sign in sign up
<<
Home , Disturbance (ecology), Mojave Desert, Sonoran Desert

Paving the way for disturbance: Different road types have distinct ecological impacts on annual communities and gall-forming in the Mojave

Maria Carias1, Emily Hascall2, Kelsey Pennington1, Jasmine Summers-Evans 2

1University of , ; 2University of California, Santa Barbara

Road disturbance can facilitate the establishment and growth of invasive plant species and herbivorous insects in adjacent . The hydrological and atmospheric impacts of roads are especially important to understand in arid desert environments that are highly sensitive to water stress and dust pollution. In this study, we looked at how impacts of road disturbance change among different road types within the . Specifically, we observed how three types of roads (paved road, dirt road, and hiking trail) and proximity to the roads impact both the and size of germinating annual and the density of galls on creosote bushes (). Additionally, we tested the effect of dust pollution on the growth of Erodium cicutarium and Bromus spp. Different types of roads produced distinct ecological impacts on the surrounding plant and communities. Paved roads had the highest gall density and largest Bromus spp., while dirt roads had smaller Erodium cicutarium. Our findings contribute to the growing knowledgebase of how road disturbances uniquely impact plant invasion patterns and herbivorous insects.

Keywords: road disturbance, Mojave Desert, Larrea tridentata, Erodium cicutarium, Bromus spp.

INTRODUCTION landscapes by altering factors such as hydrology, dust pollution, microclimate Anthropogenic transportation corridors conditions, soil erosion, and animal create habitat disturbances and mortality. Transportation corridors can also fragmentation in surrounding environments serve as conduits for plant and animal (Coffin 2007). In 1998, the term “road movement and are often cited as major ” emerged to refer to the science of causal factors in the successful invasion of how transportation corridors such as non-native flora and fauna to adjacent highways and roads affect landscapes (Coffin 2007). Species that components, processes, and structures benefit from corridor facilitation are (Coffin 2007). Since then, the subject of typically generalist species that are able to transportation infrastructure and its effects exploit highly variable environmental on ecosystems has become more widely conditions (Forman and Alexander 1998). studied. Roads have been shown to affect The construction and maintenance of roads both the abiotic and biotic components of can also remove native species and their

CEC Research | https://doi.org/10.21973/N3KX0W Winter 2021 Vol. 5 Issue 2 1/12

seed banks, making it difficult for them to roadside plants (Farmer 1993). Such impact reestablish after disturbance (Holzapfel and can lead to less favorable conditions for Schmidt 1990). Understanding how native plant communities, compounding the disturbances caused by roads impact the negative effects of road-induced ecology of surrounding biotic communities is hydrological changes. At the same time, less crucial for better informing transportation vigorous plants are also less desirable to land-use decisions (Dix et al. 2010). herbivorous insects (Cornelissen et al. 2008). While ecosystem-level impacts of These two disturbance factors can uniquely transportation corridors on adjacent alter surrounding plant and insect environments are well understood, less is communities. known about how non-native plant and The hydrological and atmospheric impacts herbivorous insect communities respond to of transportation corridors are especially different road designs. Different types of important to understand in arid desert roads vary in their level of environmental ecosystems that are highly sensitive to water disturbance (Holzapfel and Schmidt 1990). stress and dust pollution. Plant succession Paved roads pose the most ecological impact and insect responses following disturbance on nearby ecosystems, followed by unpaved are less understood in arid landscapes roads and walking trails (Holzapfel and relative to temperate (Abella 2010). Schmidt 1990). Paved roads are designed to In the Mojave Desert, the spread of non- drain water from their edges, which can native annual plants and the distribution of increase the moisture available to adjacent herbivorous insects are of particular plant communities (Holzapfel and Schmidt concern. Previous studies in the Mojave 1990). Higher water availability coupled with Desert have found the richness and additional disturbances can increase an of non-native annual plants increase with environment’s vulnerability to non-native dirt road density (Brooks and Berry 2006). plant invasions and insect . The invasion of non-native plant species is a According to the Plant Vigor Hypothesis, primary cause of decline and insect prefer to oviposit on large, threatens the existence of native plants and vigorously growing plants (Price 1991). their associated organisms (Barbosa et al. Therefore, insect herbivores are generally 2010). Non-native annual grasses can also drawn to less water-stressed plants, which increase the load of an environment, are often found along roadsides. making ecosystems like the Mojave Desert In addition to changes in hydrology, roads increasingly flammable and vulnerable to can alter atmospheric composition in (Kalwij et al. 2008). Since roads can adjacent microhabitats (Coffin 2007). Air function as corridors for parasitism and tends to be dustier near roads, especially at disease spread as well, herbivorous insects unpaved dirt roads. As roads are constructed such as gall-forming insects can serve as key and surrounding soils are eroded, dust indicators of parasitic responses to pollution is more easily spread to nearby disturbance (Lightfoot and Whitford 1991). plants. The coating of dust can impede Galls are abnormal plant tissue growth ’s ability to photosynthesize, produced in response to injected chemical which can hinder the growth and vigor of stimuli of invading organisms (Russo 2006).

