Cedar through the eyes of wildlife

Dale Rollins and Bill Armstrong


A weed is a plant whose virtues have yet to be discovered.”– Ralph Waldo Emerson

Introduction

To most Texans, cedars (Juniperus spp.) are weeds. They compete with grasses for water and sunlight. They hinder livestock gathering. They harbor annoying cedar flies. Aside from their value as posts, few ranchers would have anything good to say about the prolific shrubs. However, because wildlife is important to most Texans, either economically or esthetically, it behooves land managers to realize that cedars do have inherent value, albeit as a Dr. Jekyll – Mr. Hyde relationship. Furthermore, in some areas of Texas (e.g., Edwards Plateau) land value may be more closely tied to recreational enterprises (e.g., hunting) than traditional ranching enterprises. This trend of the “(wildlife) tail wagging the (livestock) dog” will most likely continue to increase. As it does, wildlife considerations will become increasingly important in determining land management strategies, especially relative to brush control.

Depending on the species of wildlife and site involved, cedars may provide food and/or shelter. Dissect a deer (Odocoileus spp.) pellet or ringtail (Bassaricus astutus) scat in late winter and chances are you’ll find cedar “berries” therein. Most deer diet studies conducted in cedar country have documented substantial use of cedar mast or foliage, yet most researchers consider cedar of low nutritional value as deer fodder. Cedar mast is seasonally important in the diets of some birds (e.g., American robins (Turdus migratorius), cedar waxwings (Bombycilla cedrorum) and small mammals (e.g., ringtails, raccoons [Procyon lotor]). The same stands of dense cedar that hamper livestock roundups provide thermal or escape cover to deer, quail, and other wildlife. The ecological significance of Ashe juniper (J. ashei) for the endangered golden-cheeked warbler (Dendroica chrysoparia) has caused considerable discord recently among stakeholders in the Edwards Plateau region of Texas.

Managing cedar-infested rangelands for multiple uses requires the manager to investigate how, when, where, and why cedars are important to wildlife. In this paper, we will identify the relative importance of junipers to wildlife (game and nongame species) and present suggestions for incorporating wildlife needs into cedar control strategies.

Food Value

Cedar is a common item in deer diets, especially in the Edwards Plateau region (Table 1). Relatively speaking, cedar is probably only a “fair” deer forage (Armstrong 1991). Its use is Table 1. Importance of Juniperus spp. to deer diets at various locations.

Deerspecies Location Juniperspp. Season/month % indiet Authors Remarks
White- tailed Sutton Co. Blueberry Feb 34 Bryant et al.1981 On “Poor” condition sites; no use on “Excellent” condition sites.
Kerr Co. Blueberry Nov-Dec 17 to26 Warren &Krysl 1983 Poor-Fair Condition to Good-Exc. range condition.
Kerr Co. Blueberry Annual 12 Waid et al.1984 Highest use (24%) noted in Jan and Mar.
Llano Co. Blueberry Annual 0 to40 S. Nelle(unpubl. data) 3-year study; use highest during late winter.
Mason Co. Blueberry Oct/Mar 33 S. Nelle(unpubl. data) Comprised >45% of diet in Feb and Mar.
Terrell Co. Redberry Annual 26 S. Nelle(unpubl. data) Use by goats and sheep was 11 and 13%, respectively during same period.
Southern Oklahoma Eastern Redcedar Annual <1 Gee et al.(1991)
Muledeer Hartley Co. Redberry-One-seed Annual 6 Sowell et al.(1985) Highest use (15%) noted in winter.
Donley Co. Redberry Annual 11 Sowell et al.(1985) Highest use (27%) noted in winter.
Lincoln Co., NM One-seed Annual 15 to25 Mahgoub et al.(1987) Highest use (25% ) noted in June.
Lea Co., NM One-seedAlligator Annual 14 Anderson et al. (1965) Highest use (29%) noted from Jan/Mar.

generally highest where more desirable browse is unavailable (e.g., winter seasons or “poor” condition range). Studies in northwestern Kerr County (Bryant et al. 1981, Krysl and Warren 1982, Waid et al. 1984) reported Ashe juniper comprising from 0 to 34 percent of white-tailed deer (O. virginianus) diets. Highest seasonal contributions generally occurred during late-winter (Feb-Mar). Bryant et al. (1978) found that tame deer foraging on “poor” condition range spent 34 percent of their grazing time during February consuming fruits and foliage of Ashe juniper. Interestingly, Bryant et al.’s deer were not nutritionally stressed during the trials, suggesting that cedar may not be as unpalatable as perceived. S. Nelle (unpublished data) found that Ashe juniper comprised 12 and 20% of the annual diet of white-tailed deer in Llano and Mason counties, respectively. Redberry juniper (J. pinchotii) comprised over 50% of the monthly diets of deer in Terrell County in January, February, October and December (S. Nelle, unpublished data).

