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You can help control invasive plants in several ways. First, learn how to identify the invasive plants in your area and report occurrences to private and public land managers or owners. In Arizona, for example, keeping weeds from becoming established should continue to be a very high priority. The proverbial axioms, “an ounce of prevention is worth a pound of cure” and “the easiest weed to control is the one you don’t have yet” certainly hold true here. It is critical to detect and, if possible, eradicate incipient infestations before they have a chance to spread onto un-infested land. Once a plant sets seed, takes root, and becomes well established, the amount of effort to manage the plant greatly increases.

Second, you can control problem weeds on your own property so that your weeds do not become your neighbor’s problem. There is no “cookbook” or “silver bullet” approach to controlling invasive weed infestations. Management options will vary with each weed species, the scale of the problem, and the ecological conditions unique to the area (soil type, depth of water table, timing and amount of precipitation, topography, etc.). Annual and biennial weeds can sometimes be effectively managed during the early stages of infestation with pulling or cultivation, whereas well-established perennial weeds may require timely application of herbicides that are registered for the targeted weed. When weed infestations become well entrenched, integrated management will be necessary to combine the appropriate set of tools for the targeted plant and ecological site. Possible tools for weed management include mechanical (e.g., hand pulling, grubbing), chemical (e.g., herbicides), and biological (e.g., insects, targeted grazing) methods. Keep in mind that many invasive plants have spines and/or toxic or irritating substances. When controlling weeds manually by hand-pulling, or by applying herbicides, be sure to take safety precautions by wearing the appropriate protective clothing (gloves, boots, safety glasses, etc.). Before using herbicides, always read the label and follow instructions.

Lastly, you can volunteer to help with inventories, mapping, and eradication of invasive plant species in your area. Contact your local county extension office for more information on how to control specific invasive weeds or to get more involved in weed management efforts. Go to the Invasive Species 101 webpage to learn more about what you can do to control invasive plants.

Learn about non-natives vs. weeds vs. noxious weeds:

• Not all Non-native Plants are Harmful
• Weeds vs. Noxious Weeds
• Noxious Weed Legislation

Not all Non-native Plants are Harmful

It is very important to be concerned about the damage that non-native, invasive plants can cause.  However, it is also important to recognize that while most invasive plants are not native to the United States, not all non-native plants are invasive or harmful. Of the thousands of plants that have been purposely introduced into North America, less than 10% have become problematic invaders. Although there are plenty of “horror stories” involving introduced plants, many non-native, domesticated plants have proven to be beneficial to society as crops (e.g., corn and wheat), for landscaping, and for revegetation efforts on degraded or weed-infested lands.  On the other hand, some native plants and animals can become invasive in certain settings (feral animals, mesquite, and juniper for example). 

The term ‘naturalized’ is conventionally used to describe non-native plants that are capable of surviving and reproducing without human intervention for an indefinite period of time.  Naturalized plants may or may not become invasive.  Such plants that spread into new areas, survive, and that have a harmful impact to human health, economics, or ecosystem services are often referred to as invasive plants.

Weeds vs. Noxious Weeds

What is a weed and how does it differ from a noxious weed?  Consider these 2 plants:


The plant on the left is one that most of you are probably familiar with -- common dandelion (Taraxacum officinale).  On the right, is a noxious, invasive weed -- yellow starthistle (Centaurea solstitialis).  While dandelions have certainly been problematic for anyone who has tried to maintain a ‘weed-free’ lawn, they have not impacted millions of acres as yellow starthistle has done in California.  The point is, a weed to one person may be a desirable plant to another person – how a weed is defined really requires a value judgment.  In order for a weed to be classified as “noxious” it must be regulated by law. This video Plants Out of Place provides a better understanding of weeds, noxious weeds, invasive plants and their impacts.

Important historical pieces of legislation concerning noxious and invasive plants in the U.S. are the Noxious Weed Act of 1974 (as amended by the 1990 Farm Bill), the 1999 Executive Order on Invasive Species, and the 2000 Plant Protection Act.  Go here for a list of weeds that are designated as noxious in Arizona, for an example.  For additional reading on definitions, check out a ‘white paper’ located here (click on the first link under ‘Invasive Species Information’).

Learn about the basics of invasive species:

• Origins of Introduced Invasive Plants
• Common Characteristics of Invasive Plants
• Invasive Plants act as Environmental Pollutants
• Exponential Growth Associated with Invasive Plants
• Economics Associated with Invasive Species
• Examples -- Invasive Grasses

Origins of Introduced Invasive Plants

Some of the most problematic invasive plants (weeds) in the United States were introduced from Europe or Asia (Eurasia), Africa, and the Mediterranean region either purposely or by accident.  Some invasive plants were introduced as ornamentals or with the intention of solving an environmental problem such as excessive soil erosion during the 1930’s, while others likely inadvertently hitched rides in ship ballasts, hay bales, or in agricultural seed.  For more information on the origins and impacts of invasive plants watch the video Dangerous Travelers.

Common Characteristics of Invasive Plants

The reasons why some plants become invasive while others do not are extremely complex and depend on characteristics of the plant as well as the unique abiotic and biotic idiosyncrasies of the ecosystem where the plant grows.  However, invasive plants often share one or more of the following characteristics:

1. fast growth
2. rapid reproduction
3. high seed production and dispersal ability
4. tolerance of a wide range of environmental conditions
5. aggressive and prolific vegetative reproduction (massive root systems)
6. association with humans or human activities (land management practices). 

Also, non-native invasive plants may not have the natural predators in their new environment which helps them to proliferate unchecked.

Invasive Plants act as Environmental Pollutants

Nearly 20 years ago, Dr. Steven Dewey, a weed scientist (now retired) from Utah State University, suggested that invasive plants act as environmental pollutants, to wit:

• The pollutant weakens and kills native vegetation with endangered species being especially vulnerable.
• The pollutant spreads naturally in water, wind, and/or soil, but is also spread by wildlife, livestock, and recreationists.
• Affected lands cannot “heal” themselves over time - once polluted, always polluted.
• The effects of the pollutant are not usually apparent until the spread is already out of control.

Some common environmental and economic impacts of invasive plants include:

Environmental

• Degraded watersheds.
• Decreased biodiversity.
• Decreased forage and habitat for livestock and wildlife.
• Decreased soil moisture.

Economic

• Decreased land values.
• Poisonous plant problems for livestock.
• Increased erosion.
• Control costs.

The video Hunters and Anglers Against Invasive Species provides more detailed information on the many negative economic and ecologic impacts that invasive plants can have on the environment.

