Effects of initial functional-group composition on assembly trajectory in savanna restoration

Aims Indicators that can provide information during the early stages of restoration are very useful for predicting restoration outcomes. We posed the following questions: Can savanna restoration outcomes be affected by the initial functional-group composition? Are there functional groups that, when established early, can prevent colonization by invasive grasses, trigger a successful restoration trajectory, and be used as early indicators of restoration success? Location Brazilian savanna (cerrado) in Central Brazil (14 degrees 07 ' 2.54 '' S, 47 degrees 38 ' 30.36 '' W). Methods We established 110 plots spanning a naturally occurring range of species composition in savanna areas that had been restored through direct seeding. We looked for different initial compositions of the following functional groups: perennial grasses, annual grasses, short-lived shrubs, and invasive grasses. We measured vegetation cover over two years and evaluated the effects of the initial functional composition on the successional trajectory of the plots. Results The initial dominant functional group determined the assembly trajectory. Short-lived and fast-growing species were replaced by perennial species, indicating a fast species turnover. Invasive grass cover remained stable over time, demonstrating that once they establish and dominate an area, an alternative stable state is achieved. Conclusions Our results demonstrate the importance of introducing a mixture of functional groups when restoring savannas in severely disturbed areas. Fast-growing and short-lived species are important for quickly covering the ground, creating the conditions for the establishment of perennial grasses that naturally dominate the herbaceous layer of savannas. Trees are also characteristic of the savanna structure and must be introduced. Our results indicate that invasive grasses must be eliminated and/or constantly controlled before native species are introduced.