Ecological Impacts

Biological Soil Crusts
Similar to grading, the construction of new roads and transmission lines pose a threat to biological soil crusts. As discussed in the Grading, Hydrological Modification, and Vegetation Removal section, soil crusts are extremely fragile and can be easily crushed by road construction activities and the movement of workers and vehicles across the project site. This type of disturbance to soil crusts can disrupt soil structure, which can lead to dust emissions and impede new vegetation growth. This disturbance can also alter nutrient cycles, and may change the level and pattern of water infiltration on site.

Invasive Plants
Roads, both dirt and paved, can serve as primary pathways for nonnative plant invasions into desert ecosystems.¹ Vehicles serve as major transporters of nonnative plant seeds while runoff from roads can elevate the supply of water at the edges of roads, facilitating the establishment and productivity of nonnative plants along roadsides.² Once invasive plants become established, they more easily spread away from roadsides and into natural areas.³ Maintenance roads along power lines are also a concern.⁴ Similarly to roads, the disturbed areas created by utility corridors are more susceptible to invasion by nonnative plants.⁵

The construction of new roads and utility corridors will also increase human access to previously inaccessible areas, increasing the likelihood of other human-mediated disturbances.⁶ For example, OHV use tends to be concentrated around dirt roads and can further the spread of nonnative plant seeds into the surrounding ecosystem.⁷ The tracks created by a single OHV pass can create microsites that enhance the abundance of nonnative plant species.⁸ When road densities are high in an area, the biomass and number of nonnative plant species may increase from the combined effects of high nonnative plant biomass near roads, increased seed dispersal along and away from roads by vehicles, and decreased distance from roads to other areas of the landscape.⁹

Agricultural regions serve as major sources of invasive plant propagules, where farming practices and livestock feed introduce nonnative plant species into a landscape.¹⁰ Roads and highways connect the desert ecosystem with large agricultural areas such as the Imperial Valley and the Central Valley.¹¹ The use of new solar facility roads by vehicles transporting agricultural products may inadvertently facilitate the spread of invasive species. For example, hay straw and seed can become dislodged from bales and disperse off trucks onto roadsides.¹² This problem could be compounded if developers choose to use hay bales or other straw-based materials to control erosion during the construction phase as it would provide invasive plants with multiple entry points into the ecosystem (i.e. all roads used to transport straw-based materials and the facility site where the materials are used).

Habitat Connectivity
Linear corridors such as roads, transmission lines, pipelines, and OHV trails, can serve as barriers to migration. Species like the bighorn sheep may avoid crossing large or heavily trafficked roads. Solar development that requires any substantial new roads or results in increased traffic on existing roads may further fragment habitats.¹³ In addition to this potential restriction of gene flow, an added risk to species includes increased vehicle-strike mortality.

Hydrology
Because soil can become significantly compacted after a single pass by a vehicle,¹⁴ it is likely that dirt roads to and within a solar facility site may suffer from severe soil compaction. Soil compaction from new roads specifically could redirect water flow and concentrate runoff streams, accelerating erosion.¹⁵ Additionally, the formation of pools of water along the roads could result in damage to the roads, which might force the developer to repave or regrade the roads more frequently, which would in turn increase the ecological impact of roads on the project site.

1 Matthew L. Brooks and B.M. Lair, “Ecological Effects of Vehicular Routes in a Desert Ecosystem,” in The Mojave Desert: Ecosystem Processes and Sustainability, eds. R.H. Webb and others, (Reno: The University of Nevada Press, 2009),168-195.

2 Matthew L. Brooks and B.M. Lair, “Ecological Effects of Vehicular Routes in a Desert Ecosystem,” in The Mojave Desert: Ecosystem Processes and Sustainability, eds. R.H. Webb and others, (Reno: The University of Nevada Press, 2009),168-195.

3 Matthew L. Brooks and B.M. Lair, “Ecological Effects of Vehicular Routes in a Desert Ecosystem,” in The Mojave Desert: Ecosystem Processes and Sustainability, eds. R.H. Webb and others, (Reno: The University of Nevada Press, 2009),168-195.

4 Jayne Belnap, Research Ecologist, U.S. Geological Survey, Personal Communication, November 4, 2009.

5 Matthew L. Brooks and B.M. Lair, “Ecological Effects of Vehicular Routes in a Desert Ecosystem,” in The Mojave Desert: Ecosystem Processes and Sustainability, eds. R.H. Webb and others, (Reno: The University of Nevada Press, 2009),168-195.

6 Matthew L. Brooks and B.M. Lair, “Ecological Effects of Vehicular Routes in a Desert Ecosystem,” in The Mojave Desert: Ecosystem Processes and Sustainability, eds. R.H. Webb and others, (Reno: The University of Nevada Press, 2009),168-195.

7 Matthew L. Brooks and K.H. Berry, “Dominance and environmental correlates of alien annual plants in the Mojave Desert, USA,” Journal of Arid Environments 67 (2006): 100-124.

8 Matthew L. Brooks, “Spatial and Temporal Distribution of Nonnative Plants in Upland Areas of the Mojave Desert.” in The Mojave Desert: Ecosystem Processes and Sustainability, eds. R.H. Webb and others, (Reno: The University of Nevada Press, 2009), 101-124.

9 Matthew L. Brooks and K.H. Berry, “Dominance and environmental correlates of alien annual plants in the Mojave Desert, USA,” Journal of Arid Environments 67 (2006): 100-124.

10 Matthew L. Brooks, “Spatial and Temporal Distribution of Nonnative Plants in Upland Areas of the Mojave Desert,” in The Mojave Desert: Ecosystem Processes and Sustainability, eds. R.H. Webb and others, (Reno: The University of Nevada Press, 2009), 101-124.

11 Matthew L. Brooks, “Spatial and Temporal Distribution of Nonnative Plants in Upland Areas of the Mojave Desert,” in The Mojave Desert: Ecosystem Processes and Sustainability, eds. R.H. Webb and others, (Reno: The University of Nevada Press, 2009), 101-124.

12 Matthew L. Brooks, “Spatial and Temporal Distribution of Nonnative Plants in Upland Areas of the Mojave Desert,” in The Mojave Desert: Ecosystem Processes and Sustainability, eds. R.H. Webb and others, (Reno: The University of Nevada Press, 2009), 101-124.

13 K.L. Penrod, E.S. Rubin, and C. Paulman, “Mojave Desert Habitat Connectivity ~ Phase 1: A Brief Overview of the Mojave Desert’s Previously Identified Areas of Ecological Significance,” SC Wildlands, Fair Oaks, CA, 2009.

14 Simon A. Lei, “Rates of Soil Compaction by Multiple Land Use Practices in Southern Nevada,” in The Mojave Desert: Ecosystem Processes and Sustainability, eds. R.H. Webb and others (Reno: The University of Nevada Press, 2009), 159-167.

15 Matthew L. Brooks and B.M. Lair, “Ecological Effects of Vehicular Routes in a Desert Ecosystem,” in The Mojave Desert: Ecosystem Processes and Sustainability, eds. R.H. Webb and others, (Reno: The University of Nevada Press, 2009),168-195.