Exponential Growth Associated with Invasive Plants

Infestations that were initially just a few plants can increase rapidly to become several thousand acres.  Invasive plants can sometimes lie “dormant” for decades, and then explode exponentially. One striking example of this phenomenon is yellow starthistle in California.  This Eurasian plant is believed to have been inadvertently introduced into California in the mid-1800’s.  By 1958, yellow starthistle had expanded its range to 1 million acres.  It had expanded its range by another 7 million acres by 1985, and over the next 20 years it more than doubled its acreage to >15 million acres.

Exponential growth is just one of the many insidious characteristics of invasive plants.  The cost of controlling invasive plants increases and the probability of successful control decreases as you move from left to right on the x-axis of the above figure.  Unfortunately, humans tend not to get too excited about invasive plants until it is too late to effectively manage them ecologically or economically.  Like so many things in life, the longer we wait to do something about it, the more damage it causes and the more expensive it becomes!

Humans have both intentionally and accidentally introduced many non-native plants and animals to Western rangelands. Some of them have produced benefits for humans while remaining under management control. Others have escaped and “gone wild” with unintended negative consequences. While we can debate the degree to which any particular exotic plant or organism has a right to exist on Western rangelands, one thing is for certain. Some of these plants and animals are spreading like wildfires and have become serious threats to the environment, human health, and economic well being.

Invasive species are plants, animals, or insects that have evolved elsewhere and have been purposely or accidentally moved to a new location. Some have invaded habitats by themselves. However, human exploration, colonization, and commercial trade have dramatically increased the diversity, scale, and impact of the invasions. Introduced species often find no natural enemies in their new habitat and therefore spread quickly and easily.

Invasive species are damaging to both the environment and the economy. The economic costs of non-native species invasions in the United States reaches billions of dollars each year. They disrupt the areas they invade by: replacing native species, reducing biological diversity, changing vegetation or animal productivity, placing other species at increased risk of extinction, altering wildfire intensity and frequency, and closing foreign markets to U.S. products from infested areas.

Users of natural resources — including hunters, ranchers, managers, hikers, campers, and any other outdoor enthusiasts — should do all they can to prevent the introduction and/or spread of invasive species. Information about invasive species in your area can be obtained from local Cooperative Extension offices or from the field offices of various federal and state land management agencies.

Although invasive species can come from both the plant and animal kingdoms, this module focuses on non-native, invasive plants. 

By Beth Burritt, Utah State University

• Are We Losing Our Aspen?
• Fire Ecology in Aspen Forests
• Forage: Livestock and Wildlife
• Placing Value on Aspen Ecosystems
• Aspen Management Options
• Further Reading

Before we dive into aspen ecology and issues, it is important that readers understand two key concepts. First, aspen reproduce both asexually via root suckers and sexually from seed germination. Thus, large groups of aspen trees may be genetically identical clones, many of them still attached by underground root networks. Conventional management practices rely heavily on strong suckering responses following burning or cutting. Second, aspen come in two primary forms: seral (meaning they are relatively short-lived and eventually overtopped by competing conifers) and stable (not competing with conifers; long-term growth in pure or nearly pure stands of aspen). Understanding these different aspen "functional types" is crucial to restorative efforts, otherwise well-intended actions may lead to aspen loss. Photo Credit: WanderingtheWorld (www.ChrisFord.com) / Foter / CC BY-NC

Are we Losing our Aspen? Aspen "decline" comes in two flavors: long-term decline related to conifer encroachment and short-term decline (a.k.a., Sudden Aspen Decline or SAD) initiated by drought. For decades we have been hearing about great losses in aspen coverage in the western states due to advancing conifer succession. Some of these changes were caused by past management practices, such as fire suppression and active removal of aspen or management for higher value conifer timber species. More recent evidence, however, suggests that a regionally moist 20th century generally kept fire events limited, allowing conifer expansion and aspen decline. In other locations, aspen actually expanded its range so we must be careful not to oversimplify regional patterns.  This interaction with conifers does not explain losses in stable (nearly pure) aspen forests.  Thus, we must understand at least two aspen "types" which depend on different ecological mechanisms to persist.

SAD is defined as the rapid die-off of both overstory canopy trees and supporting root systems where the end result is the death of complete aspen clones.  Strong evidence has been presented that this type of rapid die-off has occurred in southwest Colorado, but corroborating support is limited elsewhere.  There has been much broader patterns of mature tree mortality across the West and in southern Canada associated with the 2001-2004 drought.  In many instances, combined effects of overstory drought-induced die-off and intense herbivory of young aspen by browsers has led to "de facto SAD" where we witness complete aspen community collapse. Photo by Phil Kemp, US Forest Service, Mancos-Dolores District.
 

Fire Ecology in Aspen Forests. Aspen has conventionally been thought of as "fire dependent," meaning that it requires forest fires to thrive. The quick-sprouting root system of an aspen clone  rapidly regenerates after all types of disturbance (i.e., landslides/avalanches, insects, disease, drought, tree harvest) including burning. Moreover, recent discoveries of high genetic diversity in aspen communities and common occurrences of seedling (sexual reproduction) establishment following fire is leading practitioners to question traditional aspen management. Fire suppression during recent decades is thought to be partially responsible for long-term aspen decline, however several experts have questioned this assertion. Likely, there are several causes for the lack of fire, most notably long periods of climatic moisture that increased the number of conifer trees in some aspen forests over the past century. Stable (nearly pure) aspen is much less conducive to wildfire or prescribed burning; rejuvenation in these forests is dependent on more continuous, low-level, tree mortality and regeneration.

Use of fire for restoration is a viable means of reducing conifers and promoting aspen suckers and seedlings in seral forests. Where disruption of fire cycles due to past fire suppression is evident, using fire to restore aspen is recommended.  Some managers favor a combination of harvest and burning, particularly where the possibility of escaped fires can damage property. Photo by Bob Campbell, US Forest Service.

Aspen as Forage for Livestock and Wildlife. Quaking aspen are widely revered by range and wildlife managers alike for their diverse and nourishing array of understory plants. Young aspen sprouts are particularly favored by deer, elk, cattle, and sheep for their highly nutritious leaves and twigs. During the late summer and early autumn aspen may be the only green, nutritious, component of forests available as forage. Fortunately, aspen leaves contain defense compounds (phenolic glycosides and condensed tannins) that may deter herbivores, at least partly, from devouring young suckers.  However, with high animal concentrations—often a mix of wild and domestic herbivores on the same landscape—defense mechanisms may not sufficiently deter browsing on regenerating aspen suckers. If these consumption patterns persist over many years aspen forests begin to lose their age and structural complexity.  This situation seems particularly serious is stable (nearly pure) aspen forests where uncommon large disturbances offer little hope of broad forest rejuvenation.