CEC Research | https://doi.org/10.21973/N3KX0W Winter 2021 Vol. 5 Issue 2 2/12

Though the complex chemical relationships large variations among host plant species between host plants and gall-forming insects that are still widely unknown (Russo 2006). vary greatly by species, there is growing We hypothesized that areas closer to evidence that galls redirect nutrients from roads would have a higher abundance of their host plant’s roots and leaves into gall non-native annual plant species, larger non- tissues, forming nutrient sinks for the host native annual plants, fewer native annual plants. The management of non-native plants, and a higher density of galls. We also plants and parasitic insect species is hypothesized that the paved road would hampered by a lack of information on desert display the largest non-native plants and the ecosystems, making the Mojave Desert an highest density of galls compared to the dirt ideal location to further investigate the road and trail. Since paved roads typically negative effects of road disturbances funnel higher amounts of water to (Brooks and Berry 2006). surrounding landscapes (Holzapfel and In this study, we explored how annual Schmidt 1990), we expected surrounding plant species composition and regional gall non-native plant and pest communities to density differ in areas near and far from benefit the most near the paved road different types of desert roads. We studied compared to the other road types. We three road types: a paved one-lane expected dust pollution to be higher on the expressway, a dirt vehicle road, and a dirt dirt road than on the trail and paved road, hiking trail. We focused on two dominant causing plant abundance and gall density to non-native plants in the Mojave Desert— be lowest at that site. Lastly, we expected Erodium cicutarium and Bromus spp.—due native plant species abundance to be highest to their pervasiveness in the (Brooks at the trail road since it is the least disturbed and Berry 2006). We asked how road type area. We hoped answering these questions and proximity to a road would affect the would provide ecologists and those involved abundance and size of Erodium cicutarium in road construction management with vital and Bromus plants, the abundance of native information on how impacts of road annual plants, and the density of gall disturbance on the surrounding plant and parasitism. To assess gall density, we studied insect communities change between road creosote bushes (Larrea tridentata), which designs. are critical host plants for gall-forming midge flies (Cecidomyiidae) and their parasites. METHODS Creosote bushes are hosts to at least 16 species of gall midges, all from the genus 2.1 Study System Asphondylia (Russo 2006). Roadside We conducted our research between creosote shrubs tend to be larger and have February 24 and February 28, 2021, during denser foliage, as well as higher arthropod the germination period of annual plants in density (Lightfoot and Whitford 1991). As the Mojave Desert. Research was done at predicted by the Plant Vigor Hypothesis, the the Sweeney Granite Mountains Desert quantity of water availability has shown to Research Center (hereafter referred to as be a large determinant in the ability of a host “the Granites”), a field station owned by the plant to support gall midges, yet there are

