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Winter use of senescent herbaceous plants by white-tailed deer in Minnesota.

INTRODUCTION

The winter diet of white-tailed deer in the northern part of its range in North America consists primarily of current-annual-growth of woody twigs, with the remainder composed of green herbaceous plants and ferns and occasionally dried leaves and lichens (Dahlberg and Guettinger, 1956; Snider and Asplund, 1974; Pierce, 1975; Mautz et al., 1976; Mooty, 1976; Crawford, 1982; Verme and Ulrey, 1984; Hodgman and Bowyer, 1985; Dusch et al., 1989; Gray and Servello, 1995). However, in areas of moderate to high deer densities, availability of woody current-annual-growth and other nutritious forages (e.g., evergreen plants and lichens) decreases as winter progresses such that they are often of limited supply by the end of winter. Consequently, to meet minimum daily nutrient requirements, deer must choose between other low quality torage items such as: 1) less preferred woody browse, e.g., alder (Alnus spp.), spruce (Picea spp.) or raspberry (Rubus sp.); 2) older tissues on palatable woody stems that are high in fiber and low in digestible protein (Palo et al., 1992); or 3) plants or plant parts that are readily available but often lower in gross energy and digestibility, e.g., bark, leaf litter, etc. (Amman et al., 1973; Gray and Servello, 1995). Several species of herbaceous perennials present in this region, such as Solidago spp. and Desmodium spp., have relatively tall, rigid sterns that can persist after senescence and extend above the snow pack, thus presenting deer with an alternative forage. During years of high deer densities, winter use of senescent forbs, apparently during the period between snow-melt and spring green-up, has been observed several times in the 1990s in south-central Minnesota, including at Cedar Creek Natural History Area and the Twin Cities Army Ammunition Plant (TCAAP; P.A. Jordan, pers. obs.). Significant winter use of senescent herbaceous plants, however, has never been adequately documented. Our objective was to describe the winter use of senescent forbs by white-tailed deer at TCAAP.

STUDY AREA

The TCAAP (45[degrees]05'38"N, 93[degrees]10'04"W) is a 1025 ha tract completely enclosed by 2-m tall fencing with restricted access (see DeGayner and Jordan, 1987 for full description of TCAAP). Approximately 500 ha of this land is considered habitable by deer; roughly 50% is comprised of open grasslands, oak (Quercus spp.) savannas, and old fields, with the remainder comprised of lowland shrub interspersed with hardwoods (quaking aspen Populus tremuloides, cottonwood Populus deltoides, American hazel Corylus americana and willow Salix spp.), white spruce (Picea glauca) and red pine (Pinus resinosa) plantations, a cattail (Typha spp.) dominated wetland of about 60 ha and two small lakes (Baggot et al., 1988). Most of the undeveloped land is formed of well-drained soils of glacial till origin. Mean temperatures at the Minneapolis International Airport were ~1.7 C below average during the winter of 1995-96. Mean daily snow depth at the Minneapolis International Airport was above average in Dec. 1995 and Jan. 1996, but below average in Feb. and Mar. 1996.

Early winter deer densities within TCAAP were estimated by standard helicopter counts tot 1993, 1994 and 1995 to be 17.4, 23.9 and 11.4 deer/[km.sup.2], respectively. During each of those same winters, 33, 100 and 30 deer, respectively, were removed by sharpshooting between Nov.-Feb. as part of a population control program. No deer were removed in 1996 and subsequently no population estimate was made that year. However, we assume that deer densities at the start of the winter of 1996 were at least as high as they were in 1995 because of the lack of removal through sharpshooting.

METHODS

Three replicate sample areas of approximately 10 ha each were selected according to the following criteria: 1) snow cover >10 cm on 13 Mar. 1996; 2) presence of herbaceous plants above snow line; and 3) representative of the types of habitats available to deer throughout TCAAP. All three sample areas were >1 km from each other, the minimum distance sufficient to assume the sample areas were in distinct deer home ranges based on data from female white-tailed deer in a suburban matrix near the TCAAP from 1996-1999 (Grund et al., 2002), i.e., the sample areas can be considered independent replicates. We further consider that the home ranges for deer in the TCAAP are likely smaller than those reported in Grund et al. (2002) due the nature of high-density, captive deer herds to compress home ranges to reduce intra-specific competition (Grund et al., 2002), and therefore the 1 km minimum distance between samples areas is a conservative measure.