Nutritionally, cedar provides only marginal browse; crude protein averages about 7 percent for foliage and about 14 percent for seeds. The volatile oils (oxygenated monoterpenes) found in cedar foliage are believed to depress rumen function when cedar foliage in the diet exceeds some threshold value (presumably 20 to 30 percent of forage intake). However, these data were determined in vitro (i.e., in the laboratory) and may not reflect accurately in vivo situations (i.e., in the animal). Bryant et al. (1981) suggested that deer from “poor” condition range actually had higher digestible energy intakes during winter months than deer foraging on “excellent” condition range. This time period corresponded to juniper consumption on the “poor” condition site. However, estimating the energy value of juniper in vitro may inflate the actual nutritive value of juniper. The relative and absolute contribution of juniper forage and fruits to deer warrants additional study.

Deer seem to exhibit a preference for certain cedar trees, suggesting that some property (perhaps volatile oil concentration) varies intraspecifically (i.e., among individual juniper trees) (Schwartz et al. 1980, Straka 1993). Bryant et al. (1978) and Rollins (1983) observed that older female trees may be selected for by deer in search of foliage and/or fruits. If such preferred trees could be identified, they might be spared from brush control programs. Older trees with shedding bark are also essential for nesting material for the golden-cheeked warbler.

Cedar berries are common in gray fox (Urocyon cinereoargenteus), ringtail and raccoon scats, and are probably similarly important for lagomorphs (jackrabbits and cottontails) and other rodents. Cedar berries are occasionally found in quail or wild turkey crops. Chavez-Ramirez (1992) identified 19 species of birds and 9 species of mammals that consumed cedar berries at the Sonora Research Station. Cedar waxwings and robins were by far the most important avian species involved. The “average” robin was estimated to consume about 555 berries per day while the average cedar waxwing consumed 683 berries per day (Chavez-Ramirez 1992). The role of mammals and birds in dispersing juniper seeds is discussed in the chapter of this proceedings by Smeins and Fuhlendorf.

Shelter

The term shelter (i.e., cover) may connote any of the following habitat needs: thermal, escape, nesting, loafing, screening, etc. Each of these will be discussed in more of a qualitative than quantitative manner.

Thermal cover allows animals to compensate for temperature extremes. To this end, junipers are probably much more valuable for thermal cover in winter than in summer and in colder climates than in warmer ones (Leckenby 1977). The popularity of junipers (e.g., eastern redcedar) as windbreak plantings is suggestive of their value for winter cover. Relative to summer thermal relief (e.g., shade), other species of deciduous trees probably allow for more air flow and shade than do junipers. Rabbits and deer fawns sometimes frequent junipers (live trees as well as dozed ones) during all months of the year (Rollins 1983).

Escape cover is rather generic and can probably be satisfied by any species of brush of sufficient density. Cedar “breaks” certainly qualify as dense cover suitable for escape purposes for deer and other wildlife. The relative need and value of escape cover varies with factors like topography, human disturbance (e.g.,hunting), brush density, and wildlife species in question. Rollins et al. (1985) attempted to quantify cover thresholds for white-tailed deer on Ashe juniper range in Kerr County. Series of 20-acre clearings were established with progressively smaller “strips” of brush between the clearings to identify how much escape cover was necessary for deer. Their findings suggested that as much as 70 percent of the range could be cleared mechanically (e.g., chaining) without adversely affecting deer use of habitats or deer populations.

Junipers provide nesting habitat for several species of birds, including gamebirds (e.g., wild turkey [Meleagris gallopavo]), songbirds (e.g., cardinals [Cardinalis cardinalis]), and endangered species (e.g., golden-cheeked warblers). In north central Oklahoma, the majority of mourning dove (Zenaida macroura) nests studied were located in eastern redcedar (Smith 1985). Junipers are not preferred loafing coverts for bobwhites (Colinus virginianus), perhaps because of the dense foliage at ground level. Quail prefer brush coverts that are relatively thick above and open at ground level (e.g., lotebush). Following mechanical brush control, deer fawns and lagomorphs (Sylvilagus floridanus and Lepus californicus) commonly used downed brush for bedding sites (Rollins 1983). Other wildlife (e.g., skunks [Mephitis mephitis], rodents) commonly inhabit brushpiles.