CEC Research | https://doi.org/10.21973/N3KX0W Winter 2021 Vol. 5 Issue 2 3/12

University of California, Riverside. The near zone included plants within three Granites is located in the East Mojave Desert meters of the edge of the road and the far in San Bernardino County and lies within the zone included plants at least 10 meters away . Near the center’s from the edge of the road. Within each zone eastern boundary, the topography descends at each site, we conducted multiple surveys from high ridges into bajadas and washes regarding the surrounding annual plant and densely vegetated by multiple habitat types gall communities. (James Andre, Sweeney Granite Mountains Desert Research Center). The washes 2.2 Plant Surveys support creosote bush scrub and mixed desert scrub communities (Simpson et al. In order to determine how different types 1997). The landscape cover also supports an of roads distinctively serve as corridors for abundant annual plant , , we surveyed annual plant including both native and non-native species abundance and size within a 0.5 m² quadrat. such as Erodium cicutarium and Bromus We quantified the most common non-native spp.—which likely include a mix of Bromus annual species, Erodium cicutarium and madritensis and Bromus tectorum. Bromus, as well as all native annual plants We collected data from paved, dirt, and we encountered. For abundance, every trail roads. The paved road site was located Erodium cicutarium, Bromus, and native at Kelbaker Road, a one-lane expressway annual was counted. For size, five Erodium west of the Granites research facility. cicutarium and five Bromus were randomly Kelbaker Road was first developed as a dirt selected for measurement. To measure road in the 1930s. The road was paved in Erodium cicutarium, we used the length 1988 and repaved in 2018 (Pers. Comm. between the two longest leaves. For James Andre). The dirt road site was located Bromus, we pulled the single grass strand along a 1.1-mile-long vehicle road stretching straight and measured from base to tip. between Kelbaker Road and the Granites To account for possible differences in size research facility. The road was first of germinating annuals based on their developed in the 1950s but has seen a location either inside or outside the canopy dramatic increase in use over the past 15 cover of surrounding bushes (Holzapfel and years, as it provides access to campsites Mahall 1999), we replicated all plant surveys alongside the road. The trail site was located both inside and outside the canopy cover of along the Al A. Allanson trail within the creosote. To do so, we placed the quadrat boundary of the Granites research facility. inside the canopy cover, with the edge of the The trail was built in 2001, but the first 100 quadrat aligning with the bush’s longest meters of the trail dates back to the 1930s as branch. We then flipped the quadrat so it lay a portion of a previous two-track road outside the canopy cover with the same historically used by ranchers. edge still aligning with the longest branch of To disentangle road disturbance from the bush. other numerous geographical or biological factors, we looked at two zones within each road site: near and far from the road. The

CEC Research | https://doi.org/10.21973/N3KX0W Winter 2021 Vol. 5 Issue 2 4/12

2.2 Gall Survey control group and was left undusted. Plot 2 was dusted only once at 10:00 A.M. on To assess how different types of roads February 24. Plot 3 was dusted every distinctively serve as corridors for insects, morning at 10:00 A.M. for each of the five we conducted surveys on gall density in days of our experiment. An equal amount of creosote bushes. Creosote bushes were dust was administered between the two systematically selected by surveying the next experimental plots, leaving the number of available bush within our designated near times dusted as our only variable. To and far zones at each of our three road standardize the amount of dust used within types. To account for possible geographical each plot, every Erodium cicutarium differences between the left and right sides replicate was sprinkled with dust until it was of the roads, we surveyed bushes on both visibly completely covered. Every Bromus sides. To account for size differences was sprinkled with 1 tablespoon of dust. The between creosote bushes, we took dust used in the study was collected dirt measurements for the volume of an ovoid – found directly outside the plot (void of any as it best represented the shape of an rocks, debris, or other plant material). average creosote within our survey Each plant replicate was initially measured parameters. A transect tape was used to at the start of our experiment on February measure the bush’s longest radius, shortest 24 at 9:00 A.M. and remeasured at the end radius, and height of tallest branch. Galls of the experiment on February 28 at 5:00 were counted within each bush, identifying P.M. Initial measurements were subtracted and enumerating between species types. from final measurements to calculate the Binoculars aided in counting galls on tall, growth of every plant replicate across the unreachable branches. five days.

