Sage Scrub Research Articles

Multi-method approach to assessing the floral-visiting insect assemblage of rare, abophilous plant Baccharis vanessae in Southern California.

Insects are the major pollination vectors for angiosperms, and insects native to a given habitat can play an irreplaceable ecological role in food webs and plant reproduction. With precipitous declines in insect species over the last decades, it is urgent to document insect assemblages in native plant communities to support conservation efforts. Identifying pollinators and their pollination activity is challenging; however, emerging technological methods are providing new monitoring capabilities. In this study, we compare the accuracy of two different methods of monitoring to assess the flower-visiting insect assemblage and likely pollinators of Encinitas baccharis (Baccharis vanessae): focal observations and video recordings from camera traps. B. vanessae is a rare, endemic species found in Coastal Sage Scrub communities in San Diego County. This federally listed species is threatened by habitat loss and fragmentation, which may also be affecting the availability of its insect pollinators. Results indicate that B. vanessae supports and is supported by a variety of flower-visiting insect groups. The diversity of insect visitors at male and female plants were similar across all diversity measurements. The insect vectors identified were as expected given B. vanessae pollination syndrome. This syndrome also aligns with wind as a pollination vector, providing evidence of ambophily. While focal observations underreported insect activity by approximately half, the proportions of common diurnal visitors were similar with both methods. Camera traps were unable to provide sufficient detail to discern visually similar groups, but were able to record nocturnal insect activity, which was dominated by moths (Lepidoptera, 82%). While collection protocol in this study did not record the time an insect spent interacting with a flower, we anecdotally observed moths spent notably longer periods in contact with flowers than most diurnal insects. This study has implications for effective monitoring and conservation of endangered plant species and their affiliated pollinators.

Using demographic modeling to develop post‐fire restoration strategies for a native shrub in a sage scrub community

Mediterranean‐climate shrublands are key biodiversity hotspots and carbon storage pools, but are increasingly threatened by climate change, non‐native species, and altered fire regimes. Fires are important to historic shrubland disturbance cycles but can also promote non‐native plants, which may limit post‐fire native shrub recovery. Increasing drought with climate change could also reduce post‐fire shrub regeneration. I developed a stochastic, individual‐based demographic model (IBM) for the native shrub Artemisia californica, parameterized from an experimental removal of non‐native annuals after a 2013 fire in southern California. The IBM simulated A. californica recovery for 7 years after fire under different rainfall conditions (drought or pre‐drought) and non‐native removal strategies (from no years to all 7 years). Drought lowered A. californica canopy volume 7 years after fire by 90% or more. Rainfall in the second year after fire, when most A. californica germination occurred, had particularly strong effects on final canopy cover. Non‐native removal in all 7 years increased canopy volume by three times under drought conditions and 3.5 times under pre‐drought conditions. Targeting non‐native removal in the first 2 years proved nearly as effective, achieving from 88% (drought) to 95% (pre‐drought) the benefits of removal in all 7 years. In sum, low rainfall may be the most important limitation on post‐fire shrub recovery, but removal of non‐natives in years of pulsed shrub recruitment can be an effective restoration strategy even under drought conditions. More generally, this study illustrates how demographic models can help optimize the targeting of scarce management and restoration resources.

Understanding post‐fire vegetation recovery in southern California ecosystems with the aid of pre‐fire observations from long‐term monitoring

