Impacts of herbicide application and mechanical cleanings on growth and mortality of two timber species in Saccharum spontaneum grasslands of the Panamá Canal watershed

Abstract

Reforestation has been suggested as a strategy to control Saccharum spontaneum, an invasive grass that impedes regeneration in disturbed areas of the Panama Canal Watershed (PCW). In this study, the effects of different intensities of herbicide application and mechanical cleanings on the growth and mortality of Terminalia amazonia and Tectona grandis saplings were evaluated in S. spontaneum grasslands within the PCW. Both species exhibited greater height, basal diameter, wood volume index, wider crown diameters, deeper live crowns, and lower mortality with increasing intensity of mechanical cleanings and herbicide application. Height and competition of S. spontaneum correlated negatively with intensity of mechanical cleanings and herbicide application. Grass control costs did not differ between tree species but did increase significantly with intensity of mechanical cleanings and herbicide application. We recommend fire suppression, annual herbicide application, and at least four mechanical cleanings per year in Tec. grandis plantations during the first 3 years of plantation establishment. Given the slower initial growth and mortality patterns of Ter. amazonia, aggressive grass control treatments should be continued until individuals are sufficiently large to effectively shade S. spontaneum. Results from this study suggest that reforestation with commercial timber species can rapidly establish and control S. spontaneum growth in the PCW. Reforestation of areas already invaded or at risk of being invaded by S. spontaneum appears to be a viable strategy to reduce its abundance and subsequent negative ecological effects in the PCW.