Principles and Practices for Managing Rangeland Invasive Plants

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln

U.S. Department of Agriculture: Agricultural Publications from USDA-ARS / UNL Faculty Research Service, Lincoln, Nebraska

9-2001

Invited Synthesis Paper: Principles and practices for managing rangeland invasive plants

Robert A. Masters University of Nebraska-Lincoln, [email protected]

Roger Sheley University of Nebraska-Lincoln

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Masters, Robert A. and Sheley, Roger, "Invited Synthesis Paper: Principles and practices for managing rangeland invasive plants" (2001). Publications from USDA-ARS / UNL Faculty. 1079. https://digitalcommons.unl.edu/usdaarsfacpub/1079

This Article is brought to you for free and open access by the U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Publications from USDA-ARS / UNL Faculty by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. J. Range Manage. 54: 502-517 September 2001 Invited Synthesis Paper: Principles and practices for managing rangeland invasive plants

ROBERT A. MASTERS AND ROGER L. SHELEY

Authors are field development biologist, Dow AgroSciences, 3618 South 75th Street, Lincoln, Nebr. 68506 and associate professor, Department of Land Resources and Environmental Sciences, Montana State University, Bozeman, Montana 59717. At the time this manuscript was submitted, Masters was rangeland scientist, USDA-ARS, 344 Keim Hall, University of Nebraska, Lincoln, Nebr. 68583.

Abstract Resumen

Invasive plants reduce the capacity of ecosystems to provide Las plantas invasoras reducen la capacidad del ecosistema goods and services required by society, alter ecological processes, para proveer los bienes y servicios requeridos por la sociedad, and can displace desirable species. They can reduce wildlife habi- alteran los procesos ecologicos y pueden desplazar especies tat quality, riparian area integrity, rangeland economic value, deseables. Ellas tambien pueden reducir la calidad del habitat de and enterprise net returns. The invasion process is regulated by la fauna silvestre, la integridad de las aireas riberenfas, el valor characteristics of the invading plant and the community being economico del pastizal y los retornos netos de la empresa. El pro- invaded. The presence and spread of invasive plants is often ceso de invasion es regulado por las caracteristicas de las plantas symptomatic of underlying management problems that must be invasoras y la comunidad que esta siendo invadida. La presencia corrected before acceptable, long-term rangeland improvement y dispersi6n de las plantas invasoras a menudo es un sintoma de can be achieved. Disturbance appears to be important early in problemas de manejo que deben ser corregidos antes de que se the invasion process because it creates vacant niches that alien logren mejoras aceptables de largo plazo en el pastizal. El distur- plants can occupy. Control of invasive plants may only open bio parece ser importante al inicio del proceso de invasion niches for establishment of other undesirable plants unless desir- porque crea nichos vacantes que las plantas invasoras pueden able plants are present to fill the vacated niches. In many ocupar. El control de plantas invasoras puede solo abrir nichos instances, rangelands have deteriorated to the point that desir- para el establecimiento de otras plantas indeseables, a menos de able species are either not present, or in such low abundance that que esten presentes plantas deseables para llenar los nichos plant community recovery is slow or will not occur without vacantes. En muchos casos los pastizales se han deteriorado al revegetation after invasive plants are controlled. Integrated weed punto de que las especies deseables o no estan presentes o estain management employs the planned, sequential use of multiple tac- en una abundancia tan baja que la recuperacion de la comu- tics (e.g. chemical, biological, cultural, and mechanical control nidad es lenta o no ocurrira sin revegetacion despues de que las measures) to improve ecosystem function (energy flow and nutri- plantas invasoras han sido controladas. El manejo integrado de ent cycling) and maintain invasive plant damage below economic maleza emplea el uso secuencial planeado de taicticas multiples levels, and emphasizes managing rangeland ecosystem functions (por ejemplo, medidas de control quimico, biologico, cultural y to meet objectives rather than emphasizing a particular weed or mecanico) para mejorar la funcion del ecosistema (flujo de control method. Sustainable, integrated invasive plant manage- energia y reciclaje de nutrientes) y mantener el dafio de las plan- ment strategies require assessing plant impacts, understanding tas invasoras abajo de niveles economicos, y enfatiza el manejo and managing the processes influencing invasion, knowledge of de la funcion del ecosistema de pastizal para cumplir con los invasive plant biology and ecology, and are based on ecological objetivos en lugar de enfatizar en una maleza en particular o un principles. Invasive plant management programs must be com- metodo de control especifico. patible with and integrated into overall rangeland resource man- Las estrategias sustentables del manejo integrado de plantas agement objectives and plans. Because of the complexity of man- invasoras requieren de evaluar los impactos de las plantas, aging invasive plants, it is imperative that relevant ecological and entender y manjar el proceso que influye en la invasion, el economic information be synthesized into user-friendly decision conocimiento de la ecologia y biologia de la planta invasora y son support systems. basados en principios ecologicos. Los programas de manejo de plantas invasoras deben ser compatibles e integrados dentro del plan y objetivos generales de manejo de los recursos del pastizal. Key Words: Biological control, herbicides, revegetation, native Debido a la complejidad del manejo de las plantas invasoras es plants, alien plants, restoration, renovation, adaptive manage- imperativo que la informacion ecologica y economica relevante ment, integrated weed management, noxious weed sea sintetizada en sistemas de soporte de toma de decisiones ami- gables para el usuario.

This paperis a joint contributionof the USDA-ARSand the Nebraska AgricultureResearch Division Journal Series No. 13022. Manuscriptaccepted 11 Mar.01.