AbstractAimsPost‐fire vegetation recovery is often determined by the similarity of post‐burn with unburned sites because of a lack of in situ information on pre‐fire communities. The inclusion of pre‐fire data can help account for pre‐existing differences and explore recovery also in terms of return to pre‐fire conditions. We used long‐term monitoring data in coastal sage scrub and grasslands to: (a) examine vegetation cover recovery of different functional groups; and (b) determine whether vegetation composition in burned areas has recovered in 4 years after fire with burned to unburned and pre‐ to post‐fire comparisons.LocationOrange County, California, USA.MethodsWe analyzed long‐term vegetation monitoring (2007–2021) data from 39 grassland and 58 coastal sage scrub transects in southern California, including observations before and after the 2017 Canyon 2 fire. Linear mixed‐effect models were used to determine whether forb, grass, and shrub covers differed between burned and unburned sites while considering the effects of year and repeated monitoring. We used canonical analysis of principal coordinates to analyze vegetation composition based on burn status and time of sampling.ResultsWhereas vegetation cover in grassland recovered quickly, native vegetation cover in burned coastal sage scrub remained lowered 4 years after fire, though forb and non‐native grass cover were higher in some post‐fire years. Community composition in burned coastal sage scrub was still in recovery 4 years after fire when compared with unburned or pre‐fire composition. Although burned and unburned grassland differed after fire in dominant grass species, inclusion of pre‐fire data showed that this was a pre‐existing difference.ConclusionsCoastal sage scrub had not recovered pre‐fire vegetation cover and composition by 4 years after fire, whereas grassland cover rebounded quickly, albeit with shifts in composition over time; patterns that were detected only by having pre‐ and post‐fire data from long‐term monitoring efforts.

Ecosystem service values support conservation and sustainable land development: Perspectives from four University of California campuses

Urban landscapes homogenize our world at global scales, contributing to “extinction of experience”, a progressive decline in human interactions with native greenspace that can disconnect people from the services it provides. College age adults report feeling disconnected from nature more than other demographics, making universities a logical place to explore interventions intended to restore a connection with nature. This study surveyed 1088 students and staff across four university campus communities in Southern California, USA and used multicriteria decision analysis to explore their landscape preferences and the implications of those preferences for combatting extinction of experience. Our results suggest that perspectives of, and preferences for, different greenspace forms vary significantly (i.e., they are not perceived as substitutable). Support for native ecosystems, particularly coastal sage scrub (top ranked landscape) was generally high, suggesting that disaffection with wild nature is not particularly widespread. Programs for replacing turf grass lawns (lowest ranked landscape) with native plants were also well supported, but support for stormwater bioswales was more moderate (and variable). This may reflect their relative newness, both on university campuses and in urban spaces more generally. Not all members of campus communities preferred the same landscapes; preferences differed with degree of pro-environmentalism and university status (undergraduate student, graduate student, staff). Even so, all respondents exhibited landscape preferences consistent with at least one approach for combatting extinction of experience, suggesting that ecologists, engineers and urban planners have a viable set of generalizable tools for reconnecting people with nature.

Response of an Avifaunal Community to the La Tuna Fire in the Verdugo Mountains of Southern California

In California’s coastal sage scrub and chaparral, fire reshapes the distribution of vegetation and the composition of bird communities, although the direction of the response in various habitats remains unclear. We investigated changes in the bird community at one site following the 2017 La Tuna Fire in the Verdugo Mountains of southern California. We found that the community’s diversity and evenness did not change, but the structure of foraging guilds did. Counts of omnivores and aerial and generalist foragers increased significantly, whereas counts of granivores and shrub foragers decreased. The number of insectivores decreased slightly, and ground foragers appeared unaffected. Principal components analysis suggests positive, neutral, and negative responses of birds associated with these guilds were driving differences in their abundances after the fire. We show how post-fire bird distributions may be related to fire severity, vegetation structure, and interspecific interactions. However, differences between our results and those of other studies suggest that patterns of bird community response to wildfire may be dictated by factors both related and unrelated to the fire over broader time scales.

Effects of artificial light on foraging behavior of the Pacific Kangaroo Rat (Dipodomys agilis)

Abstract Artificial light at night is increasingly recognized as a cause of habitat degradation, and as a conservation threat to wildlife species. We studied the behavioral response of Pacific kangaroo rats (Dipodomys agilis) to natural and artificial light in coastal sage scrub in southern California, United States. We used digital trail cameras to monitor visits to seed trays in shrub and open, intershrub microhabitats. Under natural-light conditions, kangaroo rats were more active on full- than new-moon nights, and concentrated foraging beneath shrubs. Surprisingly, kangaroo rats frequently interacted with other rodents in seed trays. Near to an artificial light source, kangaroo rats removed fewer seeds, had fewer foraging bouts, and spent less time in trays—especially in brightly lit open microhabitats—compared to distances farther from the light. Differences between the first and second nights of trials during both experiments suggested that kangaroo rats learned locations of resource-rich seed trays and modified their behavior accordingly. Our results are similar to recent studies showing that artificial light depresses foraging activity of rodents in the areas of highest illumination, and adds to evidence of the need to mitigate impacts of urban lighting in fragments of coastal sage scrub, especially along the urban–wildland interface.

