Invasion in the riparian zone: What is the effect of Pteridium arachnoideum on topsoil permeability?

Pteridium arachnoideum is a cosmopolitan, allelopathic, pervasive species which is expanding its occurrence in many regions of the tropics. Yet, the ecohydrological effects of such colonization is virtually unknown especially when it occurs in riparian zones which are expected to perform many important ecosystem services. The objective of the present study was to evaluate the influence of Pteridium colonization on topsoil permeability in riparian zones. To do that, we selected two similar riparian zones: (i) dominated by Pteridium arachnoideum and (ii) under tropical forest. We performed infiltration, water repellency (dry and wet season) and penetration resistance measurements to evaluate soil permeability. The infiltration capacity was significantly lower in Pteridium compared to riparian forest. We attribute this reduction to the significant increase in both water repellency in the dry season and soil penetration resistance in the soil under Pteridium. Water repellency, though still present in the wet season in both riparian zones, had no significant difference. Our results show that, despite the loss of biodiversity with Pteridium invasion, water repellency has a clear reduction in the wet season which likely benefits infiltration. Thus, basic hydrological ecosystem services can probably still be provided by such invaded riparian zones.