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Development of a Biologically Centered Habitat-Monitoring Technique: SPIDER Transect Method
Stacy L. Hines

Southeastern Naturalist, Volume 15, Issue 3 (2016): 513–522

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Southeastern Naturalist 513 S.L. Hines 22001166 SOUTHEASTERN NATURALIST 1V5o(3l.) :1551,3 N–5o2. 23 Development of a Biologically Centered Habitat-Monitoring Technique: SPIDER Transect Method Stacy L. Hines* Abstract - Overabundance of Odocoileus virginianus Zimmermann (White-tailed Deer) can have negative effects on woody vegetation. I developed the SPIDER transect method to quantify an area impacted by deer overbrowsing. I compared area evaluated and time expended (effort) with the traditional belt-transect method. The SPIDER transect method had 3× less transects that were at least 20× longer and evaluated an area 50× larger (350 ha) with 50% less effort compared to the belt-transect method (6 ha). The quantifiable area is an advantage of the SPIDER method that is not obtained using the traditional belt-transect method; in this study, woody vegetation in a 304.5-ha area around a park campground exhibited overbrowsing. The SPIDER transect is a wildlife-centric, efficient method that could be beneficial for prescribing and evaluating management recommen dations. Introduction Overabundant species can modify ecosystem processes and limit resources (Healy et al. 1997). Overabundance of Odocoileus virginianus Zimmermann (White-tailed Deer; hereafter Deer) can interfere with nutrient cycling, simplify vegetation communities, and have negative effects on other species (Barrett and Stiling 2006, Cote et al. 2004, Rooney 2009). Management of Deer densities is important to avoid these negative consequences on the abiotic and biotic components of habitat. However, Deer density estimates are often inaccurate, especially in forested areas. Therefore, researchers have proposed monitoring Deer impacts on vegetation to prescribe and evaluate management recommendations (Aldous 1944, Healy et al. 1997, Morellet et al. 2001). Belt transects are widely used for evaluating woody vegetation in forested areas; established protocols include sampling all vegetation along 50–100-m transects until the species area curve levels off (e.g., no new species identified with additional transects; Andrews 1974, Barbour et al. 1987). However, biologists need better methods for assessing relative population size because established vegetationmonitoring methods can be time consuming and sample only a small portion of the landscape (Aldous 1944, Morellet et al. 2001). Vegetation monitoring completed at smaller scales may not accurately portray impacts of species because utilization of vegetation communities across the landscape can be heterogeneous (Healy et al. 1997). Development of monitoring methods based on vegetation use by individual species would provide insight into the species’ impacts and better guide management decisions. *Department of Biology, University of North Carolina at Greensboro, Greensboro, NC 27402. Current address - Caesar Kleberg Wildlife Research Institute, Texas A&M University- Kingsville, MSC#218, Kingsville, TX 78363; stacylhines@bellsouth.net. Manuscript Editor: Alvin Diamond Jr. Southeastern Naturalist S.L. Hines 2016 Vol. 15, No. 3 514 The objective of this study was to compare vegetation assessments (area evaluated and time expended) using the traditional belt-transect method (following established protocols) with a new method I developed to evaluate the impacts of overabundant deer on woody vegetation that was biologically centered, easily replicated, and required little effort and equipment. The Spherical Primary and Intermediate Directional Examination of Resources (SPIDER) transect method is biologically centered because the vegetation community is systematically evaluated in a circular pattern radiating outward from a central location—emulating Deer activity surrounding a feed site (Brown and Cooper 2006, Cooper et al. 2006, Doenier et al. 1997) or core area of use (Kilpatrick and Stober 2002, McNulty et al. 1997, Oyer and Porter 2004). A qualitative comparison of these methods is reported to illustrate how established vegetation-monitoring techniques may accurately describe the vegetation community, but may not depict a species use of the vegetation community. Field-Site Description Morrow Mountain State Park is located in the Piedmont region of North Carolina (1919 ha; 35°22'N, 80°5'W) and has been open to the public since 1939 (NC State Parks 2009). The park is part of the Uwharrie Mountains located in the eastern temperate forest ecoregion. Canopy vegetation is dominated by Quercus spp. (oaks), Carya spp. (hickories), and Pinus