Sonia A. Hall

Where to Restore Ecological Connectivity? Detecting Barriers and Quantifying Restoration Benefits

Landscape connectivity is crucial for many ecological processes, including dispersal, gene flow, demographic rescue, and movement in response to climate change. As a result, governmental and non-governmental organizations are focusing efforts to map and conserve areas that facilitate movement to maintain population connectivity and promote climate adaptation. In contrast, little focus has been placed on identifying barriers—landscape features which impede movement between ecologically important areas—where restoration could most improve connectivity. Yet knowing where barriers most strongly reduce connectivity can complement traditional analyses aimed at mapping best movement routes. We introduce a novel method to detect important barriers and provide example applications. Our method uses GIS neighborhood analyses in conjunction with effective distance analyses to detect barriers that, if removed, would significantly improve connectivity. Applicable in least-cost, circuit-theoretic, and simulation modeling frameworks, the method detects both complete (impermeable) barriers and those that impede but do not completely block movement. Barrier mapping complements corridor mapping by broadening the range of connectivity conservation alternatives available to practitioners. The method can help practitioners move beyond maintaining currently important areas to restoring and enhancing connectivity through active barrier removal. It can inform decisions on trade-offs between restoration and protection; for example, purchasing an intact corridor may be substantially more costly than restoring a barrier that blocks an alternative corridor. And it extends the concept of centrality to barriers, highlighting areas that most diminish connectivity across broad networks. Identifying which modeled barriers have the greatest impact can also help prioritize error checking of land cover data and collection of field data to improve connectivity maps. Barrier detection provides a different way to view the landscape, broadening thinking about connectivity and fragmentation while increasing conservation options.

LITTER AND DEAD WOOD DYNAMICS IN PONDEROSA PINE FORESTS ALONG A 160-YEAR CHRONOSEQUENCE

Disturbances such as fire play a key role in controlling ecosystem structure. In fire-prone forests, organic detritus comprises a large pool of carbon and can control the frequency and intensity of fire. The ponderosa pine forests of the Colorado Front Range, USA, where fire has been suppressed for a century, provide an ideal system for studying the long-term dynamics of detrital pools. Our objectives were (1) to quantify the long-term temporal dynamics of detrital pools; and (2) to determine to what extent present stand structure, topography, and soils constrain these dynamics. We collected data on downed dead wood, litter, duff (partially decomposed litter on the forest floor), stand structure, topographic position, and soils for 31 sites along a 160-year chronosequence. We developed a compartment model and parameterized it to describe the temporal trends in the detrital pools. We then developed four sets of statistical models, quantifying the hypothesized relationship between pool size and (1) stand structure, (2) topography, (3) soils variables, and (4) time since fire. We contrasted how much support each hypothesis had in the data using Akaikes Information Criterion (AIC). Time since fire explained 39-80% of the variability in dead wood of different size classes. Pool size increased to a peak as material killed by the fire fell, then decomposed rapidly to a minimum (61-85 years after fire for the different pools). It then increased, presumably as new detritus was produced by the regenerating stand. Litter was most strongly related to canopy cover (r2 = 77%), suggesting that litter fall, rather than decomposition, controls its dynamics. The temporal dynamics of duff were the hardest to predict. Detrital pool sizes were more strongly related to time since fire than to environmental variables. Woody debris peak-to-minimum time was 46-67 years, overlapping the range of historical fire return intervals (1 to > 100 years). Fires may therefore have burned under a wide range of fuel conditions, supporting the hypothesis that this regions fire regime was mixed severity.

The Development of Forage Production and Utilization Gradients around Livestock Watering Points

Large herbivores can impose spatial patterns on otherwise homogeneous vegetation, but how these patterns change through time is poorly understood. Domestic livestock pastures are model systems for studying how foraging behavior influences the development of coupled grazing and vegetation patterns. We sampled forage production and utilization by cattle along distance-from-water gradients to provide a snapshot of grazing and vegetation patterns, and then evaluated the ability of simulation models to qualitatively reproduce these patterns. In the field, forage production increased with distance from water, as expected, but utilization peaked at intermediate distances from water in two of three study areas. Likewise, simulations based on a variety of foraging strategies produced gradients in forage production and, after forage availability near water declined sufficiently, peaks in utilization at intermediate distances. Distance-from-water gradients thus represent cumulative but not necessarily present day gradients in grazing intensity. The model with a foraging strategy based on time minimization produced slightly more realistic patterns in forage abundance than a model based on energy maximization, although results were sensitive to the value of the threshold for rejecting sites of low forage biomass. However, all models produced implausible thresholds in grazing and forage distribution, suggesting that factors besides resource distribution influence herbivore distributions. Moreover, different foraging rules produced similar vegetation gradients, especially on point water source landscapes, illustrating the difficulty of inferring foraging processes from vegetation patterns.

