| Summary: | <i>Research Highlights:</i> Established stands of <i>Leucaena leucocephala </i>(Lam.) de Wit, <i>Spathodea campanulata </i>P. Beauv., and <i>Vitex parviflora </i>Juss. modified soils in Guam’s limestone forests, reducing storage pools of carbon, nitrogen, and phosphorus. <i>Background and Objectives:</i> Invasive plants may engineer negative changes in ecosystem properties. This study was conducted to determine changes in soil chemistry following infestations of three problematic tree species on Guam. <i>Materials and Methods:</i> Minerals, metals, and mineralization dynamics were measured in invaded sites and paired sites with biodiverse native tree cover. <i>Results:</i> Most soil properties were significantly changed by long-term infestations of the invasive tree species. The soils within invaded sites exhibited total carbon, total nitrogen, and available phosphorus that were less than native sites. In contrast, the carbon/nitrogen ratio increased for every species-site combination. The other chemical properties were idiosyncratic among the sites and species. <i>Conclusions:</i> Mitigation and restoration activities that include the removal of these trees from project sites may require many years for the below-ground ecosystems to return to their native state. These three invasive trees decrease the ability of Guam soils to sequester recalcitrant forms of carbon, nitrogen, and phosphorus.
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