virginiana Mill. (Virginia Pine). Understory vegetation consists of species such as Acer rubrum L. (Red Maple), Ilex opaca Aiton (American Holly), and Cornus florida L. (Flowering Dogwood). Deer density in the park was estimated at 30–34 Deer/km2 (K. Knight, NC Wildlife Resources Commission, Albemarle, NC, pers. comm.). Feeding of wildlife is prohibited in NC state parks (North Carolina General Statute § 113-35: 15A NCAC 12B .0201 [c]). However, park visitors have been feeding Deer in the campground area of the park for more than 20 years (T. McCree, retired park superintendent, Morrow Mountain State Park, Albemarle, NC, pers. comm.). Food provided to Deer by humans tends to congregate Deer and sometimes leads to increased population densities in such areas. As Deer populations become overabundant, browse lines become more noticeable (Cooper et al. 2006). For these reasons, distinct browse lines are evident in the campground area of the park, and not seen in other areas of the park although Deer populations are present (Fig. 1). Methods From February to April, just prior to spring green-up, I completed vegetation assessments of woody species in the campground area at Morrow Mountain State Park (North Carolina State Parks Research Activity Permit No. R09-03). I did not include herbaceous, non-woody vegetation in evaluations because Deer diets consist predominately of woody species during winter (Aldous 1944, Johnson et al. 1995, Swihart and Picone 1998). I chose the center of the main campground road as the central point of vegetation assessments because along this road most human feeding of Deer occurred and Deer were usually observed there every evening (S. Hines, 1.5 years of pers. observ.). Southeastern Naturalist 515 S.L. Hines 2016 Vol. 15, No. 3 SPIDER transect method I developed the Spherical Primary and Intermediate Directional Examination of Resources (SPIDER) transect method, described herein, to evaluate the impacts of Deer on woody vegetation. I named the transect method SPIDER for the 8 “legs” (number of transects) and developed an acrostic from each letter which best described the method. A central location is determined by the researcher and study question of interest, but could be identified by core area of use, feed source, water source, bedding site, etc. Resources are examined along 8 transects which radiate outward from the central location, as in the spokes of a wheel (a “spherical-like” shape), following the primary (N, S, E, W) and intermediate (NE, SE, NW, SW) magnetic directions (while it is understood the shape is not exactly a sphere, spherical was the best term that began with “S” and described a circular-type shape). I used the SPIDER method to quantify the area impacted by Deer overbrowsing. Woody vegetation is most prone to Deer browsing within 30–60 cm from the forest floor (Cote et al. 2004). If the browse-line height is higher than the range where woody vegetation is most susceptible to Deer browsing, then overbrowsing would be indicated. For this study, overbrowsing was indicated when the browse-line height was greater than 55 cm. I used 55 cm as the cutoff because it was the average browseline height of woody vegetation in an area (2.4 km from the campground) known to have active Deer population present, but without the influence of human feeding. Browse-line height of woody vegetation deer consumed, identified by the unique cut plane left from Deer browsing on twigs (Morellet et al. 2001), was measured from the forest floor to the first-encountered horizontal, twig-sized limb (≤2 cm Figure 1. Distinct browse line in the campground area of Morrow Mountain State Park, Albemarle, NC. Southeastern Naturalist S.L. Hines 2016 Vol. 15, No. 3 516 in diameter). One browse-line height measurement was taken at 50-m increments, along each of the 8 transects, within 5 m of the transect line. The 50-m increments were paced. Calibration of stride and number of steps per 50 m was determined before measurements began; the same individual completed all sampling. I recorded all points using a GPS. No pre-determined length (distance from central starting point) was used for transects because the objective was to quantify the area of overbrowsing. Therefore, browse-line height measurements continued along each transect every 50 m until browse-line height was within typical range most prone to deer browsing. The end point for each transect was established when 3 consecutive measurements were 55 cm or less or the park boundary/lake was encountered. Transect points and corresponding browse-line height at each point were mapped using ArcMap (ArcGIS software version 10.0; Redlands, CA). Browse-line heights were divided into 3 categories: ≤55 cm, 56–100 cm, and ≥101 cm. The extent of