High‐resolution riparian vegetation mapping to prioritize conservation and restoration in an impaired desert river

In highly impaired watersheds, it is critical to identify both areas with desirable habitat as conservation zones and impaired areas with the highest likelihood of improvement as restoration zones. We present how detailed riparian vegetation mapping can be used to prioritize conservation and restoration sites within a riparian and instream habitat restoration program targeting 3 native fish species on the San Rafael River, a desert river in southeastern Utah, United States. We classified vegetation using a combination of object‐based image analysis (OBIA) on high‐resolution (0.5 m), multispectral, satellite imagery with oblique aerial photography and field‐based data collection. The OBIA approach is objective, repeatable, and applicable to large areas. The overall accuracy of the classification was 80% (Cohen's κ = 0.77). We used this high‐resolution vegetation classification alongside existing data on habitat condition and aquatic species' distributions to identify reaches' conservation value and restoration potential to guide management actions. Specifically, cottonwood (Populus fremontii) and tamarisk (Tamarix ramosissima) density layers helped to establish broad restoration and conservation reach classes. The high‐resolution vegetation mapping precisely identified individual cottonwood trees and tamarisk thickets, which were used to determine specific locations for restoration activities such as beaver dam analogue structures in cottonwood restoration areas, or strategic tamarisk removal in high‐density tamarisk sites. The site prioritization method presented here is effective for planning large‐scale river restoration and is transferable to other desert river systems elsewhere in the world.     

Spatial and Temporal Considerations in Restoring Habitat for Wildlife

An accumulated body of theory and empirical evidence suggests that habitat selection by animals is a scale‐dependent, hierarchical process. Hierarchy theory predicts that habitat suitability is influenced by the interaction of factors at multiple spatial scales from the microsite to the landscape and that higher‐order factors impose constraints at lower levels. For instance, large‐scale factors such as landscape context may make a site unsuitable for a species even if the vegetation structure and composition are appropriate. In addition, the spatial arrangement of habitat elements at all scales must be considered when planning restoration efforts. For example, the presence of snags does not ensure that the site will be suitable for snag‐dependent species. The size, age, and spacing of snags and their juxtaposition to other habitat elements must also be considered. Finally, all habitats are dynamic, and therefore the ecological processes that contribute to those dynamics must be maintained or suitable substitutes included in the recovery plan. When considering restoring habitat for wildlife, we recommend that managers: (1) identify the wildlife species they want to target for restoration efforts, (2) consider the size and landscape context of the restoration site and whether it is appropriate for the target species, (3) identify the habitat elements that are necessary for the target species, (4) develop a strategy for restoring those elements and the ecological processes that maintain them, and (5) implement a long‐term monitoring program to gauge the success of the restoration efforts.     

Use of Restored Riparian Habitat by the Endangered Least Bell's Vireo (Vireo bellii pusillus)

A primary objective of riparian restoration in California is the creation of habitat for endangered species. Four restoration sites in San Diego County were monitored between 1989 and 1993 and evaluated for their suitability as nesting habitat for Vireo bellii pusillus (Least Bell's Vireo), a state and federally endangered obligate riparian breeder. Vegetation structure at each site was quantified annually and compared to a model of canopy architecture derived from Least Bell's Vireo territories in natural habitat. Vireo use of restored habitat was documented through systematic surveys and nest monitoring. By 1993, only one site in its entirety met the habitat suitability criteria of the model, but portions of each site during all years did so. Differences between sites in the time required to develop suitable habitat—well-developed layered vegetation from the ground to under 8m in height)—were attributable largely to variation in annual rainfall. Vireos visited restoration sites to forage as early as the first growing season, but they did not establish territories or nest there until at least part of the site supported suitable habitat as determined from the model. Placement of territories and nests coincided with patches of dense vegetation characteristic of natural nesting areas. Occupation of restored sites was accelerated by the presence of adjacent mature riparian habitat, which afforded birds nest sites and/or foraging habitat lacking in the planted vegetation. Vireos nesting in restored habitat achieved success comparable to that of vireos nesting in surrounding natural habitat, and there was no evidence that productivity was reduced in created areas. These findings indicate that creating nesting habitat for this target species is feasible and suggest that the critical components of vireo nesting habitat have been captured in both the design and quantitative assessment of restoration sites.     

