The Ecology and Management of Annual Rangelands Series is a 9-part online publication that provides owners and leasees of California rangelands with a comprehensive source of information pertinent to the management and enjoyment of these lands. This information will help you formulate and implement strategies for achieving your personal goals as a landowner.

California has some of the most productive croplands in the world. Recently, increasing conflicts among urban development, intensive agriculture, and protectionism have led to increasingly rigid distinctions among resource management objectives. Having a long-term perspective on the causes and interpretation of changes in the landscape can aid in resolving conflicting goals and objectives among stakeholders.

Riparian areas in arid rangelands provide a wide range of ecosystem services and are critical areas for conservation of landscape and regional biological diversity. Creeks and their associated riparian habitats also provide unique resources for livestock management, however these systems have proven to be sensitive to disturbance from livestock. Ecological site concepts and associated state-and-transition models are useful tools for understanding rangeland plant succession and the relative influence of management actions. These models have been widely developed for upland rangeland systems; however, extension of these models to rangeland riparian systems is still in its infancy. In this study I classified two ecological sites along four streams on the Tejon Ranch in the southern San Joaquin Valley, California. Using vegetation data gathered over four years at fifteen study reaches I identified three distinct vegetation states and plausible conditions precipitating transitions between states. I monitored large mammal and herpetofauna activity at each of the study reaches and compared the predictive power of the categorical ecological site and state-and-transition models in predicting wildlife activity to models based on continuous environmental variables. Finally I investigated the role of cattle and feral pig management on riparian vegetation and wildlife. Ecological sites proved to be a good predictor of observed wildlife community assemblages and was included in top models predicting activity of three of five mammal species: bobcat (Lynx rufus) deer (Odocoileus hemionus) and feral pig (Sus scrofa); and two of three reptile species: western fence lizard (Sceloporus occidentalis) and Gilbert’s skink (Plestiodon gilberti). In contrast, vegetation states proved to be a poor predictor compared to continuous variables. Cattle and feral pigs appear to have played a role in the one observed vegetation transition, and cattle and feral pig activity was correlated with increased cover of hydrophyllic vegetation and bare soil, and decreased cover of upland vegetation and forbs. Summer cattle activity and spring pig activity were the most strongly correlated with changes in vegetation attributes. Results from this study illustrate the utility of ecological sites to model riparian vegetation change and provide a framework for understanding the effect of rangeland management on riparian vegetation and wildlife.

Grasslands in California's inland Mediterranean climate zone vary greatly over time and space, largely due to fluctuating rainfall and heterogeneous geology, topography, and soils. In light of a dramatic invasion of exotic species into these grasslands, conservation management goals typically include the preservation and enhancement of native vegetation. Developing specific management targets to achieve these goals, however, is complicated by uncertainty about pre-invasion conditions and the spatial and temporal complexity of the system.

The Tejon Ranch, the largest, contiguous, privately-owned property in the state, supports 44,000 ha of California's inland Mediterranean grassland. The mission of the Tejon Ranch Conservancy (Conservancy) is to preserve, enhance, and restore the native biodiversity of Tejon Ranch. In 2009, the Conservancy partnered with the University of California Range Ecology Lab led by James Bartolome to describe the grasslands on the ranch, in order to build the understanding required for management planning. As a doctoral researcher and co-leader of the study from 2010 to 2014, my objective was to develop a scientific framework to inform reliable predictions about the distribution of plant species over space and time in the ranch's grasslands. I investigated three basic questions:

1. Does species composition correlate with geologic, topographic, and edaphic landscape composition, at differing spatial scales?