the area of Deer overbrowsing was the area contained within the perimeter defined by the furthest point (from the center outward) along each transect at which the browse-line height of that point was ≥56 cm, but does not contain the points when 3 measurements in a row were ≤55 cm. In the case a boundary was encountered before 3 measurements in a row were ≤55 cm, the area within the perimeter would not contain the furthest point (or last 2 points) on the transect if the browse-line height was ≤55 cm at those points. Traditional vegetation assessment method: belt transect Along the campground road, I evaluated woody vegetation species within belt transects according to established vegetation-assessment protocols. I assessed woody vegetation across twenty-six 1 m × 50 m belt transects, 13 on each side of the road, starting 5 m from the road (to alleviate affects from routinely mowed grass), and 50 m apart (Andrews 1974). Within every 1-m2 block of the 50-m2 transect, all woody vegetation was identified and browse-line height (cm) was measured. The number of species were plotted against increasing number of transects to determine if an adequate number of transects had been completed to be representative of the woody vegetation community (Barbour et al. 1987). Results SPIDER transect method Browse-line height was measured on 170 individual saplings and trees (range: 16–37 individuals per transect) except for Pinus spp. (Appendix A). The length of the 8 transects from the central starting location ranged from 1000 to 1750 m (Fig. 2). The S, SE, E, and NE transects continued until the park boundary/lake was encountered. The N, NW, W, and SW transects continued until 3 measurements in a row were ≤55 cm. The N transect was the longest; terrain was mostly flat with undulating hills (largest elevation change was 12 m over a distance of 100 m). The SW transect was the only transect where the browse-line height of woody vegetation gradually decreased along the transect (100 m beyond central starting location, the browse-line height was ≥101 cm for 300 m, decreasing to 56–100 cm, mostly, for Southeastern Naturalist 517 S.L. Hines 2016 Vol. 15, No. 3 Figure 2. Map of study site in Morrow Mountain State Park showing the browse-line height of woody vegetation along SPIDER transects, the area centered on the campground that is impacted by deer overbrowsing (304.5 ha; area within polygon), and the area evaluated using traditional belt transect method (6.13 ha; black filled blocks). For SPIDER survey points, white circles and triangles represent places woody vegetation was consider overbrowsed (to ≥56 cm above the ground), and black triangles represent places exhibiting typical deer browsing (≤55 cm). Southeastern Naturalist S.L. Hines 2016 Vol. 15, No. 3 518 350 m, and then was ≤55 cm). There were 1 or 2 consecutive measurements along 4 of the 8 transects where the browse-line height of woody vegetation was ≤55 cm, but immediately followed by measurements ≥56 cm, ranging from 50–500 m in length along the transect. Surrounding the campground area, woody vegetation in 304.5 ha exhibited a browse-line height ≥56 cm, with most of the area (except for 23 ha surrounding the SW transect) exhibiting a browse-line height ≥101 cm. Traditional vegetation assessment method: belt transect There were 257 woody plants of 19 species identified in the campground area (Appendix A). No new species were identified after 19 transects, therefore 26 transects were an adequate number of transects to be representative of woody vegetation community according to established protocols (Fig. 3). The total area within the perimeter of the belt transects was 6.13 ha (Fig. 2). Browse-line height could not be measured on all 257 woody plants because in forests, trees self-prune lower branches. Browse-line was within reach and measured on 170 individual saplings and trees, of which 113 individual saplings and trees were species browsed by Deer. The average browse-line height for all woody species (n = 170) and woody species browsed by Deer (n = 113) was 122.1 ± 8.8 cm and 131.2 ± 6.2 cm, respectively Figure 3. Number of woody vegetation species identified plotted against the increasing number of belt transects evaluated. One of the protocols for the belt-transect method necessitates the addition of transects until the species area curve levels off (e.g., no new species identified with additional transects) to ensure an adequate number of transects were completed to be representative of the vegetation community (Barbour et al. 1987), which occurred after 19 transects in this study. Southeastern Naturalist 519 S.L. Hines 2016 Vol. 15, No. 3 (mean ± 1 SE; n = 26). The entire area within the belt transects (6 ha) exhibited Deer overbrowsing. Comparison of