Two of the three sample areas were sampled on 13 Mar. 1996, when snow snow depths ranged from 10 to 30 cm. The third sample area was visited on 13 Apr. 1996, by which date most snow had melted. Fresh deer tracks were present in sample areas on both 13 Mar. and 13 Apr. At each sample area, we randomly placed five 1-m radius plots and recorded the plant species (woody and herbaceous) present and the number of plants (not individual plant parts) browsed and unbrowsed by deer. No live herbaceous plants were present above the snow-pack. Deer bites were easily distinguished from the clean, 45 degree-angle bite characteristic of eastern cottantail rabbits (Sylvilagusfloridanus). Evidence of browsing after senescence was determined by the absence of a die-back zone at the point of browsing. Data from the five 1-m plots were combined for each sampling area. Plant species nomenclature follows Gleason and Cronquist (1991).

Because of time limitations, an adequate quantitative assessment of woody browse use and availability within TCAAP was not possible. Instead, we assessed the quality of browse available at the end of winter by measuring the diameter (to the nearest ram) of [greater than or equal to] 3 browsed twigs for each browsed species within a 30 m radius of a random point located in each study site.

RESULTS

We recorded evidence of deer browsing on five species of senescent herbaceous plants, with 42% of the 295 individual plants in our plots showing signs of winter deer browsing (Table 1). Most plants had only the main stem browsed, with a few having evidence of multiple bites. Browsing on Solidago sp. was mostly restricted to portions of stems anterior to insect galls. No evidence of browsing on grasses was observed.

Solidago sp. was the only senescent herbaceons plant detected in all three sample areas but was also the most abundant at each sample area with a mean density of 3.9 (SD = 1.1) stems/[m.sup.2]. Mean percent of Solidago sp. stems browsed at each sample area was 35% (SD = 13%). Cirsium arvense was detected in two of the three sample areas, with a mean density of 0.7 stems/[m.sup.2] (SD = 0.8) and mean percent browsing of 37% (SD = 18%). Other species showing signs of browsing but were only detected in one sample area include Desmodium sp. (88% of stems browsed), Helianthus sp. (53% of stems browsed), and Monarda fistulosa (5% of stems browsed). Veronicestrum virginiana, Lactuca sp., Rudbeckia sp., Verbascum thapsus and five species of unidentified forbs were detected in at least one sample area, but showed no signs of winter deer browsing. When stems from all plots were combined, a Chi-square test for independence verified that browsing was not randomly distributed across species, i.e., deer demonstrated selectivity in browsing senescent plants ([chi square] = 85.9, df = 9, P < 0.001).

Browsing was also observed on 11 species of trees/shrubs (Table 2), with most individuals of each species showing signs of current winter browsing (SKW, pers. obs.). Mean diameter at point of browsing (DPB) for "all trees combined was 4.1 mm ([+ or -] 1.9). Most of the browsing observed was on red oak (mean DPB ([+ or -] SD)=- 3.6 mm [+ or -] 1.4), American hazel (2.6 [+ or -] 0.8), quaking aspen (4.3 [+ or -] 0.7) and box elder (4.3 [+ or -] 0.7).

DISCUSSION

We observed a substantial amount of browsing on tall-stemmed, senescent forbs, especially on the genera Solidago, Cirsium, Desmodium and Helianthus, by a high-density deer herd. Browsing intensities on individuals of these plant species in our study ranged from 5-88% of stems (Table 1). These browsing intensities are similar to those reported for late summer browsing by deer on five herbaceous species, including Solidago sp., in south-central Minnesota that ranged from 0.4-35.5% of stems (Augustine and Jordan, 1998). Our data also show selective foraging on senescent forbs, with several species apparently avoided. We believe that the relatively high browsing intensities we report along with the evidence of selective foraging suggests that winter browsing by white-tailed on senescent forbs is not merely "sampling" by deer, but instead represents a non-trivial contribution to deer diets in this case. While the incidence of white-tailed deer browsing on dried lichens and dead leaves has been previously reported in northern climates (e.g., Crawford, 1982; Hodgman and Bowyer, 1985), to our knowledge the phenomenon of deer browsing on these species of senescent forbs to supplement the winter diet has not. Several studies have reported significant use of evergreen forbs such as pussytoes (Annetaria spp.) and hepatica (Hepatica biloba) during early and late winter in the northern parts of the U.S. (e.g., Mooty, 1976; Crawford, 1982; McCullough and Ullrey, 1985). Coblentz (1970) reported that deer ate "grasses and forbs" during early winter, but switched to evergreen forages when snow depths became greater than 7.5 cm. Renecker and Hudson (1992) reported moose consuming small amounts of (presumably dead) Canada thistle (Circium canadensis) in Jan. in Alberta, Canada. Pierce (1975) documented limited use of senescent Solidago stems in Apr. and May in northern Minnesota. Dead and dried parts of herbaceous plants in white-tailed deer diets have been reported in South Carolina (Harlow et al., 1979), Florida (Harlow and Jones, 1965) and Missouri (Korshgen, 1962).