Reach- and catchment-scale determinants of the distribution of freshwater mussels (Bivalvia: Unionidae) in south-eastern Michigan, U.S.A.

1. We investigated the diversity and distribution of freshwater mussels at 40 sites in an agricultural catchment, the River Raisin in south‐eastern Michigan, to relate mussel assemblages and individual taxa to reach and catchment‐scale variables. Unionids were surveyed by timed searches in 100‐m reaches, and in‐stream and riparian habitat were quantified as well as flow, water chemistry and channel morphology. Land use/cover and surficial geology were determined for site subcatchments and riparian buffers. 2. Some 21 mussel species were found overall; richness ranged from 0 to 12 living species per site. From the upper to middle to lower catchment, the number of individuals, number of species, Shannon–Weaver diversity and relative abundance of intolerant unionids all declined significantly. 3. Four groupings based on overall mussel diversity and abundance were significantly related to reach‐scale habitat variables. The richest mussel assemblages were associated with sites with higher overall habitat quality, greater flow stability, less fine substratum, and lower specific conductance. 4. Stepwise multiple regressions revealed that the distribution and abundance of the total mussel assemblage, as well as the most common species, could be predicted from a combination of reach‐ and catchment‐scale variables (R² = 0.63 for total mussels, R² = 0.51–0.86 for individual species). 5. Flow stability, substratum composition and overall reach habitat quality were the most commonly identified reach‐scale variables, and measures of surficial geology were the most effective catchment‐scale variables. The spatial pattern of geology is likely to be responsible for the diversity gradient from the upper to the lower catchment. 6. Prior studies, attempting to explain mussel distributions from local habitat features alone, have found relatively weak relationships. By employing a combination of reach‐ and catchment‐scale habitat variables, this study was able to account for a substantial amount of the spatial variability in mussel distributions.     

Habitat selection of riparian birds at restoration sites along the Trinity River,California

Riparian habitats in the western United States are imperiled, yet they support the highest bird diversity in arid regions, making them a conservation priority. Riparian restoration efforts can be enhanced by information on species response to variation in habitat features. We examined the habitat selection of four riparian birds known as management indicators at restoration and reference sites along the Trinity River, California. We compared vegetation structure and composition at nest sites, territories, and random points to quantify used versus available habitat from 2012 to 2015. Vegetation in focal species' territories differed between site types, and from available habitat, indicating nonrandom site choice. Birds selected aspects of more structurally complex habitats, such as greater canopy cover, canopy height, and tree species richness. Yellow‐breasted Chats preferred greater shrub cover, and Yellow Warblers preferred greater cover by non‐native Himalayan blackberry. Territory preferences on restoration sites were often a subset of those on reference sites. One exception was canopy height, which was taller on restoration site territories than random points for all species, suggesting that birds preferentially used patches of remnant habitat. Few variables were significant in nest site selection. Restoration plantings along the Trinity River were only 3–10 years old during this study, and have not developed many of the characteristics of mature riparian habitat preferred by birds, but may improve in habitat value over time. Understanding habitat selection is especially important in recently human‐modified environments, where indirect cues used to assess habitat quality may become disassociated from actual habitat quality, potentially creating ecological traps.     