September 2001 502 JOURNAL OF RANGE MANAGEMENT54(5), Invasive plants usually have many multiple tactics to assure stable ecosystem Invasive Plant Impacts adverse impacts as they spread through function and maintain pest damage below terrestrial and aquatic ecosystems. In the economic levels, while minimizing hazard seminal text, The Ecology of Invasions, to humans, animals, plants, and the envi- Ecological Elton (1958) described the impact of exot- ronment (U.S. Congress, Office of Ecological processes may change after ic or non-indigenous organisms invading Technology Assessment 1993). Integrated invading species have established and new environments as "ecological explo- weed management emphasizes manage- spread (Walker and Smith 1997). These sions". Many of the estimated 5000 alien ment of rangeland and pasture ecosystem changes may be minimal and the plant plants that now occur in natural ecosys- function (energy flow and nutrient invader may simply increase species richness. In contrast, where tems in the United States (Morse et al. cycling) rather than a specific weed or ecological 1995) were introduced for food, fiber, or control method (Scifres 1986). With this processes are sufficiently disrupted, native ornamental purposes (U.S. Congress, in mind, the goal of invasive plant man- species can be displaced, increasing plant to Office of Technology Assessment 1993, agement should be to reclaim or restore community vulnerability further inva- Pimental et al. 2000). While many of these degraded weed-infested rangeland com- sion and regeneration of the invasive plants are of great value to agriculture, a munities so that they are less susceptible plant. When perturbation of ecosystems small number have become invasive and to re-invasion by invasive plants and can exceeds ecological thresholds, ecosystem threaten ecosystems. meet land use objectives (Masters et al. change can be so profound that controlling Predicting which plants will be invasive 1996, Sheley et al. 1996). the invader may not restore the ecosystem to and which ecosystems will be invaded is a Our purpose is to describe principles a desired condition (Hobbs and highly desirable goal, but identification of and practices to consider when developing Humphries 1995). Ecosystem processes, salient characteristics of invasiveness and integrated strategies to manage invasive including hydrological cycles (Graf 1978, invasibility remains illusive (Crawley plants on rangeland. Sustainable integrated Loope and Sanchez 1988), erosion and 1987, Mack 1989, 1996, Rejmanek and invasive plant management strategies stream sedimentation (Lacey et al. 1989), Robinson 1996, Wade 1997). Those plants require assessing their impacts, under- energy flow and nutrient cycling (Versfeld that become invasive disrupt ecosystem standing and managing the processes and van Wilgen 1986, Vitousek and processes and reduce the capacity of influencing invasion, knowledge of inva- Walker 1989, Stock and Allsopp 1992), ecosystems to recover to a desirable state sive plant biology and ecology, and inte- native plant regeneration (Tyser and Key after disturbance and provide the goods grating management tactics based on eco- 1988, Woods 1993, Belcher and Wilson and services (Costanza et al. 1997) logical principles. Ultimately, for these 1989, Kedzie-Webb et al. 2001), and fire demanded by society. strategies to be successful, they must be regimes (Hobbs and Atkins 1988, Hughes D'Antonio The presence and spread of invasive compatible with and contribute to achiev- et al. 1991, Whisenant 1990, plants on rangeland is often symptomatic ing overall rangeland ecosystem manage- and Vitousek 1992) can be altered by alien of underlying management problems that ment goals and objectives. plant invasions. Cheatgrass (Bromus tecto- must be corrected before acceptable long- rum L.) invasion in the Intermountain term progress toward control of the pests West is thought to have been facilitated by and rangeland improvement. Past range- Definitions overgrazing (Young and Longland 1996) or land management practices and climatic by cheatgrass' ability to occupy vacant changes have contributed to plant commu- niches and suppress native species recruit- According to the Executive Order 13112 ment on areas that have not been over- nity shifts by altering disturbance regimes issued by the President of the United that have accelerated invasive plant estab- grazed (Svejcar and Tausch 1991). States on 3 February 1999, alien species Cheatgrass proliferation has increased the lishment and expansion (Hobbs 1989, are, with respect to a particular ecosystem, 1991, 2000, Mack 1989, Hobbs and frequency and intensity of fires occurring any species, including its propagules that in sagebrush grasslands (D'Antonio and Huenneke 1992, Sutherst 2000). is not native to that ecosystem. Invasive The use of any single technology to con- Vitousek 1992). This altered fire regime species are alien species whose introduc- has reduced the of native trol these species is usually not successful. abundance grass- tion does or is likely to cause economic or es and shrubs in these grasslands and Removing invasive plant species with environmental harm or harm to human chemical or biological control measures enabled cheatgrass to dominate. Invasive health. Native species are, with respect to plants also pose a threat to species desig- may only open niches for other undesir- a particular ecosystem, a species that, able species to occupy or to be reinvaded nated as threatened or endangered by other than as a result of an introduction, of by the same species unless desirable reducing the quality natural areas estab- historically occurred or currently occurs in to species are present to fill the vacated nich- lished protect habitats critical to the sur- that ecosystem. Cronk and Fuller (1995) vival of these desirable species (Randall es. Where desirable species are either not considered an invasive plant as an alien present or in low abundance, plant com- 1997). plant spreading naturally (without the Invasive plants can reduce wildlife habi- munity recovery will be slow or may not direct assistance of people) in natural or occur without revegetation (Masters et al. tat quality. Areas dominated by leafy seminatural habitats, which produces a esula were used 1996, Masters and Nissen 1998). spurge (Euphorbia L.) significant change in terms of composi- less deer than Instead of relying on a single technolo- by and bison non-infested tion, structure or ecosystem processes. A areas On gy, integrated pest management empha- (Trammel and Butler 1995). noxious weed is an undesirable plant native sizes the sequential application of compli- bunchgrass sites, dense spotted species that is regulated in some way by maculosa mentary or synergistic control measures in knapweed (Centaurea Lam.) law (Dewey and Torell 1991, Sheley and populations reduced winter forage avail- an economically and ecologically effective Petroff 1999). manner (Pimentel 1982). Integrated pest able for elk in Montana (Thompson 1996). management is the coordinated use of Elk use of spotted knapweed-infested areas increased 266% after spotted knap-