Ongoing monitoring activities are attempting to document where livestock and wildlife browsing is threatening future aspen trees. In some cases, there is clear evidence of aspen collapse related to intensive browsing. The presence of large carnivores, such as wolves, grizzly bears, and cougars, may deter aspen browsing by keeping livestock and wildlife on the move. Domestic livestock may be more easily herded to prevent over browsing aspen. Range and wildlife managers are now working collaboratively to curtail aspen recruitment failure while continuing to sustainably utilize forage resources. Cooperative research and monitoring, as well as prudent use of fire, tree harvest, and post-treatment protection, will be required to overcome the widespread lack of aspen recruitment. Photo by Teresa Prendusi

Placing a value on Aspen. We often hear about the diverse values of aspen forests, but what evidence is there to support such assertions? Much of the "value" of aspen lies in its apparently innate beauty; a rich gold or fluttering green among the sea of conifer and sagebrush. Utah recently recognized aspen as its State Tree largely on the basis of esthetic appeal. Digging a little deeper, however, we can tap into, perhaps even monetize, other aspects of aspen worth. For example, aspen is among the most biodiverse vegetation types in the Intermountain West. Additionally, range managers are well aware of the high value forage resident among aspen groves. A diverse array of wildlife utilize aspen for cover, food, habitat, and water. There is some evidence that healthy aspen communities facilitate water conservation. Thriving beaver colonies create migrating water retention ponds, as well as raising water tables and increasing wildlife habitat. Aspen is valuable for a variety of wood products, including flooring, mine supports, particleboard, pet bedding, excelsior (wood fiber packaging and cooling devices), and ski/snowboard manufacturing. Aspen forests make for cherished camping and recreation destinations, popular ski resorts, and general tourism promotion. Finally, aspen may be used as a fire break via selective cutting or light burning around developed areas.What is the value of aspen?  Ask any westerner if they could go without it. License: Creative Commons 2.0 (by-nc-sa)
 

Aspen Management Options. Conventional treatments to stimulate aspen regeneration are widely available (e.g., Shepperd et al. 2008), although we now know that a strong sprouting response is not enough to protect from post-treatment browsers. In order to sustain aspen on the landscape land stewards are adopting "resilience management" strategies. In essence, this entails preserving options. Where fire was historically an important regenerative tool in seral aspen, judicious use of selective harvest practices and prescribed and wildlife fire management may be invoked. A key component of resilience management means understanding ecological function: not all aspen stands are alike in terms of their ecology and earlier human impacts. Treating aspen as a "one-size-fits-all" prospect may cause irreversible damage.  Thus, locally-based knowledge, current science, ongoing monitoring, course correction (where necessary), and institutional support—all key elements of "adaptive management"—provide a recipe for resilience. The complexity of resilience management will require multiple perspectives if they are to be successful.

These approaches will become particularly important with the advent of climate warming in the West. Changing climates are expected to bring two opposing elements into the resilience equation for aspen: 1) warming temperature may cause decreases in suitable aspen habitat as these communities move upslope, and 2) expected increases in fire frequencies and extents may provide opportunities (at least temporarily) for aspen expansion or recolonization. Photo Credit USFS

Basic Rangeland Types

The United States has 15 basic rangeland types that are economically important from the standpoint of forage production and total area.

• Alpine Tundra
• Califonia Annual Grassland
• Cold Desert (sagebrush steppe and salt desert)
• Eastern Deciduous Forest
• Hot Desert
• Mountain Browse
• Northern Mixed Prairie
• Oak Woodland
• Palouse Prairie
• Pinyon-Juniper Woodland
• Shortgrass Prairie
• Southern Mixed Prairie
• Southern Pine Forest
• Tallgrass Prairie
• Western Coniferous Forest

Adapted from: Holecheck, J.L., R.D. Pieper, and C.H. Herbel. 1998. Range Management Principles and Practices, Third Edition.

Alpine Tundra 

The highest range type in altitude is the alpine tundra which occupies those mountain areas above timberline that are characterized by short, cool growing seasons and long, cold winters. Low-growing, perennial, herbaceous, shrubby vascular plants dominate the vegetation along with cryptograms such as mosses (Selaginella sp.) and lichens (Cladonia sp.). Permafrost prevents the growth of trees. Alaska hosts the most alpine tundra in the United States, followed by Colorado, Washington, Montana, California, Oregon, Idaho, Utah, New Mexico, Arizona, and Wyoming. The 1,000 mm to 1,500 mm of precipitation occurs mainly as snow, and the land is constantly buffeted by winds and cold temperatures. Even during the growing season, air temperatures are often at or near freezing. These harsh conditions are very stressful to plants, and the flora is limited to 200 to 300 species that commonly occur in alpine tundra. Members of the bluegrass (Poaceae), sedge (Cyperaceae), saxifrage (Saxifragaceae), rose (Rosaceae), mustard (Brassicaceae), buckwheat (Polygonaceae), and pink (Caryophyllaceae) families have wide alpine distribution along with shrub species of the willow (Salicaceae) and heath (Ericaceae) families. Much of the alpine tundra has been designated as wilderness areas because of aesthetics, remoteness, and its importance as a water source in the western United States. Comparatively, livestock grazing ranks low in importance and is generally limited to sheep that are herded to minimize excessive use of rare, flat areas.

California Annual Grasslands 

California annual grasslands are found primarily west of the Sierra Nevada Mountains. The climate of the region is Mediterranean, characterized by mild, wet winters and long, hot, dry summers. Rainfall varies from about 200 mm in the southern foothills to almost 1,000 mm in some areas near the coast. Most of the precipitation comes between October and May, with almost no precipitation during the summer months. Summers are hot and long, with an average frost-free period of 200 to 260 days. Soils vary across the region with only the less fertile areas remaining as rangeland.

The California annual grassland has one of the longest livestock grazing histories of the western range types, dating back to the Spanish settlements of the seventeenth century. Under pristine conditions, the California grasslands were quite beautiful, but they have suffered severe degradation since the arrival of European settlers. The original vegetation of the California annual grasslands was comprised of cool-season bunchgrasses; however, numerous fires and overgrazing from a very early date probably account for the change from perennial to annual grasses. Presently, less than 5 percent of the native perennial grasses remain. The cool-season annuals that replaced the perennial grasses have nearly ideal environmental conditions in California. This is because they have adequate moisture and temperature for growth and reproduction in winter while their seeds remain dormant during the dry summer period. Today, the vegetation is dominated by slender oat (Avena barbata), wild oat (Avena fatua), soft brome (Bromus mollis), ripgut brome (Bromus rigidus), foxtail brome (Bromus rubens), and little barley (Hordeum pusillum).