2.2 Experimental Plot STATISTICAL ANALYSES

To assess the effect of dust pollution on All statistical analyses were done using the growth rate of germinating non-native JMP Pro 15 statistical software, (JMP®, annuals, we conducted a sub-experiment on Version < Pro 15>. SAS Institute Inc., Cary, both Erodium cicutarium and Bromus from NC, 1989-2019). February 24–28, 2021, that measured how growth rate differed given different 3.1 Plant Survey Analyses frequencies of dusting. The experiment included three different 1 m² plots located at A Two-Way ANOVA was used for all plant the Granites research facilities away from surveys. To account for variation among any road disturbances. In each of the three individual creosote bushes, creosote ID plots, 25 Erodium cicutarium and 25 Bromus number was nested as a random effect. To were randomly selected to receive the see how Erodium cicutarium and Bromus dusting treatments. spp. abundance differed, we analyzed We dusted each plot’s plant replicates at abundance across the three different roads, different frequencies. Plot 1 served as our the distance from the road, and the

CEC Research | https://doi.org/10.21973/N3KX0W Winter 2021 Vol. 5 Issue 2 5/12

interaction between road type and road RESULTS distance. To assess how Erodium cicutarium and Bromus sizes differed, we analyzed size 4.1 Plant Surveys across each road type, the distance from the road, and the interaction between road type Erodium cicutarium abundance did not and road distance. differ among road types (N= 102, F= 1.87, p= 0.16, Fig. 1), between distance from road (N= 3.2 Gall Survey Analyses 68, F= 0.017, p=0.90, Fig. 1), and there was no interaction effect between road type and To account for size differences between distance from road (N= 34, F= 2.80, p= creosote bushes when looking at galls, we 0.065). Bromus spp. abundance was lowest used gall abundance to calculate calculated at dirt roads (N= 68, F= 6.42, p= 0.0024, Fig. gall density within each cubic meter of a 2). Bromus did not differ in abundance creosote bush. First, we calculated the between near and far zones (N= 102, F= 1.73, volume of each bush replicate by using the p= 0.19, Fig. 2), and there was no interaction formula for volume of an ovoid, (4/3 * between road type and road distance (N= 34, longest radius * shortest radius * height). F= 2.87, p= 0.062). Native annual abundance Creosote volume data was log transformed was higher near trails (N= 68, F= 12.65, p= to meet the constraint of normality. Gall <0.0001, Figure 3). Native annual abundance abundance was divided by our transformed did not differ between near and far zones creosote volume to estimate gall density. (N= 102, F= 0.84, p= 0.36, Fig. 3) and there Gall density data was also log transformed was no interaction between road type and for normality. road distance (N= 34, F= 0.62, p= 0.54). A Two-way ANOVA was used for all gall Erodium cicutarium size was smallest at surveys. To assess the response of gall dirt roads, (N= 340, F= 8.92, p= 0.0003, Fig. density to different road types, we analyzed 4) larger near roads (N= 510, F= 191.64, p= road type, road distance, and the interaction <0.0001, Fig. 4), and there was an interaction between road type and road distance. between road type and road distance (N= 70, A One-Way ANOVA was used for all F= 3.16, p= 0.047). Bromus size was larger at experimental plots. To measure how paved roads when compared to trails only Erodium cicutarium growth differed (N= 340, F= 4.38, p= 0.014, Fig. 5) and larger between the experimental plots, we near roads in general (N= 510, F= 8.73, p= analyzed growth across all three plots. The 0.0039, Fig. 5). There was no interaction same test was performed for Bromus across between site and zone (N= 70, F= 2.32, P= all three plots. 0.10).

CEC Research | https://doi.org/10.21973/N3KX0W Winter 2021 Vol. 5 Issue 2 6/12

and far zones (N= 102, F= 1.73, p= 0.19). There was no interaction between road type and road distance (N= 34, F= 2.87, p= 0.062).