JOURNAL OF RANGE MANAGEMENT54(5), September 2001 503 weed was controlled. In the Intermountain Table 1. General causes of ecological succession, contributing processes, and modifying factors West, changes in fire frequency caused by (Pickett et al. 1987). cheatgrass invasions reduced native shrubs that are important for wildlife habitat Generalcauses ContributingProcess Modifying factors (Miller et al. 1994). Site availability Disturbance Size, severity, time, dispersion Riparian areas are some of the most pro- Species availability Dispersal Landscapeconfiguration, dispersal agents ductive range sites in the West, with greater Propagules Land use, time since last disturbance diversity of plant and wildlife species than Resources Soil, topography,site history Species performance Ecophysiology Germinationresponse, assimilationrates, growth adjoining lands (Sheley et al. 1995). In rates, genetic differentiation healthy riparian systems, vegetation Life history Allocation, reproductivetiming, mode of removes sediment from water before it reproduction moves into streams. Riparian vegetation Stress Climate, site history, prior occupants absorbs and dissipates the energy of flood- Competition Competition,herbivory, resource availability waters, thereby reducing streambank ero- Allelopathy Soil chemistry,microbes, neighboringspecies Herbivory Climate, predators,plant defenses, patchiness sion. It also provides critical habitat for terrestrial and aquatic wildlife. Saltcedar (Tamarisk spp.), which has invaded wet- depends on the interaction of species inva- the distribution of the earth's lands and riparian streams throughout the biota since sion and the reaction of the species in the the end of the Pleistocene have been as western United States, reduces diversity plant community. Succession is influenced radical." Many of the plants that and productivity of the herbaceous under- have by 3 general factors: site availability; invaded the New World originated in the story, and uses large quantities of water species availability; and species perfor- Mediterranean Basin and of (DiTomaso 1998). Dense populations of steppes the mance (Table 1) (Pickett et al. 1987). Middle East (Heywood 1989). saltcedar lower water tables, reduce surface These These factors are affected by various regions have been subjected to a long water, decrease native vegetation needed by his- processes including disturbance and tory of human habitation and wildlife, and alter frequency of floods. many plants plant:plant and plant:animal interactions arising from these regions co-evolved with that can be modified to alter succession. agricultural practices. This association Economic Succession can be predicted and manipu- with agricultural production systems has Economic impacts of invasive plants on lated with sufficient information about dis- enhanced development of invasive traits in rangeland have received limited attention turbance regime, site, species, and man- plants. Introductions of alien organisms (Naylor 2000). The difficulty quantifying agement tools. continue today despite global implementa- the economic value of goods and services A conceptual framework to describe tion of quarantine programs for agricultur- provided by ecosystems, i.e., ecological plant invasion can be useful in understand- al pests (Mooney and Drake 1989). economics (see Saghoff 1995, Daly 1995), ing the invasion process and in making Once the alien plant arrives at a new further constrains assessment of economic management decisions. Williamson (1996) site, community invasion is regulated by impacts of invasive plants. Attempts have provided a structure to organize invasion characteristics of the invading plant and been made to assess the impact of invasive process information. He partitioned the the existing community (Lawton 1986). plants on rangeland economic value and process into 4 phases: (1) arrival and Various, often interrelated, hypotheses enterprise net returns. Bioeconomic mod- establishment; (2) spread; (3) equilibrium about species and site invasive characteris- els were developed to estimate direct and and effects; and (4) implications. Within tics have been generated to provide a indirect economic impacts of leafy spurge each of these phases there are specific framework for ecological theory of inva- (Leitch et al. 1996) and spotted knapweed conceptual points, which further describe sion (Cronk and Fuller 1995).. The (Hirsh and Leitch 1996). The economic the invasion process. The first 3 phases absence of predator hypothesis proposes impact of leafy spurge in Montana, North represent the beginning, middle, and end that invasive plants have an advantage Dakota, South Dakota, and Wyoming is of the process. The fourth phase describes because they are introduced into new envi- estimated at $130 million each year the consequences of invasion on the com- ronments without natural enemies from (Leitch et al. 1996). Spotted knapweed munity or ecosystem. their native range. The greater reproduc- costs Montana ranchers an estimated $11 The invasion process begins with the tive potential hypothesis indicates that million annually (Hirsh and Leitch 1996) arrival of alien plant propagules at the new invasive plants are more fecund than and if allowed to spread, cost to site. Within the last 500 years, movement native species. The poorly adapted native Montana's livestock industry could exceed of alien plants has been accelerated by species hypothesis proposes that invasive $155 million each year. human-related activities, through intended plants exhibit a greater tolerance to or non-intended introductions (Crosby resource constraints than do native 1986, Di Castri 1989). Geographic dis- species. The chemical change hypothesis Invasion Process tances and physical barriers, mountain suggests that invasive plants are better ranges and oceans, are reduced as impedi- adapted to altered chemical status of an Invasive plants can alter ecosystem ments to movement of alien species given invaded site. The balance of nature processes and plant community succes- the increased efficiency and speed with hypothesis is centered on the concept that sional trajectories. When describing the which man transports materials around the species-rich communities are more resis- invasion process, it is important to consid- world. Mack (1989) indicated that temper- tant to invasion than species-poor commu- er invasion as a component of succession. ate grasslands outside Eurasia have been nities. The empty-niche hypothesis con- Johnstone (1986) defines succession as the forever changed by human activities that tends that invaded communities contain change in species composition over time. have facilitated the introduction of alien unoccupied niches ready for habitation by The rate and direction of succession plants. He wrote, "Few other changes in invasive plants. The disturbance-produced