Development of a Micropropagation Protocol for the Ex Situ Conservation of Nuttall's Scrub Oak (Quercus dumosa).

Worldwide, oak species are threatened with extinction due to habitat loss, pathogens, and changing fire regimes. Ex situ conservation through tissue culture may protect the remaining genetic diversity of Quercus dumosa, or the coastal sage scrub oak, from further loss. We designed three basal salt formulations based on the mineral composition of shoot tips and first leaves from mature Q. dumosa and explored carbohydrate source, stress-mitigating compounds, and plant growth regulator concentrations to develop a method of cultivating many Q. dumosa culture lines in vitro. All three novel basal salt formulations led to decreased necrosis compared with commercial basal salt formulas WPM, MS, and DKW. Substitution of 30 g L-1 sucrose with glucose and adding 250 mg L-1 ascorbic acid, 5.2 mg L-1 SNP sodium nitroprusside, and 103 mg L-1 y-aminobutyric acid improved culture health overall. In an experiment involving 115 culture lines, 0.66 mg L-1 6-benzylaminopurine produced the highest average shoots per explant, but 0.33 mg L-1 produced the greatest proportion of shoots 2 cm or greater. Incubation for 24 h in 20 mg L-1 indole-3-butyric acid led to the most rooting. These methods show promise for the ex situ conservation of many genotypes of endangered Q. dumosa.

Struggling to survive: A comparison of Vanessa cardui larval survivorship on putative host plants

AbstractThe painted lady butterfly (Vanessa cardui) is a generalist herbivore with a global distribution. In North America, over 100 species have been identified as V. cardui larval host plants. This cosmopolitan species is commercially available in all life stages and can be reared on an artificial diet. As a result, V. cardui commonly serves as a model organism for education and outreach. However, gaps in our knowledge remain with regard to V. cardui ecology and larval host plant suitability for supporting complete development of larvae to reproductive adulthood. In a laboratory setting, we tested host plant suitability of five reported host plants commonly found in California sage scrub ecosystems by assessing survival of V. cardui caterpillars in its entirety. We also assessed how commercially sourced larvae survived on artificial diet: both raising the caterpillars exclusively on artificial diet as well as switching diets from artificial to thistle (a commonly reported host plant) and switching from thistle to artificial diet. We found that all commercially sourced caterpillars exhibited both high larval mortality and low pupation rates when reared on host plants, although larvae reared on Malacothamnus fasciculatus and Sphaeralcea ambigua survived longest. Moreover, M. fasciculatus and S. ambigua were the only host plants tested that supported successful pupation. This contrasted with 63% higher survival of wild‐collected larvae. Our findings suggest that commercially obtained V. cardui may struggle to utilize wild host plants and that future investigations into host plant suitability in wild populations are needed. Additionally, future research using commercial larvae should consider the implications for interpreting host plant suitability as larvae may exhibit adaptations to artificial diet or the loss of adaptation to consuming plant material.

Long-term drought promotes invasive species by reducing wildfire severity.

Anthropogenic climate change has increased the frequency of drought, wildfire, and invasions of non-native species. Although high-severity fires linked to drought can inhibit recovery of native vegetation in forested ecosystems, it remains unclear how drought impacts the recovery of other plant communities following wildfire. We leveraged an existing rainfall manipulation experiment to test the hypothesis that reduced precipitation, fuel load, and fire severity convert plant community composition from native shrubs to invasive grasses in a Southern California coastal sage scrub system. We measured community composition before and after the 2020 Silverado wildfire in plots with three rainfall treatments. Drought reduced fuel load and vegetation cover, which reduced fire severity. Native shrubs had greater prefire cover in added water plots compared to reduced water plots. Native cover was lower and invasive cover was higher in postfire reduced water plots compared to postfire added and ambient water plots. Our results demonstrate the importance of fuel load on fire severity and plant community composition on an ecosystem scale. Management should focus on reducing fire frequency and removing invasive species to maintain the resilience of coastal sage scrub communities facing drought. In these communities, controlled burns are not recommended as they promote invasive plants.