Figure 1. The effect of road type on Erodium cicutarium abundance. We counted Erodium cicutarium abundance near creosote bushes by three different types of roads in the Mojave Desert—a paved one-lane expressway, a dirt vehicle road, and a Figure 3. The effect of road type on annual native hiking trail. Surveys were conducted both near plant abundance. To assess how road types affect (within 3 m of the road) and far (at least 10 m away) native plant establishment, we collected native plant from the roads. Erodium cicutarium abundance did abundance across three different road types- a paved not differ among road types (N= 102, F= 1.87, p= 0.16) one-way express lane, a dirt vehicle road, and a hiking or by distance from road (N= 68, F= 0.017, p=0.90). trail. Surveys were conducted both near (within 3 m There was no interaction effect between road type of the road) and far (at least 10 m away) from the and distance from road (N= 34, F= 2.80, p= 0.065) roads. The abundance of native annuals was higher near trails (N= 68, F= 12.65, p= <0.0001). Abundance also did not differ between near and far zones (N= 102, F= 0.84, p= 0.36) and there was no interaction between road type and road distance (N= 34, F= 0.62, p= 0.54).

Figure 2: The effect of road type on Bromus spp. abundance. We counted Bromus abundance near creosote bushes by three different types of roads in the Mojave Desert—a paved one-lane expressway, a dirt vehicle road, and a hiking trail. Surveys were conducted both near (within 3 m of the road) and far Figure 4. The effect of road type on Erodium (at least 10 m away) from the roads. The abundance cicutarium size. We measured the size of Erodium of Bromus was lowest at dirt roads (N= 68, F= 6.42, p= cicutarium near creosote bushes by three different 0.0024) but abundance did not differ between near types of roads in the Mojave Desert—a paved one- lane expressway, a dirt vehicle road, and a hiking trail.

CEC Research | https://doi.org/10.21973/N3KX0W Winter 2021 Vol. 5 Issue 2 7/12

Surveys were conducted both near (within 3 m of the paved one-lane expressway, a dirt vehicle road, and a road) and far (at least 10 m away) from the roads. The hiking trail. Gall abundance surveys were done both size of Erodium cicutarium was smallest at dirt roads near the roads (within 3 m of the road), and far (at (N= 340, F= 8.92, p= 0.0003, Figure 1), larger near least 10 m away) from the roads. Gall density was roads (N= 510, F= 191.64, p= <0.0001), and there was highest at paved roads (N= 48, F= 4.38, p= 0.014) and an interaction between road type and road distance near roads (N= 72, F= 20.36, p= <0.0001). There was (N= 70, F= 3.16, p= 0.047). no interactive effect of road type nor distance from road on gall density (N= 24, F= 0.78, p= 0.46).

Figure 7. The effect of dust on Bromus spp. and Figure 5. The effect of road type on Bromus spp. size. Erodium cicutarium growth. We set up three We measured the size of Bromus spp. near creosote experimental plots at the Sweeney Granite bushes by three different types of roads in the Mountains Research Center located in the Mojave Mojave desert—a paved one-lane expressway, a dirt Desert. Within each plot, we randomly selected 25 vehicle road, and a hiking trail. Surveys were plant replicates of both Bromus and Erodium conducted both near (within 3 m of the road) and far cicutarium. Each plot received a different dusting (at least 10 m away) from the roads. Bromus size was treatment across five days: the ‘control’ plot was not larger at paved roads when compared to trails only dusted, the ‘light’ plot was dusted only once during (N= 340, F= 4.38, p= 0.014, Figure 2) and larger near the first day, and the ‘heavy’ plot was dusted daily. To roads in general (N= 510, F= 8.73, p= 0.0039). There measure growth, initial size measurements were was no interaction between site and zone (N= 70, F= taken and compared with size measurements after 2.32, P= 0.10). the five days. Bromus grew the most in the control plot (N= 25, F= 19.05, P= <0.0001), and Erodium cicutarium grew the most in the light plot (N= 25, F= 17.36, P= <0.0001).