SPIDER and belt-transect methods The objective of the SPIDER transect method was to quantify the area impacted by Deer overbrowsing, and evaluation continued until there was a measurable difference of the impact Deer had on woody vegetation (Table 1). In contrast, according to established protocols, the objective of the traditional belt-transect method is to describe the vegetation community and evaluation continued until no new vegetation species were identified with the addition of more transects. The SPIDER transect method had 3× less transects, although these were at least 20× longer and evaluated an area 50× larger with 50% less time invested compared to the belt-transect method. Browse-line height was measured on a similar number of individual saplings and trees using both methods. However, due to differences in objectives and protocols between methods, 100% of individuals evaluated using the SPIDER transect method were species browsed by Deer compared to approximately 67% of individuals evaluated using the traditional belt-transect method. Table 1. Qualitative comparison of Spherical Primary and Intermediate Directional Examination of Resources (SPIDER) transect and traditional belt transect methods of vegetation assessment; specifically examining deer use of resources (browse line height of woody plants) following established protocols for each method. Vegetation assessment method Qualitative comparison SPIDER transect Traditional belt transect Objective1 Evaluate impacts on woody Evaluate the woody vegetation vegetation community from deer; community; specifically to specifically to quantify the area adequately describe the impacted by deer overbrowsing. vegetation community. Rule objective was met Evaluation along transect continued Evaluation of transects continued until 3 measurements in (number used) continued until a row were ≤ the height woody no new vegetation species were vegetation is most susceptible identified with the addition of to deer browsing. more transects. Number of transects 8 26 Length of transects (m) 1000–1750 50 # of individual saplings and trees2 170 170 Individuals browsed by deer 170 113 Total area within perimeter of 350 6.13 transects (ha) Area exhibited overbrowsing( ha)3 304.5 6.13 Total time invested (days) 4 9 Time in field (days) 3 6 Time for data entry/analysis (days) 1 3 1The objective is a brief summary of the protocol for each method, specifically what each method evaluates. 2Number of individual woody plants in which browse line height was measured. 3Overbrowsing is defined as browse-line height ≥56 cm, or higher than the height that woody species are most susceptible to deer browsing. Southeastern Naturalist S.L. Hines 2016 Vol. 15, No. 3 520 Discussion The SPIDER transect method is a wildlife-centric assessment of how a wildlife species impacts the vegetation community, whereas the traditional belttransect method is a vegetation-centric evaluation of the vegetation community. The SPIDER transect method is more rapid and quantifies the area Deer negatively impact, which is not obtained using the traditional belt-transect method. In addition, use of the SPIDER transect provided information regarding how the species utilized resources across the landscape. For example, Deer heavily browsed on woody species further from the central feed site when topography was flat or gently sloping (North transect). Furthermore, Deer utilization of woody vegetation was heterogeneous across the landscape (e.g., there were small patches within the area impacted by Deer overbrowsing where browse-line height was within typical range). The SPIDER transect method is not intended to replace other vegetation-assessment techniques, but can be quicker for assessing browsing impacts with fewer, albeit longer, transects focused on evaluating resources impacted by the species of interest. A primary application of this method is for species that concentrate activity around a core area of use (feeder or man-made feed plot, water source, bedding/ denning site, etc.) and there is a definable change in the use of resources (browseline height, abundance of a food resource highly selected for, standing crop of annual forbs, etc.). Length of transects would not be pre-defined, but determined from in-field evaluation using pre-established criteria to indicate that the species has changed its use or impact on resources. However, the length of transects could be fixed, for example based on the area of core use, home-range size, or study enclosure. An advantage of the SPIDER transect method is the quantifiable determination of the area impacted by particular wildlife species, with the assumption that resources between transect lines are impacted in a similar manner as defined along transect