Elevated deer densities have led to reports of forest regeneration failure and ecological damage. However, there is growing evidence that the biophysical conditions of a forest that make it attractive to deer may be a contributing factor in determining browsing levels. Thus, an understanding of settling stimulus—how attractive an area is to deer in terms of food-independent habitat requirements—is potentially important to manage deer browsing impacts. We tested the settling stimulus hypothesis by evaluating the degree to which thermal settling stimulus and deer density are related to spatial variation in browsing intensity across different forest harvesting strategies over the course of a year. We determined if deer were impacting plant communities and if they resulted in changes in plant cover. We quantified the thermal environment around each harvest and tested to see if it influenced deer density and browsing impact. We found that deer had an impact on the landscape but did not alter plant cover or diminish forest regeneration capacity. Deer density and browse impact had a relationship with thermal settling stimulus for summer and fall months, and deer density had a relationship with browse impact in the winter on woody plants. We conclude that thermal settling stimulus is an important predictor for deer density and browsing impact. 1. Introduction The slowing or failure of the regeneration of high value timber species in the northeastern USA is often attributed to high white-tailed deer (Odocoileus virginianus) abundances [1, 2]. In particular, above threshold densities of 10 to 15 deer km？2, deer are reported to alter forest composition via selective browsing of woody plant species such as eastern hemlock (Tsuga canadensis), red maple (Acer rubrum) sprouts, and Rubus spp. [1, 3–5]. Heavy browsing may in turn cause forest regeneration failure and decreased vertical structural complexity of forest stands that may impact wildlife habitat and ecosystem functions such as nutrient mineralization rates [6–10]. Selective browsing by highly abundant deer populations may also interact with forest management, causing areas to entrain into altered stable states [11] and creating savannah-like areas dominated by ferns, grasses, and sedges that inhibit forest regeneration [1]. Nevertheless, deer density and selective browsing alone may not always explain spatial and temporal variation in vegetation impacts [12, 13]. Instead, available forage in relation to settling stimulus—how attractive an area is in terms of the food-independent habitat requirements of deer,
References
[1]
W. S. Alverson, D. M. Waller, and S. L. Solheim, “Forests too deer: edge effects in Northern wisconsin,” Conservation Biology, vol. 2, no. 4, pp. 348–358, 1988.
[2]
W. M. Healy, “Influence of deer on the structure and composition of oak forests in central Massachusetts,” in The Science of Overabundance: Deer Ecology and Population Management, W. J. McShea, H. B. Underwood, and J. H. Rappole, Eds., Smithsonian Institution Press, Washington, DC, USA, 1997.
[3]
E. W. Beals, G. Cottam, and R. J. Vogl, “Influence of deer on vegetation of the Apostle Islands, Wisconsin,” The Journal of Wildlife Management, vol. 24, no. 1, pp. 68–80, 1960.
[4]
S. B. Horsley, S. L. Stout, and D. S. DeCalesta, “White-tailed deer impact on the vegetation dynamics of a northern hardwood forest,” Ecological Applications, vol. 13, no. 1, pp. 98–118, 2003.
[5]
T. P. Rooney and D. M. Waller, “Direct and indirect effects of white-tailed deer in forest ecosystems,” Forest Ecology and Management, vol. 181, no. 1-2, pp. 165–176, 2003.
[6]
J. F. Franklin, T. A. Spies, R. V. Pelt et al., “Disturbances and structural development of natural forest ecosystems with silvicultural implications, using Douglas-fir forests as an example,” Forest Ecology and Management, vol. 155, no. 1–3, pp. 399–423, 2002.
[7]
A. F. Hough, “A twenty-year record of understory vegetational change in a Virgin Pennsylvania Forest,” Ecology, vol. 46, no. 3, pp. 370–373, 1965.
[8]
N. G. Tilghman, “Impacts of white-tailed deer on forest regeneration in northwestern Pennsylvania,” Journal of Wildlife Management, vol. 53, no. 3, pp. 524–532, 1989.
[9]
D. S. DeCalesta, “Deer and ecosystem management,” in The Science of Overabundance: Deer Ecology and Population Management, W. J. McShea, H. B. Underwood, and J. H. Rappole, Eds., pp. 267–297, Smithsonian Institution Press, Washington, DC, USA, 1997.
[10]
W. J. McShea, H. B. Underwood, and J. H. Rappole, “Deer management and the concept of overabundance,” in The Science of Overabundance: Deer Ecology and Population Managment, W. J. McShea, H. B. Underwood, and J. H. Rappole, Eds., pp. 1–7, Smithsonian Institution Press, Washington, DC, USA, 1997.
[11]
O. J. Schmitz and A. R. E. Sinclair, “Rethinking the role of deer in forest ecosystem dynamics,” in The Science of Overabundance: Deer Ecology and Population Management, W. J. McShea, H. B. Underwood, and J. H. Rappole, Eds., pp. 201–223, Smithsonian Institution Press, Washington, DC, USA, 1997.
[12]
P. M. Hurley, C. R. Webster, D. J. Flaspohler, and G. R. Parker, “Untangling the landscape of deer overabundance: reserve size versus landscape context in the agricultural Midwest,” Biological Conservation, vol. 146, no. 1, pp. 62–71, 2012.
[13]
A. C. Rutherford and O. J. Schmitz, “Regional-scale assessment of deer impacts on vegetation within western Connecticut, USA,” Journal of Wildlife Management, vol. 74, no. 6, pp. 1257–1263, 2010.
