Effectiveness and costs of invasive species control using different techniques to restore cerrado grasslands

Abstract

Invasion by exotic grasses is a severe threat to neotropical grasslands conservation and a major challenge for their restoration. To restore fire-prone cerrado grasslands in southeastern Brazil, which have been massively invaded by the African grass Urochloa decumbens, we tested prescribed fire, herbicides, and hoeing, by themselves or in different combinations. Techniques were compared using ecological indicators (decreasing invasive and increasing native vegetation cover and richness) and cost-effectiveness. All treatments, except fire alone, were similarly effective in controlling the invasive grass, which was reduced to less than 5% cover after 2 years. However, only hoeing was effective in recovering both ground cover and richness of the native vegetation, which was the restoration goal. Despite not changing ground cover by native vegetation or alien grasses, fire was successful as a complementary technique, by depleting the seed bank of the invasive grass by 40%. Hoeing preceded by fire and followed by a grass-selective herbicide was the most cost-effective, requiring US$40 per hectare to increase native ground cover by one percentage point compared to US$93 per hectare if only hoeing. Despite the low cost and efficacy of glyphosate application for controlling the invasive grass, it must be followed by reintroducing the native ground cover through active restoration. If the restoration target is to recover both structure and richness of the native vegetation without planting, hoeing is the best solution to control alien grasses.