Assessing land degradation induced by recreational activities in the Algodones Dunes, California using MODIS satellite imagery

Highlights

• Vegetation cover in Algodones Dunes has declined in recent decades by OHV activity.

• Increased sand exposure resulted in decreased NDVI and increased surface albedo.

• Changes correspond with increased daytime temperatures in areas of OHV activity.

• Monitoring OHV activity are critical to reduce further land degradation.

Abstract

This research investigated spatial and temporal environmental changes associated with climatic variability and off-highway vehicle (OHV) activity in the Algodones Dunes, California, using time-series analysis of Moderate Resolution Imaging Spectroradiometer imagery from 2001 to 2016. We compared changes in land cover, surface albedo, and surface temperatures between the Imperial Sand Dunes Recreation Area (ISDRA) and areas with no OHV activity in the North Algodones Dunes Wilderness area (NADW). Both areas showed a decreasing normalized difference vegetation index (NDVI) and an increasing albedo from 2001 to 2016; however, ISDRA had a lower NDVI value and higher albedo compared to the adjacent NADW. Transects across these adjoining areas revealed substantial differences in daytime and nighttime land surface temperatures. ISDRA had an appreciably higher mean daytime temperature and a lower mean nighttime temperature compared to those within NADW. Results suggest direct association between increasing OHV activity and reduced vegetation cover, increased soil exposure, and higher daytime temperatures in the Algodones Dunes. We recommend enhanced monitoring of ecosystem and land use changes coupled with enhanced land use management to reduce the contributions of recreational OHV activity on land degradation and to maintain habitat for key species and ecosystems of interest in the dune field.

Introduction

Use of off-highway vehicles (OHVs) in natural landscapes is one of the fastest growing recreational activities in the United States. OHVs include a variety of motorized vehicles and motorcycles that are capable of traveling over land, sand, ice, snow, desert surfaces, rangeland, or other natural landscapes (Davenport and Switalski, 2006). OHVs have become increasingly popular for recreational purposes since the 1970s and have allowed people to travel into more remote areas. Between 1982 and 2003, the registration of OHVs increased rapidly in the United States from 3 million to 51 million (Groom et al., 2007; Cordell et al., 2008). In California, over roughly the same time interval, there was a 90% increase in OHV registration (Van Dam and Van Dam, 2008). By 2016, 78% of total visitation (5.6 million visitors) on public lands in California managed by the Bureau of Land Management (BLM) was OHV-related (California State Department of Parks and Recreation, 2017).

Concerns with the growth of OHV activity include substantial ecological impacts on a wide range of ecosystem structures and functions, including the destruction of vegetation cover, increased root exposure, enhanced soil erosion, and reduction of native or endangered species (Groom et al., 2007; Al-Hurban, 2014). In particular, much research has shown that OHV activity results in substantial impacts on soil ecosystems and vegetation. For example, intensive OHV use in vegetated landscapes results in physical breaking, crushing, and root exposure of vegetation and, eventually, death of plant cover (Stebbins, 1974; Lathrop, 1983; Luckenbach and Bury, 1983; Davenport and Switalski, 2006; Groom et al., 2007). In addition, soil ecosystems experience significant impacts with vehicular activity such as soil compaction, increased bulk density, and reduced moisture infiltration and soil water retention that, combined, reduce root growth, seed germination, and plant stability (Stebbins, 1974; Webb et al., 1978; Misak et al., 2002; Sack and Da Luz, 2003; Olive and Marion, 2009; Al-Hurban, 2014).

Sand dunes and arid landscapes are among the most common environments for OHV use, given the relative ease with which they can be accessed and ridden. Although biomass per unit land area might be lower than in forest ecosystems, plants play critical roles in arid ecosystems, particularly for protecting and stabilizing sand and soil surfaces against wind and water erosion and for providing habitat for many faunal species. Many semi-arid plant species are slow growing and/or vulnerable to soil disturbance or physical damage, so when exposed to OHV activities, they may take decades to recover to their initial state (Stebbins, 1974). In the early 1970s, an OHV race in Johnson Valley in the Mojave Desert resulted in the deterioration of 30% of the creosote bushes, 39% of the burroweed bushes, and 45% of the Mormon tea bushes (Gibson, 1973). Reducing the amount of the vegetation cover in arid and semi-arid environments is a form of land degradation and may lead to desertification as sand surfaces become more susceptible to wind and water erosion, as arid top soils become degraded, and as dune migration rates may change (Belnap, 1995; Al-Awadhi, 2013). In addition, soil temperatures may also increase after removal of vegetation cover as more insolation reaches the soil directly and there is less thermal insulation provided by vegetation cover (Webb et al., 1978).

The Algodones Dunes, which hosts the Imperial Sand Dunes Recreation Area (ISDRA), is one of the most popular sand dune systems in California for OHV usage. The ISDRA sees over 1 million visitors a year and often more than 90,000 OHV drivers in the dune field during holidays (Camden Bruner, email to author, January 31, 2018). The use of OHVs in the dune field has resulted in reduced vegetation cover, enhanced soil and wind erosion, and, in turn, is associated with decreased presence of key endemic species, such as the fringe-toed lizard (Uma notata) and desert kangaroo rat (Dipodomys desert) (Luckenbach and Bury, 1983; Groom et al., 2007; Van Dam and Van Dam, 2008). Despite these observed impacts and associations, there is generally a lack of research on the spatial-temporal changes of vegetation cover in the Algodones Dunes in response to anthropogenic disturbances, such as OHV activity. In other landscapes, spatial-temporal approaches are commonly used to assess and monitor deforestation, forest degradation, urbanization, and the urban heat island effect (Verbesselt et al., 2010; Hansen et al., 2013; Wang et al., 2016; Wang and Myint, 2016). Given recent rises in recreational activities in semi-arid and arid landscapes, coupled with climatic variability (e.g., drought) and longer-term climate changes, it is essential to monitor and analyze the trends of land degradation in these areas using available remote sensing products and spatial-temporal approaches. In response, this paper addresses a distinct research gap related to the impacts of OHV activity in one of the most intensively used dune systems in North America.

This paper investigates the spatial-temporal changes in land cover (plants, bare soils) and regional climatic variability and change to explore associations with human-induced land degradation related to OHV use in the Algodones Dunes of southeastern California. Interpretations are referenced to an adjacent protected area, the North Algodones Dunes Wilderness Area (NADW) that has not seen OHV activity in at least 25 years by analyzing long-term and seasonal trends in key land cover variables, including normalized vegetation index (NDVI), albedo, and land surface temperature from 2001 to 2016.