our tree ring analysis," says Weigel. On the contrary, the pines displace native species and increase the risk of forest fires due to their dense needle litter—especially during periods of drought and climate stress. The isotope analysis also indicated greater water loss and overall higher water consumption by the introduced pines, which is problematic in the face of climate change.

"Our findings highlight that non-native species should only be introduced into existing systems after careful consideration. We recommend prioritizing native tree species in future reforestation efforts and reducing the expansion of pine plantations in northern Patagonia," Weigel concludes.