4.2 Gall Surveys

Within 144 creosote bushes, we counted 2,117 galls belonging to four main species – 493 Asphondylia resinosa galls, 1,047 Asphondylia auripala galls, 210 Asphondylia clavata galls, and 351 Asphondylia foliosa galls, (Table 1, Table 2). Figure 6. The effect of road type on gall density. We

counted gall density on creosote bushes across three different types of roads in the Mojave Desert—a

CEC Research | https://doi.org/10.21973/N3KX0W Winter 2021 Vol. 5 Issue 2 8/12

Table 1. Total number of galls of each species found 4.3 Experimental Plots per road type. Within 144 creosote bushes, we counted 2,101 galls belonging to four main species of gall Erodium cicutarium grew the most in the midges. The most abundant species was Asphondylia resinosa, accounting for 49.8% of total galls. plot that was dusted only once (N = 25, F = 17.36, p = <0.0001, Fig. 7), while Bromus ROAD TYPE grew the most in the plot that was not dusted at all (N = 25, F = 19.05, p = <0.0001, GALL SPECIES DIRT PAVED TRAIL TOTAL Fig. 7).

A. auripala 74 250 169 493 DISCUSSION A. clavata 10 73 127 210 5.1 Annual Plant Abundance and Size A. foliosa 52 156 143 351 As expected, road type influenced A. resinosa 295 485 267 1,047 abundance and size of invasive annual TOTAL 431 964 706 2,101 plants. Road proximity did not influence the capacity for Bromus to grow, but the varying disturbances among the different types of Table 2. Total number of galls of each species found roads influence the rate at which it can grow. per zone. Within 144 creosote bushes surveyed, 70% We speculate its resilient nature initially of all total galls counted were found in creosote bushes less than three meters from the roads. allows Bromus to become uniformly established across a landscape, which

ZONE explains why abundance does not seem to change closer to roads. However, with GALL SPECIES NEAR FAR TOTAL prolonged water stress, paved roads may support higher growth rates of Bromus than A. auripala 319 174 493 trails due to higher levels of water runoff. A. clavata 156 54 210 We reason we found the smallest abundance of Bromus near dirt roads A. foliosa 278 73 351 because they cause the most dust to be kicked up onto the adjacent plant A. resinosa 717 330 1,047 communities and are therefore not TOTAL 1,470 631 2,101 conducive to Bromus establishment. Another disturbance factor that can facilitate the establishment of Bromus is Overall gall density was higher at paved disrupted (Chambers et roads (N= 48, F= 4.38, p= 0.014, Fig. 6) and al. 2016). Soil crust can inhibit the near the roads (N= 72, F= 20.36, p= <0.0001, germination and spread of Bromus, Fig. 6). There was no interactive effect of especially in areas of high disturbance. The road type nor distance from road on gall construction, maintenance, and usage density (N= 24, F= 0.78, p= 0.46). frequency of paved roads poses greater destruction to surrounding soil crust,

CEC Research | https://doi.org/10.21973/N3KX0W Winter 2021 Vol. 5 Issue 2 9/12

potentially allowing Bromus to grow in was consistent with our hypothesis that road greater abundance near paved roads disturbance facilitates a higher density of compared to dirt roads and trails. gall-forming insects. Previous studies have shown Erodium cicutarium is a generalist species, meaning it 5.3 Future Research is resistant to drought and low levels of disturbance (Kimball et al. 2014). The Due to the timing of our study, we were resilient nature of Erodium cicutarium only able to observe annual plants that had supports our finding that abundance did not begun germinating a few weeks prior. A change across different road types. Though longer-term observational study on annual its ability to establish was not influenced by plants could provide additional insight into roads, our finding that its size was higher in factors that affect non-native annual plant the zones near paved roads and trails, as well as abundance and growth near desert roads. A in the lightly dusted experimental plots, leads previous study conducted on the effects of us to believe Erodium cicutarium was able to and on survivorship thrive under conditions of light disturbance. and community structure of desert annuals High levels of disturbance can be in the found that detrimental to native species and destroy competition among annual plants reduced seed banks (Holzapfel and Schmidt 1990). As species’ biomass and growth rates (Inouye et expected, the road type with the lowest level al. 1980). As the density of Erodium spp. of disturbance supported the highest decreased due to rodent predation, other abundance of native annual species. This annual species were able to increase in finding shows how different road types not abundance across the landscape. only influence non-native plant species but Specifically, it would be interesting to assess also impact the success of native species. if Erodium cicutarium and Bromus experience interspecific competition that 5.2 Gall Density alters their distribution and survivorship over the course of their lifespan. Higher water availability from runoff can According to the Plant Vigor Hypothesis, produce more vigorous creosote bushes that insect herbivores such as gall-forming would attract more gall-forming insects midges may prefer plants that are less water (Ludwig and Blanche 2001). Creosote bushes stressed (Price 1991). Thus, creosote bushes have been observed to have faster already parasitized by other species known vegetative growth rates and higher leaf to increase water stress on plants production when provided additional water (Sangüesa-Barreda et al. 2013)—such as (Sharifi et al. 1988). We observed larger, mistletoe (Viscum album)—could exhibit more vigorous creosote bushes near our less gall density compared to creosote road sites, which aligns with prior research bushes not already parasitized by mistletoe, on the correlation between water especially when mistletoe increases water availability and creosote health. Our findings stress on plants. Within our gall survey, we that gall density was highest near roads in observed three different occurrences of general and especially high near paved roads mistletoe, but there were not enough