Riparian management: A restoration tool for New Zealand streams

Many New Zealanders are planning and implementing riparian management, and riparian fencing and planting are now standard best practice tools for water quality and habitat restoration. New Zealand has a long history of action, with the first catchment riparian schemes and science dating back to the 1970s. As a result of this, there is now solid scientific evidence that demonstrates the value of a range of management actions including the following: riparian zones and buffers for livestock exclusion (fencing with or without planting), nutrient processing, shading small streams for temperature control, providing leaf and wood input to stream ecosystems, and enhancing fish and invertebrate habitat. In the last decade or so, on‐ground action has accelerated significantly with the introduction of dairy industry and government agreed targets. In 2015, 96% of dairy cows had been excluded from waterways >1 m wide and >30 cm deep on land that cows graze during the milking season providing impetus for on‐ground action to spread into other pastoral industries. Tools for planning, managing and implementing successful riparian restoration have proliferated, informed by on‐ground successes and failures. Despite this, there remain challenges for individuals or communities planning riparian restoration. Careful case‐by‐case assessment is recommended to ensure that plans match design to local landscape constraints and can realistically contribute to improved water quality or habitat outcomes.     

Evaluating the efficacy of seasonal grazing and livestock exclusion as restoration tools for birds in riparian habitat of the Okanagan Valley,British Columbia,Canada

Riparian habitat supports the highest density and diversity of songbirds in Western North America despite covering less than 1% of the land area. Widespread destruction and degradation of riparian habitat, especially by livestock grazing, has led to habitat restoration efforts. In 2000, restoration activities in the form of permanent and seasonal exclusion of livestock from riparian areas were initiated to improve habitat for the endangered Western Yellow‐breasted Chat (Icteria virens auricollis) population, which is dependent on early successional shrub habitat for nesting, in the Okanagan Valley of British Columbia, Canada. We assessed the effectiveness of livestock exclusion by examining temporal changes in the abundance, richness, and breeding performance of birds in restoration and reference sites. The abundance of W. Yellow‐breasted Chats significantly increased between 2002 and 2013 in areas where restoration activities occurred. However, restoration did not have significant effects on the abundance, richness, or breeding performance of other riparian birds at the restoration sites independent of temporal changes that occurred at reference sites. Our results provide evidence that limiting livestock grazing in temperate riparian areas can lead to recovery of endangered riparian songbirds that rely on early successional shrub habitat but may have limited effects on common species that are not strictly reliant on this habitat.     

A restoration suitability index model for the eastern oyster (Crassostrea virginica) in the Mission-Aransas Estuary, TX, USA

Oyster reefs are one of the most threatened marine habitats on earth, with habitat loss resulting from water quality degradation, coastal development, destructive fishing practices, overfishing, and storm impacts. For successful and sustainable oyster reef restoration efforts, it is necessary to choose sites that support long-term growth and survival of oysters. Selection of suitable sites is critically important as it can greatly influence mortality factors and may largely determine the ultimate success of the restoration project. The application of Geographic Information Systems (GIS) provides an effective methodology for identifying suitable sites for oyster reef restoration and removes much of the uncertainty involved in the sometimes trial and error selection process. This approach also provides an objective and quantitative tool for planning future oyster reef restoration efforts. The aim of this study was to develop a restoration suitability index model and reef quality index model to characterize locations based on their potential for successful reef restoration within the Mission-Aransas Estuary, Texas, USA. The restoration suitability index model focuses on salinity, temperature, turbidity, dissolved oxygen, and depth, while the reef quality index model focuses on abundance of live oysters, dead shell, and spat. Size-specific Perkinsus marinus infection levels were mapped to illustrate general disease trends. This application was effective in identifying suitable sites for oyster reef restoration, is flexible in its use, and provides a mechanism for considering alternative approaches. The end product is a practical decision-support tool that can be used by coastal resource managers to improve oyster restoration efforts. As oyster reef restoration activities continue at small and large-scales, site selection criteria are critical for assisting stakeholders and managers and for maximizing long-term sustainability of oyster resources.     

