Drawing a line in the sand: Effectiveness of off-highway vehicle management in California's Sonoran desert

Abstract

Public land policies manage multiple uses while striving to protect vulnerable plant and wildlife habitats from degradation; yet the effectiveness of such policies are infrequently evaluated, particularly for remote landscapes that are difficult to monitor. We assessed the use and impacts of recreational vehicles on Mojave Desert washes (intermittent streams) in the Chemehuevi Desert Wildlife Management Area (DWMA) of southern California. Wash zones designated as open and closed to off-highway vehicle (OHV) activity were designed in part to protect Mojave desert tortoise (Gopherus agassizii) habitat while allowing recreation in designated areas. OHV tracks were monitored in washes located near access roads during winter and early spring holidays - when recreation is typically high - and at randomly dispersed locations away from roads. Washes near access roads had fewer vehicle tracks within closed than open zones; further away from roads, OHV tracks were infrequent and their occurrence was not different between wash designations. Washes were in better condition in closed zones following major holidays as indicated by less vegetation damage, presence of trash, and wash bank damage. Furthermore, the frequency of washes with live tortoises and their sign was marginally greater in closed than open wash zones. Collectively, these results suggest that low impacts to habitats in designated closed wash zones reflect public compliance with federal OHV policy and regulations in the Chemehuevi DWMA during our study. Future monitoring to contrast wash use and impacts during other seasons as well as in other DWMAs will elucidate spatial and temporal patterns of recreation in these important conservation areas.

Linear and landscape disturbances alter Mojave desert tortoise movement behavior

“…Indeed, movements by a wide variety of species are influenced by anthropogenic habitat disturbance and human presence (Doherty et al, 2021). Both OHV activity and livestock grazing reduce plant cover, damage tortoise burrows, and cause tortoise mortalities (Lovich, 1999;Switalski, 2018) (Custer et al, 2017). As we noted in the results for the Nipton site, tortoises may be using washes as movement areas, and some of the signal that we found may be from the use of the washes by both tortoises and OHV recreationalists for movement.…”

“…Off-highway vehicle recreation has proliferated on public lands in the desert southwest, further spreading invasive plant species, and causing soil compaction/ erosion, vegetation damage, and disturbance/mortality of animals (Ouren et al, 2007;Switalski, 2018). Prior research suggests that desert tortoise density is reduced or eliminated in areas of high OHV use, and that the closing of areas to OHV use benefits tortoise populations (Bury and Luckenbach, 2002;Custer et al, 2017;Berry et al, 2020b).…”

Using movement to inform conservation corridor design for Mojave desert tortoise

“…Our finding that tortoises avoid large washes may be related to preference for higher perennial vegetation cover; large washes often have less shrub cover due to occasional flooding. Off-highway vehicle recreation, especially within washes, is associated with reduction of vegetation cover, tortoise mortality/reduced activity, burrow destruction, and soil compaction; washes with OHV activity had high wash characteristics in our wash layer [ 98 , 99 ]. Although soil compaction may allow for easier movement, the loss of both forage and cover vegetation within these washes reduces the quality of these anthropogenically disturbed washes as tortoise movement habitat.…”

Quantifying development to inform management of Mojave and Sonoran desert tortoise habitat in the American southwest

“…Limiting access to roads may be more effective at reducing tortoise road mortality, and can be achieved through existing agency processes, such as BLM travel management planning, which periodically evaluate and propose changes to road presence and activity levels within individual BLM field offices. Indeed, these efforts appear to positively influence road use in some areas (Custer et al 2017). Because many smaller unpaved roads on public lands are not mapped in national datasets (O'Donnell et al 2014), recalculating a 'transportation' development index based on nationally available roads data augmented with locally available data for smaller roads and offroad vehicle trails may be helpful for local applications such as BLM travel management planning.…”