Dryer Pantanal wetlands may increase Leucaena leucocephala (Fabaceae) invasion

Leucaena leucocephala (hereafter L. leucocephala) is considered one of the 100 most invasive plant species in the world and has been found in areas subject to wildfire events and flooding. The rapid L. leucocephala invasion capacity can lead to decrease in local diversity due to the exclusion of native plant species. In this way, the L. leucocephala pro­liferation has advanced across the Pantanal. Here, we assess the effects of the fire, flooding and distance to the source population on the invasion of L. leucocephala, and whether this dynamic negatively affects the richness of native plant species in the Brazilian Pantanal. Our results showed that at intermediate fire frequencies (areas burnt twice) and aver­age flood levels, there is a decrease in L. leucocephala and an increase in native species. The effect of fire is limited to the medium flood level, where the occurrence of two burns reduces L. leucocephala compared to one and four burns. When the area is burned twice, the flood gradient reduces L. leucocephala invasion from the least to the most flooded area. In both high (four times) and low (once) fire frequen­cies the L. leucocephala regenerants only decrease when the flood level is high. In an expected scenario for the Pantanal is longer droughts this could mean a pronounced increase in L. leucocephala invasion over time. Therefore, reduc­ing the flood period by climate changes or hydric enterprise projects that affect flood pulse may increase alien species invasion. Finally, it is necessary to find management meth­ods that prevent the growth and spread of L. leucocephala without harming the native seed bank.