lines. Thus, the SPIDER transect could be beneficial for prescribing and evaluating management recommendations. Acknowledgments I would like to thank A.E. Hershey for the use of equipment; J. Amoroso, B. Beck, E. Beverly, and G. Queen for their assistance with ArcMap; K. Knight for assisting with field research; and T.E. Fulbright, D.G. Hewitt, and S.L. Webb for reviewing this manuscript. Funding for this project was provided through the Advisory Council with the University of North Carolina at Greensboro’s Dean of Undergraduate Studies. Publication funding was provided by Caesar Kleberg Wildlife Research Institute (CKWRI) at Texas A&M – Kingsville; this is CKWRI publication number 15-113. Literature Cited Aldous, S.E. 1944. A deer-browse survey method. Journal of Mammalogy 25:130–136. Andrews, W.A. 1974. A Guide to the Study of Terrestrial Ecology. Prentice-Hall, Inc., Englewood Cliffs, NJ. 246 pp. Barbour, M.G., J.H. Burk, and W.D. Pitts. 1987. Terrestrial Plant Ecology. Benjamin and Cummings Publishing Company, Menlo Park, CA. 634 pp. Southeastern Naturalist 521 S.L. Hines 2016 Vol. 15, No. 3 Barrett, M.A. and P. Stiling. 2006. Key deer impacts on hardwood hammocks near urban areas. The Journal of Wildlife Management 70:1574–1579. Brown, R.D., and S.M. Cooper. 2006. The nutritional, ecological, and ethical arguments against baiting and feeding White-tailed Deer. Wildlife Society Bulletin 34:519–524. Cooper, S.M., M.K. Owens, R.M. Cooper, and T.F. Ginnett. 2006. Effect of supplemental feeding on spatial distribution and browse utilization by White-tailed Deer in semi-arid rangeland. Journal of Arid Environments 66:716–726. Cote, S.D., T.P. Rooney, J-P. Tremblay, C.Dussault, and D.M. Waller. 2004. Ecological impacts of deer overabundance. Annual Review of Ecology, Evolution, and Systematics 35:113–147. Doenier, P.N., G.D. DelGuiduice, and M.R. Riggs. 1997. Effects of winter supplemental feeding on browse consumption by White-tailed Deer. Wildlife Society Bulletin 25:235–243. Healy, W.M., D.S. deCalesta, and S.L. Stout. 1997. A research perspective on Whitetailed Deer overabundance in the northeastern United States. Wildlife Society Bulletin 25:259–263. Johnson, A.S., P.E. Hale, W.M. Ford, J.M. Wentworth, J.R. French, O.F. Anderson, and G.B. Pullen. 1995. White-tailed Deer foraging in relation to successional stage, overstory type, and management of southern Appalachian forests. American Midland Naturalist 133:18–35. Kilpatrick, H.J., and W.A. Stober. 2002. Effects of temporary bait sites on movements of suburban White-tailed Deer. Wildlife Society Bulletin 30:760–766. McNulty, S.A., W.F. Porter, N.E. Mathews, and J.A. Hill. 1997. Localized management for reducing White-tailed Deer populations. Wildlife Society Bulletin 25:264–271. Morellet, N., S. Champely, J-M. Gaillard, P. Ballon, and Y. Boscardin. 2001. The browsingindex: New tool uses browsing pressure to monitor deer populations. Wildlife Society Bullein 29:1243–1252. North Carolina (NC) State Parks. NC State Parks website. Available online at http://www. ncparks.gov. Accessed January 2009. Oyer, A.M., and W.F. Porter. 2004. Localized management of White-tailed Deer in the central Adirondack Mountains, New York. The Journal of Wildlife Management 68:257–265. Rooney, T.P. 2009. High White-tailed Deer densities benefit graminoids and contribute to biotic homogenization of forest ground-layer vegetation. Plant Ecology 1:103–111. Swihart, R.K., and P.M. Picone. 1998. Selection of mature growth stages of coniferous browse in temperate forests by White-tailed Deer (Odocoileus virginianus). American Midland Naturalist 139:269–274. Southeastern Naturalist S.L. Hines 2016 Vol. 15, No. 3 522 Appendix A. Woody vegetation species identified in the belt transects conducted in the campground area at Morrow Mountain State Park, Albemarle, NC. One of the protocols for the belt transect method requires the identification of all vegetation species within each transect to ensure an adequate number of transects were completed to be representative of the vegetation community (see Fig. 3; Barbour et al. 1987). Common name Scientific name American Hazelnut Corylus americana Walter American Holly Ilex opaca Aiton Chalk Maple Acer leucoderme Small Chestnut Oak Quercus montana Willd. Eastern Redcedar Juniperus virginiana L. Flowering Dogwood Cornus florida L. Loblolly Pine Pinus taeda L. Mockernut Hickory Carya tomentosa (Lam.) Nutt. Muscadine Vitis rotundifolia Michx. Red Maple Acer rubrum L. Shagbark Hickory Carya ovata (Mill.) K. Koch Shortleaf Pine Pinus echinata Mill. Sourwood Oxydendrum arboretum (L.) DC. Sweetgum Liquidambar styraciflua L. Virginia Pine Pinus virginiana Mill. Yellow Poplar Liriodendron tulipifera L. Oak Species Quercus sp. Unknown 1 - Unknown 2 -