Brush as an integral component of wildlife habitat

STEVE NELLE, USDA Natural Resources Conservation Service, San Angelo, TX 76903-6432
Abstract: Shrubs and trees are absolutely essential to most kinds of wildlife which inhabit rangelands. Without at least moderate amounts of woody plants, Texas rangeland would not have such an abundance and variety of wildlife. So, consider yourself fortunate if you have rangeland with shrubs and trees on it. Your range, in all likelihood, is more valuable and more profitable than range without woody plants.

What is brush?

The word “brush” is often misused. Unfortunately, the word is often used in a generic sense to describe all of the various combinations of shrubs, trees, and vines which grow on rangeland. All definitions of the word in the rangeland context carry primarily negative connotations. In decades past, adjectives like “worthless” and “noxious” were used to describe brush. A more modern (and acceptable) definition is: “shrubs and trees which are considered undesirable to the planned use of the area”. This definition sheds a whole new light on the concept of brush since it defines brush relative to the objectives for a given parcel of land.

For the individual who desires to create an open prairie, all shrubs and trees might be incompatible with his goals, and would rightfully be considered brush. To the cattleman seeking to maximize grass production, and who cared little or nothing about wildlife, only a few scattered trees for shade would be desirable; the remainder would be considered brush. However, to the cattleman who desires both grazing and wildlife habitat, a moderate density of shrubs and trees would not only be tolerated, but desirable. According to his objectives, it would not be considered brush. To the rancher interested primarily in maximizing habitat for deer at the expense of grazing, a thick canopy of shrubs and trees over much of the ranch would be desirable and would not be considered brush.

Obviously, not all shrubs and trees are of equal value to wildlife. Some species are highly desirable to a great many wildlife species, while other kinds have less value. The temptation is to call the most desirable species “good brush” and the less desirable species “sorry brush”. However, as will be shown, even much of the so called “sorry brush” has considerable value. The other temptation is to call the more aggressive species “brush”, while acknowledging that non aggressive species may have their place. But again, some very aggressive species are desirable to certain land management objectives at certain densities.

As with most things in life, it is possible to have too much of a good thing. Some things may be good in moderation, but undesirable if excessive, e.g., rain, fire, cattle, deer, children and wives! Ditto for shrubs and trees. Yes, even mesquite, cedar, pricklypear and blackbrush are often desirable in the right amount. Conversely, hackberry, oak, coma and other more highly-valued woodies can be undesirable in large amounts, at least for certain objectives.

So, the growth of shrubs and trees on rangeland should be considered either desirable or brushy depending on the kinds and the amounts of woody plants, and the intended purpose for the land. What may be a hideous brush-infested pasture to one person, may be a tract of excellent wildlife habitat to another. What may be a worthless, brushy jungle to the cattleman may be an exceptional browse pasture to the goat raiser. Truly, brush is in the eye of the beholder.

Wildlife use shrubs and trees for two main purposes: (a) they eat it, and (b) they live in it. The different ways in which wildlife use woody plants will be described in general without doing an extensive review of scientific literature.

Food value

Browse is the leaves and tender twigs which are eaten. Browse can be a very stable source of productive and high quality forage for a select group of wildlife species. Browse is a mainstay in the diet of game species such as white-tailed deer, mule deer, bighorn sheep and many exotic hoofstock. Browse is of some importance to pronghorn antelope and elk which rely more on forbs and grass. Browse is of virtually no direct importance to the majority of mammals, birds and reptiles. For those interested in the health and well being of browsing animals, a thorough knowledge of the browse value of shrubs and trees is important, as well as a knowledge of how to manage rangeland to maintain or improve browse.

The fruits and/or seeds of woody plants are extremely important to many species of wildlife. Fleshy fruits (often called berries or soft mast) are used heavily by hoofstock (deer, javelina, hogs); carnivores (coyotes, fox, ringtail, raccoon, skunk); songbirds (bluebirds, robins, thrashers, orioles, tanagers, jays, chickadees); game birds (quail, turkey); and reptiles (box turtle, Texas tortoise). Some examples of shrubs and trees which produce fleshy fruits are: hackberry, granjeno, bumelia, lotebush, condalia, grape, honeysuckle, juniper, pricklypear, algerita, persimmon, plum, mulberry, possumhaw and elderberry.

Non-fleshy fruits (sometimes called nuts or hard mast) are also important to many of the same species of wildlife. Examples of non-fleshy fruits are: acorns, pecans, mesquite beans, sumac fruit, and pricklyash fruit.

In many cases, the fleshy or pulpy material of the fruit is what is digested by an animal, with the actual seed passing through intact. Often the digestive system enhances germination of these seed, making this a primary method of seed dispersal and establishment of many woody plants, including both highly desirable species as well as invasive species.

In other cases, animals digest the seed along with the outer parts of the fruit (hulls, pulp and flesh). Examples include acorns and pecans. Birds with strong gizzards such as turkey and quail are able to digest seeds which pass through other birds. Even hard seed such as mesquite and acacia can be digested by these birds.