504 JOURNAL OF RANGE MANAGEMENT54(5), September 2001 gaps hypothesis suggests that some level disturbance as any relatively discrete event There is evidence that species-rich com- of disturbance is necessary to allow an in time that disrupts ecosystem, communi- munities contain a greater number of alien invading species to gain a foothold in a ty, or population structure, and changes species than species-poor communities community. These hypotheses provide a resources, substrate availability, or the (Pickard 1984, Knops et al. 1995, foundation upon which to build theory and, physical environment. Events that affect Robinson et al. 1995, Planty-Tabacchi et ultimately, to predict species invasions. resource availability and community al. 1996, Palmer and Maurer 1997). Attempts to classify species according demographic processes such as fire, Following an analysis of data collected to their invasiveness have resulted in list- storms, floods, grazing management, and from 184 sites, Lonsdale (1999) deter- ings of genetic, physiological, and ecolog- fertilization are considered to be distur- mined that communities richer in native ical attributes most often associated with bances. Roads are disturbances that pro- species contained more alien plants than successful invaders (Baker 1965, 1986, vide corridors for invasive plant dispersal species-poor communities. There was no Baker and Stebbins 1965, Gray 1986, (Lonsdale and Lane 1994, Parendes and causal relationship between native and Lonsdale 1994). Mack (1996) reviewed Jones 2000) and alter the physical and invasive plant diversities when measured the advantages and disadvantages of chemical components of the environment at the community scale. Low-diversity approaches to assess plants invasiveness. (Trombulak and Frissell 2000), which fur- shortgrass steppe and dry meadow com- These approaches included: listing traits of ther facilitate invasion. Disturbances asso- munities were more resistant to invasion the invasive plant; characterizing the ciated with global change (global warm- than high-diversity wet meadow and ripar- native range of the invasive plant; devel- ing, increasing atmospheric C02, increas- ian communities (Stohlgren et al. 1998, oping models to predict invasiveness; ing nitrogen deposition, etc.) will likely 1999). They suggested that shortgrass quantifying growth characteristics of the influence distributions of invasive plants steppe and dry meadow communities invasive plant under different conditions (Bazzaz 1990, Johnson et al. 1993, resist invasion because of the low levels in controlled environments; comparing Patterson 1995, Vitousek et al. 1997, and availability of resources (soil nutrients characteristics of invasive and non-inva- D'Antonio 2000, Dukes 2000). and water), which are essentially monopo- sive cogeners; and planting the species in Disturbance is an important factor lized by the native vegetation. In contrast, the field with and without manipulation of affecting community structure and dynam- high diversity communities are relatively resources. Panetta (1993) and Reichard ics (Cooper 1926, Watt 1947, Elton 1958) resource rich, and resources become avail- and Hamilton (1997) suggest that the best that promotes invasion by alien plant able following disturbance that can be predictor of whether or not a species species (Ewel 1986, Fox and Fox 1986, exploited by invading species. would become invasive in a new environ- Hobbs 1989, 1991, Forcella and Harvey Disturbance appears to be critically ment was its invasiveness elsewhere. 1983, Pickard 1984), especially where dis- important in the beginning of the invasion Nobel (1989) determined that high popula- turbance disrupts species interactions and process because it creates openings for tion numbers at any life stage in the native reduces competition (Crawley 1986, 1987, alien plants to occupy. Fluctuations in environment was a good indicator of inva- Kruger et al. 1986, Macdonald et al. 1986, local species abundance in species-rich siveness, while adult and seed longevity Crawley 1987, Orians 1986, Fox and Fox communities may provide an opening for and plant perenniality were not reliable 1986). Invasion success appears to be alien plants to become established (Peart indicators of invasive potential. He con- dependent on the extent and type of distur- and Foin 1985). Elton (1958) indicated cluded that knowledge of the invaded bance, propagule pressure (number of alien that the lack of invaders into a given com- environment was as important as the char- plant propagules in the community and munity was the result of competitors, acteristics of the invading species in pre- durationof community exposure to propag- predators, parasites, and diseases that dicting the invasion process. ules) (Rejmanek 1989), and time interval enabled the community to resist invasion. To continue the invasion process, alien between disturbance events (Hobbs and Invasions were successful only when these plant propagules must be dispersed into Huenneke 1992). Community susceptibility barriers were reduced or removed by dis- the new site and arrive at microsites that to invasion is increased when disturbances turbance, or in the case of an alien species, provide an environment conducive to plant deviate from historical pattermsbecause the natural enemies were left behind in the establishment. The location where the resident species are not adapted to the new native habitats. In contrast, Simberloff immigrant plant can germinate and grow disturbance regime (Burke and Grime (1989) suggested that the vulnerability of has been referred to as a "safe site" 1996). Managing invasive plants requires a community to invasion was not because (Harper 1977), "regeneration niche" manipulating the process of disturbance to of these barriers, but rather the greater fre- (Grubb 1977), or "invasion window" favor desirable species. quency of human-mediated introductions (Johnstone 1986). Safe sites meet the Species diversity may be another factor of alien species into disturbed communi- requirements of the alien species for ger- that influences community invasibility. A ties. Obviously, the invasion process can mination, growth, and development and commonly cited concept is that communi- be affected by a multitude of interacting enable the plant to reach reproductive ty invasibility increases as the number of factors including those described by Elton maturity. species decreases (Elton 1958, Rejmanek (1958) and Simberloff (1989). Disturbance often increases safe site 1989, Lodge 1993, Tilman 1996, 1997, Once alien species establish, the next availability for invasive plant establish- 1999). Proposed mechanisms that support phase is their spread through the commu- ment (Grubb 1977, Harper 1977, this premise are that diverse communities nity (Williamson 1989, Elton 1958, Silvertown 1981, Fox 1985, Hobbs 1991). have a greater variety of ways to capture Okubo 1980). An important component of Various definitions of disturbance have resources or possess species that more spread is the rate at which the invading been proposed (Rykiel 1985, Pickett et al. fully utilize resources than less diverse species colonizes new sites in the commu- 1987, van Andel and van den Berg 1987, communities (Naeem et al. 1994, Tilman nity (Mooney and Drake 1989). Rate of Petraitis et al. 1989, Hobbs and Huenneke 1997); therefore, niches are already occu- spread is a function of both the alien 1992). White and Pickett (1985) defined pied when a potential invader arrives. species characteristics and the characteristics of the ecosystem through which the