2. What are the drivers of inter-annual community change at the ecological site scale?

3. What are the alternative states of the ecological sites?

Chapter 1 is a description of how I investigated the first question in the western Mojave Desert landscape of the ranch. I collected topographic, edaphic, and ground cover data at 35 small (0.25 m2) plots across a 64 km2 (6.4 x 107 m2) extent in the spring of 2010. Fortuitously, the timing and amount of rainfall in 2009-2010 resulted in high diversity and abundance of native annual forbs and grasses across the landscape. I encountered 46 species; all were annuals except for three perennial bunchgrass species in 9 plots. I found that elevation, soil cation exchange capacity, soil silt percentage, and soil total nitrogen explained 40% of the spatial variation of the 25 species encountered at more than one plot. I identified nine distinct species assemblages, four with plant cover dominated by native annual species, and five with plant cover dominated by exotic annual species. The five exotic assemblages were constrained to two geographic areas of the landscape. Both areas contained sediments from degraded dolomitic roof pendants of the Tehachapi Mountains and featured soils high in clay and nitrogen. I hypothesized that atmospheric nitrogen deposition is preferentially increasing soil nitrogen in these zones, promoting persistent exotic species dominance there. Overall, results suggested that species composition did in fact correlate with landscape composition, as perceived at the scales of geology type and landform, and measured at the smaller scale of the plot. I conclude by recommending that restoration management planning incorporate considerations of biogeochemical nitrogen cycling.

In Chapter 2, I explain how the Range Ecology Lab and Tejon Ranch Conservancy investigated my first and second research questions in the San Joaquin Valley landscape of Tejon Ranch. Using thirty-five 3024 m2 study plots across a 294 km2 extent, we discovered that species distribution was more strongly correlated with geology, slope, and elevation than with USDA Major Land Resource Area or soil map unit. Accordingly, we used geology, slope class, and elevation class to divide the grasslands into 52 ecological sites (with 14 ecological sites representing physical conditions of 85% of the grassland area). With a focus on four geographically extensive ecological sites, I demonstrate how we verified the accuracy of our ecological site model, identified community types (i.e., community phases) at the ecological sites, and determined the drivers of community phase shifts between years at the ecological sites (i.e., community pathways). The Pleistocene terraces and Mafic bedrock slopes ecological sites each supported a single community phase in all three years. In contrast, at both the Holocene flats and the Miocene hills ecological sites, phase shifts were observed from 2010 to 2011, and again from 2011 to 2012. These inter-annual shifts in community phases were driven more strongly by variation in rainfall than by rodent bioturbation or livestock grazing. At both ecological sites, October and November rainfall exceeding 2 cm was a prerequisite for community phases dominated by exotic annual grasses, whereas less precipitation in those months promoted community phases with a higher relative abundance of native annual forbs. A concurrent wildlife study on the Holocene flats ecological site revealed that community phases with dense exotic annual grasses are unsuitable for a suite of special-status vertebrates. The Conservancy is using fall rainfall exceeding 2 cm as a cue to suppress exotic annual grass biomass using cattle grazing, in order to enhance conditions for native annual forbs and wildlife. This management prescription would not have been possible without organizing the landscape into ecological sites and tracking the grassland community on those ecological sites across multiple years.

In Chapter 3 I describe how we explored my third research question. We used state-and-transition models to catalogue our understanding about historical and contemporary states at the four focal ecological sites in the San Joaquin Valley landscape of Tejon Ranch. Landscape reconnaissance revealed that all but the Pleistocene terraces currently support an alternative state in addition to the herbaceous state measured in 2010-2012 - one with greater relative cover of perennial grasses, shrubs, and/or oaks. Using soil phytoliths and historical accounts, we developed hypotheses about historical states (circa 1772) for the four ecological sites. We propose that the Holocene flats ecological site likely supported a native forbland with an open canopy of Atriplex sp., the Mafic bedrock slopes ecological site likely supported a forbland-oak savanna matrix, and the Pleistocene terraces and Miocene hills ecological sites likely supported grasslands dominated by perennial grasses. Using the state-and-transition models as guides, I describe potential restoration management for each ecological site. The Conservancy is currently spending limited restoration funds to enhance conditions for native annual forbs and wildlife in the current annual grassland state of the Holocene flats. However, significant recovery of native biodiversity appears possible on the Pleistocene terraces and Mafic bedrock slopes ecological sites, if the Conservancy elects to spend the time and money required to cross the thresholds from the current annual grassland states to alternative states on those ecological sites.

