Thomas D. Sisk

A PREDICTIVE MODEL OF EDGE EFFECTS

Edge effects are among the most extensively studied ecological phenomena, yet we lack a general, predictive framework to understand the patterns and variability observed. We present a conceptual model, based on resource distribution, that predicts whether organismal abundances near edges are expected to increase, decrease, or remain unchanged for any species at any edge type. Predictions are based on whether resources are found predominantly in one habitat (decreased abundance in preferred habitat, increase in non-preferred), divided between habitats (predicts an increase near both edges), spread equally among habitats (predicts a neutral edge response), or concentrated along the edge (increase). There are several implications of this model that can explain much of the variability reported in the edge literature. For instance, our model predicts that a species may show positive, negative, and neutral responses, depending on the edge type encountered, which explains some intraspecific variability observed ...

Identifying Extinction Threats

Relatively pristine habitats around the world are being lost at unprecedented rates (Melillo et al. 1985, Skole and Tucker 1993) as an expanding human population converts them to agriculture, forestry, and urban centers (Hall 1978, Vitousek et al. 1986). As these habitats are altered, untold numbers of species are disappearing before they have been recognized, much less studied (Wilson 1989), and the functioning of entire ecosystems is threatened. This loss of biodiversity, at the very time when the value of biotic resources is becoming widely recognized (Malone 1992), has made it strikingly clear that current strategies for conservation are failing dismally (Ehrlich 1992, Ehrlich and Wilson 1991).

Identifying Extinction Threats: Global Analyses of the Distribution of Biodiversity and the Expansion of the Human Enterprise

Relatively pristine habitats around the world are being lost at unprecedented rates (Melillo et al. 1985, Skole and Tucker 1993) as an expanding human population converts them to agriculture, forestry, and urban centers (Hall 1978, Vitousek et al. 1986). As these habitats are altered, untold numbers of species are disappearing before they have been recognized, much less studied (Wilson 1989), and the functioning of entire ecosystems is threatened. This loss of biodiversity, at the very time when the value of biotic resources is becoming widely recognized (Malone 1992), has made it strikingly clear that current strategies for conservation are failing dismally (Ehrlich 1992, Ehrlich and Wilson 1991).

Remotely sensed indicators of habitat heterogeneity: use of synthetic aperture radar in mapping vegetation structure and bird habitat

An integrated remote sensing/field ecology project linked the use of synthetic aperture radar (SAR) and aerial photography to studies of landscape spatial heterogeneity and bird community ecology. P-, L-, and C-band SAR data, collected over a section of Kakadu National Park in Australias Northern Territory during the Joint NASA/Australia DC-8 data acquisition campaign, were analyzed in light of field data integrating vegetation structure and floristics with bird abundances across a heterogeneous study site. Results indicate that SAR data are able to discern structural differences relevant to bird habitat quality within floristically homogeneous stands, while multispectral sensors successfully identified floristic differences among habitat types. Simplifying indices of bird diversity showed ambiguous changes across the site; however, the abundances of individual species were observed to change significantly across both floristic and structural gradients. These results suggest that efforts to map bird diversity should focus on species-specific habitat relationships and that some measure of vegetation structure is needed to understand bird habitat. The approach employed here advances the use of SAR data in the three-dimensional mapping of animal habitats from remotely sensed data, and extends current capabilities for mapping and modeling large-scale patterns in the distribution of biological diversity.

Prioritizing conservation effort through the use of biological soil crusts as ecosystem function indicators in an arid region

Conservation prioritization usually focuses on conservation of rare species or biodiversity, rather than ecological processes. This is partially due to a lack of informative indicators of ecosystem function. Biological soil crusts (BSCs) trap and retain soil and water resources in arid ecosystems and function as major carbon and nitrogen fixers; thus, they may be informative indicators of ecosystem function. We created spatial models of multiple indicators of the diversity and function of BSCs (species richness, evenness, functional diversity, functional redundancy, number of rare species, number of habitat specialists, nitrogen and carbon fixation indices, soil stabilization, and surface roughening) for the 800,000-ha Grand Staircase-Escalante National Monument (Utah, U.S.A.). We then combined the indicators into a single BSC function map and a single BSC biodiversity map (2 alternative types of conservation value) with an unweighted averaging procedure and a weighted procedure derived from validations performance. We also modeled potential degradation with data from a rangeland assessment survey. To determine which areas on the landscape were the highest conservation priorities, we overlaid the function- and diversity-based conservation-value layers on the potential degradation layer. Different methods for ascribing conservation-value and conservation-priority layers all yielded strikingly similar results (r= 0.89-0.99), which suggests that in this case biodiversity and function can be conserved simultaneously. We believe BSCs can be used as indicators of ecosystem function in concert with other indicators (such as plant-community properties) and that such information can be used to prioritize conservation effort in drylands.

