Grassland restoration in a world of change—including nitrogen deposition and invasion—requires solutions that can be sustained and effective in the face of novel drivers. This challenge is amplified in systems characterized by high spatiotemporal variability, as management to address novel drivers may affect a system differently across its range of variability. California serpentine grasslands epitomize this challenge: they host a high diversity of native species, are characterized by temporal and spatial variability, and are experiencing atmospheric nitrogen deposition that leads to a conversion from native annual forbs to non‐native annual grasses. Here, we test the interactive effects of grazing and fire to restore native serpentine species following annual grass invasion and litter accumulation. We assess management outcomes (burned‐grazed, burned‐ungrazed, and unburned‐ungrazed) using a long‐term (2004–2012) monitoring dataset. A 2004 wildfire led to a reduction in annual grasses and a transient increase in native species (forb) richness. In 2008, cattle grazing was reintroduced and crossed with the burn legacy, which sustained post‐fire diversity and eventually led to native recovery in unburned areas, with a caveat that a period of high precipitation promoted the growth of annual grasses. Our study indicates that short‐term management, such as fire, can promote native forb recovery in invaded serpentine grassland communities, but that ongoing treatments like grazing are necessary to maintain restoration outcomes. We speculate that this recovery may be due to the presence of a robust native seed bank, which may persist despite a period of annual grass conversion.

Monarch butterflies (Danaus plexippus) are in steep decline and threatened by loss of breeding habitat, loss of wintering habitat, pesticide use, and climate change (Pelton et al. 2019;Schultz et al. 2017).The population that winters along the coast of California has declined 97% since the 1980s (Pelton et al. 2019) andSchultz et al. (2017) conclude that this population, or at least the overwintering phenomenon, is at a high risk of extinction within 50 years.Factors associated with this decline include land use most strongly, encompassing increasing use of pesticides (e.g., glyphosate herbicide and neonicotinoid insecticides) and coastal development, and then less so climate, which remains a looming threat (Crone et al. 2019;Espeset et al. 2016).Historically, the largest threat to overwintering groves was development (Lane 1981(Lane [1984]]) but recent analysis of overwintering survival (Pelton et al. 2019) suggests that grove quality itself is also in decline through senescence (Pelton et al. 2016).Protecting and managing wintering habitat is a top conservation priority (Pelton et al. 2019; Western Monarch Working Group 2018).Preferred winter roosting habitat for monarchs in California is made up of groves of trees that provide particular microclimatic conditions that protect the butterflies from winter storms (Leong 2016;Leong et al. 1991;Weiss et al. 1991).Overwintering groves can provide suitable microclimates with different tree densities, species composition, and topography (Leong et al. 2004), but essential features, including a windbreak to protect against winter storms and a range of sunlight from full to filtered to shaded, must be present (Leong 1990).At nearly every overwintering site on the current landscape, those conditions are created by exotic trees, and in particular by eucalyptus species (Bell et al.

mospheric nitrogen deposits are overloading the ability of plant species to live and thrive. Bringing the complex and underestimated link between nitrogen and biodiversity to light is necessary to start restoration projects.

Great Basin bristlecone pine (Pinus longaeva) and foxtail pine (Pinus balfouriana) are valuable paleoclimate resources due to their longevity and climatic sensitivity of their annually-resolved rings. Treeline research has shown that growing season temperatures limit tree growth at and just below the upper treeline. In the Great Basin, the presence of precisely dated remnant wood above modern treeline shows that the treeline ecotone shifts at centennial timescales tracking long-term changes in climate; in some areas during the Holocene climatic optimum treeline was 100 meters higher than at present. Regional treeline position models built exclusively from climate data may identify characteristics specific to Great Basin treelines and inform future physiological studies, providing a measure of climate sensitivity specific to bristlecone and foxtail pine treelines. This study implements a topoclimatic analysis-using topographic variables to explain patterns in surface temperatures across diverse mountainous terrain-to model the treeline position of three semi-arid bristlecone and/or foxtail pine treelines in the Great Basin as a function of growing season length and mean temperature calculated from in situ measurements. Results indicate: (1) the treeline sites used in this study are similar to other treelines globally, and require a growing season length of between 147-153 days and average temperature ranging from 5.5 degrees C-7.2 degrees C, (2) site-specific treeline position models may be improved through topoclimatic analysis and (3) treeline position in the Great Basin is likely out of equilibrium with the current climate, indicating a possible future upslope shift in treeline position.

