Influence of land use on the riparian zone condition along an urban-rural gradient on the Sabinal River, Mexico

Background: Riparian vegetation is strongly influenced by the surrounding land use. While it is known that urbanization processes can affect plant species composition and the ecological condition of the riparian zone, the specific responses require a fuller understanding. Hypothesis: The quality of riparian zones is inversely related to the degree of urbanization of adjacent areas, and that land uses that provide forest cover ensure a less degraded condition and greater diversity of species. Study site and year of study: Sabinal River basin, Chiapas, Mexico, 2015. Methods: Measures of the Riparian Quality Index (RQI) and plant species composition were compared among three different land use conditions (secondary forest, grasslands and crops, and human settlements). Results: Riparian zones adjacent to secondary forest showed higher RQI than those next to grasslands and crops and human settlements. Riparian zones within secondary forest also had a higher woody species richness and better substrate condition, whereas reaches adjacent to human settlements appeared paved and eroded, exhibiting soil compaction. Species richness and diversity were positively correlated to the RQI and were greater in riparian zones adjacent to secondary forest than in those next to human settlements. Conclusions: While grazing and cultivation affect the riparian zone, expansion of urban areas has a greater impact by reducing woody species richness and diversity, altering species composition and favoring soil compaction and bank erosion, which results in reduced riparian quality.