Spatial pattern of invasive and native graminoids in the Brazilian cerrado

Invasive grasses are an important threat in tropical savannas and grasslands and may be affected by natural and anthropogenic features of the environment. They may affect native species at a variety of scales, but a spatially explicit assessment of their effects is lacking. We studied the spatial pattern of native and invasive graminoids in Brazilian cerrado in southeastern Brazil and assessed the effects of vegetation type, elevation, and edges. We sampled native grasses, native sedges, and two invasive grass species (Urochloa decumbens and Melinis minutiflora) along three 301-to 1334-m-long transects encompassing grassland, forest, and savanna. We used wavelet transforms, generalized additive models, and null model simulations for analysis. Invasive grasses were mostly found in open vegetation. Neither native nor invasive species were consistently affected by elevation or edges. Much of the spatial variation could be explained by small-scale autocorrelation, but M. minutiflora had a more heterogeneous pattern than U. decumbens. Invasive grasses were negatively related to native ones at a variety of scales, from 1 to 66 m, and we observed both positive and negative relations between the two invasive species, with positive ones a finer scales. We hypothesize that spatial pattern characteristics of different invasive species may be related to their invasion potential.