Rangewide occupancy of a flagship species, the Coastal California Gnatcatcher (Polioptila californica californica) in southern California: Habitat associations and recovery from wildfire.

The Coastal California Gnatcatcher (Polioptila californica californica), a federally threatened species, is a flagship species for regional conservation planning in southern California (USA). An inhabitant of coastal sage scrub vegetation, the gnatcatcher has declined in response to habitat loss and fragmentation, exacerbated by catastrophic wildfires. We documented the status of gnatcatchers throughout their California range and examined post-fire recovery of gnatcatchers and their habitat. We used GIS to develop a habitat suitability model for Coastal California Gnatcatchers using climate and topography covariates and selected over 700 sampling points in a spatially balanced manner. Bird and vegetation data were collected at each point between March and May in 2015 and 2016. Presence/absence of gnatcatchers was determined during three visits to points, using area searches within 150 x 150 m plots. We used an occupancy framework to generate Percent Area Occupied (PAO) by gnatcatchers, and analyzed PAO as a function of time since fire. At the regional scale in 2016, 23% of the points surveyed were occupied by gnatcatchers, reflecting the effect of massive wildfires in the last 15 years. Similarly, PAO in the post-fire subset of points was 24%, with the highest occupancy in unburned (last fire <2002) habitat. Positive predictors of occupancy included percent cover of California sagebrush (Artemisia californica), California buckwheat (Eriogonom fasciculatum), and sunflowers (Encelia spp., Bahiopsis laciniata), while negative predictors included laurel sumac (Malosma laurina) and total herbaceous cover; in particular, non-native grasses. Our findings indicate that recovery from wildfire may take decades, and provide information to speed up recovery through habitat restoration.

Nitrogen deposition suppresses ephemeral post-fire plant diversity.

Fire is a dominant force shaping patterns of plant diversity in Mediterranean-type ecosystems. In these biodiversity hotspots, including California's endangered coastal scrub, many species remain hidden belowground as seeds and bulbs, only to emerge and flower when sufficient rainfall occurs after wildfire. The unique adaptations possessed by these species enable survival during prolonged periods of unfavorable conditions, but their continued persistence could be threatened by nonnative plant invasion and environmental change. Furthermore, their fleeting presence aboveground makes evaluating these threats insitu a challenge. For example, nitrogen (N) deposition resulting from air pollution is a well-recognized threat to plant diversity worldwide but impacts on fire-following species are not well understood. We experimentally evaluated the impact of N deposition on post-fire vegetation cover and richness for three years in stands of coastal sage scrub that had recently burned in a large wildfire in southern California. We installed plots receiving four levels of N addition that corresponded to the range of N deposition rates in the region. We assessed the impact of pre-fire invasion status on vegetation dynamics by including plots in areas that had previously been invaded by nonnative grasses, as well as adjacent uninvaded areas. We found that N addition reduced native forb cover in the second year post-fire while increasing the abundance of nonnative forbs. As is typical in fire-prone ecosystems, species richness declined over the three years of the study. However, N addition hastened this process, and native forb richness was severely reduced under high N availability, especially in previously invaded shrublands. An indicator species analysis also revealed that six functionally and taxonomically diverse forb species were especially sensitive to N addition. Our results highlight a new potential mechanism for the depletion of native species through the suppression of ephemeral post-fire bloom events.

Composition and activity of soil microbial communities in native and non-native vegetation of southern California