Effects of Cedar Control on Wildlife

Vast, dense stands of juniper are not conducive to either wildlife or livestock management. Even golden-cheecked warblers are not well served by juniper monocultures; they prefer a diversity of woody plants, including mature Ashe juniper. Ideally, enough juniper should be cleared to increase forage production and handling ease for livestock, but maintain sufficient cover for wildlife. As mentioned ealier, such cover thresholds are species- and habitat-specific. The impacts of cedar control on wildlife depend upon how much cedar is cleared (acreage), how it is cleared (e.g., mechanically, goats), and the subsequent management on the cleared land (i.e., grazing management). Impacts to wildlife may be both acute (e.g., forage response) and chronic (e.g., habitat fragmentation promoting in nest parasitism by brown-headed cowbirds [Molothrus ater]).

Cedars are generally controlled by mechanical, biological, or pyric means, either singly or in combination. Mechanical treatments like grubbing or chaining generally increase forage production, at least temporarily. Annual forbs respond to the ground disturbance caused by mechanical treatments. Further, browse availability generally increases by topkilling such species as shinoak and liveoak. Similarly, burning tends to promote the growth of annual and perennial forbs and also enhances browse availability and/or palatability.

Effects on Deer

The biggest concern for deer relative to mechanical treatments is the scale of the clearing operation. Ideally, brush should be cleared in order to promote forage availability up to the point that cover (rather than food) becomes the limiting factor. As clearing size exceeds some threshold value (e.g., 50 acres), wildlife use of some portions (i.e., the center) of the clearing decreases. Smaller clearings have proportionately more edge, thus less habitat is”lost.” For optimum use by white-tailed deer, clearing size should be no larger than 40 acres. Rollins et al. (1988) evaluated deer response to different proportions of brush to clearing. They recommended that 50 to 70 percent of a pasture could be chained in a series of 20-acre clearings (about 200 yards wide by 500 yards long) while improving habitat conditions for deer. At 70 percent clearing, 20-acre clearings are established with about 70 yards of brush left between them. Clearing up to 70 percent of the brush also improved the distribution of deer across the habitat compared to control areas.

Obviously clearing too much cedar (or too large an area) could negatively impact deer, but the other extreme (clearing too little) is also troublesome, albeit for different reasons. Small, isolated clearings (e.g., 2 acres) are subjected to intensive grazing pressure by wild and domestic herbivores. The repeated browsing on plants like sumacs and oaks will eventually kill these species. Regardless of the intensity and scale of clearing, herd and grazing management are important for maintaining healthy plant populations.

Biological control of cedar involves heavy stocking with goats. This type of cedar control is not conducive to wildlife management because at the stocking pressures required to obtain juniper control, desirable browse species will likely disappear before juniper does. If and when a breed of goat can be developed that prefers junipers over shinoak, then perhaps goating will be more compatible with deer management. Similarly, it may be possible to used “prescribed goating” (strategic stocking of goats at certain times) to minimize impacts of goating on more desirable browse plants, but these strategies have yet to be tested.

Burning, alone or in conjunction with mechanical treatments, can benefit most species of wildlife. Burning is most effective in controlling junipers less than 5 feet in height. Burning tends to promote desirable forbs and increases the availability and/or palatability of browse. When grubbing and raking cedars with a bulldozer, slash plies should be located on shinoak if possible. The tremendous heat generated under such slash piles will temporarily sterilize the soil on some sites, but rarely kills the shinoak. Deer readily graze the shinoak regrowth on such hotspots.

Effects on Other Wildlife

As the clearing intensity increases, shrublands are converted to grasslands. Predictably, birds and mammals associated with more open conditions will be favored over those that require more brush cover. Rollins (1983) noted that jackrabbits tended to become more common as clearing intensity increased, especially on sites dominated by sodforming grasses (e.g., common curlymesquite [Hilaria belangeri]. Bird species responded similarly. Grassland sparrows like Lincoln’s (Melospiza lincolnii)and lark sparrows (Chondestes grammacus) become more common as clearing intensity increased. Overall, species richness (total number of species ) was highest at the control site, but species diversity was highest at the 70 percent cleared site.