Tree rings have long been used to make inferences about the environmental factors that influence tree growth. Great Basin bristlecone pine is a long-lived species and valuable dendroclimatic resource, but often with mixed growth signals; in many cases, not all trees at one location are limited by the same environmental variable. Past work has identified an elevational threshold below the upper treeline above which trees are limited by temperature, and below which trees tend to be moisture limited. This study identifies a similar threshold in terms of temperature instead of elevation through fine-scale topoclimatic modeling, which uses a suite of topographic and temperature-sensor data to predict temperatures across landscapes. We sampled trees near the upper limit of growth at four high-elevation locations in the Great Basin region, USA, and used cluster analysis to find dual-signal patterns in radial growth. We observed dual-signal patterns in ring widths at two of those sites, with the signals mimicking temperature and precipitation patterns. Trees in temperature-sensitive clusters grew in colder areas, while moisture-sensitive cluster trees grew in warmer areas. We found thresholds between temperature- and moisture-sensitivity ranging from 7.4 degrees C to 8 degrees C growing season mean temperature. Our findings allow for a better physiological understanding of bristlecone pine growth, and seek to improve the accuracy of climate reconstructions.

We provide updated spatial distribution and inventory data for on-road NH3 emissions for the continental United States (U.S.) On-road NH3 emissions were determined from on-road CO2 emissions data and empirical NH3:CO2 vehicle emissions ratios. Emissions of NH3 from on-road sources in urbanized regions are typically 0.1–1.3tkm−2yr−1 while NH3 emissions in agricultural regions generally range from 0.4–5.5tkm−2yr−1, with a few hotspots as high as 5.5–11.2tkm−2yr−1. Counties with higher vehicle NH3 emissions than from agriculture include 40% of the U.S. population. The amount of wet inorganic N deposition as NH4+ from the National Atmospheric Deposition Program (NADP) network ranged from 37 to 83% with a mean of 58.7%. Only 4% of the NADP sites across the U.S. had <45% of the N deposition as NH4+ based on data from 2014 to 2016, illustrating the near-universal elevated proportions of NH4+ in deposition across the U.S. Case studies of on-road NH3 emissions in relation to N deposition include four urban sites in Oregon and Washington where the average NH4-N:NO3-N ratio in bulk deposition was 2.3. At urban sites in the greater Los Angeles Basin, bulk deposition of NH4-N and NO3-N were equivalent, while NH4-N:NO3-N in throughfall under shrubs ranged from 0.6 to 1.7. The NH4-N:NO3-N ratio at 7–10 sites in the Lake Tahoe Basin averaged 1.4 and 1.6 in bulk deposition and throughfall, and deposition of NH4-N was strongly correlated with summertime NH3 concentrations. On-road emissions of NH3 should not be ignored as an important source of atmospheric NH3, as a major contributor to particulate air pollution, and as a driver of N deposition in urban and urban-affected regions.

Nitrogen (N) pollution is increasingly recognized as a threat to biodiversity. However, our understanding of how N is affecting vulnerable species across taxa and broad spatial scales is limited. We surveyed approximately 1400 species in the continental United States listed as candidate,. threatened, or endangered under the US Endangered Species Act (ESA) to assess the extent of recognized N-pollution effects on biodiversity in both terrestrial and aquatic ecosystems. We found 78 federally listed species recognized as affected by N pollution. To illustrate the complexity of tracing N impacts on listed species, we describe an interdisciplinary case study that addressed the threat of N pollution to California Bay Area serpentine grasslands. We demonstrate that N pollution has affected threatened species via multiple pathways and argue that existing legal and policy regulations can be applied to address the biodiversity consequences of N pollution in conjunction with scientific evidence tracing N impact pathways.