Linking Ecosystem Health Indicators and Collaborative Management: a Systematic Framework to Evaluate Ecological and Social Outcomes

Collaborative management has gained popularity across the United States as a means of addressing the sustainability of mixed-ownership landscapes and resolving persistent conflicts in public lands management. At the same time, it has generated skepticism because its ecological and social outcomes are seldom measured. Evaluating the success of collaborative efforts is difficult because frameworks to assess on-the-ground outcomes are poorly developed or altogether lacking. Ecosystem health indicators are valuable tools for evaluating site-specific outcomes of collaboration based on the effects of collaboration on ecological and socioeconomic conditions. We present the holistic ecosystem health indicator, a promising framework for evaluating the outcomes of collaborative processes, which uses ecological, social, and interactive indicators to monitor conditions through time. Finally, we draw upon our experience working with the Diablo Trust, a community-based collaborative group in northern Arizona, USA, to illustrate the development of an indicator selection model generated through a stakeholder-driven process.

Fuel-Reduction Treatment Effects on Avian Community Structure and Diversity

Abstract We assessed responses of the breeding bird community to mechanical thinning and prescribed surface fire, alone and in combination, between 2000 and 2006 in ponderosa pine (Pinus ponderosa) forests in northern Arizona, USA. Fuel-reduction treatments did not affect species richness or evenness, and effects on density of 5 commonly detected species varied among species. Populations of some species, such as the western bluebird (Sialia mexicana), increased following burning treatments, whereas others, such as the mountain chickadee (Poecile gambeli), decreased in response to thinning treatments. Our results also identified a temporal response component, where avian community composition and structure changed synchronously on all treatments over time. Given the modest effects these small-scale fuel-reduction treatments had on avian composition and the specific density responses of particular species, our results suggest that land managers should consider implementing prescribed surface fire after thinning projects, where appropriate.

A Framework to Evaluate Ecological and Social Outcomes of Collaborative Management: Lessons from Implementation with a Northern Arizona Collaborative Group

As collaborative groups gain popularity as an alternative means for addressing conflict over management of public lands, the need for methods to evaluate their effectiveness in achieving ecological and social goals increases. However, frameworks that examine both effectiveness of the collaborative process and its outcomes are poorly developed or altogether lacking. This paper presents and evaluates the utility of the holistic ecosystem health indicator (HEHI), a framework that integrates multiple ecological and socioeconomic criteria to evaluate management effectiveness of collaborative processes. Through the development and application of the HEHI to a collaborative in northern Arizona, the Diablo Trust, we present the opportunities and challenges in using this framework to evaluate the ecological and social outcomes of collaborative adaptive management. Baseline results from the first application of the HEHI are presented as an illustration of its potential as a co-adaptive management tool. We discuss lessons learned from the process of selecting indicators and potential issues to their long-term implementation. Finally, we provide recommendations for applying this framework to monitoring and adaptive management in the context of collaborative management.

Landscape Models to Predict the Influence of Forest Structure on Tassel-Eared Squirrel Populations

Abstract The tassel-eared squirrel (Sciurus aberti) is often used as an indicator species in southwestern ponderosa pine (Pinus ponderosa) forests. Because of more than a century of fire suppression, grazing, and timber harvest, these forests have become increasingly prone to catastrophic wildfire, resulting in pressure to implement large-scale treatments to reduce fire threat and restore ecosystem function. However, such treatments could have dramatic effects on tassel-eared squirrels and other wildlife. Because of emerging plans for thinning southwestern forests to reduce fire threat, we undertook a modeling effort to produce spatial data to examine the results of proposed management actions on squirrel habitat. We used squirrel density and recruitment data from 9 study areas located in the Flagstaff region of northern Arizona, USA, linked with spatial data on forest structure developed from remote-sensing imagery. We used a multiscale approach to analyze relationships between forest structure and squirrel density and recruitment. We then used an information-theoretic approach to identify the most parsimonious models for both squirrel density and recruitment. The most strongly supported models of squirrel density included local-scale basal area and >60% canopy cover at the 65-ha spatial scale. For squirrel recruitment, 4 different models that included both local-scale basal area (m2/ha) and variations of canopy cover over extents of approximately 160–305 ha were strongly supported. Using the most parsimonious models, we created spatial data layers representing both squirrel density and recruitment across an 800,000-ha landscape in northern Arizona. Our approach resulted in spatially explicit models that can be used in efforts to predict the effects of forest management on squirrel populations.

Integrating Landscape Ecology into Natural Resource Management: Incorporating the effects of habitat edges into landscape models: Effective area models for cross-boundary management

Sisk, T.D., and N.M. Haddad. 2002. Incorporating the effects of habitat edges into landscape models: Effective area models for cross-boundary management. Chapter 8, Pp. 208-240 in J. Liu and W.W. Taylor, Integrating landscape ecology into natural resource management, Cambridge University Press, Cambridge, UK. Abstract: Natural resource managers are increasingly charged with meeting multiple, often conflicting goals in landscapes undergoing significant change due to shifts in land use. Conservation from native to anthropogenic habitats typically fragments the landscape, reducing the size and increasing the isolation of the resulting patches, with profound ecological impacts. These impacts occur both within and adjacent to areas under active management, creating extensive edges between habitat types. Boundaries established between management areas, for example, between timber harvest units or between reserves and adjacent agricultural fields, inevitably lead to differences in the quality of habitats on either side of the boundary, and a habitat edge results. Although edges are common components of undisturbed landscapes, the amount of edge proliferates rapidly as landscapes are fragmented. Insightful analysis of the complex issues associated with cross-boundary management necessitates an explicit focus on habitat quality in the boundary regions.