Articleshttps://doi.org/10.1038/s41893-020-0574-x

Reduced ecosystem services of desert plants from ground-mounted solar energy developmentSteven M. Grodsky   1 ✉ and Rebecca R. Hernandez   1,2

1Wild Energy Initiative, John Muir Institute of the Environment, Davis, CA, USA. 2Department of Land, Air & Water Resources, University of California, Davis, Davis, CA, USA. ✉e-mail: smgrodsky@ucdavis.edu

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Supplementary information for

Reduced ecosystem services of desert plants from ground-mounted solar energy development

Steven M. Grodsky & R. R. Hernandez

Correspondence to: smgrodsky@ucdavis.edu

This PDF file includes: Supplementary Methods Supplementary Text Supplementary Tables 1-5

Methods

Study area

We conducted the study in Ivanpah Solar Electric Generating System (ISEGS) and surrounding

natural desert. ISEGS is located on a bajada at the base of Clark Mountain in the Ivanpah Valley,

San Bernardino County, CA (35°33′ 8.5″ N, 115°27′ 30.97″ W) in the Californian Mojave Desert

(US). ISEGS consists of 173,500 heliostats (~350,000 individual mirrors) and generates up to

392 MW of electricity. ISEGS was constructed in 2011 on a 1,400-ha tract of previously

undeveloped Mojave Desert creosote scrubland near the Mojave River corridor, the Mojave

National Preserve, and Mesquite and Stateline Wildernesses.

Field sampling

We sampled plants in 15 spatially independent plots in each of the three treatment units in blocks

(five plots/treatment/block) and in control sites (total plots = 60). We situated plots in controls

along five randomly selected transects – three north of each block and two south of two blocks.

Each transect contained three plots stratified at 250 m, 500 m, and 1 km from the boundary of the

nearest block. We chose the upper limit of stratification based on spatial analysis of aerial

photography, which indicated that plots established at a distance greater than 1 km from ISEGS

would be confounded by other landscape features potentially affecting plants, including Clark

Mountain to the north (e.g., elevational plant community shift) and a golf course and highway to

the south.

We measured plant composition, plant structure, species richness, and species evenness of plants

in each photosynthetic pathway, individual species, and reproductive individuals using a

combination of the line intersect method and whole-plot visual vegetation surveys during peak-

spring growing season in the Mojave Desert, 28 April - 8 May 2018. We established four, 10-m

long transects radiating from the center of each plot in each cardinal direction. We walked along

each transect and measured each individual plant ≥2 cm that we encountered within 5 cm of

either side of the transect line. For each plant intersecting the transect-line area, we recorded

species and cover [length of transect covered by plant canopy (cm)]. We used a 2-m tall, 4.8-cm

diameter rod marked at 1-dm increments to measure the maximum height of each individual

plant and determined whether individuals were reproductive based on presence or absence of

flowers on perennials and spikelets on grasses. After we sampled vegetation along all transects in

a plot, we visually surveyed the entire plot area (macroplot = 100 m2) and recorded all plant

species undocumented during the line-intersect survey for use in community-level analyses. We

also recorded presence/absence and type of biological soil crusts at each plot.

We calculated plant height per individual as the sum of heights for each individual plant in each

plot divided by the total number of individual plants in each plot. We calculated plot-level

percent cover as the total plant cover divided by the total transect length in each plot; total

transect length in the Bladed, Mowed, and Control treatment plots was 4,000 cm, and transect

lengths in the Halo treatment plots were determined by the variable dimensions of each

individual “halo”. Because transects differed in length, we calculated percent cover for

perennials, annuals, individual species, and reproductive individuals by dividing total cover for

each category per plot by the total transect length in meters for each respective plot. We used

counts of individual species and abundance of individual species pooled over the total plot area

(i.e., transects and macro-plots) to generate species richness and species evenness measures,

respectively. To elucidate comprehensive patterns of species richness and evenness among

treatments, we computed mean Shannon diversity indices (H`) for each plot (“vegan” in R).

Landscape measurements

We calculated heliostat density for each plot as the number of heliostats (any portion of either

mirror on heliostat) contained within a 10-m buffer centered around each plot using QGIS. We

used the ‘distance matrix’ function in QGIS to measure the distance from each plot to the power

tower in each block. We extracted elevation values provided in NASA’s Shuttle Radar

Topography Mission raster layer for each plot.

