Riparian remnant species registered at headwater streams in San Juan Zitácuaro, Mich.

Studying riparian vegetation allows understanding the floristic diversity patterns along the fluvial network, and because of the level of transformation they show, it is essential to generate knowledge to guide further recovery. This paper analyzed the remaining riparian tree vegetation in 30 sites in streams located in the Monarch Butterfly Biosphere Reserve, by describing the structure, species richness, and geographic setting (elevation, precipitation, hydrological order, and land cover), and by identifying possible invasive species. Elevation of the sites was associated with precipitation, hydrologic order, and land cover being crossed by the streams. Fifty-six mostly tree species were recorded, which increased in density and height with elevation. Some of the species with the highest importance value include Roldana angulifolia, Cestrum fulvescens, Ilex tolucana, Alnus acuminata, Buddleja cordata, and Fraxinus udhei. Four physiognomic groups emerged based on the number of species, genera and families, the number of branches, and the number, height, and diameter of individuals. High species turnover was found between sites, mainly with those located at higher elevations. The occurrence of potentially invasive species was shown to be associated with the density of individuals, with Shannon's diversity index (H'), and with geographic attributes such as elevation and hydrological order. The analyzed riverbanks show human intervention, being necessary to discriminate those impacts associated with flow alteration from those associated with land cover change.