[14]
A. Leopold, Game Management, Charles Scribner's Sons, New York, NY, USA, 1933.
[15]
F. Reimoser and H. Gossow, “Impact of ungulates on forest vegetation and its dependence on the silvicultural system,” Forest Ecology and Management, vol. 88, no. 1-2, pp. 107–119, 1996.
[16]
F. Reimoser, “Steering the impacts of ungulates on temperate forests,” Journal for Nature Conservation, vol. 10, no. 4, pp. 243–252, 2003.
[17]
S. Reimoser, E. Partl, F. Reimoser, and S. Vospernik, “Roe-deer habitat suitability and predisposition of forest to browsing damage in its dependence on forest growth-Model sensitivity in an alpine forest region,” Ecological Modelling, vol. 220, no. 18, pp. 2231–2243, 2009.
[18]
E. Partl, V. Szinovatz, F. Reimoser, and J. Schweiger-Adler, “Forest restoration and browsing impact by roe deer,” Forest Ecology and Management, vol. 159, no. 1-2, pp. 87–100, 2002.
[19]
S. Vospernik and S. Reimoser, “Modelling changes in roe deer habitat in response to forest management,” Forest Ecology and Management, vol. 255, no. 3-4, pp. 530–545, 2008.
[20]
S. D. C？té, T. P. Rooney, J.-P. Tremblay, C. Dussault, and D. M. Waller, “Ecological impacts of deer overabundance,” Annual Review of Ecology, Evolution, and Systematics, vol. 35, pp. 113–147, 2004.
[21]
J.-P. Tremblay, J. Huot, and F. Potvin, “Density-related effects of deer browsing on the regeneration dynamics of boreal forests,” Journal of Applied Ecology, vol. 44, no. 3, pp. 552–562, 2007.
[22]
G. E. Belovsky, “Optimal activity times and habitat choice of moose,” Oecologia, vol. 48, no. 1, pp. 22–30, 1981.
[23]
O. J. Schmitz, “Thermal constraints and optimization of winter feeding and habitat choice in white-tailed deer,” Holarctic Ecology, vol. 14, no. 2, pp. 104–111, 1991.
[24]
D. M. Waller and W. S. Alverson, “The white-tailed deer: a keystone herbivore,” Wildlife Society Bulletin, vol. 25, no. 2, pp. 217–226, 1997.
[25]
D. B. Kittredge and P. M. S. Ashton, “Impact of deer browsing on regeneration in mixed stands in southern New England,” Northern Journal of Applied Forestry, vol. 12, no. 3, pp. 115–120, 1995.
[26]
M. A. Barrett and P. Stiling, “Effects of Key deer herbivory on forest communities in the lower Florida Keys,” Biological Conservation, vol. 129, no. 1, pp. 100–108, 2006.
[27]
R. M. A. Gill, “A review of damage by mammals in north temperate forests: 1. Deer,” Forestry, vol. 65, no. 2, pp. 145–169, 1992.
[28]
T. P. Rooney, R. J. McCormick, S. L. Solheim, and D. M. Waller, “Regional variation in recruitment of hemlock seedlings and saplings in the upper Great Lakes, USA,” Ecological Applications, vol. 10, no. 4, pp. 1119–1132, 2000.
[29]
T. P. Rooney, S. L. Solheim, and D. M. Waller, “Factors affecting the regeneration of northern white cedar in lowland forests of the Upper Great Lakes region, USA,” Forest Ecology and Management, vol. 163, no. 1–3, pp. 119–130, 2002.
[30]
L. Eberhardt and R. C. V. Etten, “Evaluation of the pellet group count as a deer census method,” The Journal of Wildlife Management, vol. 20, no. 1, pp. 70–74, 1956.
[31]
D. J. Neff, “The pellet-group count technique for big game trend, census, and distribution: a review,” The Journal of Wildlife Management, vol. 32, no. 3, pp. 597–614, 1968.
[32]
D. M. Forsyth, R. J. Barker, G. Morriss, and M. P. Scroggie, “Modeling the relationship between fecal pellet indices and deer density,” Journal of Wildlife Management, vol. 71, no. 3, pp. 964–970, 2007.
[33]
F. F. C. Marques, S. T. Buckland, D. Goffin et al., “Estimating deer abundance from line transect surveys of dung: sika deer in Southern Scotland,” Journal of Applied Ecology, vol. 38, no. 2, pp. 349–363, 2001.
[34]
W. P. Porter and D. M. Gates, “Thermodynamic equilibria of animals with environment,” Ecological Monographs, vol. 39, no. 3, pp. 227–244, 1969.
[35]
A. N. Moen, “Seasonal changes in heart rates, activity, metabolism, and forage intake of white-tailed deer,” The Journal of Wildlife Management, vol. 42, no. 4, pp. 715–738, 1978.
[36]
A. N. Moen, “Surface temperatures and radiant heat loss from white-tailed deer,” The Journal of Wildlife Management, vol. 32, no. 2, pp. 338–344, 1968.
[37]
W. M. Tzilkowski and G. L. Storm, “Detecting change using repeated measures analysis—white-tailed deer abundance at Gettysburg National Military Park,” Wildlife Society Bulletin, vol. 21, no. 4, pp. 411–414, 1993.
[38]
F. L. Russell, D. B. Zippin, and N. L. Fowler, “Effects of white-tailed deer (Odocoileus virginianus) on plants, plant populations and communities: a review,” American Midland Naturalist, vol. 146, no. 1, pp. 1–26, 2001.
[39]
R. T. Brooks and T. D. Kyker-Snowman, “Forest floor temperature and relative humidity following timber harvesting in southern New England, USA,” Forest Ecology and Management, vol. 254, no. 1, pp. 65–73, 2008.