Climate change is raising challenging concerns for systematic conservation planning. Are methods based on the current spatial patterns of biodiversity effective given long‐term climate change? Some conservation scientists argue that planning should focus on protecting the abiotic diversity in the landscape, which drives patterns of biological diversity, rather than focusing on the distribution of focal species, which shift in response to climate change. Climate is one important abiotic driver of biodiversity patterns, as different climates host different biological communities and genetic pools. We propose conservation networks that capture the full range of climatic diversity in a region will improve the resilience of biotic communities to climate change compared to networks that do not. In this study we used historical and future hydro‐climate projections from the high resolution Basin Characterization Model to explore the utility of directly targeting climatic diversity in planning. Using the spatial planning tool, Marxan, we designed conservation networks to capture the diversity of climate types, at the regional and sub‐regional scale, and compared them to networks we designed to capture the diversity of vegetation types. By focusing on the Conservation Lands Network (CLN) of the San Francisco Bay Area as a real‐world case study, we compared the potential resilience of networks by examining two factors: the range of climate space captured, and climatic stability to 18 future climates, reflecting different emission scenarios and global climate models. We found that the climate‐based network planned at the sub‐regional scale captured a greater range of climate space and showed higher climatic stability than the vegetation and regional based‐networks. At the same time, differences among network scenarios are small relative to the variance in climate stability across global climate models. Across different projected futures, topographically heterogeneous areas consistently show greater climate stability than homogenous areas. The analysis suggests that utilizing high‐resolution climate and hydrological data in conservation planning improves the likely resilience of biodiversity to climate change. We used these analyses to suggest new conservation priorities for the San Francisco Bay Area.

Most conservation planning to date has focused on protecting today's biodiversity with the assumption that it will be tomorrow's biodiversity. However, modern climate change has already resulted in distributional shifts of some species and is projected to result in many more shifts in the coming decades. As species redistribute and biotic communities reorganize, conservation plans based on current patterns of biodiversity may fail to adequately protect species in the future. One approach for addressing this issue is to focus on conserving a range of abiotic conditions in the conservation-planning process. By doing so, it may be possible to conserve an abiotically diverse "stage" upon which evolution will play out and support many actors (biodiversity). We reviewed the fundamental underpinnings of the concept of conserving the abiotic stage, starting with the early observations of von Humboldt, who mapped the concordance of abiotic conditions and vegetation, and progressing to the concept of the ecological niche. We discuss challenges posed by issues of spatial and temporal scale, the role of biotic drivers of species distributions, and latitudinal and topographic variation in relationships between climate and landform. For example, abiotic conditions are not static, but change through time-albeit at different and often relatively slow rates. In some places, biotic interactions play a substantial role in structuring patterns of biodiversity, meaning that patterns of biodiversity may be less tightly linked to the abiotic stage. Furthermore, abiotic drivers of biodiversity can change with latitude and topographic position, meaning that the abiotic stage may need to be defined differently in different places. We conclude that protecting a diversity of abiotic conditions will likely best conserve biodiversity into the future in places where abiotic drivers of species distributions are strong relative to biotic drivers, where the diversity of abiotic settings will be conserved through time, and where connectivity allows for movement among areas providing different abiotic conditions.