JOURNAL OF RANGE MANAGEMENT54(5), September 2001 505 species spreads. Moody and Mack (1988) indicated that the rate of spread of an invader will be geometric if spread is from widely spaced patches versus a linear rate CarryingCapacity if spread is from a "nascent foci" or single patch. Early in the invasion process there is a lag phase where the invasive plant populations remains small and localized 1 QO20 . Co 4 for long periods before expanding expo- j C, C2 nentially (Fig. 1) (Mack 1985, Auld and Tisdell 1986, Braithwaite et al. 1989, Griffin et al. 1989, Lonsdale 1993, 1999). Hobbs and Humphries (1995) attributed this lag phase to several factors including the time needed for the invading plant to adapt to the site before spreading rapidly, the invading plant's requirement for a spe- X Invasion cific event or series of disturbance events that facilitate rapid spread, or the invading plant is simply not noticed until it becomes widespread. Time Integrated Invasive Plant Fig. 1. Phases of weed invasion and priorities for action at each phase: Qo-quarantine prior- Management ity phase; CO-eradication priority stage; C1-control priority phase (exponential growth phase); C2-maximum populationlevel, effective control unlikely without massive resource Ease of treatment declines and and cost increases from left to Integrated weed management evolved inputs. difficulty moving right (Hobbs and Humphries 1995 after Chippendale from the concept of integrated pest man- 1991). agement in agricultural crops. Integrated manner, and selected, integrated, and environmental risks (U.S. Congress, pest management was developed by ento- implemented with consideration of eco- Office of Technology Assessment 1993). in mologists during the late 1950s nomic, ecological, and sociological conse- Placing value-laden judgements on the response to problems created by excessive quences (Walker and Buchanan 1982). various pest management tools and rank- use of insecticides et al. and (Thill 1991), Shaw (1982) indicated that integrated ing them according to subjective criteria was supported by public concerns about weed management is an approach in should be avoided. All available tools environmental of consequences pesticide which principles, practices, methods, and should be considered during development use that were catalyzed by Rachel strategies are chosen to control pests, of integrated weed management programs Carson's Silent Spring (1962). Integrated while minimizing undesirable results. and those selected should optimize attain- pest management has been defined in a Thill et al. (1991) defined integrated weed ment of specific management objectives. Two common definitions number of ways. management as the integration of effec- Developing effective integrated weed are that this management strategy tive, environmentally safe, and sociologi- management programs requires a thorough involves: a combination of (1) biological, cally acceptable control tactics that reduce understanding of the biology and ecology and cultural methods for main- chemical, weed interference below the economic of the invasive plant and invaded commu- below economic taining pests crop injury injury level. Sheley et al. (1996), empha- nity. Information about plant demography, thresholds et al. Flint and van (Bum 1987, sizing management and not control of propagule dynamics, seedling recruitment, den Bosch or non-chemical 1983) (2) pest noxious rangeland weeds, indicated that plant growth and development, and meth- control measures to reduce reliance on integrated weed management strives to use ods of reproduction could help identify chemical pesticides (Goldstein 1978). the most economically, ecologically, and vulnerabilities to be exploited in integrated Integrated pest management programs environmentally effective combination of weed management systems (Radosevich et should be from developed interdiscipli- principles, technologies, and systems to al. 1997). In addition, it is critical that the efforts that information about: nary gather meet management goals. causes of plant invasion be understood so the basis of the (1) ecological pest prob- Integrated weed management provides a that they can be alleviated (Hobbs and how to make the environ- lem; (2) crop context for managing pests that is ecosys- Norton 1996). ment unfavorable for when pests; (3) pes- tem-centered, and not specific to a species Adapting the basic concepts of integrat- ticide treatments are needed based on pest or pest control technology. Frequently, the ed weed management on cropland to inte- and natural enemy populations dynamics; stated or implied goal of integrated weed grated weed management on rangeland and (4) benefits and risks of the integrated management is pesticide-use reduction. appears relatively straightforward. pest management strategy for agriculture We believe that this is not in keeping with However, there are differences in manage- and society (Pimental 1982). the basic concept of integrated weed man- ment intensity and management objectives Integrated weed management emerged agement, which is a sustainable approach between cropland and rangeland that need as a viable concept among crop weed sci- to managing pests by combining biologi- to be considered. First, monocultures of entists in the 1970s. Integrated weed man- cal, cultural, mechanical and chemical agronomic species are grown on cropland agement was defined as the application of tools that minimize economic, health and and are often intentionally disturbed sever- technologies in a mutually supportive

506 JOURNAL OF RANGE MANAGEMENT54(5), September 2001 al times during the production cycle. eradication of the invader is usually not a to enhance the effect of existing natural Cropland is managed intensively and realistic goal. Instead, the emphasis should enemies and is usually used to manage resource inputs, e.g., pesticides, fertilizer, be to reduce the impact of the invader to native weeds. Augmentation employs peri- and cultivation, often improve economic an acceptable level and keep the plant odic release of natural enemies and is returns. In contrast, rangeland supports from dominating the plant community and restricted to managing weeds in high- heterogeneous mixtures of plant species substantively altering ecosystem process- value food crops because it requires large and is managed extensively. The relatively es. After the invader has reached its maxi- investments of time and money and low value of rangeland per unit area mum abundance, containment of the repeated intervention. Importation, also reduces the economic viability of resource invader or implementation of intensive known as classical biological control, is inputs compared with cropland. Second, restoration efforts may be the only feasible the planned relocation of natural enemies identification of economic thresholds of management options. of exotic weeds from their native habitats injury caused by pests are central to devel- Monitoring and assessment of invasive onto weeds in their naturalized habitats. opment of integrated weed management plant distributions during invasion and in This strategy seeks to reestablish weed programs in cropland. Determining eco- conjunction with management provides and natural enemy interactions that reduce nomic thresholds for rangeland invasive the basic information necessary for plan- the weed population to an acceptable level plants is difficult and has not been ade- ning (Cooksey and Sheley 1997, Johnson (DeBach and Rosen 1990). Synchrony in quately addressed. Furthermore,control of 1999). Remote sensing tools such as aerial the life cycles of host plant and agent, rangeland invasive plants designated as videography, geographic information sys- adaptation of the agent to a new climate noxious is often mandated by law without tems, global positioning systems, and and habitats, ability of the agent to find the regard to economic thresholds. Finally, satellite-borne, narrow-band, multispectral host at varying densities, capacity of the impacts of invasive plants on rangeland imaging technology have the potential to agent to reproduce rapidly, and the nature, ecosystem function and structure may be improve accuracy and reduce the time extent, and timing of the damage caused the of more concem than economic impacts, needed to assess invasive plant distribu- by the biocontrol agent are among factors that determine biocontrol effec- especially on rangeland where other prod- tions (Everitt et al. 1995, 1996a, 1996b, agent tiveness (Louda and Masters 1993). ucts besides livestock, e.g. wildlife, recre- Bork et al. 1998). Time-repeated surveys Success of biological weed control dur- ation, aesthetics, and water, are important. allow continual assessment of management effectiveness and provide the infor- ing the past 200 years has been variable. mation necessary to modify strategies to Julien (1992) documented 610 biological Invasive Plant Management optimize management. Knowledge of control projects that involved 94 weed Strategy Components invasive and native plant distributions is species in 53 countries. There have been The magnitude and complexity of important for developing invasion risk some phenomenally successful biocontrol rangeland weeds, combined with the costs assessment models based on invasion projects including control of Opuntia spp. for their control, necessitate the use of dynamics, environmental characteristics, in Australia by the moth Cactoblastus cac- integrated weed management (Sheley et and weed dispersal processes. torum and control of St. Johnswort al. 1996). Education, prevention, detec- An adaptive management approach can (Hypericum perforatum L.) in the Pacific tion, monitoring and assessment, and weed complement integrated programs to man- Northwest by the beetles, Chrysolina control methods are key components of age invasive plants on rangeland. This quadrigemina and C. hyperici. There are integrated management strategies. approach requires establishing manage- 72 examples worldwide where weed bio- Education is an under-emphasized, but ment goals, developing and implementing control programs have been underway for a sufficient to assess control. Of important part of invasive plant manage- management programs based on the goals, period these programs, 28% have resulted in con- ment. Public awareness about the ecologi- monitoring and assessing impacts of man- trol that could be rated as sometimes com- cal, environmental, and economic impacts agement efforts, and modifying goals and associated with plete (Sheppard 1992). In contrast, no con- invasive plants may help invasive plant management in light of new provide the and resources trol was achieved in 35% of these pro- political support information (Schwarz and Randall 1995, necessary for invasive plant grams even though biological control management. Randall 1997). Adaptive management has Awareness also can promote activities, agents were established. Important factors been developed as an integrated, multidis- such as early detection of newly arriving that have contributed to the limited suc- ciplinary approach to deal with the uncer- species, in which the general public can cess of biological weed control programs tainty associated with natural resource participate. On-going educational pro- include a high level of genetic diversity in management (Holling 1978, Walters 1986, grams provide practitioners and the gener- the target species, limited compatibility of Gunderson 1999). This approach provides al public with knowledge of current man- agents with the invasive plant genotype, a way to move from a reactive to a pro- agement strategies essential to sustainable and opportunistic predation and parasitism active mode of invasive plant management. invasive plant management. of biocontrol agents in the introduced Preventing invader introduction by environment (Sheppard 1992). restricting movement of propagules from Weed Control Methods The release of imported biological con- infested areas can minimize invader dis- Biological. Quimby et al. (1991) trol agents on invasive plants is not with- persal into new habitats. Early detection defined biological control of weeds as the out risk (Harris 1988, Howarth 1991, followed by swift, intensive, and aggres- planned use of living organisms to reduce Follett and Duan 1999). By its very nature, sive implementation of effective control the plant's reproductive capacity, density, classical biocontrol involves release of measures during the invasion lag phase and effect. Biological control can involve alien organisms to control other alien (Fig. 1) are essential to eliminate the any of 3 strategies: conservation; augmen- organisms and alter botanical composition. invader, or at least to prevent seed produc- tation; and importation of natural enemies The consequences of natural enemy uti- tion (Zamora et al. 1989). Once the inva- (Harley and Forno 1992). Conservation lization of native relatives of the alien sion process is in the exponential phase, involves manipulation of the environment weeds are considered a potentially detri-