The proliferation of non-native plant species in novel habitats has altered plant community diversity, ecosystem carbon (C) and nutrient cycling, and disturbance regimes worldwide. However, the impacts of non-native plants on soil microbial community composition and activity are still poorly known, especially in semi-arid woodlands. Here we utilized next generation sequencing (16S rRNA sequencing of the V3-V4 regions) and measurements of microbial activity (respiration, net N mineralization, and enzyme assays) to determine how soil microbial composition and activity varied between native and non-native vegetation patches in coastal sage scrub (CSS) woodlands. We sampled eight CSS sites and collected topsoil (0–10 cm) samples from six paired native and non-native vegetation patches at each site. Native patches had significantly (p < 0.05) higher vegetation cover, dissolved organic C (DOC), and dissolved inorganic nitrogen (DIN) concentrations than non-native patches. β-glucosidase activity was significantly higher (ca. 10 nM g−2 h−1) and peroxidase activity was significantly lower (ca. 60 nM g−2 h−1) in non-native vegetation, while rates of net N mineralization and nitrification, phosphatase and NAGase activities, and respiration were not significantly different in native and non-native vegetation but were positively correlated with total soil C and N (r > 0.60; p < 0.05). Bacterial alpha- and beta-diversity were not significantly different (p > 0.05) between native and non-native patches; however, bacteria/archaea in the phyla Gemmatimonadota, Planctomycetota, Armatimonadota, Fibrobacterota, Thermoplasmatota, and Entotheonellaeota were over-expressed in non-native patches. Within these phyla there were 20 orders that were differentially expressed in native or non-native vegetation, and more than half (60 %) had significantly higher relative abundance in native vegetation. Our results indicate that the expansion of non-native vegetation in semi-arid woodlands significantly alters soil C and N, which feeds back on microbial activity and community composition.

Native and non‐native mulch resulted in increased soil moisture and reduced plant recruitment in container plant restoration of coastal sage scrub

One challenge of habitat restoration is establishing healthy native plants that survive, grow, and reproduce. The addition of mulch after initial planting is thought to enhance native plant establishment. In our efforts to restore degraded sites at Crystal Cove State Park in Southern California, we compared two experimental mulch treatments made from native and non‐native plant material to unmulched plots. We planted four different native shrub species: Eriogonum fasciculatum, Malosma laurina, Isocoma menziesii, and Diplacus aurantiacus, and measured plant size, soil moisture, and plant density in the first year. In the second year, the same measurements were taken for I. menziesii and D. aurantiacus, which had greater survivorship in the first year. Our results showed significant differences in plant height, length, and width among the species but not between mulch treatments. However, soil moisture significantly varied between treatments, with native mulch plots having the greatest volumetric water content. In addition, mulch treatments had a significant effect on naturally recruiting plant density, with both mulch treatments having fewer native and non‐native seedling densities compared to control plots. Regarding survivorship, significant differences between species and treatment were observed only in the first year. Our results confirmed that mulch effectively helped retain higher soil moisture. Both locally sourced native and non‐native mulch had this benefit, although native mulch resulted in greater increases in soil moisture. While mulch reduced non‐native plant establishment, it also limited native recruitment, leading us to recommend that mulch be used only during the initial establishment of container plants.

Increase in heat tolerance following a period of heat stress in a naturally occurring insect species.

Climate warming is the defining environmental crisis of the 21st century. Elucidating whether organisms can adapt to rapidly changing thermal environments is therefore a crucial research priority. We investigated warming effects on a native Hemipteran insect (Murgantia histrionica) that feeds on an endemic plant species (Isomeris arborea) of the California coastal sage scrub. Experiments conducted in 2009 quantified the temperature responses of juvenile maturation rates and stage-specific and cumulative survivorship. The intervening decade has seen some of the hottest years ever recorded, with increasing mean temperatures accompanied by an increase in the frequency of hot extremes. Experiments repeated in 2021 show a striking change in the bugs' temperature responses. In 2009, no eggs developed past the second nymphal stage at 33°C. In 2021, eggs developed into reproductive adults at 33°C. Upper thermal limits for maturation and survivorship have increased, along with a decrease in mortality risk with increasing age and temperature, and a decrease in the temperature sensitivity of mortality with increasing age. While we cannot exclude the possibility that other environmental factors occurring in concert could have affected our findings, the fact that all observed trait changes are in the direction of greater heat tolerance suggests that consistent exposure to extreme heat stress may at least be partially responsible for these changes. Harlequin bugs belong to the suborder Heteroptera, which contains a number of economically important pests, biological control agents and disease carriers. Their differential success in withstanding warming compared to beneficial holometabolous insects such as pollinators may exacerbate the decline of beneficial insects due to other causes (e.g. pollution and pesticides) with potentially serious consequences on both biodiversity and ecosystem functioning.