CEC Research | https://doi.org/10.21973/N3KX0W Winter 2021 Vol. 5 Issue 2 10/12

replicates to see any trends in regard to how communities, especially when making mistletoe parasitism impacted gall decisions on road design. abundance. Based on our study results, we speculate creosote bushes parasitized by ACKNOWLEDGMENTS mistletoe may not be as impacted from road disturbance as non-mistletoe parasitized This work was performed at the University creosote would be, and that mistletoe of California’s Sweeney Granite Mountains parasitism on creosote bushes may produce Desert Research Center, doi: the greatest impact along paved roads 10.21973/N3S942. Thank you to reserve compared to other road types. This would be directors, Jim André and Tasha La Doux, for important to further investigate how roads welcoming us to the Granites and sharing impact the surrounding plant communities your knowledge of the area with us. Thank within the Mojave Desert. you to our instructors, Tim Miller and Sarah Kingston, for the continuous support, 5.4 Conclusion guidance, and enthusiasm throughout our research. Additional thanks to Jake Overall, this study contributes to the Hernandez, MC Moazed, and Elyse growing literature on how different road Fitzsimons for mentoring and advising us designs impact the ecology of surrounding along the way. plant and animal communities within the Mojave Desert—specifically non-native REFERENCES plant species and gall-forming midges. Our Abella, S. R. 2010. Disturbance and plant succession findings suggest road disturbances are in the Mojave and Sonoran of the American facilitating higher success of non-native Southwest. International Journal of Environmental annual plants. These non-native annuals Research and Public Health 7:1248–1284. could potentially be outcompeting native Andre, J. 2021, March 4. History of roads at Sweeney plants, which could be a cause for concern if Granite Mountains Desert Research Center. it leads to state shifts within such a fragile Personal Communication. desert ecosystem (Sheffer et al. 2001). Additionally, our findings displayed Barbosa, N. P. U., G. W. Fernandes, M. A. A. Carneiro, and L. A. C. Júnior. 2010. Distribution of non-native increased gall density due to road invasive species and soil properties in proximity to disturbance, specifically along paved roads. paved roads and unpaved roads in a quartzitic Though gall midges are native species, an mountainous of southeastern Brazil increase in gall density may serve as a proxy (rupestrian fields). Biological Invasions 12:3745– for disease invasion. This raises concern for 3755. the negative health implications of plant Brooks, M. L., and K. H. Berry. 2006. and hosts within the Mojave Desert (Russo environmental correlates of alien annual plants in 2006). Within the Mojave Desert, our study the Mojave Desert, USA. Journal of Arid provides information that could be helpful to Environments 67:100–124. conservation efforts of road disturbance Chambers, J. C., Germino, M. J., Belnap, J., Brown, C. impacts on the surrounding plant S., Schupp, Eugene W., St. Clair, S. B. 2016. Plant community to invasion by Bromus

