African grass invasion in a tropical freshwater marsh: Effects on vegetation, soil, and water, and a proposal of restoration with experimental disturbances

The integrity of freshwater marshes in the coastal zone of the Gulf of Mexico is threatened by the introduction and invasion of African grasses. These species are introduced to the wetlands because their flooding tolerance and to maintain the extensive cattle raising. In this work we evaluated the invasion process in a coastal freshwater marsh (popal-tular) of Veracruz (Mexico) by the African grass Echinochloa pyramidalis. Experimental quadrats mounted in border areas between the popal-tular and the area of E. pyramidalis showed an important invasion by this grass. Also, we planted individuals of the invader in the non-invaded area and we obtained that the native area doesn't offer resistance to the invasion. An experiment of interspecific competence between the invader and two major native hydrophytes in different hydroperiods showed that the performance of the invader is higher in drier than in flooded conditions, and that the higher performance is positively correlated with vertical accretion in the marsh. Finally, we evaluate the response of plant vegetation to experimental disturbances focused to the elimination or reduction of the dominance of E. pyramidalis and to propose a restoration strategy. We obtained that the elimination of E. pyramidalis of the invaded areas is very difficult, but successful results can be obtained if the rhizomes are destroyed with soil disked treatment and increasing the density of native species such as Sagittaria lancifolia. The use of shade cloth is successful to eliminate the invader but no to recover the native community.