Browsing by Author "George Hess, Committee Member"

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Butterfly Conservation in Fragmented Landscapes
(2009-01-30) Leidner, Allison Kara; Rob Dunn, Committee Member; Fred Gould, Committee Member; George Hess, Committee Member; Nick Haddad, Committee Chair
Human activities disturb and fragment many natural areas, thereby altering the way in which species interact with their landscape. In natural settings, species often evolved to disperse through areas unsuitable for habitation, but in a world dominated by human-modified landscapes, species face novel features that may disrupt their movement, increasing the isolation of populations. Consequently, there is a pressing need to understand if animals can persist in small natural areas separated by agricultural or urban development. The way in which species respond to fragmentation will inform if conservation actions are necessary to protect a species and what strategies might mitigate the consequences of fragmentation. My dissertation addresses these conservation problems using two studies of butterflies in fragmented landscapes. First, I used a novel synthesis of behavioral, mark-recapture, and population genetic studies to identify the effects of urban fragmentation on a rare butterfly. I present the synthesis in the context of a butterfly endemic to barrier islands in North Carolina, Atrytonopsis new species 1. Atrytonopsis sp1 occupies sand dune habitat, which in this region has largely been converted to residential and commercial development. Many studies rely on a single method to measure movement, but combining methods may help elucidate the effects of natural or anthropogenic fragmentation. To test edge permeability, I conducted butterfly releases at four edge types: sand dune â€“ beach, sand dune â€“ maritime forest/shrub, sand dune â€“ urbanization, and beach â€“ ocean. I then used mark-recapture to compare Atrytonopsis sp1 movement rates in continuous sand dune habitat and between habitat patches separated by urban areas. Finally, I conducted a range-wide population genetic study to assess if there was significant population structure across the range of Atrytonopsis sp1, and to determine how the structure was partitioned relative to natural barriers and urbanization. All three studies independently indicate that natural features, not urbanization, are barriers to Atrytonopsis sp1 movement. Analyzed separately, each study would point to the same general conclusion, but could result in different conservation recommendations. Both linear corridors and stepping-stones are conservation strategies that can increase connectivity of fragmented landscapes. For stepping stones to work, however, Atrytonopsis sp1 must be willing to enter the matrix, successfully find new habitat, and integrate its genes into the new population. The edge behavior studies indicate that Atrytonopsis sp1 will fly into urban areas, and the mark-recapture studies confirm that it can successfully disperse over short distances. The population genetic studies indicate that longer distances of urbanization are not intrinsically barriers to movement. Consequently, I recommend conservation strategies that focus on preserving stepping stones, rather than on habitat corridors. In a separate study, I examined the effects of habitat fragmentation on tropical butterfly communities. Habitat fragmentation is a major driver of biodiversity loss, but its effects may be obscured by the ways in which different species respond to fragmentation. One reason that species display varying responses to fragmentation may be that variability itself is an effect of fragmentation. I tested whether forest fragmentation causes long-term hyperdynamism in butterfly communities, a taxon that naturally displays large variations in species richness and community composition. Using an 11-year dataset from an experimentally fragmented landscape in the central Amazon, I evaluated the effect of fragmentation on changes in species richness and community composition through time. Butterfly species richness did not differ between fragmented forest and intact forest. However, spatial and temporal patterns of butterfly species richness in fragmented forests were significantly more variable than in intact forest. Fragmented forest had a significantly lower proportion of understory shade species and a significantly higher proportion of edge species. I conclude that fragmentation fundamentally alters the natural dynamics of butterfly communities.