Because the grasslands of California are dominated by annuals, they have some unique problems. Generally, they are not very responsive to grazing intensity, although heavy grazing does cause erosion problems, some change in species composition, and reduced forage production. Season-long grazing has been superior to specialized systems. These ranges should be grazed lightly during plant germination and establishment in the fall, but grazing intensity can be increased substantially in the early spring. Primary problems in this type of rangeland include inadequate forage quantity in the fall and winter and inadequate forage quality in the summer. Forage quantity fluctuates drastically from year to year, necessitating operators to be able adjust their stocking rates rapidly or have a good reserve of harvested forage.

Cold Desert 

The cold desert type, often referred to as the Great Basin, is comprised of two distinct vegetation communities, the sagebrush grassland and the salt desert. These two rangeland types intermingle with each other over vast portions of the intermountain United States (the area between the Cascade Mountains and the Rocky Mountains). Differences in vegetation and managerial components between the two cold deserts warrant a separate discussion of each.

Sagebrush grassland

Encompassing nearly 39 million hectares, the sagebrush grassland is one of the most extensive of the western range types. It covers parts of Oregon, Idaho, Nevada, Utah, Montana, Washington, and Wyoming, with about 65% of the land mass in federal control and 35% in private ownership. Compared to the salt desert, sagebrush grassland has higher precipitation and less saline soils and typically occurs at the higher elevations of the cold desert. Precipitation ranges between 200 mm and 500 mm. Summers are dry in the northern half of this range type, and most of the precipitation comes in the late fall, winter, and early spring as snow. In the southern part, most of the precipitation also comes in the winter, but slightly more precipitation comes in the summer. At higher elevations the growing season is often no more than 100 days. Soils are primarily volcanic material of the order Aridisols. Depth varies from shallow to deep, and topography is highly variable.

The dominant shrub of the region is big sagebrush (Artemisia tridentata). Important grasses of the sagebrush grassland are bluebunch wheatgrass (Pseudoregneria spicata), bottlebrush squirreltail, (Elymus elymoides), Idaho fescue (Festuca idahoensis), western wheatgrass (Pascopyrum smithii), Indian ricegrass (Oryzopsis hymenoides), needle-and-thread (Hesperostipa comata ), and basin wildrye (Leymus cinereus). Bluebunch wheatgrass dominates the understory in the northern half, with western wheatgrass dominating the understory in the southern half if grazing has not been abusive. Abusive grazing replaces the bunchgrasses with cheatgrass (Bromus tectorum) and increases sagebrush density.

Other important shrubs are rabbitbrush (Chrysothanmnus sp.) and antelope bitterbrush (Purshia tridentata). Sagebrush grasslands generally recover very slowly from overgrazing. Control of invasive and shrubby species can speed recovery.

Salt desert

The salt desert shrubland inhabits the lower areas of the Great Basin, where drainage is often restricted and the water table is high. This region occurs primarily in the states of Utah and Nevada as a mosaic with sagebrush grassland. The salt desert shrubland is one of the least productive of the range types because of climate and soils. Precipitation in the region ranges from 80 mm to 250 mm, the lowest precipitation of all types except the Mojave Desert. The xeric climate is exacerbated by the high salt content of the soil, produced when evaporation causes salts to accumulate at the soil surface. Generally, summers are quite dry with one-half of the precipitation falling as snow in winter and the remainder as rain in the spring or fall. Precipitation is highly variable from year to year, and there is very little vegetation growth in the dry years. Despite the cold winters and hot summers, the growing season is approximately 200 days. Soils are primarily Aridisols with varying degrees of alkalinity and salinity. Vegetation is characterized by a few species of low, spiny, grayish, and widely spaced microphyllous (small-leaved) shrubs in the Chenopodiaceae and Asteraceae families. Shadscale saltbrush (Atriplex confertifolia) dominates the area, with winterfat (Krascheninnikovia lanata) being the second most common shrub. Vegetation canopy cover is usually less than 10%. Much of the salt desert has historically been severely overgrazed, and vegetation recovery is slow but can be accomplished with moderate stocking rates. Traditionally, the range type was used as winter range for sheep which summer in the surrounding mountains. However, control of undesirable plants has not been economically feasible, enabling halogeton (Halogeton glomeratus), a poisonous forb to become dominant in much of the salt desert shrub.

Eastern Deciduous Forest 

Although much of the eastern deciduous forest has been heavily modified by farming, logging, and industrialization, it is becoming increasingly important for livestock production. Many of these areas are managed using ecological rather than agronomic principles. The growing season lasts from 120 to 240 days, with snow and frost common in the winter. The 800 millimeter (mm) to 2,000 mm annual precipitation is uniformly distributed throughout the year. Soils of the order Alfisol support deciduous forest trees, including maples (Acer sp.), birches (Betula sp.), oak (Quercus sp.), hickories (Carya sp.), beeches (Fagus sp.), and basswood (Tilia sp.). Grasses such as bluestem (Andropogon sp., fescue (Festuca sp.), timothy (Phleum sp.), bluegrass (Poa sp.), brome (Bromus sp.), ryegrass (Lolium sp.), and orchardgrass (Dactylis sp.) thrive in open canopy areas where trees have been thinned or completely removed. Nitrogen and phosphorus fertilization can further boost forage production in the low fertility soils.

Hot Desert 

The hot desert is one of the largest western rangeland types, yet compared to the other rangeland types, it is relatively unimportant from the standpoint of livestock production. This type is found in southern California, southern Nevada, Arizona, New Mexico, southwestern Texas, and northern Mexico. Elevations range from 925 m to 1,400 m. Precipitation in the desert climate varies from 130 mm to 500 mm and increases with elevation above sea level. Precipitation occurs primarily during winter, peaking in January and during summer with the wettest months being July, August, and September. May and June are extremely dry. Summer rains occur as convection storms because of solar heating. The frost-free period is generally over 200 days during the year, and it is not uncommon for areas to go two to three years without a killing frost. The Mojave Desert, Sonoran Desert, and Chihuahuan Desert occur in this type.