Effects of Stream Restoration on Woody Riparian Vegetation of Southern Appalachian Mountain Streams,North Carolina,U.S.A

Riparian revegetation, such as planting woody seedlings or live stakes, is a nearly ubiquitous component of stream restoration projects in the United States. Though evaluations of restoration success usually focus on in‐stream ecosystems, in order to understand the full impacts of restoration the effects on riparian ecosystems themselves must be considered. We examined the effects of stream restoration revegetation measures on riparian ecosystems of headwater mountain streams in forested watersheds by comparing riparian vegetation structure and composition at reference, restored, and degraded sites on nine streams. According to mixed model analysis of variance (ANOVA), there was a significant effect of site treatment on riparian species richness, basal area, and canopy cover, but no effect on stem density. Vegetation characteristics at restored sites differed from those of reference sites according to all metrics (i.e. basal area, canopy cover, and species composition) except species richness and stem density. Restored and degraded sites were structurally similar, with some overlap in species composition. Restored sites were dominated by Salix sericea and Cornus amomum (species commonly planted for revegetation) and a suite of disturbance‐adapted species also dominant at degraded sites. Differences between reference and restored sites might be due to the young age of restored sites (average 4 years since restoration), to reassembly of degraded site species composition at restored sites, or to the creation of a novel anthropogenic ecosystem on these headwater streams. Additional research is needed to determine if this anthropogenic riparian community type persists as a resilient novel ecosystem and provides valued riparian functions.     

Development of Vegetation and Aquatic Habitat in Restored Riparian Sites of California's North Coast Rangelands

The preponderance of short‐term objectives and lack of systematic monitoring of restoration projects limits opportunities to learn from past experience and improve future restoration efforts. We conducted a retrospective, cross‐sectional survey of 89 riparian revegetation sites and 13 nonrestored sites. We evaluated 36 restoration metrics at each site and used project age (0–39 years) to quantify plant community and aquatic habitat trajectories with a maximum likelihood model selection approach to compare linear and polynomial relationships. We found significant correlations with project age for 16 of 21 riparian vegetation, and 11 of 15 aquatic habitat attributes. Our results indicated improvements in multiple ecosystem services and watershed functions such as diversity, sedimentation, carbon sequestration, and available habitat. Ten riparian vegetation metrics, including native tree and exotic shrub density, increased nonlinearly with project age, while litter and native shrub density increased linearly. Species richness and cover of annual plants declined over time. Improvements in aquatic habitat metrics, such as increasing pool depth and decreasing bankfull width‐to‐depth ratio, indicated potentially improved anadromous fish habitats at restored sites. We hypothesize that certain instream metrics did not improve because of spatial and/or temporal limitations of riparian vegetation to affect aquatic habitat. Restoration managers should be prepared to maintain or enhance understory diversity by controlling exotic shrubs or planting shade‐tolerant native species as much as 10 years after revegetation.     

Comparison of bird community indices for riparian restoration planning and monitoring

The use of a bird community index that characterizes ecosystem integrity is very attractive to conservation planners and habitat managers, particularly in the absence of any single focal species. In riparian areas of the western USA, several attempts at arriving at a community index signifying a functioning riparian bird community have been made previously, mostly resorting to expert opinions or national conservation rankings for species weights. Because extensive local and regional bird monitoring data were available for Nevada, we were able to develop three different indices that were derived empirically, rather than from expert opinion. We formally examined the use of three species weighting schemes in comparison with simple species richness, using different definitions of riparian species assemblage size, for the purpose of predicting community response to changes in vegetation structure from riparian restoration. For the three indices, species were weighted according to the following criteria: (1) the degree of riparian habitat specialization based on regional data, (2) the relative conservation ranking of landbird species, and (3) the degree to which a species is under-represented compared to the regional species pool for riparian areas. To evaluate the usefulness of these indices for habitat restoration planning and monitoring, we modeled them using habitat variables that are expected to respond to riparian restoration efforts, using data from 64 sampling sites in the Walker River Basin in Nevada and California. We found that none of the species-weighting schemes performed any better as an index for evaluating overall habitat condition than using species richness alone as a community index. Based on our findings, the use of a fairly complete list of 30–35 riparian specialists appears to be the best indicator group for predicting the response of bird communities to the restoration of riparian vegetation.     