JOURNAL OF RANGE MANAGEMENT54(5), September 2001 507 mental side effect of biocontrol (Harris graphic origins of invasive plants and pro- are essential for plant growth and develop- 1988, 1990, Ehler 1990, Howarth 1991). vide a means to direct the search for com- ment; are phytotoxic at very low rates; and Within a decade after release of 2 beetles, patible biocontrol agents. have low toxicity to vertebrates and inver- Chrysolina quadrigemina and C. hyperici, Chemical. Herbicides are assigned to tebrates. Imazapic applied at 140 to 210 g to control St. Johnswort (Huffaker and groups according to their chemistry and ai ha-', controls leafy spurge (Masters et Kennett 1959), larvae of C. quadrigemina mode of action (Devine et al. 1993, Ross al. 1998, Thompson et al. 1998) and is tol- were found feeding on an introduced orna- and Lembi 1999) (Table 2). Mode of erated by many species in the Gramineae, mental, H. calycinum L., and to a limited action refers to the system, process, or tis- Fabaceae and Compositae families. extent on a related native species, H. sue affected by the herbicides. A herbicide Another unique attribute of imazapic and concinnum Beth (Andres 1985). The seed- is usually selective within certain rates, other imidazolinone herbicides is the abili- head weevil, Rhinocyllus conicus Froel., environmental conditions, and methods of ty to control many annual grass and introduced from Europe into North application. Foliar-active herbicides are broadleaf weed species during establish- America to control musk thistle (Carduus applied directly to the leaves or stems of ment of desirable native warm-season nutans L.) (Kok and Surles 1975) has been plants where they are absorbed and grasses, forbs, and legumes (Masters et al. reared from flowerheads of several native translocated in the plant. These herbicides 1996, Frye et al. 1997, Rivas-Pantoja et al. Cirsium species in California (Goeden and may or may not remain active once moved 1997, Beran et al. 1999a, 1999b, 2000). Ricker 1986, 1987, Turner et al. 1987). It into the soil. Soil-active herbicides are Imazapyr controls saltcedar in New Mexico has also reduced seed production of native absorbed by the roots from the soil water when applied at 0.56 to 0.84 kg ai ha-I in Cirsium species at several locations in the solution. Herbicides can be categorized as late summer to early fall (Duncan and central Great Plains (Louda et al. 1997). to whether they are applied before planti- McDaniel 1998). Sulfometuron is currently Once an insect is released into a new envi- ng and before (preemergence) or after registered to control cheatgrass, medusa- ronment, little can be done to restrict its (postemergence) weed emergence. head [Taeniatherum caput-medusae (L.) distribution or host affinity. Monitoring Herbicides have been the dominant tools Nevski], and cheat (Bromus secalinus L.) candidate biological control agents for used to control invasive plants on range- on non-cropland administered by state and range expansions, host shifts, and effects land (Bovey 1995). Potential for ground or federal land management agencies in the on related nontarget plants is critical surface water contamination, adverse IntermountainWest (EPA Registration No. (Howarth 1991). effect on desirable plants, and cost of 352-401). Genetic variation in populations of the repeated application to control weeds are Cultural. Cultural practices include fire, natural enemy and invasive plant can some of the concerns associated with her- grazing, revegetation or reseeding, plant influence biocontrol program success bicide use. The myriad of herbicides cur- competition, and fertilization. These meth- (Roush 1990). High levels of genetic vari- rently available, with different modes of ods are generally aimed at enhancing desir- ability in traits that influence insect impact action and selectivity, provide land man- able vegetation to minimize weed invasion. should increase the probability that the agers with many options to control unde- Fire, along with climate and herbivory, insect will adapt to the new environment. sirable plants and manipulate plant com- were the primary forces responsible for Furthermore, genetic variation extends the position (Table 2). The most commonly the formation and maintenance of grass- range over which the natural enemy can used herbicides on rangeland are auxin- land ecosystems in North America occur and utilize the weed (Harris and like growth regulators (phenoxy, benzoic, (Wright and Bailey 1982). As with any Peschken 1971). Identification of impor- or picolinic acid herbicides) that selective- disturbance, fire effects on ecosystems are tant genetic variation and its maintenance ly control broadleaf plants and do not influenced by its frequency, intensity, sea- in importation, mass-rearing, and release injure grasses when used at recommended son of occurrence, and interactions with should enhance chances of success. rates. other disturbances. North American grass- Biological diversity is usually highest in Glyphosatel used on rangeland to con- land fire regimes were shaped by sources the center of origin of a taxon (Vavilov trol grass and broadleaf weeds, which has of ignition, lightning and humans, and cli- 1992) and the greatest genetic variation in no activity in the soil. This is a postemer- mate (Pyne 1984). Fire is a useful, if not the natural enemies may be found in the gence herbicide that is translocated within essential, practice to meet management areas of weed origin (Bartlett and Van den the plant and selectivity is usually deter- objectives for many plant communities in Bosch 1964, Zwolfer et al. 1976). mined by the plant growth status. Control North America (Wright and Bailey 1982). Molecular biology offers tools to quanti- is optimized if the target plant is growing Selectivity by herbivores alters competi- fy invasive plant genetic diversity and to at the time of application and negated tive interactions within plant communities better match natural enemies with the tar- when the plant is dormant. In the Great (Crawley 1983, Luken 1990). In some sit- get invasive plant (Nissen et al. 1995, Plains, glyphosate was applied in the fall uations sheep or goat grazing (Bowes and Rowe et al. 1997). Taxonomists, evolu- to control cool-season grasses, such as Thomas 1978, Landgraf et al. 1984, tionary biologists and breeders use mole- Kentucky bluegrass (Poa pratensis L.) and Walker et al. 1994, Lym et al. 1997) can cular techniques to measure plant genetic smooth brome (Bromus inermis L.), but control leafy spurge. Appropriate grazing diversity and determine how plants are will not injure warm-season grasses that by animals preferring weeds can shift the related. Selected DNA-based molecular are dormant at application time (Bush et plant community toward more desired marker techniques offer an approach to al. 1989). species (Walker 1994, 1995). In contrast, quantify invasive plant genetic diversity in The imidazolinone and sulfonylurea her- excessive cattle grazing without periodic native and introduced habitats and provide bicides: disrupt the synthesis of amino rest can selectively reduce grass competi- a better understanding of the complex acids, leucine, isoleucine, and valine, that tiveness, shifting the competitive advan- relationships between invasive plants and tage to weeds (Svejcar and Tausch 1991). potential biocontrol agents. This informa- Revegetation with desirable plants may Refer to Table 2 for chemical names of herbicides tion could provide insights into the geo- mentionedin text. be the best long-term alternative for managing weeds on sites that lack suffi-