Vegetation of the hot desert type did not evolve with grazing by large herbivores; however, this area was one of the first types in the United States to receive grazing by domestic livestock. Severe overuse and lack of adaptation to grazing probably explain the large-scale decline of black grama and other climax grasses in the past 100 years. Almost all the plants found in the hot desert type are warm-season species. The warm, sunny climate of the Mojave and Sonoran deserts has attracted large numbers of people to these desert areas. Currently, tourism, wildlife, water, and recreation are the most important products of this rangeland type. Livestock grazing is still an important rangeland use in the Chihuahuan desert; however, large tracts of the Sonoran Desert are being converted into housing and other urban uses in Arizona. Management of livestock focuses on water development to improve livestock distribution and carefully adjusting stocking rates to forage availability. Recovery from overgrazing in these arid regions is often slow to non-existent.

Mountain Browse 

The mountain browse range type occurs primarily in the Rocky Mountains and Sierra-Cascade Mountains of the western United States and is most prevalent in Colorado, Utah, Oregon, and Idaho. The climate is intermediate between that favoring grassland and that favoring forest, although at an average of 460 millimeters (mm) to 500 mm precipitation is not high enough to sustain forests. Temperatures range from 35°C in the summer to -34°C in the winter, with a growing season of 100 to 120 days. Soils are mostly Entisols and Inceptisols. The topography of the mountain browse type is variable, and elevations range from 1,200 meters (m) to 2,800 m. The ridges and dry, rocky slopes are dominated by shrubs 1 m to 10 m tall. Important species occurring throughout the type are chokecherry (Prunus virginiana) and several species of buckbrush (Ceanothus sp.). Gambel oak and true mountain mahogany (Cercocarpus montanus) are two of the most important shrubs associated with this type in the Southwest. The occurrence of antelope bitterbrush (Purshia tridentat) and other important forage species make this range type an important winter feeding area for big game.

Northern Mixed Prairie 

The northern mixed prairie encompasses the western half of North and South Dakota, the eastern two-thirds of Montana, the northeastern one-fourth of Wyoming, and the southeastern part of Alberta and southern Saskatchewan in Canada. The climate is characterized by long, severe winters and warm summers. Average frost-free period ranges from about 140 days in the south to less than 100 days in Canada. Two-thirds of the 300 millimeters (mm) to 650 mm of average annual precipitation comes as rains during the summer, with the majority falling in June. Most soils are of the order Mollisols; however, much of the region is still rangeland due to the short growing season, drought, and severe winters. It is the second most important western range type from the standpoint of livestock production. The northern mixed prairie is home to the highest diversity of grasses of all the western range types, including short, mid-, and tall grasses, as well as cool- and warm-season grasses. Consequently, the northern mixed prairie is one of the best of all types for both wildlife and livestock from a nutritional standpoint. The diversity of grasses provides a continuous excellent feed source throughout the year: cool-season bluebunch wheatgrass (Pseudoregneria spicata) and various bluegrasses provide early spring feed; green needlegrass (Nassella viridula) and needle-and-thread (Hesperostipa comata), western wheatgrass (Pascopyrum smithii), and various forbs provide excellent late spring feed. Little bluestem (Schizachyrium scoparium), blue grama (Bouteloua gracilis), and sideoats grama (Bouteloua curtipendula)provide high-quality summer and fall forage, while the shrubs and blue grama provide excellent winter feed. Nevertheless, supplementation is often required for livestock during the winter because of frequent snow cover. The northern mixed prairie hosts the widest variety of shrubs of all the western range types. This is a primary reason why it supports an abundant and diverse wildlife population.

Oak Woodland 

Rangelands dominated by oak species (Quercus sp.) can be divided into three categories: the shinnery oak (Quercus havardii) type found in southeastern New Mexico, west Texas, and south into Chihuahua, Mexico; the Gambel oak (Quercus gambelii) types in the central and southern Rocky Mountains; and the open savannah dominated by tree oaks in California, Oregon, southern Arizona, and central Texas. Oaks are sensitive to winter cold and occur primarily in areas with a maximum temperature near 36°C and a minimum temperature of about -34°C. Oak species occur on rolling uplands and foothills with a variety of well-drained soils. Precipitation in the oak woodland type ranges from 360 mm per year in the chaparral ranges of southern Arizona and New Mexico to around 1,000 mm per year in the California chaparral. In general, the size of the oak trees decreases in response to decreasing precipitation as one moves from the east to the west in the southern Great Plains.

Although most oaks have limited forage value for livestock, they are a valuable food source for many wildlife species. Deer, elk collared peccary, wild turkey, and other upland game birds forage on the acorns. Deer and elk also browse on the leaves of Gambel oak. The new growth of deciduous oaks such as shinnery and Gambel is poisonous to cattle and sometimes sheep, but goats can browse most oak species without harm and can even be used to control some oaks on rangeland. Oaks are sprouters, making control with herbicides and fire difficult. However, widespread control of oaks is not recommended. Rather, management should be focused on maintaining a mosaic of habitats to provide adequate forage for wildlife and livestock while preserving the aesthetic and ecological values of the oak woodland range type.

Palouse Prairie 

The Palouse prairie occurs primarily in eastern Washington, north central and northeastern Oregon, and western Idaho. However, only remnants remain after the majority was converted into farmland. Soils are primarily loessal dunes in the order Mollisol. They have excellent textural, structural, and chemical properties for agriculture. Rainfall in the area ranges from 30 centimeters (cm) to 64 cm annually, with approximately 65% to 70% falling during the winter months. Peak precipitation occurs in December and January. The months of July and August have the lowest precipitation, although these months are wetter than in the California annual grassland type. The growing season lasts from 140 to 160 days, extending from May 10 to October 10. Winters in the Palouse country are relatively mild, and summer temperatures are seldom over 35°C.

The Palouse prairie is one of the most productive and beautiful grasslands in the world. The major characteristics distinguishing the Palouse prairie from other North American grasslands is that the climax vegetation is dominated by bluebunch wheatgrass (Pseudoroegneria spicata) or bluebunch wheatgrass and Idaho fescue (Festuca idahoensis). Grasses are almost entirely cool-season bunchgrasses because of the dry summers. The Palouse prairie supports a wide variety of forbs, most of them belonging to the Composite (Compositae) family.

The Palouse prairie grasses evolved with little grazing pressure from large herbivores. The American bison did not use this type because barriers such as the Rocky Mountains and Snake River Canyon restricted access. Both bluebunch wheatgrass and Idaho fescue have very low grazing resistance. For this reason, the Palouse prairie responds rapidly to overuse. The Palouse prairie was the first of the northern ranges to support a livestock industry. Unfortunately, overgrazing has resulted in an increase of downy brome (Bromus tectorum) and Sandberg bluegrass (Poa sandbergii) which can replace perennial bunchgrasses.

