Phenological and reproductive traits and their response to environmental variation differ among native and invasive grasses in a Neotropical savanna

Phenology is a key component of the life-history of plants, and non-native plant species with distinctive phenological traits may have an advantage over native species. In tropical savannas, water and light availability are often spatially and temporally heterogeneous, so that non-native species capable of changing their phenology in response to these factors are more likely to succeed in these ecosystems. We compared flowering onset and flowering period among African and native grasses in a Brazilian Neotropical savanna and assessed if these traits and the production of flowering tillers differ between two consecutive years and respond to spatial heterogeneity in water table depth and canopy closure. Non-native species showed multiple flowering patterns; Urochloa decumbens flowered from the mid-rainy season to the mid-dry season, Melinis minutiflora flowered during the dry season and Mepens repens flowered throughout the year. In addition, they were responsive to annual and abiotic variation, as U. decumbens also showed longer flowering period and produced more flowering tillers in the second year, except over shallow groundwater and high canopy closure, whereas M. minutiflora produced fewer flowering tillers under high canopy closure and M. repens showed large reproductive decline in the second year. Native grasses flowered in the middle of the rainy season regardless of annual and abiotic variation, although in the second year one species produced more flowering tillers in seasonally flooded sites. The phenology of M. repens is consistent with a ruderal life-history, so that it is only likely to become dominant under repeated disturbances. By contrast, the ability of changing flowering period and reproductive output according to growing conditions showed by U. decumbens and the distinct flowering timing showed by M. minutiflora may favour these species over less plastic native grasses, suggesting that phenological attributes contribute to the dominance of African grasses in Neotropical savannas.