James H. Thorne

Compounded effects of climate change and habitat alteration shift patterns of butterfly diversity.

Climate change and habitat destruction have been linked to global declines in vertebrate biodiversity, including mammals, amphibians, birds, and fishes. However, invertebrates make up the vast majority of global species richness, and the combined effects of climate change and land use on invertebrates remain poorly understood. Here we present 35 years of data on 159 species of butterflies from 10 sites along an elevational gradient spanning 0–2,775 m in a biodiversity hotspot, the Sierra Nevada Mountains of Northern California. Species richness has declined at half of the sites, with the most severe reductions at the lowest elevations, where habitat destruction is greatest. At higher elevations, we observed clear upward shifts in the elevational ranges of species, consistent with the influence of global warming. Taken together, these long-term data reveal the interacting negative effects of human-induced changes on both the climate and habitat available to butterfly species in California. Furthermore, the decline of ruderal, disturbance-associated species indicates that the traditional focus of conservation efforts on more specialized and less dispersive species should be broadened to include entire faunas when estimating and predicting the effects of pervasive stressors.

Modeling plant ranges over 75 years of climate change in California, USA: temporal transferability and species traits

Species distribution model (SDM) projections under future climate scenarios are increasingly being used to inform resource management and conservation strategies. A critical assumption for projecting climate change responses is that SDMs are transferable through time, an assumption that is largely untested because investigators often lack temporally independent data for assessing transferability. Further, understanding how the ecology of species influences temporal transferability is critical yet almost wholly lacking. This raises two questions. (1) Are SDM projections transferable in time? (2) Does temporal transferability relate to species ecological traits? To address these questions we developed SDMs for 133 vascular plant species using data from the mountain ranges of California (USA) from two time periods: the 1930s and the present day. We forecast historical models over 75 years of measured climate change and assessed their projections against current distributions. Similarly, we hindcast contemporary models and compared their projections to historical data. We quantified transferability and related it to species ecological traits including physiognomy, endemism, dispersal capacity, fire adaptation, and commonness. We found that non-endemic species with greater dispersal capacity, intermediate levels of prevalence, and little fire adaptation had higher transferability than endemic species with limited dispersal capacity that rely on fire for reproduction. We demonstrate that variability in model performance was driven principally by differences among species as compared to model algorithms or time period of model calibration. Further, our results suggest that the traits correlated with prediction accuracy in a single time period may not be related to transferability between time periods. Our findings provide a priori guidance for the suitability of SDM as an approach for forecasting climate change responses for certain taxa.

Twentieth-century shifts in forest structure in California: Denser forests, smaller trees, and increased dominance of oaks

Significance Declines in the number of large trees in temperate and tropical forests have attracted attention, given their disproportionate importance to forest structure, function, and carbon storage. Yet, factors responsible for these declines are unclear. By comparing historic (1930s) and contemporary (2000s) surveys of California forests, we document that across 120,000 km2, large trees have declined by up to 50%, corresponding to a 19% decline in average basal area and associated biomass, despite large increases in small tree density. Contemporary forests also exhibit increased dominance by oaks over pines. Both large tree declines and increased oak dominance were associated with increases in climatic water deficit, suggesting that water stress may be contributing to changes in forest structure and function across large areas. We document changes in forest structure between historical (1930s) and contemporary (2000s) surveys of California vegetation through comparisons of tree abundance and size across the state and within several ecoregions. Across California, tree density in forested regions increased by 30% between the two time periods, whereas forest biomass in the same regions declined, as indicated by a 19% reduction in basal area. These changes reflect a demographic shift in forest structure: larger trees (>61 cm diameter at breast height) have declined, whereas smaller trees (<30 cm) have increased. Large tree declines were found in all surveyed regions of California, whereas small tree increases were found in every region except the south and central coast. Large tree declines were more severe in areas experiencing greater increases in climatic water deficit since the 1930s, based on a hydrologic model of water balance for historical climates through the 20th century. Forest composition in California in the last century has also shifted toward increased dominance by oaks relative to pines, a pattern consistent with warming and increased water stress, and also with paleohistoric shifts in vegetation in California over the last 150,000 y.