Pinyon-Juniper Woodland 

One of the most widely distributed rangeland types in the western United States, the pinyon-juniper woodland (also spelled pinon-juniper), occurs from the state of Washington to 220 kilometers (km) north of Mexico City. Annual precipitation varies from 300 millimeters (mm) to 450 mm, with local areas receiving up to 500 mm. The frost-free period is variable and ranges from 91 to 205 days. Soils are poorly developed and are primarily of the orders Entisol and Aridisol. The climate is characterized by low precipitation, hot summers, high wind, low relative humidity, high evaporation rates, and much clear weather and intense sunlight, making it relatively harsh for tree growth. Nevertheless, a combination of overgrazing, absence of fires, dissemination of seeds by mammals and birds, and possibly climatic change has sparked tree encroachment onto grasslands and prompted original stands to become more dense. Overgrazing of understory species has reduced protective soil cover and resulted in severe soil erosion over much of this range type. As the tree overstory increases, perennial grasses and forbs decrease because of shading and increased competition from the trees. The pinyon-juniper woodland is one of the most depleted rangeland types occurring in the United States, particularly in the northern extent of the region, where very few areas presently support a good grass understory. Recovery from overgrazing is considered to be slow to nonexistent in most areas without control of the trees. Presently, wood from this type may have more economic value as a biofuel and carbon sink than the forage it provides for domestic animals.

Shortgrass Prairie 

The shortgrass prairie extends from northern New Mexico into northern Wyoming, encompassing much of eastern Colorado. The low precipitation of the region (300 millimeters to 500 mm) has prevented cultivation, despite the fertile soils that are primarily Mollisols. Therefore, much of the region remains as rangeland. It ranks third in importance for livestock production among the western rangeland types. The climate is characterized by cool winters and warm summers, with the majority of the yearly precipitation coming from light rains falling throughout the summer. This climate favors warm-season grasses such as blue grama and buffalograss, which have shallow but extensive root systems. The region evolved under intense bison grazing, prompting the most abundant grass species to develop physiological and morphological adaptations to heavy grazing pressure. Livestock are generally grazed year-round on the shortgrass prairie with little hay provision; however, a protein supplement can substantially reduce livestock weight losses.

Winterfat is an important shrub that is palatable for livestock and wildlife and important for pronghorn antelope that thrive in this rangeland type. Scarlet globemallow is an important forb heavily used by cattle, sheep, and pronghorn. Throughout history, people have repeatedly attempted to cultivate portions of the shortgrass prairie, despite the fact that it will not sustain cultivation without irrigation and is subject to wind erosion.

Southern Mixed Prairie

The most important of the western rangeland types for livestock production is the southern mixed prairie, which extends from eastern New Mexico to eastern Texas and from southern Oklahoma to northern Mexico. The precipitation ranges from 300 millimeters (mm) to 700 mm across the region with a frost-free period generally at least 180 days in length. This vast area hosts a wide range of soils and climatic conditions that result in variable production and vegetation communities. There are four basic subtypes of the southern mixed prairie. These are: true mixed prairie, desert prairie, high plains bluestem, and oak savannah.

Soils of the region belong to the order mollisols, entisols, and aridisols. The southern mixed prairie has a long history of grazing, beginning with the buffalo and then domestic livestock brought in by the Spaniards in the 17th century. As a result, most grasses are relatively grazing resistant. Important grasses of the southern mixed prairie are: blue grama (Bouteloua gracilis), buffalograss (Buchloe dactyloides), little bluestem (Schizachyrium scoparium), various threeawn species (Aristida sp.) silver bluestem (Bothriochloa saccharoides), vine mesquite (Panicum obtusum), and sideoats grama (Bouteloua curtipendula). Texas wintergrass (Stipa leucotricha), is the only cool season grass of significance in the southern mixed grass prairie and as such provides an important winter feed source. Several woody invasive plants, such as mesquite (Prosopis sp.), create challenges for land managers and livestock producers over most of the southern mixed prairie, particularly when overgrazing occurs. Multi-species grazing is commonly used in this range type to increase animal production and improve range condition. The Merrill four-pasture, 30-herd grazing system appears to be more beneficial to soils, vegetation, and livestock and wildlife performance and health than continuous grazing.

Southern Pine Forest 

The largest and most important rangeland type in the United States is the southern pine forest. With an annual precipitation of 1,250 millimeters (mm) and a frost-free period of 200 to 365 days, it is also the most important of all rangeland types for livestock production. The warm temperatures and large amount of precipitation ensure high vegetation production limited only by the acidic soils of the region. These highly leached soils are primarily of the order Ultisol.

Pine trees such as longleaf pine (Pinus palustris), shortleaf pine (Pinus echinata), and loblolly pine (Pinus teada) occupy much of the area and are grown for lumber. Most grazing occurs on open or cutover forests where grasses in the genera Andropogon, Panicum, Aristida, Paspalum, Sporobolus, and Cynodon provide abundant forage. Protein and phosphorus deficiencies in the forage require that livestock be supplemented for at least part of the year. Livestock production is second to timber production as the most important land use in the Southeast.

Tallgrass Prairie

The tallgrass prairie is located primarily in the central United States. Climate and disturbance have worked together to keep the area a grassland. Precipitation ranges from 500 millimeters(mm) in the north to 1,000 mm annually in the south, with most of it falling as rain in the summer growing season. Periodic summer drought combined with relatively frequent fires, every three to four years, prevented the successful establishment of trees. The subhumid, temperate environment coupled with the deep fertile soils (Mollisols) of the region make it ideally suited for cultivation. Consequently, much of the tallgrass prairie now grows wheat and corn. Very little rangeland still exists in this region and is confined to the Flint Hills of eastern Kansas and the Osage Hills of Oklahoma because of their thin, rocky soils unsuitable for cultivation.

The tallgrass prairie evolved under grazing by wild ungulates, primarily, the American bison. It is one of the most grazing-resistant range types, due to the high amount and favorable timing of precipitation. The tallgrass prairie is particularly well-suited for grazing in the summer and fall, but grasses become coarse and have little nutritional value to offer livestock during the winter months. However, extreme overgrazing can shift a tallgrass prairie from tallgrass prairie to mid-grasses to short grasses. A rotational grazing plan is recommended for the tallgrass prairie to optimize livestock performance and range condition.

