Herbicide application and mechanical clearance enhances growth and reduces mortality of two tree species in invasive Kans grass Saccharum spontaneum grasslands of the Panama Canal Watershed near Santa Clara, Panama

  • Published source details Craven D., Hall J. & Verjans J. (2009) Impacts of herbicide application and mechanical cleanings on growth and mortality of two timber species in Saccharum spontaneum grasslands of the Panama Canal Watershed. Restoration Ecology, 17, 751-761


In parts of Panama, the tall invasive grass Saccharum spontaneum (native to Asia) threatens forests by promoting fire and preventing regeneration in disturbed area (e.g. former cultivated land). Reforestation has been suggested as a Saccharum control strategy in the Panama Canal Watershed. In this study undertaken at a Smithsonian Tropical Research Institute study site (9°09′N, 79°51′W) in the watershed, effects of different intensities of herbicide application and mechanical clearing in S. spontaneum grassland on white olive Terminalia amazonia and non-native teak Tectona grandis (valuable timber trees) sapling growth and mortality, were evaluated.

In June 2003, vegetation in 2.8 ha of S. spontaneum-dominated grassland was machete-cleared. Teak and olive seedlings were planted in 56 (21 × 18 m) plots, 56 per plot. Seven combinations of weed control treatments were applied: 28 plots received an annual application in mid-wet season (July-August) of Round Up Max (glyphosate; 73.3 l water/kg Round Up); 28 received no herbicide. Within all plots, grass clearance was undertaken at one of four intensities: one or two times/year (in the wet season) and four or seven times (every 2-3 months).
Height, basal diameter, crown height and diameter, and tree mortality were recorded each July (2003 -2006). Competition between S. spontaneum and trees was visually estimated per plot on a scale of 1 to 4 (4 = high level of competition, 1 = very little). Time and cost to undertake treatments was calculated.

Both tree species had higher growth parameters and lower mortality with increasing intensity of grass clearance and herbicide application. Mortality after 3 years was for T. amazonia, initial live saplings 1,568, dead 386; and for T. grandis, initial live saplings 1,586, dead 486.
S. spontaneum height and competition was negatively correlated with treatment intensity. Grass control costs did not differ between tree species, however T. amazonia grew more slowly than T. grandis indicating a requirement for grass control beyond the initial 3 years. The results suggest that S. spontaneum grassland reforestation is economically feasible.
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