Statistical analyses

We grouped desert plants by the following functional groups: 1) photosynthetic pathway

(crassulacean acid metabolism [CAM], C3, and C4); 2) perennials; 3) annuals; and 4) invasive

species. We also isolated individual species of the two most abundant perennial and annual

species, respectively, for analyses. We implemented a randomized complete block design to test

for differences in plant composition, plant structure, species richness, and species evenness of

plants in each photosynthetic pathway, individual species, and reproductive individuals among

treatments in blocks and in controls. We paired individual plots in each treatment and in controls

based on spatial proximity and conducted pair-wise comparisons of aforementioned metrics

among treatments and controls using Wilcoxon signed-rank tests (wilcox.test; R). We calculated

95% bias corrected, accelerated confidence intervals on all medians based on 10,000 bootstrap

replicates (package ‘boot’; R).

To determine effects of solar energy development decisions on plant-based ecosystem services,

we compared mean number of ecosystem service-based values of plants contributing to

provisioning, regulating, habitat-based, and cultural services, respectively, across blocks

(dependent variables) using one-way ANOVAs, with solar energy development decision (i.e.,

blading, mowing, halo vs. control) as the independent variable. We conducted post hoc Tukey’s

honestly significant difference tests to make pairwise comparisons between treatments and

controls for each ANOVA.

We tested for correlation among landscape measurements using Pearson product-moment

correlation tests (cor.test; R). If we detected correlation between variables, we ran a linear model

to determine the relationship between variables and randomly excluded one of the variables from

the analysis. We developed binomial generalized linear models to test effects of heliostat density

and elevation on the percent cover of plants in each photosynthetic pathway, perennials, annuals,

individual species of the two most abundant perennials and annuals, respectively, and the

invasive grasses Schismus spp. (S. arabicus and S. barbatus indistinguishable in the field) in

ISEGS. For all models, we assumed overdispersion when the residual deviance divided by the

residual degrees of freedom was > 1.0. We ran quasibinomial GLMs when we detected

overdispersion. We used percent cover of plants in each photosynthetic pathway, perennials,

annuals, individual species of the two most abundant perennials and annuals, respectively, and

the invasive grasses Schismus spp. in each plot in each block as dependent variables and heliostat

density, elevation, block, and the log of effort (defined as total transect length per plot) as

explanatory variables. For all analyses, we set a = 0.05.

Supplementary Text

Selected list of ethnobotanical references for plant-based cultural services conferred to Native American ethnic groups of the Desert Southwest

1. A. M. Rea, At the Desert’s Green Edge, An Ethnobotany of the Gila River Pima (U, Arizona Press, Tucson, AZ, 1998).

2. A. M. Rea, Resource utilization and food taboos of Sonoran Desert peoples. J. Ethnobiol. 1, 69–83 (1981).

3. C. O. Cherry, Variation and transmission of Sonoran wild food knowledge in southern Arizona. Ecol. Food Nutrit. 53, 1–23 (2014).

4. D. B. Halmo, R. W. Stoffle, M. J. Evans, “Paitu Nanasuagaindu Pahonupi” (Three Scared Valleys): Cultural significance of Gosiute, Paiute, and Ute Plants. Human Organ. 52, 142–150 (1993).

5. D. P. Barrows, The Ethno-botany of the Coahuilla Indians of southern California. (U. of Chicago Press, Chicago, 1909).

6. D. Yetman, T. R. Van Devender, Mayo Ethnobotany, Land, History, and Traditional Knowledge in Northwest Mexico (U. California Press, Berkeley, 2002).

7. Dunmire, W. W., G. D. Tierney. Wild Plants and Native Peoples of the Four Corners. (Museum NM Press, Santa Fe, 1997).

8. L. Hooper, The Cahuilla Indians. Am. Archaeo. Ethno. 16, 315–380 (1920). 9. L. J. Bean, K. S. Salibel, Temalpakh, Cahuilla Indian Knowledge and Usage of Plants

(Malki Museum, Inc., Banning, 1972). 10. M. C. Stevenson, Ethnobotany of the Zuni Indians (Bureau of American Ethnology,

Washington, D. C, 1915). 11. R. O. Clemmer, Seed-eater and chert-carriers: The economic basis for continuity in

historic Western Shoshone identities. J. Califo. Great. Basin Anthrop. 13, 3–14 (1991). 12. R. S. Felger, M. B. Moser, People of the Desert and Sea, Ethnobotany of the Seri Indians

(U. Arizona Press, Tuscon, 1985). 13. R. W. Stoffle, D. B., Halmo, M. J. Evans, J. E. Olmsted, Calculating the cultural

significance of American Indian plants: Paiute and Shoshone Ethnobotany at Yucca Mountains, Nevada. Americ. Anthrop. 92, 416–432 (1990).