Invasive species pose a threat to the persistence of the sensitive endemic biotic communities on oceanic islands. The direct ecological, social and economic effects of invasions have been well documented and can be significant on both islands and continents. The indirect effects on the interactions between species has received less attention despite being of critical importance to the long term stability of ecosystems facing multiple threats from anthropogenic impacts. In this dissertation, I examined how seed dispersal relationships are modified by the presence of multiple introduced species on the islands of Tahiti and Moorea in the Society archipelago of French Polynesia. Additionally, I evaluated the risks associated with one of my research methods; the use of mist nets to capture wild birds.

I first evaluated how the local abundance of the invasive Miconia calvescens modifies seed dispersal relationships between birds and plants. The species is an invasive fruit-bearing tree that currently covers much of the island of Tahiti and is present at much lower densities on Moorea. I found that while the overall size of networks was similar across sites, networks on the highly invaded island of Tahiti were less diverse and less even because birds concentrated a greater proportion of their foraging on Miconia calvescens. There were fewer links between birds and native plants at highly invaded sites where birds switched their diets away from a broader range of fruit and insects. The endemic Grey-green Fruit Dove (Ptilinopus purpuratus) consumed native fruit in larger quantities and more total species than two introduced frugivores. This study demonstrates that the impacts of invasive fruit-bearing plants on seed dispersal networks depends in part on their abundance, and are likely to increase as a species becomes increasingly dominant in a community. Additionally, the dispersal of native plants continues to depend heavily on the single extant native fruit dove on these islands despite the presence of multiple introduced frugivores.

The impact of invasive plants on seed dispersal networks is the result of the cumulative effects of foraging decisions by birds. The available evidence suggests that birds choose which fruit to consume based on the complementarity between fruit traits and their own preferences as well as the relative abundance of fruit in a community. I used fruit choice experiments with captive Red-vented Bulbuls (Pycnonotus cafer) to uncouple fruit preferences from the effects of abundance to determine which operates more strongly on foraging decisions in birds. Birds showed both reliable and consistent preferences for some fruits over others and a strong response to abundance. However, when included simultaneously in the same experiment, the patterns of preference remained intact while the effect of abundance disappeared. Taken together, experimental and field data suggest that foraging decisions are highly context-dependent, and neutral models that consider only the relative abundance of fruit in the community are unlikely to provide reliable predictions about how seed dispersal networks will change in response to invasion.

In the final study of my thesis, I evaluated the risks associated with one of my primary research methods; the use of mist nets to capture birds. Mist nets are used widely for monitoring avian populations. While the method is assumed to be safe, very few studies have addressed how frequently injuries and mortalities occur, and no large-scale comprehensive evaluation has been conducted to determine the associated risks. In collaboration with several banding organizations, I quantified the rates of mortality and injury at 22 banding organizations in the United States and Canada and used capture data from five organizations to determine what kinds of incidents occur most frequently. I compiled a dataset including nearly 350,000 records of capture over a 22 year period and evaluated what makes birds most at risk to incident. I found that the risks varied among species and factors such as body mass and the number of previous captures were related to the probability of an incident. Additionally, I found that birds that were released back into the wild after an injury were recaptured at similar rates compared to birds that were released without an injury, indicating that injured birds survived in similar numbers as those released uninjured. This study fills a gap by providing the first comprehensive evaluation of the risks associated with mist netting and concludes that while overall risks are low, species and traits can predict a bird's susceptibility to incident. These results can be useful for organizations that use mist netting, and should be incorporated into protocols aimed at minimizing injury and mortality. Finally, I emphasize that projects using mist nets should monitor their performance and compare their results to those of other organizations.

