Regrowing tropical forests shaded out many non-native trees

Secondary forests across the Neotropics start out with a noticeable share of non-native trees, then those trees thin out as the canopy closes. Phys.org reported the pattern on October 22, 2026, from a Nature Plants paper led by Angélica Faria de Resende, a postdoctoral researcher at ESALQ, the University of São Paulo's agriculture school in Piracicaba. About 60 institutions measured 1,561 plots of regrowing forest in Bolivia, Brazil, Colombia, Costa Rica, French Guiana, Mexico, Panama, Peru, Puerto Rico, and Venezuela. The plots are a chronosequence, a set of forests of different ages, not the same stands watched for decades.

Of 3,735 species, 131 were non-native but not invasive, 14 were potentially invasive, and 11 were invasive. Non-native trees showed up in 18 percent of dry-forest plots and 41 percent of humid ones. In humid forest during the first 10 to 20 years, exotic trees made up 28 percent of trunks and 22 percent of species. In dry forest the share was 9 percent for both. They declined after that, though some persisted at low density. Slash pine is invasive in Brazil. Eucalyptus is widely planted there and, in this dataset, was generally not spreading on its own. A species that is not on an official invasive list can still dominate a site: the paper notes cases above 25 percent of trunks. Non-native richness rose with the human-development index of the surrounding area. Density fell where more native forest remained nearby, where agriculture was close, and where rainfall was higher. The researchers' conclusion is narrow. Natural regeneration, in landscapes that still have intact forest, can help keep non-native trees in check. It does not make them vanish.