Road Networks as Catalysts for Plant Invasion of Burned Landscapes

Abstract

Invasive species pose one of the greatest threats to ecological integrity and economic viability in dryland ecosystems, including Nevada's Great Basin. The positive feedback between invasive annual plants and wildfire ultimately displaces native species and decreases biodiversity. Managing the expansion of invasive plants, like Bromus tectorum or "cheatgrass," is challenging because they can disperse widely and regenerate rapidly following disturbances such as fires and roads. While most studies of invasive plants focus on grazing and plant community structure, few emphasize or quantify how roads aid dispersal of invasive plants into burned patches. This is especially pertinent in the Great Basin where dendritic networks of dirt roads often span across fire scars. Our study explores how the interaction of road networks and fires facilitates the expansion of invasive grasses. We employed ArcGIS and R software to build upon previous niche models to elucidate landscape level shifts in invasive annual grasses from 2000 to 2016. Using a Mann-Kendall correlation, we found increasing trends in annual invasive cover across large swaths of Nevada. Our statistical model revealed a significant interaction between fires and roads and identified areas at risk for future invasion. More public and managerial awareness of the role of roads and fires in the expansion of invasives could reduce the risk of more cheat grass spread.