Changes in climate projected for the 21st century are expected to trigger widespread and pervasive biotic impacts. Forecasting these changes and their implications for ecosystem services is a major research goal. Much of the research on biotic responses to climate change has focused on either projected shifts in individual species distributions or broad-scale changes in biome distributions. Here, we introduce a novel application of multinomial logistic regression as a powerful approach to model vegetation distributions and potential responses to 21st century climate change. We modeled the distribution of 22 major vegetation types, most defined by a single dominant woody species, across the San Francisco Bay Area. Predictor variables included climate and topographic variables. The novel aspect of our model is the output: a vector of relative probabilities for each vegetation type in each location within the study domain. The model was then projected for 54 future climate scenarios, spanning a representative range of temperature and precipitation projections from the CMIP3 and CMIP5 ensembles. We found that sensitivity of vegetation to climate change is highly heterogeneous across the region. Surprisingly, sensitivity to climate change is higher closer to the coast, on lower insolation, north-facing slopes and in areas of higher precipitation. While such sites may provide refugia for mesic and cool-adapted vegetation in the face of a warming climate, the model suggests they will still be highly dynamic and relatively sensitive to climate-driven vegetation transitions. The greater sensitivity of moist and low insolation sites is an unexpected outcome that challenges views on the location and stability of climate refugia. Projections provide a foundation for conservation planning and land management, and highlight the need for a greater understanding of the mechanisms and time scales of potential climate-driven vegetation transitions.

This paper presents the use of soil charcoal analyses in order to identify the origin of a Nardus stricta grassland in a mountain system (Mont Lozère, France), and the use of environmental resources and the construction of a cultural landscape. Two opposing theories have been proposed to explain the origin of this open landscape (1450–1700 m altitude): natural or anthropogenic. The identification and radiocarbon dates of charcoal fragments of Fagus sylvatica, which were found in all of the pits located in the current grassland area and dated to 3695–3633 cal BC, demonstrate that this species has been present on the upper part of Mont Lozère since the Middle Neolithic. In addition, the presence of pioneer species (Betula, Salix, Corylus avellana), as well as mid- (Prunus cf avium) and late-successional species (F. sylvatica) supports the hypothesis that the grassland contained both pioneer and mature phases of forest landscapes. The 14C dates, ranging from c. 4200 cal BC to 1200 cal AD, show that fire events occurred with different climatic influences. Fire events may correspond to one or several fires in a short period at the scale of the slope. Moreover, the dates coincide with the early and extensive human impact detected in the Massif Central and Mont Lozère. To explain the regular occurrences of fire events from the Middle Neolithic to the Central Middle Ages, agro-pastoral clearings have been postulated, as have been identified in other areas in the Pyrenees and in the Alps. Such human impact may have been magnified, or least facilitated, by climatic conditions. Comparison with additional data (pollen, archaeology, ecology) demonstrates that this grassland area is not natural and corresponds to an ancient forested system that has been used and transformed by societies since the Neolithic, although climate change may have certainly affected this transformation. The aim of this research is to promote this cultural heritage in collaboration with the National Park of the Cévennes in order to protect its future.

We sought to identify appropriate treatments to restore a small, urban patch of habitat for the endangered Clarkia franciscana (Presidio clarkia) in serpentine grassland. Goals included identifying effective and pragmatic treatments for introducing disturbance to the site and determining whether treatments used to establish Presidio clarkia would be appropriate in areas already occupied by this endangered serpentine endemic. This experiment tested fall burning, fall flaming, fall mowing with thatch reduction, fall scraping, fall tarping, spring burning, and spring mowing with and without thatch reduction. Half of all treated plots were seeded with clarkia. Clarkia density and vegetation composition were measured one and two years after treatment. Fall scraping, fall tarping, and fall flaming stood out as the most effective methods for increasing density. Fall scraping and fall flaming enhanced clarkia populations in unseeded plots where clarkia was initially present. In Year 1, these three treatments were also most successful in reducing annual grass cover and decreasing nonnative plant cover. Although other studies have shown spring treatments to be useful for reducing annual grass and thatch, and increasing native forbs, this study found that treating in late fall, after annual grasses had germinated, was critical for this site – and not, as was previously presumed, harmful to the clarkia.