Food limitation for deer at TCAAP has been observed periodically throughout the 1950s-1980s as a result of overbrowsing by an overabundant deer herd (Baggot et al., 1988). Baggot et al. (1988) also estimated that winter deer densities in 1988 were 5-7 times greater than those that could be supported based on available digestible energy in woody browse, although they considered their available energy estimates conservative. Though the qualitative measure of overall browsing pressure on woody plants we used in this study was crude, the large diameter of browsed twigs for several species suggests that overbrowsing by relatively high deer densities had again caused food limitation during the winter of 1995-1996 (Table 2). Shafer (1963) reported mean DPB for red oak (3.5 mm) and quaking aspen (3.8 mm) at unknown winter deer densities in Pennsylvania, while Peek et al. (1971) reported mean DPB for quaking aspen (3.1-3.9 mm) and beaked hazel (2.6-3.0 mm) for two deeryards in northern Minnesota. The diameters-at-point-of browsing we observed were, in general, even greater than those reported for moose browsing on similar species in Alberta (Renecker and Hudson, 1992). Also, our observations of deer browsing on low preference foods such as box-elder and cottonwood is further evidence of above-average nutritional stress. In a another study of the interactions between deer and woody plants at the TCAAP, Paron (1997) documented severe overbrowsing on Quercus spp. during the winter of 1996-1997, further suggesting that deer at TCAAP were generally food limited in winter during the periods of high deer densities recorded in the mid-1990s.

McCullough and Ullrey (1985) reported high calcium concentrations in Solidago spp. and Desmodium sessifolium in summer in Lower Michigan. Calcium concentrations remain constant or increase after senescence due to high Ca content in cell walls (Aerts, 1996). While it is possible deer eat senescent forbs to obtain calcium and other macronutrients, it is more likely that senescent forbs provide an alternative forage for deer during late winter/early spring in areas of depleted woody browse.

Senescent forbs are composed mostly of cell wall constituents of low digestibility, and therefore typically have low digestible energy content. However, McCullough and Ullrey (1985) reported peak crude protein contents of green Solidago spp. and Desmodium sp. as 16.6 and 28.0 g/100 g dry matter, respectively. Assuming most perennial forbs resorb up to 50% of nitrogen from senescing tissues for storage in the root system (Aerts, 1996), senescent tissues of Solidago spp. and Desmodium sp. should contain ~8.4 and 14.0 g/100 g of crude protein. These values are much higher than those reported by McCullough and Ullrey (1985) for senescent leaves and dormant twigs for several species of oaks (4.4-7.2 g/100 g dry matter) and as high or higher for other browse species such as aspen (9.0 g/100 g dry matter) and willow (8.6 g/100 g dry matter). Further, as most dry herbaceous tissue have much lower concentrations of tannins than leaves and dormant twigs of most northern browse species, reduction in digestible protein from tannins would be much less in senescent forbs (Robbins et al., 1987). Finally, considering that DDM, digestible energy and digestible protein content of most woody browse species decreases with increasing twig diameter (Hjeljord et al., 1982; Vivas et al., 1991; Palo et al., 1992), digestible protein content of senescent forbs is likely even greater than in 2- and 3-y old woody twigs while digestible energy content may be comparable.