The Development and Testing of a Procedure for Monitoring Visitor-Horse Interactions at Assateague Island National Seashore
(2005-04-13) Ingle, Margaret Christine; Yu-Fai Leung, Committee Chair; J. Douglas Wellman, Committee Member; George Hess, Committee Member
Developing visitor impact indicators and associated monitoring techniques are critical first steps to sustain a balance between two national park mandates, protecting resources and providing recreation opportunities. The first paper of this thesis provides a comprehensive and organized assessment of major techniques that have been developed for monitoring visitor impacts in coastal areas, with a special focus on sandy coasts and barrier islands. Four major types of monitoring techniques are identified: remote sensing, on-site assessment, behavior observation, and perception survey. Current trends in impact monitoring, including a global expansion of impact studies, integrated methodological approaches, and an increase in the application of technology, are discussed. The second paper of this thesis describes the development of a procedure to monitor visitor-feral horse interactions at Assateague Island National Seashore. The procedure uses behavior observation of visitors and wildlife and remote sensing with Global Positioning System units. The behavior observation portion adopts behavior sampling and one-zero recording based on the ethological literature. General categories of behaviors of both visitors and wildlife are recorded: neutral, attraction, avoidance, and aggression. For visitors, two additional behaviors, touching and feeding, are recorded because they are illegal behaviors and of special concern to park managers. The behavior observation portion was tested on undergraduate students for inter-observer reliability and accuracy using video surveys. Wildlife aggression was the highest in accuracy and inter-observer reliability, but did not occur on the video clips. Wildlife neutral, visitor touching, and visitor neutral were within the acceptable ranges for inter-observer reliability and accuracy. Visitor avoidance was outside of the acceptable range in both inter-observer reliability and accuracy. Implications for the implementation of the monitoring protocol include a thorough training session that includes video clips of behaviors to help observers better understand the behaviors and monitored practice observation sessions in the field.
The effect of spatial resolution on an object-oriented classification of downed timber
(2007-08-10) Swain, Jeff B; Heather Cheshire, Committee Chair; Stacy Nelson, Committee Member; George Hess, Committee Member
Implications of exotic species invasion for restoration of urban riparian forests
(2004-07-12) Vidra, Rebecca Lynn; Thomas R. Wentworth, Committee Member; George Hess, Committee Member; Jon M. Stucky, Committee Member; Nick M. Haddad, Committee Member; Theodore H. Shear, Committee Chair
Urban forests serve as remnant natural areas in otherwise degraded landscapes. Yet, these forests are commonly threatened by invasion of exotic plant species, which may compromise the structure and ecological functions of native communities. Restoration of these forests will inevitably require removal and continued control of exotic species invasions. I focused my research on urban riparian forests within Raleigh and Cary, North Carolina, USA. My goals are to understand the impacts of exotic species invasion on these forest communities, identify factors that make these sites susceptible to invasion, and make appropriate restoration recommendations. To address these goals, three major studies structured my research. First, I tested two major paradigms of current exotic species ecology using observational data from 23 urban riparian buffers. The competition paradigm was borne out by negative relationships between exotic and native species richness (r = -0.66, p = 0.0009). I also detected shifts in species composition away from native woody species in sites that have been invaded by exotic species. As suggested by the resource availability paradigm, certain environmental conditions do seem to favor exotic species in this study system. While light availability was not significantly correlated to invasion of exotic species, several measures of soil fertility were negatively correlated to native species and positively correlated to exotic species. Therefore, efforts to reduce fertilization from adjacent and upstream landscapes should be part of any restoration plan. My second approach involved conducting an experimental removal study at the North Carolina Museum of Art. I compared the species composition and native species recovery in three treatments: control, initially removing all vegetation and allowing regeneration, and initial removal with repeated removal of new exotic recruits. While the repeated removal treatment featured a different species composition than either of the other two treatments, this difference can be attributed to the lack of exotic species, not to the recovery of native species. These results indicate that repeated removal is necessary to prevent invasion in urban forests but that native supplemental plantings may be necessary to create a diverse community. My third approach involved evaluating the influence of landscape structure on patterns of exotic species invasion in urban riparian buffers. I found that invasion, measured as total percent cover of exotic species, is highest in the narrowest buffers. Buffers surrounded by more forest canopy cover are also more heavily invaded than those surrounded by less canopy cover. These findings suggest that processes outside the buffer, such as bird dispersal and vegetative spreading of ornamental plantings, may contribute to the invasion inside the buffer. Exotic species invasion does have implications for restoration of urban forests. Not only does invasion threaten native species richness, but native woody species appear to be most at risk for extirpation from these sites, with potential consequences for long-term forest succession. Because these forests are invaded by a suite of exotic plants, targeted efforts to remove those that are likely outcompeting native species is a good first step. Managing land use practices outside of the forests, while difficult, is necessary to reduce both the stress on the forest (e.g., fertilization) and invasion opportunities (e.g., bird dispersal, ornamental plantings). The results of this research will help managers identify sites at future risk for invasion and focus efforts on managing both the exotic species and site conditions to restore the health of these ecologically valuable forest communities.