Coastal wetland restoration improves habitat for juvenile sportfish in Tampa Bay,Florida, U.S.A.

Increasing human populations and urban development have led to losses of estuarine habitats for fish and wildlife. Where resource managers are restoring coastal wetlands, in addition to meeting goals related to hydrologic connectivity, biodiversity, and recreational opportunities, efforts are being made to provide habitat that is suitable for juvenile sportfish. An 18‐month study was conducted to compare juvenile sportfish use of natural, restored, and impacted sites along Tampa Bay, Florida, shorelines. Juvenile sportfish densities at restored sites were broadly comparable to natural sites and greater than at impacted sites. However, site‐specific differences in sportfish use did occur within site types. For example, one restored site had significantly higher densities of red drum Sciaenops ocellatus than any other site, while black drum Pogonias cromis were found exclusively at another restored site. To evaluate whether the restored sites are providing suitable habitat for juvenile fish, we assessed growth (estimated from counts of daily rings on otoliths) and condition (determined by lipid analyses) of juvenile common snook Centropomus undecimalis, an archetypal coastal wetland‐dependent species. Growth (0.43–0.56 mm SL/day) and condition (4.6–6.1% lipid of dry weight) exhibited only site‐specific differences and did not vary among natural, restored, and impacted site types. Although mortality rates of juvenile sportfish were not determined, use of a 40‐m seine found that densities of potential piscine predators in these coastal wetlands were relatively low compared to published studies of open estuarine shorelines. The restoration and creation of coastal wetlands in Tampa Bay provides improved habitat for juvenile sportfish.     

Site effects outweigh riparian influences on ground-dwelling beetles adjacent to first order streams in wet eucalypt forest

In wet eucalypt forest with a rainforest understorey the vegetation adjacent to first order streams does not form a distinct riparian strip. This study investigated the riparian response of terrestrial ground-dwelling beetles adjacent to four such streams in Tasmania, Australia. Beetle assemblages varied more between the four sites than they did with distance from stream within sites, where they exhibited a measurable but subtle riparian response. The extent of the riparian zone varied between the four study sites, with a 1–5 m riparian zone at three sites and a gradually changing community up to 50–100 m upslope at one site. There was a trend for greater between plot variability immediately adjacent to the streams, possibly because this is a more highly disturbed environment. None of the habitat variables measured were consistently associated with riparian or upslope assemblages of beetles, probably explaining the subtlety of the beetles’ riparian response. Forest conservation efforts for terrestrial species should not necessarily be focused on the riparian zone in preference to upslope areas.     

Western Yellow-Billed Cuckoo Nest-Site Selection and Success in Restored and Natural Riparian Forests

The western distinct population segment of yellow-billed cuckoo (Coccyzus americanus; western cuckoo) has been extirpated from most of its former breeding range in the United States because of widespread loss and degradation of riparian cottonwood (Populus spp.)-willow (Salix spp.) forests. Restoration and management of breeding habitat is important to the recovery of this federally threatened species, and identification of high-quality breeding habitat can help improve the success of recovery. In 2005, the Lower Colorado River Multi-Species Conservation Program, a long-term, multi-agency effort, was initiated to maintain and create wildlife habitat within the historical floodplain of the lower Colorado River (LCR) for federally endangered and threatened species, including western cuckoos. We conducted an empirical, multi-scale field investigation from 2008–2012 to identify habitat characteristics selected by nesting western cuckoos along the LCR. Multiple logistic regression models revealed that western cuckoos selected nest sites characterized by increased densities of small, native, early successional trees measuring 8–23 cm diameter at breast height, and lower diurnal temperature compared to available habitat in restoration and natural forests. Nesting cuckoos selected sites with increased percent canopy closure, which was also important for nest success in restoration sites along the LCR. Our results show habitat components selected by nesting western cuckoos in restoration and natural riparian forests and can help guide the creation, enhancement, and management of riparian forests with habitat conditions necessary to promote nesting of western cuckoos. © 2021 The Wildlife Society.     