Systematic Conservation Planning in the Face of Climate Change: Bet-Hedging on the Columbia Plateau

Systematic conservation planning efforts typically focus on protecting current patterns of biodiversity. Climate change is poised to shift species distributions, reshuffle communities, and alter ecosystem functioning. In such a dynamic environment, lands selected to protect todays biodiversity may fail to do so in the future. One proposed approach to designing reserve networks that are robust to climate change involves protecting the diversity of abiotic conditions that in part determine species distributions and ecological processes. A set of abiotically diverse areas will likely support a diversity of ecological systems both today and into the future, although those two sets of systems might be dramatically different. Here, we demonstrate a conservation planning approach based on representing unique combinations of abiotic factors. We prioritize sites that represent the diversity of soils, topographies, and current climates of the Columbia Plateau. We then compare these sites to sites prioritized to protect current biodiversity. This comparison highlights places that are important for protecting both todays biodiversity and the diversity of abiotic factors that will likely determine biodiversity patterns in the future. It also highlights places where a reserve network designed solely to protect todays biodiversity would fail to capture the diversity of abiotic conditions and where such a network could be augmented to be more robust to climate-change impacts.

Object-based classification of semi-arid wetlands

Wetlands are valuable ecosystems that benefit society. However, throughout history wetlands have been converted to other land uses. For this reason, timely wetland maps are necessary for developing strategies to protect wetland habitat. The goal of this research was to develop a time-efficient, automated, low-cost method to map wetlands in a semi-arid landscape that could be scaled up for use at a county or state level, and could lay the groundwork for expanding to forested areas. Therefore, it was critical that the research project contain two components: accurate automated feature extraction and the use of low-cost imagery. For that reason, we tested the effectiveness of geographic object-based image analysis (GEOBIA) to delineate and classify wetlands using freely available true color aerial photographs provided through the National Agriculture Inventory Program. The GEOBIA method produced an overall accuracy of 89% (khat = 0.81), despite the absence of infrared spectral data. GEOBIA provides the automation that can save significant resources when scaled up while still providing sufficient spatial resolution and accuracy to be useful to state and local resource managers and policymakers.

Focal species and landscape “naturalness” corridor models offer complementary approaches for connectivity conservation planning

ContextThe dual threats of habitat fragmentation and climate change have led to a proliferation of approaches for connectivity conservation planning. Corridor analyses have traditionally taken a focal species approach, but the landscape “naturalness” approach of modeling connectivity among areas of low human modification has gained popularity as a less analytically intensive alternative.ObjectivesWe compared focal species and naturalness-based corridor networks to ask whether they identify similar areas, whether a naturalness-based approach is in fact more analytically efficient, and whether agreement between the two approaches varies with focal species vagility.MethodsWe compared focal-species and naturalness-based connectivity models at two nested spatial extents: greater Washington State, USA, and, within it, the Columbia Plateau ecoregion. We assessed complementarity between the two approaches by examining the spatial overlap of predicted corridors, and regressing organism traits against the amount of modeled corridor overlap.ResultsA single naturalness-based corridor network represented connectivity for a large (>10) number of focal species as effectively as a group of between 3 and 4 randomly selected focal species. The naturalness-based approach showed only moderate spatial agreement with composite corridor networks for large numbers of focal species, and better agreed with corridor networks of large-bodied, far-dispersing species in the larger scale analysis.ConclusionsNaturalness-based corridor models may offer an efficient proxy for focal species models, but a multi-focal species approach may better represent the movement needs of diverse taxa. Consideration of trade-offs between the two approaches may enhance the effectiveness of their application to connectivity conservation planning.

Rethinking Conservation Practice in Light of Climate Change

Predicted changes in climate present unusual challenges to conservation planners, land managers, and restoration efforts directed toward preserving biodiversity. Successful organisms will respond to these changes by persisting in suitable microsites, adapting to novel conditions, or dispersing to new sites. We describe three general categories of strategies for restoring and managing natural systems in light of likely changes in future climate that collectively embrace many of the approaches that The Nature Conservancy is applying or considering in the state of Washington. Component redundancy suggests that in natural systems greater ecosystem resilience, despite changing climates, may be achieved by increasing species and community redundancy. Functional redundancy is the idea that different components of a system can fulfill the same functions, thereby producing the same result. Restoration projects and managers of natural systems can introduce ecologically equivalent species or novel associations of species, which may help avoid losses in biodiversity. Increased connectivity suggests that success is achieved by ensuring that suitable habitats are always within easy reach of one another. This includes conservation approaches that provide linkages, corridors, or other mechanisms to facilitate the movement of organisms as they respond to climate changes. We acknowledge that these approaches are not without risk, nor do they necessarily ensure success. However, we propose them as potential solutions among a growing suite of alternative strategies for incorporating climate change into conservation actions.

Getting the most connectivity per conservation dollar

The importance of connectivity for species conservation has resulted in myriad attempts to identify corridors linking habitat patches and conservation areas. However, making smart decisions for restoring connectivity requires information beyond simple maps of corridors. Here, we combine land-parcel cost estimates with a new analytical approach that pinpoints where barrier removal can best improve connectivity to develop a return-on-investment framework for connectivity restoration. An iterative series of barrier analyses followed by simulated restorations allowed us to incorporate cumulative effects of previous restoration decisions, which can alter the potential value of future restorations. To demonstrate our approach, we identify specific sites that, if restored, would most increase habitat connectivity for the Washington ground squirrel (Urocitellus washingtoni). The analysis was performed in two ways: first without consideration of economic costs and then again, explicitly incorporating the costs of ...