The flowers and flower stalks of some woody plants are also eaten by wildlife. The most notable examples are deer and javelina use of pricklypear flowers and young yucca and lechuguilla stalks. Quail also use algerita flowers

A listing of shrubs and trees of central and south Texas, and their value as browse and fruit, is provided in Tables 1 and 2.

Woody species such as mesquite, pricklypear, cedar, persimmon, huisache and others are often considered poor quality, non-preferred browse, and often placed in the “brush” category. However, the fact is, that due to their abundance, and the relative scarcity of the more preferred species, these often make up the bulk of the browsing animal’s diet in some regions of Texas. The “top 3” woody plants used as food for white-tailed deer in eleven different diet studies are listed in Table 3. It should be remembered that deer also eat large amounts of forbs when they are present, and in some of these studies, forbs did make up a significant portion of the diet. Mistletoe, an excellent browse, is counted in with mesquite for obvious reasons.

An interesting relationship exists between quail and cattle for a favorite food item. Cattle relish mature mesquite beans, but they cannot digest the seed. Quail relish the individual seed, but cannot separate the seed from the bean pods. After the cow eats the beans and digests the sweet pod, she deposits the seeds where a quail can pick them out. Possibly the tumble bug plays a part in this relationship, scattering the piles out for easier picking.

In addition to woody plants, which are directly consumed as food, shrubs and trees are also critical in the food chain of many other species. Myriad species of insects use woody plants for food, which in turn feed other animals. Examples include the use of small caterpillars found in shrub and tree canopies as food for warblers, vireos, kinglets, and wrens. Larger birds such as cuckoos, tanagers, orioles and woodpeckers live off of these shrub and tree insects during the spring and summer. Likewise, the hawks that feed on small birds, which feed on insects, are indirectly dependent on woody plants.

Cover value

Most species of wildlife in Texas depend upon woody plants for cover, shelter or protection of some kind. Most animals require cover both from predators and harsh weather. Protection from direct hot sun, cold wind, rain, wet snow and sleet are all important. The reproductive period is often the most critical time of the year for wildlife. Cover to protect nesting females, eggs and unfledged young is critical for birds. Fawning and denning cover is needed for mammals especially during the early phases of nursing. The actual woody species which provide this cover are usually not as critical as the structure or growth form of the cover. When considering cover for wildlife, more is not necessarily better. For just about any wildlife species, there can be either too much or too little cover. Some of the major kinds of cover provided by shrubs and trees for various wildlife groups will be described.

1. A moderate to dense canopy of low, shrubby cover is important to many species, white-tailed deer, javelina, ocelot, bobcat and numerous birds. Some animals require an almost continuous dense canopy while others prefer the dense, low cover to be in a pattern interrupted with openings of various size.

2. A sparse canopy of low shrubby cover is used by mule deer, pronghorn antelope, quail, and many grassland birds.

3. A dense closed canopy of taller trees with an open understory is required for many woodland birds.

4. A sparser canopy of taller trees is used by savanna birds.

5. Large hollow trees especially near water are used as den and nest trees by raccoon, squirrel, wood ducks and tree ducks.

6. Smaller snags (dead trees or dead branches) are used extensively by woodpeckers, wrens, chickadees, and bluebirds for nest cavities.

7. Larger snags are used as perch locations for hawks and owls.

8. Large trees are used as roosts by wild turkeys and turkey vultures, nest sites for various hawks, and if near water, herons and egrets.

Indirect benefits

Besides their use as food and cover, shrubs and trees have some less obvious, but nevertheless important side-benefits to wildlife habitat and to land health in general. Under the canopies of most shrubs and trees lies a layer of fallen and decaying leaves. This layer of composting mulch greatly improves soil structure, fertility, infiltration and moisture holding capacity. The improved soil, in combination with the cooler, more moist, shady conditions often allows certain beneficial plants to grow. In the absence of shrubs and trees, some of these associated plants would otherwise not exist in the pasture. Two prime examples of this are bloodberry rouge plant and Texas nightshade. Both of these perennial forbs are exceptionally good wildlife plants, producing excellent grazing for deer as well as fruit for birds. These forbs exist almost exclusively under and near the edges of shrub mottes.

The leaf fall of shrubs and trees also contributes greatly to the proper mineral cycling of a site. Whereas grass litter adequately cycles organic carbon back into the soil, shrubs and trees cycle significant amounts of nitrogen and phosphorus as well as carbon. Other minerals found beneath the rooting zone of grasses may also be cycled to the surface by deep-rooted woody plants.

Woody legumes, most notably mesquite, are nitrogen-fixing plants. Like alfalfa, vetch and clover, they can convert atmospheric nitrogen into soil nitrogen. This boost in fertility benefits all plants growing nearby.