The effects of riparian restoration following saltcedar (Tamarix spp.) biocontrol on habitat and herpetofauna along a desert stream

Amphibians and reptiles (herpetofauna) have been linked to specific microhabitat characteristics, microclimates, and water resources in riparian forests. Our objective was to relate variation in herpetofauna abundance to changes in habitat caused by a beetle used for Tamarix biocontrol (Diorhabda carinulata; Coleoptera: Chrysomelidae) and riparian restoration. During 2013 and 2014, we measured vegetation and monitored herpetofauna via trapping and visual encounter surveys (VES) at locations affected by biocontrol along the Virgin River in the Mojave Desert of the southwestern United States. Twenty‐one sites were divided into four riparian stand types based on density and percent cover of dominant trees (Tamarix, Prosopis, Populus, and Salix) and presence or absence of restoration. Restoration activities consisted of mechanically removing non‐native trees, transplanting native trees, and restoring hydrologic flows. Restored sites had three times more total lizard and eight times more yellow‐backed spiny lizard (Sceloporus uniformis) captures than other stand types. Woodhouse's toad (Anaxyrus woodhousii) captures were greatest in unrestored and restored Tam‐Pop/Sal sites. Results from VES indicated that herpetofauna abundance was greatest in the restored Tam‐Pop/Sal site compared with the adjacent unrestored Tam‐Pop/Sal site. Tam sites were characterized by having high Tamarix cover, percent canopy cover, and shade. Restored Tam‐Pop/Sal sites were most similar in habitat to Tam‐Pop/Sal sites. Two species of herpetofauna (spiny lizard and toad) were found to prefer habitat components characteristic of restored Tam‐Pop/Sal sites. Restored sites likely supported higher abundances of these species because restoration activities reduced canopy cover, increased native tree density, and restored surface water.     

Multi-scale analysis on wintering habitat selection of Reeves's Pheasant (Syrmaticus reevesii) in Dongzhai National Nature Reserve, Henan Province, China

Reeves's Pheasant (Syrmaticus reevesii), endemic to China, is an endangered species of pheasants. The wintering habitat selection by the species was investigated at three scales (10, 115 m and 250 m) in Dongzhai National Nature Reserve from 2000 to 2002. At each scale, a range of habitat variables were compared between the used and the control sites. At the smallest scale (10 m), the variables influencing wintering habitat selection were slope, tree cover, and the interaction between the cosine of slope aspect and the shrub height. At the mid-scale (115 m), the area of shrub, the area of broad-leaved forest, and the area of conifer forest were the key factors. At the largest scale (250 m), broad-leaved and conifer forest coverages and their interaction were the key factors. According to the lowest AIC and AIC_c values at the mid-scale, the characteristics at this scale were stated as the ultimate factors influencing the habitat selection of the bird. When a range of habitat variables at all scales within a multivariate regression were considerred, the most important variables were conifer forest coverage at the mid-scale, broad-leaved forest coverage, and the interaction between the conifer forest and shrub coverages at the large-scale, and the distance to beach and farmland. These results highlight the importance of multiscale analyses when habitat selection by pheasants are considerred.     