Tallgrass prairie should be burned every two to three years in the spring to prevent excessive mulch accumulation. The most notable grass species of the tallgrass prairie are little bluestem (Schizachyrium scoparium), big bluestem (Andropogon gerardii), yellow indiangrass (Sorghastrum nutans), and switchgrass (Panicum virgatum). Important forbs of the tallgrass prairie are leadplant (Amorpha canescens) and scurfpea (Psoralea sp.). Buckbrush (Symphoricarpos orbiculatus) is the primary shrub on the tallgrass prairie, providing valuable food and cover for wildlife.

Western Coniferous Forest 

Two main plant communities, ponderosa pine (Pinus ponderosa) and Douglas fir (Pseudotsuga menziesii)-aspen (Populus tremuloides), dominate the 33 million hectares that comprise the western coniferous forest rangeland type. Early adoption of good grazing management and high precipitation have prevented this forest from suffering the ecological damage seen in the pinyon-juniper vegetation type. The western coniferous forest supports many different land uses including recreation, watershed, wildlife, and scenic value in addition to livestock production.

As the largest of the true forest types in the western United States, ponderosa pine is found from inland California east to Nebraska and from southern Alberta south into northern Mexico. It is found at elevations between the pinyon-juniper and the Douglas fir zone ranging from 2,000 meters (m) to 2,500 m in the Southwest to as low as 1,100 meters in the northern areas. The ponderosa pine forest is also the most xeric forest type in the western United States receiving between 450 millimeters (mm) and 650 mm of precipitation, with most falling as snow in the north and as rain in the south. Frost can occur in any month of the year, and the growing season encompasses 105 to 140 days. The primary soils are Entisols with Inceptisols occupying the benchlands and ridges and Mollisols common in areas with more level topography.

Immediately above the ponderosa pine zone from 2,500 m to 3,100 m elevation is the Douglas fir-aspen forest. This forest type occurs primarily in Colorado, Idaho, Wyoming, Montana, Oregon, and Washington. The bulk of the Douglas fir-aspen forest type occurs in seral stages dominated by lodgepole pine (Pinus contorta) quaking aspen (Populus tremuloides) and western larch (Larix occidentalis). Soils in the region are primarily Alfisols, Entisols, and Inceptisols, and the topography is very steep. The growing season lasts from 100 to 125 days, and the zone receives 640 mm to 900 mm of precipitation falling mostly as snow.

Learn about Rangeland Plants

• Origin of Range Plants
• Life Span of Range Plants
• Season of Growth of Range Plants
• Cool-Season and Warm-Season Forages

Origin of Range Plants

The "origin" of a range plant is the area where it evolved. It is important to know the origin of a plant because it can affect the way that a plant responds to the environment.

Native plants are those that originated and evolved in North America.

Introduced plants were brought to North America from another continent. Several of these plants were intentionally introduced to rangeland because they have good forage value. Other plants were accidentally introduced to North America, usually as contaminants in crop seeds. Weedy introduced plants were accidentally introduced or brought in for their ornamental value but then "escaped" into rangelands.

Life Span of Range Plants

Annual plants live only one growing season. There are two types of annuals:

• Winter annuals germinate in the fall and form a small rosette of leaves that persist through the winter. The following growing season, the plant continues to grow, flowers, produces seeds sometime in the summer, and then dies.

• Summer annuals germinate in the spring and complete all growth, including seed production, by the end of the growing season and then die.

Biennial plants live two growing seasons. Normally these plants form a basal cluster of leaves the first year, called a rosette, and send up a seed stalk (bolt) the second year.

Perennial plants live from one year to the next, producing leaves and stems for more than two years from the same crown. Most range plants are perennial.

Season of Growth of Range Plants

Cool-season plants make their principal growth during cool weather. At lower elevations, these plants grow in the spring and set seed in late spring or early summer. New growth can appear in the fall if moisture is adequate. Plants that grow at high elevations are usually cool-season plants because of the cool temperatures throughout the growing season.

Warm-season plants make most of their growth during late spring and summer. Seed develops in midsummer and early fall.

Cool-Season and Warm-Season Forages

Learn about grass growth:

• Basics of Grass Growth
• Components of Grass Growth
• Vegetative Growth of Grasses
• Reproductive Growth of Grasses
• Carbohydrate Reserves in Grasses

Basics of Grass Growth

The root crown usually has several to dozens of buds (growing points), and each bud can produce new tillers and roots. New tillers are anatomically and physiologically connected to older tillers. Therefore, several connected tillers may all live and share water, carbohydrates, and nutrients. If one tiller dies, an adjacent tiller with established roots often continues to live and/or the plant can produce a new tiller from a bud located on either the root crown or the base of a tiller.

Perennial bunchgrasses perpetuate from one year to the next by developing buds on the root crown each fall, storing enough energy in those buds for them to survive the winter dormant period, and having enough additional stored energy in the bud for it to produce the initial growth on the tiller's first two to three leaves the next spring. If the plant cannot form buds at the base of a tiller before it enters summer or fall dormancy, or if the buds that do develop lack enough energy reserves to keep the bud alive during the long winter dormant period, the tiller and eventually the plant will die. Only after a tiller produces the first few millimeters of growth on the first two to three leaves is there enough photosynthetically active leaf material for the plant to produce a surplus of energy (carbohydrates) that can be used to produce many leaves (forage) and store energy for growth the next year.

Components of Grass Growth

Plant growth has two components: the creation of new cells and the enlargement of those cells. All new cells in a plant are produced by meristematic tissue. Once a bud has initiated growth of a new tiller, there are only four microscopic growing points on that tiller than can produce new cells for plant growth. One growing point is at the base of the leaf blade. All of the cells that form the leaf blade, which usually is the bulk of the most palatable forage, come from the microscopic growing point at the base of the leaf blade. The second growing point is at the base of the leaf sheath, where the sheath attaches to a node. This growing point can only produce cells used to create the leaf sheath. The growing points at the base of the leaf blade and the base of the sheath, collectively, are called the intercalary meristem. At the very tip of a tiller is the terminal growing point or apical meristem. The apical meristem is the growing point that produces the seedhead of a grass plant. The fourth growing point is the axillary bud at each node. If proper growing conditions occur, the plant may activate this bud to produce an entirely new tiller. Some tillers stay vegetative, while others become reproductive and produce seedheads. Whether a tiller becomes reproductive depends on the environment and hormones produced in the plant.