Fine-scale hydrologic modeling for regional landscape applications: the California Basin Characterization Model development and performance

IntroductionResource managers need spatially explicit models of hydrologic response to changes in key climatic drivers across variable landscape conditions. We demonstrate the utility of a Basin Characterization Model for California (CA-BCM) to integrate high-resolution data on physical watershed characteristics with historical or projected climate data to predict watershed-specific hydrologic responses.MethodsThe CA-BCM applies a monthly regional water-balance model to simulate hydrologic responses to climate at the spatial resolution of a 270-m grid. The model has been calibrated using a total of 159 relatively unimpaired watersheds for the California region.ResultsAs a result of calibration, predicted basin discharge closely matches measured data for validation watersheds. The CA-BCM recharge and runoff estimates, combined with estimates of snowpack and timing of snowmelt, provide a basis for assessing variations in water availability. Another important output variable, climatic water deficit, integrates the combined effects of temperature and rainfall on site-specific soil moisture, a factor that plants may respond to more directly than air temperature and precipitation alone. Model outputs are calculated for each grid cell, allowing results to be summarized for a variety of planning units including hillslopes, watersheds, ecoregions, or political boundaries.ConclusionsThe ability to confidently calculate hydrologic outputs at fine spatial scales provides a new suite of hydrologic predictor variables that can be used for a variety of purposes, such as projections of changes in water availability, environmental demand, or distribution of plants and habitats. Here we present the framework of the CA-BCM model for the California hydrologic region, a test of model performance on 159 watersheds, summary results for the region for the 1981–2010 time period, and changes since the 1951–1980 time period.

Vegetation Change Over Sixty Years In the Central Sierra Nevada, California, USA

Abstract In California, the Vegetation Type Map (VTM) project of the 1930s has provided valuable historical vegetation data. Albert Wieslander led this effort to survey the forests of California in the 1930s. His crews surveyed over 150,000 km2, drawing detailed vegetation maps, taking 3000 photos and 17,000 vegetation plots. We developed a technique to digitize the Placerville 30′ quadrangle VTM, rendering it to a Geographic Information System (GIS). The map covers 2408.8 km2 of the west slope of the Sierra Nevada. In this area VTM crews identified 59 dominant plant species and eight genera or land cover classes and mapped their distribution into 3422 polygons. They identified recently disturbed areas that covered 13.5% of the landscape. We compared the digital VTM quad to CALVEG, a satellite-derived vegetation map from 1996. Land cover change for California Wildlife Habitat Relationship (WHR) vegetation types had occurred on 42.1% of the area. WHR types with the largest gains were: Montane Hardwood, Douglas-Fir, and Annual Grassland. Low elevation hardwoods, particularly Blue Oak Woodland (dominated by Quercus douglasii, Fagaceae), chaparrals and upper elevation conifers were the types that lost the most area. Differences in mapping techniques are unlikely to be the cause of this change because the analysis used controlled for map-based errors. Potential causes of the observed change at these physiognomic levels of classification include human perturbation, succession, and climate change.

A Conservation Design for the Central Coast of California and the Evaluation of Mountain Lion as an Umbrella Species

Abstract Conservation planners use several methods to select conservation target areas. These include the use of umbrella species for large area requirements, site-specific locations of important biodiversity elements, and indications of ecosystem health. We tested the adequacy of using an umbrella species to represent finer-scale biodiversity elements on 45,205 km2 of the central coast of California. A network of core and linkages for mountain lion (Puma concolor [Kerr]) was developed and 22,069 km2, or 49% of the region, was selected. We analyzed network representation of a variety of biodiversity elements. The conservation network contained between 8% and 27% of five different endangered species locations in the region. It captured 77% of mapped serpentine rock, a surrogate for rare plants, 88% of the old-growth redwood (Sequoia sempervirens [(D. Don) Endl.]), 55% of the The Nature Conservancy conservation portfolio areas, a surrogate for biodiversity, a majority of three types of oak woodlands, and 79% of the watersheds with extant steelhead (Oncorhynchus mykiss) populations. The mountain lion network more than proportionally represented most of the biodiversity elements examined. However, endemic amphibian, reptile, and mammal populations were less than proportionally represented, suggesting the need for testing levels of biodiversity representation in conservation designs that are based on carnivore habitat. We discuss implications for conservation plans based on this approach, and the potential synergies of linking aquatic health assessments with terrestrial umbrella species for conservation planning. Finally, we discuss the rankings of cores and corridors in the region.

