Weed dynamics during the change of a degraded pasture to agroforestry system

This study evaluates weed dynamics during the first 4 years (2008–2011) of the implementation of an agroforestry system in the municipality of Tomé-açu in the state of Pará, Brazil. The study was conducted in a degraded pasture of Brachiaria humidicola, and treatments (T) included mixed plantations of oil palm with short-cycle leguminous species (T1) with the inclusion of manioc in T2 and forest species and palm trees in T3. In 2008, a floristic survey was conducted in 12 plots of 2 × 2 m per treatment. In 2009, herbicide was applied to one half of the area in each treatment. A total of 19,367 individuals of height <1.5 m were surveyed, of which 51 % were B. humidicola and 21 % were leguminous species that had been planted. Overall, an increase in plant density was observed between 2009 and 2010, followed by a decrease over the following year in areas without herbicide and a tendency for high densities to persist in areas with herbicide. Species richness increased over the study period in all areas (with or without herbicide), which might be related to habitat availability resulting from the reduced density of B. humidicola due to the effects of the herbicide, the leguminous species planted and the development of the agroforestry system. The association of short-cycle leguminous plants with afforestation appears to be an effective method for controlling weeds in the absence of herbicides.