When a tiller becomes reproductive, the tiller elongates, and the growing points located on the leaves and at the nodes and apical meristem (terminal growth point) become elevated above the ground surface. Elevated growing points are at risk of being removed by a grazing animal. Whether one or more of these growing points are grazed off has implications for how the plant responds to defoliation. When the terminal growth point is removed, the plant cannot produce any additional leaves or a seedhead. New leaves can only be produced if the plant activates either a crown or axillary bud to produce a new tiller. Complete tiller replacement is a slow process and may use substantial amounts of stored energy. Removal of the terminal growth point may have negative or positive outcomes depending upon management goals, how much leaf area remains after grazing, and the ability of the plant to regrow after defoliation and store energy for growth the following growing season.

A reproductive tiller may remain vegetative if the terminal growing point (apical meristem) is removed by grazing. Vegetative growth, therefore, is favored by some grazing, which reduces the number of seedheads produced and may stimulate the formation of new tillers. Vegetative tillers usually are less stemmy and more nutritious than reproductive tillers. Forage grasses in irrigated pastures often are maintained in a vegetative state by periodic removal of the terminal growth point. Following removal of the terminal growing point, existing leaves may continue to grow and produce forage if defoliation did not remove the growing point at the base of the leaf blade. In addition to continued leaf growth, the plant also may activate a bud to produce a new (replacement) tiller which can create additional forage from both existing leaves and new tillers. The addition of irrigation water permits the replacement tiller to grow toward completion of its full growth cycle. When soil moisture is available the entire growing season, this process can be repeated many times and a large amount of forage produced. Because some of the leaf blade always remains after grazing, growth continues unimpeded, which results in ample storage of energy (carbohydrates) in the buds used to initiate growth of tillers the following year. Removal of the terminal and other growing points late in the growth phase, however, can harm plants when they lack the resources (water and nutrients) to activate the bud, produce a new tiller, and complete the growth cycle. In this scenario, the buds do not develop or they do not store enough energy to initiate growth the following year.

Vegetative Growth of Grasses

An apical meristem (expanded portion of Figure 1) is responsible for leaf formation. The intercalary meristems at the base of leaf blades and sheaths are responsible for leaf expansion (insert in Figure 2). Each leaf is rolled into a tube-like form in its lower portion and unfurls as the blade extends. Subsequent leaves follow the same pattern.

As new leaves push up from the center of the rolled tube portion of the first leaf, the growth is similar to the extension of a telescope. In Figure 1, leaf 1 is the oldest; leaf 8, the youngest, is emerging. In this example, the growing point (apical meristem) is at or near the soil surface , which provides protection from defoliation by large grazing animals. Defoliation, therefore, removes leaf tissue but, in most cases, will not harm the growing point at the base of the leaf blade. It is this growing point that produces the bulk of the forage.

Grass growth, for either cool- or warm-season species, begins in spring when the soil warms. As the first grass leaf emerges its length or height increases due to new cells being produced at the base of each leaf blade. This growth area (intercalary meristem) is at the base of the leaf blade and adjacent to the growing point for the leaf sheath (insert in Figure 2), which has not yet developed.

Leaves have a definite life span, as do tillers. The first spring leaf normally dies in the summer. Leaves are most photo-synthetically active when they reach full expansion. As they age, their capacity for photosynthesis declines. The excess carbohydrates produced through photosynthesis helps produce additional leaves, seed, roots and buds for new tillers the following year. Thus, photosynthate produced by the plant is used efficiently in growth and maintenance. Once a leaf can no longer produce enough carbohydrates through photosynthesis for its own needs, it dies.

Reproductive Growth of Grasses

As the growing season progresses, grasses begin to allocate their resources to seed production rather than leaf production. Similar to animals and humans, hormones within the plant signal when it is time to start producing reproductive tissue. Hormones signal the apical meristem, which is the growing point of grasses, to produce a seedhead.  The tiller begins to elongate, and as it grows, it elevates the growing points (with the exception of basal buds) above the surface of the ground.  Plants differ in how early and how quickly they initiate tiller elongation and seedhead production.  Differences in this timing affect the plants ability to withstand grazing by herbivores. If a herbivore grazes an elongated stem and removes the elevated growing points, seed production is stopped for that tiller. Consequently, if seed production is a management goal, grazing should cease when tillers begin to elongate. The period of tiller elongation to mature seed is often called the "critical period." Allowing reproductive tillers to mature and produce seeds can increase the density of plants in the stand. Many bunchgrass species are dependent on seed production for reproduction; in these plant communities annual grazing during the critical period can decrease stand density since plant mortality is not matched by new plant recruitment. However, annual seed production is not essential for stand maintenance because few plants typically die each year, and some grasses reproduce by vegetative means from underground rhizomes or above-ground stolons.  In rhizomatous species, grazing during seed production may stimulate future tiller production from the basal buds if there is adequate soil moisture to allow for continued plant growth.

Carbohydrate Reserves in Grasses

The energy (carbohydrates) used to produce the first one to three leaves of a grass plant each spring does not occur from photosynthesis (the production of carbohydrates from CO2 and water that become the leaves, roots, and seeds of the plant), but rather from carbohydrates stored by the plant the previous growing season. Carbohydrates produced the previous growing season that the plant does not use to produce its leaves, stems, roots, or seeds that year are called soluble carbohydrates and can be stored in the plants buds, the root crown, roots, and/or tiller bases. The role of the stored energy is to keep the plant organs alive during the dormant period and to provide the energy needed to produce the first few leaves that emerge the following spring. Most, if not all, of the energy used by the first few emerging leaves comes from energy stored in the bud. Once the first leaves extend, the plant has enough leaf area to successfully conduct photosynthesis to meet the energy needs of the plant and produce the carbohydrates needed for additional leaf production and growth. These carbohydrates also provide enough energy for the roots to grow and the plant to produce seed. When defoliation removes the growing points on the plant’s tillers, the plant must use carbohydrates stored in its buds, root crown, and/or roots to initiate new growth. If the plant does not have the time or resources to fully regrow its leaves and also produce enough soluble carbohydrates to keep its buds alive during the coming dormant season and produce the first few leaves the following spring, the plant can die. The primary role of the stored carbohydrates is to keep plant buds alive during dormant periods and initiate new growth in the spring, not initiate regrowth after grazing. After grazing, regrowth from growing points at the base of the leaf blade allows plants to rapidly regrow without having to use stored energy the plant needs the following spring.

See the fact sheet Carbohydrate Reserve Theory: What You Learned May Be Wrong

There are no clear boundaries that define vegetation types across rangeland landscapes. However, grasses are generally a major component of rangeland vegetation so becoming familiar with grass plant growth is essential.  Rangeland plant species are often grouped into vegetation types to provide a framework for managers to assess the ecological status and trend of plant communities.