Much of the Edwards Plateau harbors free-ranging exotics such as axis (Axis axis), fallow (Dama dama), and sika (Cervus nippon) deer, blackbuck antelope (Antelopa cervicapra), and aoudads (Ammotragus lervia). Rollins (1983) speculated that the cover requirements for these species is roughly sika >fallow > axis > aoudad > blackbuck antelope.

Endangered Species

Two endangered birds, the golden-cheeked warbler and the black-capped vireo (Vireo atricapillus), are often associated with Ashe juniper woodlands. Golden-checked warblers nest only in Texas and the primary nesting habitat is characterized as “closed canopy Ashe juniper – oak- woodland” (Wahl et al. 1990). A mixture of hardwoods are often found within nesting territories, including Texas oak (Quercus buckleyi), live oak (Q. virginiana), elm (Ulmus sp.), walnut (Juglans microcarpa), Texas ash (Fraxinus texensis), Mexican buckeye (Ugnadia speciosa)and hackberry (Celtis spp.) (Keddy-Hector 1992). There are no records of this warbler being found in association with pure stands of redberry juniper.

Prime nesting habitat for golden-cheeked warblers is often found along streams and or canyon slopes along the eastern part of the Edwards Plateau. Typically these sites harbor the species of deciduous hardwoods that complement Ashe juniper for providing quality nesting habitats. Rollins (1983) failed to detect any warblers in northwestern Kerr County on sites where mature Ashe juniper was abundant, but no running streams or seeps were present.

Golden-cheeked warblers feed exclusively on insects during the breeding season. Vast, dense monocultures of junipers (i.e., cedar brakes) typically do not harbor the abundance or diversity of insects required. Thus, the mixed hardwoods are critical for food availability. Hardwoods like Texas oak also provide nest sites and singing perches.

The other species of endangered bird often found in cedar country is the black-capped vireo. Unlike the warbler, the black-capped vireo does not require Ashe juniper for any particular habitat requirement, it is merely associated with other plants that often occur in conjunction with Ashe juniper. Studies at Ft. Hood have shown that vireos select against areas with dense cedar. Key habitats for vireos are mid-successional stages that feature a variety of low growing deciduous shrubs like shinoak (Quercus spp.), Texas persimmon (Diospyros texana), and sumacs (Rhus spp.) (Grzybowski 1991).

Habitat Fragmentation

Much of the debate over golden-cheeked warbler habitat revolves around how much (i.e., how big a “block”) of Ashe juniper needs to be preserved to provide quality warbler habitat. There is not unanimous agreement about the relative values of large blocks of undisturbed habitat or smaller tracts with increased “edge” (Keddy-Hector 1992). However, most warbler biologists believe that larger blocks are more disirable. So, how large is “large?” Some literature suggests preserving blocks of 500 acres or more. Warblers have been located in blocks of 20 acres or less, but these populations were found in close proximity to other blocks of cedar. These arguments center around the issue of “fragmentation.”

Habitat fragmentation occurs when large blocks of suitable habitat become smaller and subdivided (e.g., cleared areas). Thus, fragmentation indicates the size and relative spacing of suitable habitats. Some species (e.g., golden-cheeked warblers) live in loosely organized “colonies” with each individual animal or breeding pair occupying its own territory. The integrity of these colonies is vital to the long-term survival of such species. There is much concern that the integrity of warbler colonies has deteriorated over the last 50 years because of human-caused disturbances (e.g., land clearing). While habitat fragmentation might be construed as “edge enhancement” (at least to a degree) for species like deer and quail (i.e., niche “generalists”), it would be detrimental to some niche “specialists” (e.g., endangered species). There is speculation that fragmentation and other human-related disturbances (e.g., livestock grazing) increase the incidence of nest parasitism by brown-headed cowbirds. Nest parasitism is an important factor in the decline of both the golden-cheeked warbler and the black-capped vireo.

Isolated populations of golden-cheeked warblers (or other animals) may be less effective at finding suitable habitat and/or rearing young. If suitable habitats are too far apart (i.e., highly fragmented), recruitment of new individuals into that habitat does not occur and the total population gradually declines below some threshold value necessary for species survival. Fragmentation is especially important to endangered species like golden-cheeked warblers, black-capped vireos, and Attwater’s prarie chickens (Tympanuchus cupido attwateri).

