Habitat availability for multiple avian species under modeled alternative conservation scenarios in the Two Hearted River watershed in Michigan, USA
Introduction
As conservation strategies increasingly span large geographic areas and often involve multiple land owners, it is important to understand and anticipate impacts of various management strategies over broad spatial and temporal scales in order to achieve resource and conservation goals (Jin et al., 2010, Price et al., 2012, Shifley et al., 2008, Zollner et al., 2008). For example, the unit area, intensity, and return interval of forest management activities affect the availability of habitat for wildlife species by influencing stand composition and landscape pattern (Jin et al., 2010, Scolozzi and Geneletti, 2011, Shifley et al., 2006, Zollner et al., 2008). The ability to project, visualize, and assess the impacts of alternative scenarios of management activities and natural disturbances could benefit the understanding of how long-term forest management strategies affect biodiversity and could aid in conservation planning.
Loss and fragmentation of habitat are two of the greatest threats to biodiversity in forest landscapes (Ohman et al. 2011), and the importance of fragmentation, edge effects, and corridors for species survival and reproductive success have been widely discussed in scientific literature (Knowlton and Graham, 2010, Venier et al., 2007). In conservation and metapopulation theories, it is generally accepted that larger and more connected patches can support greater species richness as well as population abundance and persistence than smaller, isolated ones (Prugh et al. 2008). Larger patch sizes may reduce a population's probability of extinction by supporting larger population sizes, enabling greater colonization rates, and reducing edge effects and predator invasions (Etienne et al., 2004, Shanahan et al., 2011). Greater patch connectivity may enhance dispersal success, colonization, and population interchange, especially for rare and specialist species in degraded or fragmented landscapes (Davies et al., 2000, Knowlton and Graham, 2010, Shanahan et al., 2011). Consequently, conservation plans should consider not only the amount and quality but also the spatial configuration of suitable habitat in the landscape, including properties such as patch size, shape, and connectivity (Larson et al., 2004, Rittenhouse et al., 2007, Shifley et al., 2006, Venier et al., 2007).
Due to the differences in species’ responses to landscape patterns, planning an optimal strategy in the face of contrasting habitat needs can be difficult (Gottschalk et al., 2010, Monkkonen et al., 2011, Watts et al., 2010, Zollner et al., 2008). This difficulty explains the tendency of researchers to perform single-species habitat or population assessments or use landscape pattern metrics as proxies for multiple species representation (Edenius and Mikusinski, 2006, Nicholson and Possingham, 2006, Venema et al., 2005). A suite of species which are sensitive to differing threats can represent the diversity of spatial, compositional, and functional attributes that are of conservation concern in a landscape (Edenius and Mikusinski, 2006, Mace et al., 2007, Scolozzi and Geneletti, 2011). Landscape modeling may reveal which species among a suite of species, in terms of habitat availability, might be more sensitive to alternative management strategies or landscape changes and therefore may require special or urgent consideration in management planning.
Considering the vast amount of time and resources needed for long term monitoring at broad spatial and temporal scales, landscape simulation models and GIS technologies offer a convenient method of evaluating potential effects of long-term management strategies in landscapes and enable a more timely flow of information to inform management decision making (Ferrier and Drielsma, 2010, Jin et al., 2010, Shifley et al., 2006, Shifley et al., 2008, Zollner et al., 2008). In recent years, several spatially explicit landscape modeling programs have been developed, used in forest planning, and reviewed (Barrett, 2001, Jin et al., 2010, Larson et al., 2004, Mladenoff, 2004, Scheller and Mladenoff, 2007, Shifley et al., 2008). These models have the ability to simulate forest successional dynamics over long time periods and project future conditions of the landscape. When local knowledge from various stakeholders is incorporated into the modeling through a collaborative process, more plausible outcomes may be realized (Price et al. 2012).
The ability to model alternative scenarios and analyze future landscapes provides a means of assessing potential changes in habitat availability and comparing the potential effectiveness of conservation strategies. Such comparisons could benefit managers who are interested in the impacts of their decisions, provide insight into how and where habitat management could be improved, and allow more adaptive planning.
Our partners at The Nature Conservancy (TNC) were particularly interested in comparing the long-term conservation effectiveness of working forest conservation easements and fee simple ownership of land in the Two Hearted River watershed, a 53,653 ha forested landscape in Michigan's Upper Peninsula. The purpose of working forest conservation easements is to keep land productive while preventing subdivision and fragmentation of land, thus being beneficial for habitat conservation. Since property is not fully purchased, easements are a less costly strategy up front than fee simple acquisition, potentially allowing conservation efforts and resources to be more broadly distributed across a landscape (Silbernagel et al. 2011). They provide tax relief to the land owners and generally allow resource extraction (e.g. sustainable timber harvesting), thus contributing to the local economy. However, they require long-term monitoring and enforcement and may carry added transaction costs of working with multiple landowners and unique ecological conditions (Fishburn et al., 2009, MIDNR, 2012a). It is not known whether easements can provide the same level of biodiversity protection as acquiring land under fee simple ownership (Fishburn et al., 2009, Merenlender et al., 2004), which may also require continuous human and financial resources to manage the land into the future. Without long-term ecological monitoring, the effectiveness of these strategies, or any conservation strategies that attempt to balance resource extraction with conservation, remains unclear, and there is little evidence that can inform future acquisitions and help gain public and financial support in favor of certain strategies (Rissman et al., 2007, Silbernagel et al., 2011).