Waste Not,Want Not: The Need to Utilize Existing Artificial Structures for Habitat Improvement Along Urban Rivers

Urban rivers have often experienced substantial engineering modification and consequently are highly degraded aquatic ecosystems with minimal riparian habitat. Habitat restoration and improvement efforts are needed within urban rivers to support ecological communities and increase ecosystem integrity. Most river restoration techniques are not feasible within large urban rivers, and so there is a need to develop novel methodologies. Artificial structures such as river walls can function as habitat for plant and invertebrate species in urban rivers, and in some cases can be more diverse than remnant habitat. Along the River Thames through central London, plant species richness was found to be significantly higher on river walls than intertidal foreshore, which represents the only remnant habitat for riparian species. Both this survey and other studies have suggested that the physical and environmental characteristics of river walls are likely to influence their capacity to function as ecological habitat, for example, walls composed of more complex construction materials (brick and boulders) being more diverse than simpler structures (concrete and sheet piling). The opportunity exists to use river walls and other artificial structures (e.g., jetties) to improve habitat along urban rivers by installing walls which are designed to be more complex, or by adding modifications to existing walls. Some trial modifications, such as the addition of wall ledges and timber fenders to sheet piling, have been installed at Deptford Creek along the River Thames, and have so far greatly supported the colonization and development of plant communities. The restoration possibilities of such modifications should be considered, and further development and rigorous testing of installations is required in urban rivers to make sound restoration recommendations.     

Simulated Effects of Stream Restoration on the Distribution of Wet‐Meadow Vegetation

Meadow restoration efforts typically involve the modification of stream channels to re‐establish hydrologic conditions necessary for the maintenance of native vegetation. To predict change in the distribution of common meadow plant species in response to meadow restoration, a hydrologic model was loosely coupled to a suite of individual plant species distribution models. The approach was tested on a well‐documented meadow/stream restoration project on Bear Creek, a tributary to the Fall River in northeastern California, U.S.A. We developed a surface‐water and groundwater hydrologic model for the meadow. Vegetation presence and absence data from 170 plots were combined with simulated water‐table depth time series to develop habitat‐suitability models for 11 herbaceous plant species. In each model, the habitat suitability is predicted as a function of growing‐season, water‐table depth, and range. The hydrologic model was used to simulate water‐table depth time series for the pre‐ and post‐restoration conditions. These results were used to predict the spatial distribution of habitat suitability for the 11 herbaceous plant species. Model results indicate that restoration changed water levels throughout the study area, extending well beyond the near‐stream region. Model results also indicate an increase in the spatial distribution of suitable habitat for mesic vegetation and a concomitant decrease in the spatial distribution of suitable habitat for xeric vegetation. The methods utilized in this study could be used to improve setting of objective and performance measures in restoration projects in similar environments, in addition to providing a quantitative, science‐based approach to guide riparian restoration and active revegetation efforts.     

A Spatial Modeling Approach to Identify Potential Butternut Restoration Sites in Mammoth Cave National Park

Incorporation of disease resistance is nearly complete for several important North American hardwood species threatened by exotic fungal diseases. The next important step toward species restoration would be to develop reliable tools to delineate ideal restoration sites on a landscape scale. We integrated spatial modeling and remote sensing techniques to delineate potential restoration sites for Butternut (Juglans cinerea L.) trees, a hardwood species being decimated by an exotic fungus, in Mammoth Cave National Park (MCNP), Kentucky. We first developed a multivariate habitat model to determine optimum Butternut habitats within MCNP. Habitat characteristics of 54 known Butternut locations were used in combination with eight topographic and land use data layers to calculate an index of habitat suitability based on Mahalanobis distance (D²). We used a bootstrapping technique to test the reliability of model predictions. Based on a threshold value for the D² statistic, 75.9% of the Butternut locations were correctly classified, indicating that the habitat model performed well. Because Butternut seedlings require extensive amounts of sunlight to become established, we used canopy cover data to refine our delineation of favorable areas for Butternut restoration. Areas with the most favorable conditions to establish Butternut seedlings were limited to 291.6 ha. Our study provides a useful reference on the amount and location of favorable Butternut habitat in MCNP and can be used to identify priority areas for future Butternut restoration. Given the availability of relevant habitat layers and accurate location records, our approach can be applied to other tree species and areas.