14. R. W. Stoffle, D. Halmo, Puchuxwavaats Uapi (To Know About Plants): Traditional knowledge and the cultural significance of Southern Paiute Plants. Human Organ. 58, 416–421. (1999).

15. Stewart, K. M. A brief history of the Chemehuevi Indians. KIVA. 34, 9–27. (1968). 16. D. Tull, Edible and Useful Plants of the Southwest. (U. of Texas Press, Austin, 2013). 17. V. L. Bohrer, Ethnobotanical aspects of Snaketown, a Hohokam village in southern

Arizona. Am. Antiquity 35, 413–430 (1970).

Supplementary Table 1. Desert scrub plant species with assigned life histories and photosynthetic pathways documented during plant surveys in Ivanpah Solar Electric Generating System and surrounding natural desert, 28 April – 8 May 2018, Ivanpah Valley, California, Mojave Desert, USA.

Species Life history Photosynthetic pathway Adenophyllum cooperi Perennial herb C3 Ambrosia dumosa Perennial shrub C3 Ambrosia salsola Perennial shrub C3 Amsonia tomentosa Perennial herb C3 Baileya multiradiata Perennial herb C3 Bromus madritensis Annual grass C3 Chaenactis fremontii Annual herb C3 Chorizanthe brevicornu Annual herb C3 Chorizanthe rigida Annual herb C3 Coryphantha chlorantha Perennial cactus CAM Cryptantha angustifolia Annual herb C3 Cylindropuntia acanthocarpa Perennial cactus CAM Cynlindropuntia echinocarpa Perennial cactus CAM Cylindropuntia ramosissima Perennial cactus CAM Dalea mollissima Annual herb C3 Dasyochloa pulchella Perennial grass C4 Descurainia pinnata Annual herb C3 Echinocereus engelmannii Perennial cactus CAM Echinocactus polycephalus Perennial cactus CAM Encelia frutescens Perennial shrub C3 Ephedra funereal/nevadensis Perennial shrub C3 Ericameria cooperi Perennial shrub C3 Eriogonum fasciculatum Perennial shrub C3 Eriogonum inflatum Perennial herb C3 Eriogonum palmerianum Annual herb C3 Erodium cicutariuma Annual herb C3 Euphorbia albomarginata Perennial herb C4 Ferocactus cylindraceus Perennial cactus CAM Hilaria rigida Perennial grass C4 Krameria erecta Perennial shrub C3 Larrea tridentata Perennial shrub C3 Lepidium lasiocarpum Annual herb C3 Lycium andersonii Perennial shrub C3 Lycium cooperi Perennial shrub C3 Malacothrix glabrata Annual herb C3 Mentzelia albicaulis Annual herb C3 Mirabilis multiflora Perennial herb C3 Opuntia basilaris Perennial cactus CAM Porophyllum gracile Perennial herb C3 Scutellaria mexicana Perennial shrub C3

Schismus spp.a Annual grass C3 Senegalia greggii Perennial shrub C3 Sphaeralcea ambigua Perennial herb C3 Stephanomeria exigua Annual herb C3 Stephanomeria pauciflora Annual herb C3 Thymophylla pentachaeta Perennial herb C3 Yucca schidigera Tree CAM

aInvasive species

Supplementary Table 2. Median species richness and Shannon-Weaver diversity index (H`) of perennials and annuals recorded in

treatments within Ivanpah Solar Electric Generating System and surrounding natural desert, Ivanpah Valley, California, Mojave

Desert, USA. We derived bias corrected, accelerated 95% percent confidence intervals from 10,000 bootstrap replicates. Different

letters in bold indicate significant differences among treatments and controls based on paired Wilcoxon signed-rank tests with

significance levels set at " = 0.05.

Bladed Mowed Control Halo

Median 95% CIBCa Median 95% CIBCa Median 95% CIBCa Median 95% CIBCa All plants Species richness 4.00b 2.91, 4.71 12.00a 9.21, 14.49 11.00a 8.93, 13.19 9.00a 5.01, 11.82

Shannon-Weaver (H`) 0.73b 0.51, 0.85 1.84a 1.62, 2.30 1.91a 1.25, 2.17 1.89a 1.70, 2.27

Perennials

Species richness 1.00b 0.30, 2.10 8.00a 6.00, 9.49 10.00a 8.00, 12.54 9.00a 6.65, 12.56

Shannon-Weaver (H`) 0b 0, 0.64 1.69a 1.09, 1.81 1.86a 1.39, 2.08 1.73a 1.11, 1.87

Annuals Species richness 3.00a 1.00IQR* 4.00a 2.54, 5.78 1.00b 0, 1.67 3.00a 1.72, 5.44

Shannon-Weaver (H`) 0.70b 0.46, 0.83 1.07a 0.68, 1.10 0b 0.69IQR* 1.10a 0.54, 2.20 *IQR presented when 95% CI was incalculable

Supplementary Table 3. Median perennial plant measurements recorded in treatments within Ivanpah Solar Electric Generating

System and surrounding natural desert, Ivanpah Valley, California, Mojave Desert, USA. We derived bias corrected, accelerated 95%

percent confidence intervals from 10,000 bootstrap replicates. Different letters in bold indicate significant differences among

treatments and controls based on paired Wilcoxon signed-rank tests with significance levels set at " = 0.05.