I conclude that the indirect effect of species invasions are variable and depend in part on the abundance of the invasive species. Thus, consequences for seed dispersal networks are likely to be most pronounced at the highest levels of invasion. Despite the effects of abundance, birds also showed strong preferences for certain kinds of fruits. Thus, the integration of novel fruit into native seed dispersal networks is likely to depend not only on the relative abundance of fruit but also on the preferences for each fruit relative to others that are available. The Grey-green Fruit Dove is the sole disperser for several native plants, and the maintenance of viable populations of these plants is likely to depend on conservation of this protected and sensitive endemic species. Similarly, it is likely that the Fruit Dove also depends on native plants despite the integration of many exotic fruit into its diet. There is an urgent need for more research evaluating the habitat requirements and population dynamics of this frugivore in order to ensure the long term persistence of the species.

Maintaining and enhancing soil organic carbon storage can mitigate climate change while promoting forage growth. California has adopted incentive programs to promote rangeland practices that build soil organic carbon. However, there is no standard framework for assessing the baseline level of soil organic carbon at the ranch scale. Here, we use the Ecological Site Description — a land-type classification system — to help ranch managers set priorities about where to implement practices to increase soil organic carbon. We measured baseline carbon stocks at 0 to 15 and 15 to 30 centimeters' depth across three ecological sites and two vegetation states (shrubland and grassland) at Tejon Ranch, California. We discovered increased levels of soil carbon at ecological sites in higher elevations, and more soil carbon in shrublands as compared to grasslands. Slope, elevation, and soil texture, as well as plant litter and shrub cover, were significant predictors of soil carbon. The Ecological Site Description framework can serve as an important tool to help range managers keep carbon in the soil and out of the atmosphere.

A study was conducted to estimate the retention efficiency of vegetative buffers for Escherichia coli deposited on grasslands in cattle fecal deposits and subject to natural rainfall-runoff conditions. The study was conducted on annual grasslands in California's northern Sierra Nevada foothills, a region with a distinct wet–dry season Mediterranean climate. We used 48, 2.0- by 3.0-m runoff plots to examine the efficacy of 0.1-, 1.1-, and 2.1-m buffers at three land slopes (5, 20, and 35%) and four dry vegetation matter levels (225, 560, 900, and 4500 kg/ha) across 27 rainfall-runoff events during two rainfall seasons. Buffer width treatments were implemented by placement of cattle fecal material containing known loads of E. coli 0.1, 1.1, or 2.1 m upslope of the plot runoff collector. Mean total runoff to total rainfall ratio per plot ranged from 0.014:1 to 0.019:1 and reflected the high infiltration capacity of these soils. Approximately 94.8 to 99.995% of total E. coli load applied to each plot appears to be either retained in the fecal pat and/or attenuated within 0.1 m downslope of the fecal pat, irrespective of the presence of a wider vegetated buffer. Relative to a 0.1-m buffer, we found 0.3 to 3.1 log10 reduction in E. coli discharge per additional meter of vegetative buffer across the range of residual dry vegetation matter levels, land slope, and rainfall and runoff conditions experienced during this project. Buffer efficiency was significantly reduced as runoff increased. These results support the assertion that grassland buffers are an effective method for reducing animal agricultural inputs of waterborne E. coli into surface waters.

Several historical data sets from the UC Hopland Research and Extension Center (HREC) provide valuable information on vegetation dynamics at multiple spatial and temporal scales. An early botanical survey by Harold Heady and Al Murphy provides a baseline for examining landscape-level changes in species richness and distribution over 50 years. We conducted a floristic survey between 1995 and 1999 and found gains and losses of native and non-native species abundance across the field station. On two sites where sheep were removed in 1958, permanent transects provide valuable information about plant community responses to protection from livestock grazing; in the oak understory, native perennial blue wildrye increased steadily, while in grasslands native purple needlegrass was less abundant after 43 years. On a cleared watershed, originally diverse in hardwood species, we found that only interior live oak and coast live oak were significantly reestablished after 30 years.