Effects of Peri-Urbanization on Coastal Sage Scrub Ant Species in Baja California

Increasing urbanization on the Baja California Peninsula threatens ant diversity. Reductions in ant species diminish ecosystem services provided to semiarid coastal scrub areas. Peri-urban areas in particular are at high risk of reductions in ant biodiversity due to development. To document and evaluate ant species diversity and richness in a rapidly developing area, nine sites were sampled within areas of coastal sage scrub (CSS) encircling the urban periphery of Ensenada, Baja California. Forty species and 17 genera of ants were collected, only one of which was non-native. Although the sampled area represents less than 1% of the peninsula and 3% of the State of Baja California, approximately one-third of the total species recorded for the peninsula and state were collected. Environmental variables (compass orientation, slope, and vegetation cover) were not significant determinants of species richness. Sandy soils were associated with the highest species abundance, richness, and functional diversity of feeding guilds. Despite limitations, our results present a historically significant snapshot of ant diversity in the sage scrub areas surrounding Ensenada. Sandy regions of semiarid coastal scrub are prime conservation management areas as they support the greatest functional diversity and have the highest potential to supply environmental services to the surrounding CSS ecosystem.

Assessing spatial and temporal variation in obligate resprouting, obligate seeding, and facultative seeding shrub species in California’s Mediterranean-type climate region

Mediterranean-climate region (MCR) shrublands have evolved a set of regeneration strategies in response to periodic, high intensity wildfires: obligate seeding (OS), obligate resprouting (OR), and facultative seeding (FS) species. In the North American MCR, data on their spatial and temporal variability is currently lacking, which is a significant information gap for resource managers. We developed a multinomial model using dynamic and static variables to predict the distribution of the three shrub post-fire regeneration strategies, plus trees and herbs, in southern California. Cross-validation showed 50% of the predicted values for each of the five plant groups were within 8–24 percent of the actual value. We assessed variation in shrub regeneration strategies in three ways. First, we found the three major shrub community types (mixed chaparral, chamise-redshank chaparral, and coastal sage scrub) had proportionally greater biomass of FS (37–43% of total biomass) than OR or OS. Second, we assessed the spatial variability using (a) moisture availability (climatic water deficit and solar radiation) and found FS accounted for an increasingly greater proportion of total aboveground live biomass as water became limited, while OR biomass decreased; and (b) ecosystem productivity (NDVI) which showed the proportion of OS, OR, and tree biomass increased with productivity (with a corresponding dramatic decrease in herb biomass). We also assessed temporal variability using time since fire and found OS represented an initially small proportion of total biomass immediately post-fire (8–10%) which increased with time since fire (13–17%). Third, spatial outputs from the multinomial model indicated FS dominated pixels were most widely distributed across the study area (~3.4 million ha, 71%), compared to OR and OS covering 5% each. FS also occurred more frequently on warmer, south facing slopes and summits whereas OR preferred cooler, north facing slopes and valleys (p &amp;lt; 0.0001). Better understanding the distribution of OS, OR, and FS shrubs is important for resource management, including quantifying shrubland carbon storage and identifying areas for post-fire restoration, as described in a case study of the Bobcat Fire on the Angeles National Forest.

A Drone-Powered Deep Learning Methodology for High Precision Remote Sensing in California’s Coastal Shrubs

Wildland conservation efforts require accurate maps of plant species distribution across large spatial scales. High-resolution species mapping is difficult in diverse, dense plant communities, where extensive ground-based surveys are labor-intensive and risk damaging sensitive flora. High-resolution satellite imagery is available at scales needed for plant community conservation across large areas, but can be cost prohibitive and lack resolution to identify species. Deep learning analysis of drone-based imagery can aid in accurate classification of plant species in these communities across large regions. This study assessed whether drone-based imagery and deep learning modeling approaches could be used to map species in complex chaparral, coastal sage scrub, and oak woodland communities. We tested the effectiveness of random forest, support vector machine, and convolutional neural network (CNN) coupled with object-based image analysis (OBIA) for mapping in diverse shrublands. Our CNN + OBIA approach outperformed random forest and support vector machine methods to accurately identify tree and shrub species, vegetation gaps, and communities, even distinguishing two congeneric shrub species with similar morphological characteristics. Similar accuracies were attained when applied to neighboring sites. This work is key to the accurate species identification and large scale mapping needed for conservation research and monitoring in chaparral and other wildland plant communities. Uncertainty in model application is associated with less common species and intermixed canopies.