Spatial Tools for Managing the Hemlock Woolly Adelgid in the Southern Appalachians
(2005-12-06) Koch, Frank Henry Jr.; Heather Cheshire, Committee Chair; Hugh Devine, Committee Member; Fred Hain, Committee Member; George Hess, Committee Member
Native to Asia, the hemlock woolly adelgid (Adelges tsugae) has recently spread into parts of the southern Appalachian region. This insect pest attacks both native hemlock species (Tsuga canadensis and T. caroliniana), has no natural enemies, and can kill hemlock trees within just a few years. While biological control displays promise for combating the pest, such counter-measures are significantly hampered because neither adelgid nor hemlock distribution patterns have been detailed explicitly. We developed a spatial management system to better target control efforts. The system has two components: (1) a protocol for mapping hemlock stands, and (2) a technique to map areas at risk of imminent hemlock woolly adelgid infestation. To map hemlock stands, we utilized topographically normalized satellite imagery from Great Smoky Mountains National Park. Because hemlocks are difficult to distinguish using just satellite data, we constructed a decision tree classifier that supplemented the imagery with a suite of topographic, environmental, and proximity variables. We then implemented the classifier in a geographic information system and generated hemlock distribution maps. Our final decision tree had 27 terminal nodes and nine variables, with elevation, image band ratios, topographic relative moisture index, and distance to the closest stream among the most important variables. Accuracy assessment—based on field data and aerial photos—of the maps resulting from this tree yielded an overall thematic accuracy of 90% for one study area and 75% accuracy in capturing hemlocks in a second study area. To map areas at risk, we combined known first-year infestation locations from Great Smoky Mountains National Park and the Blue Ridge Parkway with points from uninfested hemlock stands, recording a suite of environmental variables for each point. We applied four different techniques (discriminant analysis, k-nearest neighbor, logistic regression, and decision tree) to generate models from these data in order to predict locations at high risk of imminent hemlock woolly adelgid infestation. We then used the resulting models to generate risk maps of the study region. All techniques performed well, accurately capturing 70-90% of training and validation samples. Discriminant analysis was the most accurate technique, but logistic regression yielded a more practical map from a management standpoint, with large, discrete risk zones. In any case, our results suggest that roads, major trails, and riparian corridors provide an important degree of connectivity enabling long-distance dispersal of the hemlock woolly adelgid, probably by humans or birds. Both components of our hemlock woolly adelgid management system are built on readily available or easily calculable spatial data. Furthermore, they are constructed generally enough that they should be applicable throughout the southern Appalachians. Overlay of derived maps will allow forest managers to prioritize hemlock stands and allocate resources more efficiently.
Using GIS and LIDAR to Map Headwaters Stream Networks in the Piedmont Ecoregion of North Carolina
(2005-03-03) Garcia, Valerie Cover; James Gregory, Committee Member; George Hess, Committee Member; Heather Cheshire, Committee Chair
A large percentage of nonpoint source pollution found in our Nation's waterbodies is suspected to occur through first- and second-order (headwaters) streams. Such streams drain a much greater proportion of watershed area and have a much greater length of riparian zone interaction with the land than the higher-order streams typically studied for nonpoint source water quality problems. The State of North Carolina and the U.S. EPA are interested in examining the contribution of lowerorder streams to the overall nonpoint source pollution problem; however, the mapping of first- and second-order streams is extremely poor. The recent availability of fine resolution Light Detection and Ranging (LIDAR) data for portions of the State of North Carolina provides the opportunity for developing improved methods of mapping lower-order streams using Geographic Information System (GIS) approaches. In this study, I investigated the state-of-science for mapping topography and extracting headwaters stream networks using LIDAR data and GIS approaches. I applied these techniques to map headwaters streams at a study site in the Piedmont Ecoregion of North Carolina. I found that LIDAR produced more accurate elevation maps (elevation accuracy within 1.2') than currently available maps, such as the USGS 7.5 minute Digital Elevation Models (elevation accuracy within 49'). The Triangulated Irregular Network (TIN) produced the best topographic maps, but the Digital Elevation Model (DEM) was better for automatically extracting headwaters streams. The best headwaters stream maps were derived by using a hydro-enforced TIN for generating the base DEM,and extracting the stream network from this base DEM using ArcHydro and the AGREE algorithm. These improved headwaters stream maps will enable decision-makers to assess and mitigate nonpoint source water quality problems.