To evaluate the potential long-term impacts of four alternative conservation scenarios on habitat availability for five diverse bird species of concern in the Two Hearted River watershed, we performed habitat assessments on the spatial output of 100-year forest landscape models. The scenarios represented current-day management as well as three alternative hypothetical management strategies across the landscape, each informed by the management goals and practices of major forest landowners in the area (Fig. 1). The four scenarios were: A) current management scenario (Current scenario), B) no conservation action (NCA) scenario, C) working forest conservation easement scenario (Easement scenario), and D) ecological forestry scenario (Ecological scenario). Each scenario simulated different amounts, intensities, and general spatial characteristics of forest harvest activities. The Ecological scenario contained the greatest area of TNC managed land, and we expected this scenario to be the most beneficial for target species because of its emphasis on restoration and conservation of native and old-growth habitat, cooperative and broad-scale nature of management, and low amount of even-aged timber harvest. The NCA scenario, on the other hand, contained the largest area of industrially managed private lands, and we expected it to be the least beneficial for target species due to its nature of having a high amount of productivity-driven even-aged harvest, as well as a great number of land owners acting independently in the landscape, resulting in spatially fragmented management. In the Easement scenario, current-day TNC fee title lands were instead placed under a working forest conservation easement, which allows even-aged harvest but restricts subdivision of land and thus provides a spatially aggregated management outlook. We expected this scenario to be more beneficial than the NCA scenario, but not as beneficial as the Ecological or Current scenarios.
In an attempt to identify an optimal scenario, we developed a scoring system to rank scenario outcomes based on three metrics of habitat availability: 1) total area of habitat, 2) average size of habitat patches, and 3) average distance to nearest neighboring habitat patches for each target species. We hypothesized that 1) all of the habitat metric response variables would be significantly influenced by scenarios representing alternative management strategies over 100 years; 2) scenarios with smaller total area of even-aged timber harvest would provide the most beneficial habitat conditions for species overall; and 3) species that have more specific habitat requirements such as a limited number of preferred cover types, a large patch size requirement, or require proximity to additional necessary habitat elements would be the most sensitive to alternative scenarios.
Section snippets
Study Area and Scenario Modeling
The “Forest Scenarios” project team, based at the University of Wisconsin at Madison, has built a set of spatial landscape simulation models for the Two Hearted River watershed, a 53,653 ha forested landscape in the northeastern region of Michigan's Upper Peninsula (46–42′06′’ N and 085–24′52′’ W). This landscape contains a mixture of upland hardwood forests, pine stands, coniferous forests, and interspersed wetland systems (Table 1). Together, the Michigan Department of Natural Resources (DNR),
All species
The amount and configuration of primary habitat patches differed significantly (P < 0.05) across alternative scenarios for all species (Appendix, Table 2). Total habitat area decreased after 100 years for all species in all scenarios with the exception of the Ecological scenario for the Black-backed Woodpecker and the Red-shouldered Hawk. The results of the relative ranks scoring method revealed that the Ecological scenario ranked the highest, followed by the Current scenario, the Easement
Discussion
The habitat responses for all five target species in the Two Hearted River watershed varied greatly under alternative management scenarios. All three habitat metrics – total habitat area, average habitat patch size, and average habitat patch nearest neighbor distance – were significantly influenced by the alternative scenarios at model year 100, supporting the hypothesis that management strategies and alternative spatial arrangements of those strategies influenced these habitat characteristics
Limitations and future directions
The outcomes of this study were reliant upon characteristics of the target species chosen, inherent characteristics of the landscape, including the amounts and locations of cover types, as well as characteristics of local management regimes. Therefore, the scenario outcomes may not be generalizable outside the study area.
Most predictive models carry some uncertainty which may accumulate with successive time steps. Additionally, it is difficult to anticipate changes in practices and
Conclusions and implications for conservation planning
The results in this study reveal that land management decisions will have significant and long term influence on the amount and configuration of habitat for diverse wildlife species in the Two Hearted River watershed and that strategies which are less economically-driven may have more advantages for wildlife. Although one scenario outranked others, it was not the most beneficial across all response variables, indicating a need to adjust for specific objectives and to use a combination of
Acknowledgements
Funding for this study and for the Forest Scenarios project was provided in part by The Nature Conservancy's Rodney Johnson and Katherine Ordway Stewardship Endowment grant, the USDA Forest Service State and Private Forestry Redesign, the Doris Duke Charitable Foundation, the NSF IGERT Fellowship Program (DGE-0549407), and the University of Wisconsin at Madison. We would like to thank land managers, conservation practitioners, and scientists from the Michigan Department of Natural Resources,
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