This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The presence of non-native trees is often seen as an obstacle to the recovery of tropical forests regrowing in previously deforested areas. To better understand the behavior of these plants over time in both humid and dry forests, researchers from approximately 60 institutions analyzed data from over 1,500 areas of forest regeneration across the Americas.
The results, published in the journal Nature Plants, indicate that the initial dominance of exotic species is temporary. They multiply easily during the first 10 to 20 years, taking advantage of abundant sunlight in open areas. However, they decline as native trees grow and shade the forest.
According to the first author of the article, Angelica Faria de Resende, the initial concern about these plants is justified because "by replacing the role of one or more native species and altering natural processes, invasive species can modify food webs and functional, structural and biological diversity in the forest." Resende conducted the study during her postdoctoral research at the Luiz de Queiroz College of Agriculture at the University of São Paulo (ESALQ-USP) in southeastern Brazil. The team's data show that this interference is more pronounced in humid forests, where exotic trees accounted for 28% of the tree trunks and 22% of the total species in the first two decades, than in dry forests, where they reached 9% for both indicators. According to the researcher, the impact tends to be partial or temporary.
"It caught our attention that both species diversity and the number of individuals decreased significantly shortly after that initial peak," says Resende, pointing out that although some non-native trees remain in the mature stage of the forest, their presence decreases as the forest matures. This decline occurs because the exotic trees in these areas tend to resemble native "pioneer" species in that they grow rapidly and require abundant light to thrive, as is found in recently abandoned pastures. Initially, both compete for space, but eventually, they give way to slow-growing native trees that germinate in the shade and gradually dominate the landscape.
"Non-native species are opportunistic and take advantage when conditions are favorable," Resende summarizes. According to the researcher, as the forest canopy closes and the environment becomes less suitable for species that depend on full sunlight, these species persist only at low densities. Some of the areas monitored in this study are part of the "Understanding Restored Forests for the Benefit of People and Nature—NewFor" project.
Of the 3,735 species sampled, 131 were considered non-native/non-invasive, 14 were considered non-native/potentially invasive (reported as invasive in another country) and 11 were considered non-native/invasive. Non-native species were present in 18% of the dry forest plots studied and 41% of the humid forest plots. Two examples from Brazil illustrate the difference between non-native/invasive and non-native/non-invasive species.
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