CEC Research | https://doi.org/10.21973/N3KX0W Winter 2021 Vol. 5 Issue 2 11/12

species: The roles of community attributes, Bromus Kalwij, J. M., S. J. Milton, and M. A. McGeoch. 2008. interaction with plant communities, and Bromus Road verges as invasion corridors? A spatial traits. Exotic Brome-Grasses in Arid and Semiarid hierarchical test in an arid ecosystem. Landscape Ecosystems of the US. Springer Series on Ecology 23:439–451. Environmental Management, pp. 275–304. Kimball, S., J. R. Gremer, G. A. Barron-Gafford, A. L. Coffin, A. W. 2007. From roadkill to road ecology: A Angert, T. E. Huxman, and D. L. Venable. 2014. High review of the ecological effects of roads. Journal of water-use efficiency and growth contribute to Transport Geography 15:396–406. success of non-native Erodium cicutarium in a Sonoran Desert winter annual community. Cornelissen, T., G. W. Fernandes, and J. Vasconcellos- Conservation Physiology 2. Neto. 2008. Size does matter: variation in herbivory between and within plants and the plant vigor Lightfoot, D. C., and W. G. Whitford. 1991. hypothesis. Oikos Synthesising Ecology 117:1121– of creosote bush foliage and 1130. associated canopy arthropods along a desert roadside. The American Midland Naturalist Dix, M. E., M. Buford, J. Slavicek, and A. M. Solomon. 125:310–322. 2010. Invasive species and disturbances: Current and future roles of Forest Service Research and Ludwig, J. A., and K. R. Blanche. 2001. Species Development. U.S. Forest Service Southern Richness of gall-inducing insects and host plants Research Center. along an altitudinal gradient in Big Bend National Park, Texas. The American Midland Naturalist Farmer, A. M. 1993. The effects of dust on vegetation. 145:219–232. Environmental Pollution 79:63–75. Price, P. W. 1991. The plant vigor hypothesis and Forman, R. T. T., and L. E. Alexander. 1998. Roads and attack. Oikos Synthesising Ecology their major ecological effects. Annual Review of 62:244–251. Ecology and Systematics 29:207–232. Russo, R. 2006. Field guide to plant galls of California Hansen, M., and A. P. Clevenger. 2005. The influence and other western states. First edition. University of disturbance and habitat on the presence of non- of California Press. native plant species along transport corridors. Biological Conservation 125:249–259. Sangüesa-Barreda, G., J. C. Linares, and J. J. Camarero. 2013. Drought and mistletoe reduce growth and HE, H., T. A. Monaco, and T. A. Jones. 2017. Functional water-use efficiency of Scots pine. trait differences between native bunchgrasses and and Management 296:64–73. the invasive grass Bromus tectorum. Higher Education Press, Beijing, China. Sharifi, M. R., Meinzer, F. C., Nilsen E. T., Rundel, P. W., Virginia, R. A. 1988. Effect of manipulation of Holzapfel, C., and Mahall, B. E. 1999. Bidirectional water and nitrogen supplies on the quantitative facilitation and interference between shrubs and phenology of Larrea tridentata (creosote bush) in annuals in the Mojave Desert. Ecology 80:1747– the Sonoran Desert of California. American Journal 1761. of Botany 75:1163-1174.

Holzapfel, C., and W. Schmidt. 1990. Roadside Sheffer, M., S. Carpenter, J. A. Foley, C. Folke, and B. vegetation transects in the Judean desert. Israel Walker. 2001. Catastrophic shifts in ecosystems. Journal of Botany 39:263–270. Nature 413:591–596.

Inouye, R. S., G. S. Byers, and J. H. Brown. 1980. Mabry, T.J., Hunziker, J.H., and D.R. DiFeo Jr. 1977. Effects of predation and competition on Creosote bush: Biology and chemistry of Larrea in survivorship, fecundity, and community structure deserts. Dowden, Hutchinson, and of desert annuals. Ecology 61:1344–1351. Ross, Stroudsburg, Pennsylvania, pp. 92–114.

CEC Research | https://doi.org/10.21973/N3KX0W Winter 2021 Vol. 5 Issue 2 12/12