Cedar Control and the Endangered Species Act

Endangered species like the golden-cheeked warbler are afforded special protection by state and federal regulations. These regulations may restict the use of certain land management practices (e.g., brush control) within the affected species’ range. Such is the case with clearing cedar in some parts of the Edwards Plateau. By law, an endangered species cannot be “harmed or harassed”, which includes habitat alteration. If you clear brush on areas that would be considered golden-cheeked warbler habitat, you would be culpable under the provisions of the Endangered Species Act (ESA). Such provisions have produced much anxiety among landowners in the Edwards Plateau who desire to clear brush for forage production, fence construction, etc.

Under the current interpretation of the ESA, there is no distinction between currently occupied golden-cheeked warbler habitat and historical areas of habitat. If habitat for the warbler presently exists, then that site comes under the jurisdiction of the Act regardless of historical land descriptions. Another confusing descriptor is “potential habitat.” Potential habitat as used by the U. S. Fish & Wildlife Service (USFWS) refers to habitat that currently exists in a form that is presently acceptable to an endangered species even if there are no endangered species currently occupying the habitat. If an area does not presently have the structure or vegetative species required, even though at some time it might, this habitat is NOT considered to be potential habitat.

So, when can a landowner safely clear junipers on his rangeland? At the present time, stands of cedar with an average height of less than 10 feet do not constitute critical habitat and are legal to clear. The decision as to whether it is permissible or not to clear cedar is often based on both objective and subjective measurements such as location of the cedar tract relative to known populations, relative to other tracts of occupied or potential habitat, tract size, other hardwood species associated with the stand. and past land use practices. A checklist of factors to evaluate for identifying potential warbler habitat is found in Table 2.

Table 2. Suggested guidelines for recognizing golden-cheeked warbler habitat.

The following checklist is recommended as a guide to identify potential golden-cheeked warbler habitat. This checklist should be applied to an area not necessarily under one ownership. For example, if your wooded stand is contiguous with your neighbor’s, the entire stand should be evaluated.
Characteristic of Site Yes No
1. Is the site found within the 33 county area designated as potential golden-cheeked warbler habitat?
2. Are Ashe juniper and broad-leaved trees (e.g., Spanish oak, cedar elm, walnut) present in your wooded stand?
3. Are most of the trees in the stand 10 feet or taller?
4. Is the total canopy cover (average of entire stand) grater than 50%?
5. If the answer to items 1-4 is “Yes”, then is the woodland stand greater than 12 acres in size?
If a landowner answers “Yes” to questions 1-5, then the site may contain golden-cheeked warbler habitat. If the landowner answers “No” to any question, then the landowner does not have golden-cheeked warbler habitat. Woodland patches that are relatively isolated from similar patches may not be habitat, even though they may satisfy all criteria listed above. Only surveys during the breeding season will confirm whether a woodland patch is or is not warbler habitat. If uncertain, then contact Texas Parks and Wildlife Department, USDA Natural Resources Conservation Service, or National Audubon Society for assistance.

Source: Beardmore et al. (1995)

For instance, a block of 25 acres of cedar mixed with Spanish oak located 0.5 miles from a major golden-cheeked warbler colony in Travis County would be critical to the bird and should not be cleared. A similar sized tract in the western Edwards Plateau located 100 miles frorn the nearest known territory may not be considered critical to the warbler. After consultation with the USFWS, it may be possible to clear such a tract. Please note however, that the final say on the matter rests with USFWS. Landowners contemplating cedar control in areas designated as critical habitat should consult with USFWS or other qualified biologists.

Applied Landscaping

Clearing large tracts of brush may be attractive to some ranchers, but such practices will negatively influence land values. Over most of the Edwards Plateau, land value is more a function of wildlife habitat (i.e., recreational hunting) than land productivity per se. Clearing operations should take into account the resulting impacts on land value. Clearing can be conducted (to a degree at least) that will be pleasing to the eye and attractive to prospective buyers. Generally, clearing is done in irregular patterns that enhance the features of the land (i.e., landscaping). Follow contours and avoid long straight lines. Preserve brush on the tops of hills and along drainages. Mark and preserve species like Texas oaks, chittam (Bumelia lanuginosa), and hackberry. Clearings can be made more habitable to many birds by leaving scattered mottes (e.g., liveoak) within the clearings.

The relative amount of cedar to be cleared and preserved varies with the individual landowner and his management goals. Cedar can be managed in such a manner to provide increased forage production for livestock while maintaining and/or improving wildlife habitat. However, for such goals to be achieved simultaneously, it is imperative that the planning start well before the bulldozer does.

Literature Cited

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Comments: Allan McGinty, Professor and Extension Wildlife Specialist