An Illusion of Barriers to Gene Flow in Suburban Coyotes (Canis latrans): Spatial and Temporal Population Structure across a Fragmented Landscape in Southern California

Carnivores with large home ranges are especially vulnerable to habitat fragmentation. As coyotes (Canis latrans) are often found living in highly modified landscapes, it is unclear how urban and suburban development impact gene flow between their populations. This study evaluated gene flow among coyotes inhabiting California sage scrub fragments within the highly developed Pomona Valley, California. We genotyped microsatellites from scat samples collected from four study sites to examine population structure between coyotes separated by a major freeway, coyotes separated by suburban development, and finally, coyotes in contiguous, natural habitat sites over 15 months. Though coyotes from all four sites were genetically distinct, near-complete turnover of individuals in sites and examination of temporal genetic structure and relatedness within one site indicated the movement of family groups through natural fragments over time. Thus, we argue that solely examining spatial genetic structure may create the illusion of genetic barriers among coyote populations where they may not exist, and that incorporating temporal components of genetic variation is critical to understanding gene flow across space and time in highly mobile animals. Understanding how to better study and manage coyotes, an apex predator, is key to the conservation of the endangered California sage scrub ecosystem.

Three-way species interactions reverse the positive pairwise effects of two natives on an exotic invader

The disruptive effects of tertiary species on otherwise positive pairwise species interactions (e.g. context-dependent parasitism in pollinator syndromes) is well-known. However, few—if any—studies have investigated how invasive plants affect interactions between facilitative plants and their native plant communities. Further, if tertiary invasive species can change interactions among native species from positive to negative, then a tertiary native should be capable of the same phenom for pairwise interactions between natives and invasives. Our previous research indicates invasive black mustard (Brassica nigra) changes interaction signs for otherwise positive species interactions between the dominant, native facilitator California buckwheat (Eriogonum fasciculatum) and its co-dominant beneficiary California sagebrush (Artemisia californica) in semi-arid California coastal sage scrub habitat. Here, E. fasciculatum and A. californica seedlings increased B. nigra shoot growth in pairwise species interactions in the greenhouse. However, in three-way species interactions, E. fasciculatum and A. californica together reduced B. nigra SLA, height, and reproductive potential while not increasing shoot DW. In three-way species interactions, B. nigra did not significantly reduce E. fasciculatum facilitation of A. californica. Also surprisingly, light competition with B. nigra resulted in an increase in A. californica height, which reduced the negative effects of A. californica light competition on shade-intolerant E. fasciculatum. In an additive field experiment, A. californica protected E. fasciculatum from facilitating germination and growth of B. nigra when water competition was minimized. Taken together, this study demonstrates the importance of studying species interactions between competitive, native perennials in the current ecological context of invaded ecosystems.

Effects of Mustard Invasions on Soil Microbial Abundances and Fungal Assemblages in Southern California

Although mustards (family, Brassicaceae) are common across southern California, research has not focused on the effects of type-conversion of native California sage scrub (CSS) to areas dominated by invasive mustards. To better understand how mustard invasions, primarily the short-pod mustard, Hirschfeldia incana, impact soil microbial assemblages, we examined microbial abundance and assemblages from intact CSS and adjacent mustard-dominated soils at three sites. We also explored if germination rates for various plant species differed between CSS and mustard soils. We found that mustard invasions reduce soil microbial abundances by more than 50% and alter soil fungal assemblages. Fungal richness, diversity, and evenness did not differ between habitats, highlighting that these habitats harbor unique microbial assemblages. While mustard allelopathy is predicted to be the primary driver of these changes, mustard invasions also increased soil pH. Although functional consequences of these shifts are unknown, low mustard germination in CSS soils supports biological resistance to mustard invasion in CSS. Overall, our results demonstrate that mustard invasions, H. incana in particular, exert a strong selecting force on soil microbial assemblages, which can influence effective CSS restoration and preservation of ecosystem services.