508 JOURNAL OF RANGE MANAGEMENT54(5), September 2001 Table 2. Selected herbicides that are currently registered for use on rangeland, pastures, or non-cropland.1

Plants Application Chemical group Common name Chemical name Mode of action controlled Activity3 timing4 Benzoic acid Dicamba 3,6-dichloro-2-methoxybenzoicacid Auxin-typegrowth B F, S PRE, POST regulator Benzonitrile Bromoxynil 3,5-dibromo-4-hydroxybenzonitrile Photosyntheticinhibitor B F POST Bipyridilium Paraquat 1,1'-dimethyl-4,4'-bipyridiniumion Photosystem 1 energized B, G F POST cell membranedisrupter Semicarbazones Diflufenzopyr 2-[1-[[[(3,5-difluorophenyl)amino] Auxin transportinhibitor B F POST carbonyl]hy-drazono]ethyl]-3-pyridine- carboxylic acid Imidazolinone Imazethapyr 2-[4,5-dihydro-4-methyl-4- Branched-chainamino B, G F, S PRE, POST (1-methylethyl)-5-oxo-1H-imidazol-2-yl]- acid inhibitor 5-ethyl-3-pyridinecarboxylicacid Imazapyr 2-[4,5-dihydro-4-methyl-4- Branched-chainaminor B, G F, S PRE, POST (1-methylethyl)-5-oxo-lH-imidazol-2-yl]- acid inhibitor 3-pyridinecarboxylicacid Imazapic 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)- Branched-chainamino B, G F, S PRE, POST 5-oxo-1H-imidazol-2-yl]-5-methyl-3- acid inhibitor pyridinecarboxylicacid Phenoxy acid 2,4-D (2,4-dichlorophenoxy)aceticacid Auxin-type growth regulator B F POST 2,4-DB 4-(2,4-dichlorophenoxy)butanoicacid Auxin-type growth regulator B F POST MCPA (4-chloro-2-methylphenoxy)aceticacid Auxin-type growth regulator B F POST Phenylurea Diuron N'-(3,4-dichlorophenyl)-N,N-dimethylurea Photosyntheticinhibitor B, G F, S PRE, POST Tebuthiuron N-[5-(l,1-dimethylethyl)-1,3,4-thiadiazol- Photosyntheticinhibitor B, G F, S PRE, POST 2-yl]-N,N'-dimethylurea Picolinic acid Clopyralid 3,6-dichloro-2-pyridinecarboxylicacid Auxin-type growth regulator B F, S PRE, POST Picloram 4-amino-3,5,6-trichloro-2-pyridine- Auxin-type growthregulator B F, S PRE, POST carboxylic acid Triclopyr [(3,5,6-trichloro-2-pyridinyl)oxy]aceticacid Auxin-type growth regulator B F, S PRE, POST s-Triazine Atrazine 6-chloro-N-ethyl-N'-(l-methylethyl)-1,3,5- Photosyntheticinhibitor B, G F, S PRE, POST triazine-2,4-diamine Hexazinone 3-cyclohexyl-6-(dimethylamino)-1-methyl- Photosyntheticinhibitor B, G F, S PRE, POST 1,3,5-triazine-2,4(1H,3H)-dione Simazine 6-chloro-N,N'-diethyl-1,3,5-triazine- Photosyntheticinhibitor B, G F, S PRE, POST 2,4-diamine Sulfonyl urea Chlorsulfuron 2-chloro-N-[[(4-methoxy-6-methyl-1,3,5- Branched-chainamino B, G F, S PRE, POST triazin-2-yl)amino]carbonyl] acid inhibitor benzenesulfonamide Metsulfuron 2-[[[[(4-methoxy-6-methyl-1,3,5-triazin- Branched-chainamino B, G F, S PRE, POST 2-yl) amino] carbonyl]amino]sulfonyl] acid inhibitor benzoic acid Sulfometuron 2-[[[[(4,6-dimethyl-2-pyrimidinyl)amino] Branched-chainamino B, G F, S PRE, POST car-bonyl] amino]sulfonyl]benzoicacid acid inhibitor Uracil Bromacil 5-bromo-6-methyl-3-(1-methylpropyl)- Photosyntheticinhibitor B, G F, S PRE, POST 2,4(1H, 3H)pyrimidinedione Unassigned Fosamine ethyl hydrogen (aminocarbonyl)phosphonate Unknown B F POST

