Impacts of riparian restoration on vegetation and avifauna on private and communal lands in northwest Mexico and implications for future efforts

Restoring and enhancing riparian vegetation on private and communal lands in Mexico is important for biodiversity conservation given the ecological significance of these areas and the scarcity of public protected areas. To enhance riparian vegetation and wildlife habitats and train local people in restoration techniques, we implemented restoration and outreach efforts on private and communal lands in the Sky Islands region of northwest Mexico. We fenced 475 ha of riparian zones from livestock, erected erosion-control structures, planted trees, and developed management agreements for cool-season grazing with landowners on 10 ranches across three sites in 2012-2013, then repaired fences and renegotiated agreements in 2017-19. To foster evaluation, we used a before-after/control-impact design to measure attributes of vegetation structure and bird communities, and compare baselines from 2012 with post-treatment estimates from 2019. As predicted, understory vegetation volume generally increased in treatments relative to controls (p = 0.09), especially when one treatment area with the lowest pre-treatment grazing impacts was censored (p = 0.01). Although canopy cover also increased, there was little differential change in treatments relative to controls (p ≥ 0.23) due likely to longer time periods needed to realize responses. Densities of most focal bird populations varied across time periods in directions that typically matched observed changes in vegetation structure, but fewer species showed signs of differential positive change linked to treatments relative to controls. Densities of Yellow-breasted Chat, a key understory obligate and important focal species, increased in treatments relative to controls across sites, as did densities of Sinaloa Wren, which also use dense underbrush (p ≤ 0.05). Positive changes by other understory obligates (e.g., Common Yellowthroat, Song Sparrow) were more local but sometimes of high magnitude (>8-fold) also suggesting positive impacts of treatments. Despite mixed results over a limited time period, these patterns suggest restoration efforts drove localized recovery of understory vegetation and associated bird populations, but benefits varied widely with environmental and social factors linked to management. Greater ecological benefits to riparian areas on private and communal lands in this region can be fostered by further incentivizing construction, maintenance, and proper use of restoration infrastructure, through education, and by building relationships based on trust and credibility with landowners.