Bladed Mowed Control Halo

Median IQR* Median 95% CIBCa Median 95% CIBCa Median 95% CIBCa Structure and composition Height (cm)/individual 0c 10.84 38.08b 30.86, 47.95 55.44a 45.28, 66.33 56.15a 41.33, 71.00

Percent cover 0c 0.19 18.88b 15.15, 19.25 33.38a 23.48, 36.93 29.20a 25.70, 36.77

Percent cover (%) Reproductive individuals 0c 0.47 13.25b 10.38, 14.25 22.13a 14.00, 25.50 18.18ab 13.71, 21.28

Ambrosia dumosa 0b 0 5.75a 4.08, 8.38 7.25a 4.13, 9.63 6.74a 2.75, 12.42

Larrea tridentata 0c 0 6.38b 5.75, 8.25 13.88a 7.25, 22.88 11.11a 8.16, 14.35 *IQR presented when 95% CI was incalculable

Supplementary Table 4. Median annual plant measurements recorded in treatments within Ivanpah Solar Electric Generating System

and surrounding natural desert, Ivanpah Valley, California, Mojave Desert, USA. We derived bias corrected, accelerated 95% percent

confidence intervals from 10,000 bootstrap replicates. Different letters in bold indicate significant differences among treatments and

controls based on paired Wilcoxon signed-rank tests with significance levels set at " = 0.05.

Bladed Mowed Control Halo

Median 95% CIBCa Median 95% CIBCa Median IQR* Median IQR*

Structure and composition Height (cm)/individual 1.09a 0.50, 1.17 1.82ab 0.54, 3.64 0b 0.41 0ab 1.02

Percent cover 13.85a 4.70, 17.63 0.95b 0.03, 1.33 0b 0.27 0b 0.27

Percent cover (%) Cryptantha angustifolia 6.55a 2.88, 7.90 0.15b 0, 0.53 0c 0 0c 0

Lepidium lasiocarpum 0.30a 0.05, 1.68 0.03b 0, 0.13 0b 0 0b 0

*IQR presented when 95% CI was incalculable

Supplementary Table 5. Results of binomial generalized linear models to test effects of heliostat density and elevation on the percent cover of plants in each photosynthetic pathway, perennials, annuals, individual species of the two most abundant perennials and annuals, respectively, and the invasive grasses Schismus spp. (S. arabicus and S. barbatus indistinguishable in the field) in Ivanpah Solar Electric Generating System, Ivanpah Valley, California, Mojave Desert, USA. We percent cover of plants in the crassulacean acid metabolism (CAM) photosynthetic pathway, perennials, annuals, individual species of the two most abundant perennials and annuals, respectively, and the invasive grasses Schismus spp. in each plot in each block as dependent variables and heliostat density, elevation, block, and the log of effort (defined as total transect length per plot) as explanatory variables. Significant heliostat density effects in bold. We set a = 0.05.

Estimate Standard Error z value p-value Perennials Heliostat density -0.40 0.09 -4.49 <0.001 Elevation 0.010 0.009 1.13 0.27 CAM plants

Heliostat density -0.55 0.24 -2.32 0.03 Elevation 0.01 0.02 0.84 0.41 Ambrosia dumosa Heliostat density -0.35 0.09 -3.99 <0.001 Elevation -0.01 0.01 -1.05 0.30 Larrea tridentata Heliostat density -0.35 0.11 -3.06 0.004 Elevation -0.01 0.01 0.48 0.64 Annuals Heliostat density 0.41 0.09 4.45 <0.001 Elevation -0.002 0.02 -0.11 0.92 Cryptantha angustifolia Heliostat density 0.45 0.09 4.81 <0.001 Elevation -0.004 0.02 -0.25 0.80 Lepidium lasiocarpum Heliostat density 0.37 0.13 2.93 0.01 Elevation -0.003 0.02 -0.12 0.90 Schismus spp. Heliostat density 0.40 0.12 3.45 0.001 Elevation -0.002 0.02 -0.09 0.93