Spatial scale effects on conservation network design: trade-offs and omissions in regional versus local scale planning

Ecological patterns and processes operate at a variety of spatial scales. Those which are regional in nature may not be effectively captured through the combination of conservation plans derived at the local level, where land use planning frequently takes place. Conversely, regional conservation plans may not identify resources important for conservation of intraregional ecological variation. We compare modeled conservation networks derived at regional and local scales from the same area in order to analyze the impact of scale effects on conservation planning. Using the MARXAN reserve selection algorithm and least cost corridor analysis we identified a potential regional conservation network for the Central Valley ecoregion of California, USA, from which we extracted those portions found within five individual counties. We then conducted the same analysis for each of the five counties. An overlay of the results from the two scales shows a general pattern of large differences in the identified networks. Especially noteworthy are the trade-offs and omissions evident at both scales of analysis and the disparateness of the identified corridors that connect core reserves. The results suggest that planning efforts limited to one scale will neglect biodiversity patterns and ecological processes that are important at other scales. An intersection of results from the two scales can potentially be used to prioritize areas for conservation found to be important at several spatial scales.

Integration of Regional Mitigation Assessment and Conservation Planning

Government agencies that develop infrastructure such as roads, waterworks, and energy delivery often impact natural ecosystems, but they also have unique opportunities to contribute to the conservation of regional natural resources through compensatory mitigation. Infrastructure development requires a planning, funding, and implementation cycle that can frequently take a decade or longer, but biological mitigation is often planned and implemented late in this process, in a project-by-project piecemeal manner. By adopting early regional mitigation needs assessment and planning for habitat-level impacts from multiple infrastructure projects, agencies could secure time needed to proactively integrate these obligations into regional conservation objectives. Such practice can be financially and ecologically beneficial due to economies of scale, and because earlier mitigation implementation means potentially developable critical parcels may still be available for conservation. Here, the authors compare the integration of regional conservation designs, termed greenprints, with early multi-project mitigation assessment for two areas in California, USA. The expected spatial extent of habitat impacts and associated mitigation requirements from multiple projects were identified for each area. They used the reserve-selection algorithm MARXAN to identify a regional greenprint for each site and to seek mitigation solutions through parcel acquisition that would contribute to the greenprint, as well as meet agency obligations. The two areas differed in the amount of input data available, the types of conservation objectives identified, and local land-management capacity. They are representative of the range of conditions that conservation practitioners may encounter, so contrasting the two illustrates how regional advanced mitigation can be generalized for use in a wide variety of settings. Environmental organizations can benefit from this approach because it provides a platform for collaboration with infrastructure agencies. Alone, infrastructure agency mitigation obligations will not satisfy all greenprint objectives, but they can be a major contributor to the ongoing process of implementing ecologically sustainable regional plans.

Spatial Patterns of Endemic Plants in California

ABSTRACT: California endemic vascular plant range patterns were quantified using a flora-based geodatabase technique that defined species range by geographic area and elevation band. Resulting species spatial patterns are reported for 228 geographic units. Over 60% of the endemic species range size distributions were found to have range sizes less than 10,000 km2. The largest endemic taxon range was 275,749 km2, or 67% of the state. California endemic plant richness distribution patterns are summarized by 228 geographic units, and reported by various criteria. Californias Central Coast Ranges, Sierra Nevada foothills, high elevation Sierra Nevada Mountains, Channel Islands, San Jacinto Mountains, Napa and Lake Counties, Inyo Mountains, sections of the Mojave Desert, and San Bernardino Mountains were all identified as areas with unique endemic plant attributes. We compared endemic species richness between map units in zones containing similar topography and climate, and found that area only weakly correlated with species richness, suggesting other factors have stronger influence on endemism in continental California. The findings have implications for developing conservation plans that target endemic species. In particular, we identify areas of the state, previously de-emphasized, that deserve greater recognition based on the characteristics of their restricted endemic plants. This analysis underestimates the level of endemism near the borders with Oregon and Baja California because of the artificial limitation of the database to the boundaries of the state of California. However, range distribution estimates produced from digital renditions of floral keys proved effective in this study, an inexpensive approach that could be implemented in other regions of the world for which floras have been published.

Changing forest structure across the landscape of the Sierra Nevada, CA, USA, since the 1930s

Understanding the dynamics of forest structure aids inference regarding future forests and their distributions around the world. Over the last few decades, several papers have addressed changing forest structure in the Sierra Nevada, CA, USA, but these studies were limited in scope. We carried out a broad comparison of forest density and composition in the 1930s versus the 2000s for the west slope of the central and northern Sierra Nevada, using the two most extensive data sets available. Forests in this region have endured a long, complex history of human disturbance, and are now experiencing climatic shifts. We subdivided the landscape into elevation and latitude zones and compared historical and modern tree densities within each zone. We compared densities in historical plots to burned and unburned modern plots, as well as densities of individual tree species in historical vs. modern plots for their entire elevational distribution. Density of small trees (10.2–30.4 cm dbh) was significantly higher in t...