Deer primarily select forage items for digestible energy content during winter. Consequently, senescent forbs, despite being of relatively high digestible protein content, are likely less preferred by deer in winter than current-annual-growth or dried leaves of many woody plants. However, as winter progresses and the most preferred forage items are depleted, it appears that senescent forbs may be consumed instead of or in addition to other low preference items such as older woody browse tissues.

Acknowledgments.--We thank Ed Cushing for his help with herbaceous plant identification and TCAAP staff for providing access. This project was funded in part through the Minnesota Agricultural Experiment Station.

Submitted 27 August 2007; Accepted 4 January 2008.

LITERATURE CITED

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AUGUSTINE, D. J. AND P. A. JORDAN. 1998. Predictors of white-tailed deer grazing intensity in fragmented deciduous forests. J. Wildl. Manage., 62:1076-1085.

COBLENTZ, B. E. 1970. Food habits of George Reserve deer. J. Wildl. Manage., 34:535-540.

BAGGOT, C., W. CLARK, R. GARROTT, R. MOEN, E. OLEXA, A. VEITCH AND K. WINSOR. 1988. A vegetation classification system and forage inventory for the Twin Cities Army Ammunition Plant. Unpublished manuscript. 49 p.

CRAWFORD, H. S. 1982. Seasonal food selection and digestibility by tame white-tailed deer in central Maine. J. Wildl. Manage., 46:974-982.

DAHLBERG, B. L. AND R. C. GUETTINGER. 1956. The white-tailed deer in Wisconsin. Technical Wildlife Bulletin #14. Madison: Wisconsin Conservation Department. 282 p.

DEGAYNER, E. J. AND P. A. JORDAN. 1987. Skewed fetal sex ratios in white-tailed deer: evidence and evolutionary speculations, p. 178-188. In: C. M. Wemmer (ed.). Biology and Management of the Cervidae. Smithsonsian Institution Press, Washington, D.C. 577 p.

DUSCH, G. L., R.J MACKIE, J. D. HERRIGES, JR. AND B. B. COMPTON. 1989. Population ecology of white-tailed deer along the Lower Yellowstone River. Wildl. Monogr., 104:68.

GLEASON, H. A. AND A. CRONQUIST. 1991. Manual of vascular plants of northeastern United States and adjacent Canada - 2nd ed. The New York Botanical Garden, Bronx. 910 p.

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GRUND, M. D., J. B. MCINNICH AND E. P. WIGGINS. 2002. Seasonal movements and habitat use of female white-tailed deer associated with an urban park. J. Wildl. Manage., 66:123-130.

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--, D. F. URBSTON AND J. G. WILLIAMS. JR. 1979. Forages eaten by deer in two habitats at the Savannah River Plant. Forest Service Research Note SE-275.4 p.

HJELJORD, O., E. SUNDSTOL AND Hans HAAGENRUD. 1982. The nutritional value of browse to moose. J. Wildl. Manage., 46:333-343.

HODGMAN, T. P. AND R. T. BOWER. 1985. Winter use of arboreal lichens, Ascomycetes, by white-tailed deer, Odocoileus virginianus, in Maine. Can. Field-Nat., 99:313-316.

KORSHGEN, L.J. 1962. Foods of Missouri deer, with some management implications. J. Wildl. Manage., 26:164-172.

MAUTZ, W. W., H. SILVER, J. B. HOLTER, H. H. HAYES AND W. E. URBAn, JR. 1976. Digestibility and related nutritional data for seven northern deer browse species. J. Wildl. Manage., 40:630-638.

McCULLOUGH, D. R. AND D. E. ULLREY. 1985. Chemical composition and gross energy of deer forage plants on the George Reserve, Michigan. Research Report 465, Michigan State University Agricultural Experiment Station. 20 p.

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PALO, R. T., R. BERGSTROM AND K. DANELL. 1992. Digestibility, distribution of phenols, and fiber at different diameters of birch in winter. Implications for browsers. Oikos, 65:450-454.

PARON, D. 1997. Oak regeneration survey--Twin Cities Army Ammunition Plant. Unpublished report to Department of Defense, Twin Cities Army Ammunition Plant. 10 p.

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SHAFER, E. L. 1963. The twig-count method for measuring hardwood deer browse. J. Wildl. Manage., 27:428-437.

SNIDER, C. C. AND J. M. ASPLUND. 1974. In vitro digestibility of deer foods from the Missouri Ozarks. J. Wildl. Manage., 38:20-31.