Another great benefit of some woody plants is their ability to serve as a protective nursery area for the establishment of desirable species of forbs, grasses and shrubs. Unfortunately, over much of Texas’ rangeland, there are too many deer, livestock, exotics or combinations of these. Due to overuse, the best, most preferred plants are often absent or rare in pastures except in the protection of spiny or thorny shrubs. Protected by the canopy of shrubs such as algerita, lotebush, condalia, allthorn, wolfberry, pricklypear and tasajillo are a great variety of desirable wildlife and grazing plants. These desirable species are able to survive and produce seed when protected by spiny or thorny shrubs, even if the rest of the pasture is being grazed or browsed too heavily. When enlightened management corrects the problem of too many grazing or browsing animals, there will still be a viable remnant of better plants able to disperse from the protected areas.


1. You are lucky to have shrubs and trees on your ranch. Be thankful.

2. Brush is in the eye of the beholder. All that’s woody is not brush.

3. The fruit and seed of shrubs and trees are more important to a wide variety of wildlife than is browse.

4. Several of the shrubs and trees often considered undesirable are among the most heavily used as food for deer.

5. The greatest variety in kinds, densities and patterns of woody growth will provide food and cover for the most kinds of wildlife.

6. Shrubs and trees enrich the soil under their canopies with leaf litter.

7. Mesquite and other woody legumes fix nitrogen into the soil.

8. Spiny shrubs serve as nursery areas to protect desirable plants.

9. When sculpting a masterpiece, selectively remove small bits at a time, using the right tools.

Table 1. Shrubs and trees used by wildlife in Central Texas.

Most highly preferred
Kidneywood Carolina buckthorn* Shrubby boneset
White honeysuckle* Spanish oak* Mountain mahogany
Hawthorne* Texas sophora Texas mulberry*
Rusty blackhaw* Possumhaw* Mistletoe*
Littleleaf leadtree Inland ceanothus*
Hackberry* Bumelia* Elbowbush*
Ephedra* Roemer acacia* Virginia creeper*
Netleaf forestiera* Redbud* Poison ivy*
Western soapberry Grapevine* Greenbriar*
Old man’s beard Wild plum* Black cherry*
Ivy treebine* Carolina snailseed* Elms*
Blackjack oak* Southwest bernardia*
Moderately preferred
Live oak* Flameleaf sumac* Feather dalea
Pricklyash* Shin oaks* Skunkbush sumac*
Guajillo* Hogplum* Evergreen sumac*
Silktassel* Bush croton* Roughleaf dogwood*
Littleleaf sumac* Button willow* Post oak*
Redberry juniper* Algerita* Persimmon*
Mesquite* Blueberry juniper* Lotebush*
Condalias* Javelinabush* Pricklypear*
Catclaw acacia* Catclaw mimosa* Cenizo
Mountain laurel Whitebrush Willow baccharis
Little walnut Pecan* Sacahuiste
Yucca* Mexican buckeye

* Denotes plants with demonstrated wildlife value as fruit, seed or flower.

Table 2. Shrubs and trees used by wildlife in South Texas.

Most Highly Preferred
Guayacan Bernardia* Chomonque
Kidneywood Ebony* Tenaza*
Coma* Fourwing saltbush
Granjeno* Hackberry* Colima*
Guajillo* Brasil* Ephedra*
Narrowleaf forestiera* Roemer acacia* Calderon ratany
Clematis Huisache* Catclaw acacia*
False mesquite* Wright acacia*
Moderately preferred
Live oak* Cenizo Pricklypear*
Blackbrush* Twisted acacia* Lotebush*
Persimmon* Hogplum* Skeletonleaf goldeneye
Desert yaupon* Anaqua* Peachbrush*
Bush croton* Spiny aster
Mesquite* Whitebrush Wolfberry*
Allthorn goatbush Dwarf screwbean Creosotebush
Saladilla Allthorn Knifeleaf condalia*
Coyotillo* Mountain laurel Mariola
Algerita* Retama* Palo verde
Lantana* Shrubby blue sage


Table 3. Top three browse species used by deer in various regions of Texas.

County Top 3 Woody Plants in Diet Conducted By Season
Throckmorton Mesquite/Mistletoe; Pricklypear; Bumelia TTU1 Yearlong
Tom Green Pricklypear; Littleleaf sumac; Mesquite ASU2 Yearlong
Llano Oak; Mesquite/Mistletoe; Persimmon NRCS3 Yearlong
Llano Oak; Cedar; Persimmon NRCS Yearlong
Mason Oak; Mesquite/Mistletoe; Persimmon NRCS Yearlong
Mason Cedar; Oak; Persimmon NRCS Yearlong
Sutton Oak; Persimmon; Cedar TAES4 Winter
Terrell Cedar; Pricklylpear; Oak NRCS Yearlong
San Patricio Huisache; Pricklypear; Lime pricklyash WWF5 Summer
Zapata Prickypear; Mesquite; Coma TAMUK6 Yearlong
Zapata Pricklypear; Mesquite; Granjeno TAMUK Spring

1Texas Tech University, 2Angelo State University, 3Natural Resources Conservation Service,

4Texas Agricultural Experiment Station, 5Welder Wildlife Foundation, 6Texas A&M – Kingsville

Comments: Dale Rollins, Professor and Extension Wildlife Specialist
Updated: Mar. 18, 1997

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