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ROBBINS, C. T., T. A. HANLEY, A. E. HAGERMAN O. HJELJORD, D. L. BAKER, C. C. SCHWARTZ AND W. W. MAUTZ. 1987. Role of tannins in defending plants against ruminants: reduction in protein availability. Ecology, 68:98-107.

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STEVE K. WINDELS, (1) Voyageurs National Park, Minnesota 56649; and PETER A. JORDAN, Department of Fisheries and Wildlife, University of Minnesota, St. Paul 55108.

(1) Corresponding author: e-mail: steve_windels@nps.gov
TABLE 1.--Senescent herbaceous plants browsed in winter by
white-tailed deer at the Twin Cities Army Ammunition Plant, St.
Paul, Minnesota, Mar.-Apr., 1996. Data from each sample area were
summed from 5 1-m radius plots

                                          Sample area

                                               1

                                      Stems/        %
 Common name      Scientific name    [m.sup.2]   Browsed

Goldenrod        Solidago sp.           4.8         42
Canada Thistle   Cirsium arvense        0
Tick-Trefoil     Desmodium sp.          2.1         88
Sunflower        Helianthus sp.         1.9         53
Wild Bergamot    Monarda fistulosa      1.2          5
Lettuce          Lactuca sp.            0
Coneflower       Rudbeckia sp.          0
Common           Verbascum              0
  Mullein          thapsus
Culver's Root    Veronicestrum          0.2          0
                   virginiana
unidentified                            0
  forbs

                                 Sample area

                           2                     3

                  Stems/        %       Stems/        %
 Common name     [m.sup.2]   Browsed   [m.sup.2]   Browsed

Goldenrod           2.6         20        4.1         45
Canada Thistle      1.6         24        0.2         50
Tick-Trefoil        0                     0
Sunflower           0                     0
Wild Bergamot       0                     0
Lettuce             0.8          0        0
Coneflower          1.9          0        0
Common              0.4          0        0
  Mullein
Culver's Root       0                     0

unidentified        0.1          0        0.4          0
  forbs

                     Mean (SD)

                  Stems/        %
 Common name     [m.sup.2]   Browsed

Goldenrod        3.9 (1.1)   35 (14)
Canada Thistle   0.7 (0.8)   37 (18)
Tick-Trefoil     0.7 (1.2)   88 (na)
Sunflower        0.6 (1.1)   53 (na)
Wild Bergamot    0.4 (0.7)    5 (na)
Lettuce          0.3 (0.4)    0
Coneflower       0.6 (1.1)    0
Common           0.1 (0.3)    0
  Mullein
Culver's Root    0.1 (0.1)    0

unidentified     0.2 (0.2)    0
  forbs

TABLE 2.--Mean diameter at point of browsing (DPB) for woody plants
browsed in winter by white-tailed deer at the Twin Cities Army
Ammunition Plant, St. Paul, Minnesota, Mar.-Apr., 1996. N = number
of DPBs measured for each species for all sample areas combined

                                                  DPB (mm)

Common name            Scientific name       Mean (SD)   Range   N

Red Oak                Quercus rubra         3.6 (1.4)   2-8     31
White Oak              Quercus alba          4.9 (0.9)   3-6      9
Bur Oak                Quercus macrocarpa    3.0 (0.0)   NA       2
American Hazel         Corylus americana     2.6 (0.8)   2-4     17
Box Elder              Acer negundo          4.3 (0.7)   2-5     32
Quaking Aspen          Populus tremuloides   4.3 (0.7)   3-6     18
Cottonwood             Populus deltoides     3.5 (0.6)   3-4      7
Willow sp.             Salix sp.             2.0 (0.7)   1-3      5
Staghorn Sumac         Rhus typhina          9.2 (0.8)   8-10    11
Kentucky Coffee-Tree   Gymnocladus dioica    2.0 (0.0)   NA       4
European Buckthorn     Rhamnus cathartica    2.0 (0.0)   NA       3
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Title Annotation:Notes and Discussion
Author:Windels, Steve K.; Jordan, Peter A.
Publication:The American Midland Naturalist
Article Type:Report
Geographic Code:1USA
Date:Jul 1, 2008
Words:3569
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