Glyphosate N-(phosphonomethyl)glycine Aromaticamino B, G F, S POST acid inhibitor Quinclorac 3,7-dichloro-8-quinolinecarboxylicacid Cell wall formationinhibitor B, G F, S PRE, POST 1Chemicalgroup and mode of actionfrom Ross and Lembi (1999) and common name and chemical names from (Weed Science Society of America1994). B = broadleafspecies and G = grassspecies 3F = takenup by plantfoliage and S = hasactivity in thesoil 4PRE= appliedbefore plant emerges and POST = appliedafter plant emerges cient abundance of desirable species. Nissen 1998, Whitson and Koch 1998). ing decisions about how to select plant Establishing competitive grasses, forbs, Selecting plant species is a critical con- materials for rangeland revegetation. Site and legumes may suppress invasive plants, sideration when developing a desired plant potential, desired landscape, seeding enhance plant community resistance to fur- community if the desirable species are not objectives, conflicting land-use philoso- ther invasion, and improve forage produc- present in sufficient abundance to enable phies, appropriateplant materials, invasive tion and quality (Masters et al. 1996, Lym regeneration within an acceptable time- plants, community seral status, and eco- and Tober 1997, Bottoms and Whitson frame. Jones and Johnson (1998) nomic limitations are key components of 1998, Ferrell et al. 1998, Masters and described an integrated approach for mak- the decision-making process.

JOURNAL OF RANGE MANAGEMENT54(5), September 2001 509 Table 3. Examples of integrated strategies for control of invasive plants on rangeland (modified after DiTomaso 2000).

Invasive Plant Strategycomponents Citation Acroptilon repens (L.) DC Tillage, herbicide, and revegetation Dershied et al. 1963, Bottoms and Whitson 1998, Benz et al. 1999 Bromus tectorumL. Tillage, herbicide, and revegetation Eckertand Evans 1967, Evans et al. 1967 Whitson and Koch 1998 Herbicideand grazing Whitson and Koch 1998 Centaureaspp. Herbicide,revegetation, and biocontrol Enloe and DiTomaso 1999 Herbicide and revegetation Sheley et al. 2001 Burning and herbicide Lacey et al. 1995 Cirsiumarvense (L.) Scop. Herbicideand revegetation Wilson and Kachman 1999 Euphorbiaesula L. Herbicide and biocontrol Nelson et al. 1998 Tillage, herbicide, and revegetation Selleck et al. 1962, Ferrellet al. 1998 Lym and Tober 1997 Tillage, herbicide,and fertilization Lym and Messersmith 1993 Grazingand herbicide Lym et al. 1997 Herbicide,burning, and revegetation Masters and Nissen 1998, Masterset al. 2001 Hypericumperforatum L. Tillage and revegetation Gates and Robocker 1960 Lepidiumlatifolium L. Mowing and herbicide Renz and DiTomasa 1999 Linaria dalmatica (L.) Mill. Tillage and revegetation Gates and Robocker 1960 Opuntiastricta (Haworth)Haworth Herbicideand biocontrol Hoffman et al. 1998 Taeniatherumcaput-medusae (L.) Nevski Burning,herbicide, and revegetation Horton 1991 Tillage, herbicide,and revegetation Young et al. 1969

A question faced by land managers con- plants that have the capability to reproduce stands of introduced and native perennial sidering revegetation is whether to use vegetatively can actually exacerbate weed grasses have been successfully used to native and/or introduced plant materials interference by stimulating production of suppress leafy spurge and improve forage (Lesica and Allendorf 1999). The value of new stems from vegetative buds below the production on rangeland. In Wyoming, local ecotypes (Knapp and Rice 1994, cut surface. However, perennial plants that seedbed preparation consisted of multiple Linhart and Grant 1996), native or intro- reproduce vegetatively can be severely glyphosate applications in spring and sum- duced plant cultivars with improved agro- damaged or killed by tillage (Derscheid et mer followed by tillage before planting nomic traits developed by formal breeding al. 1985), bulldozing, root-plowing, or introducedcool-season grasses (Ferrell et al. programs (Vogel et al. 1989, Vogel 2000, grubbing (Vallentine 1989). The high cost 1998). Introducedcool-season grasses were Casler et al. 1996), and mixed populations of these mechanical treatments limits their planted in a tilled seedbed following broad- or hybrid genotypes (Millar and Libby use to control rangeland weeds. cast applications of glyphosate and 2,4-D in 1989, Munda and Smith 1995) in revegeta- North Dakota (Lym and Tober 1997). The tion programs has been detailed. Another Integrating Multiple planted grasses that were most effective in perspective is that rather than emphasizing Weed suppressing leafy spurge were 'Bozoisky' individual species, the focus of revegeta- Control Strategies Russian wildrye [Psathyrostachys juncea tion programs should be on establishing There are several examples of integrated (Fisch.) Nevski] and 'Luna' pubescent functional groups (Walker 1992) that strategies used to manage invasive plants wheatgrass [Elytrigia intermedia (Host) maintain ecosystem processes (Noss 1991). and improve rangeland communities (Table Beauv.] in Wyoming, and 'Rebound' Johnson and Mayeux (1992) argue that no 3). Efforts to assess the compatibility of smooth brome and 'Reliant' intermediate special quality should be attributed to a insect biocontrol agents and herbicides dur- wheatgrass [Thinopyrum intermedium species labeled as a "native,"rather the focus ing development of integrated management (Host) Barkw. & D.R. Dewey] in North should be on ecosystems as "self-sustaining systems are increasing (Messersmith and Dakota. In Nebraska, monoculture stands systems in terms of physiognomic structure Adkins 1995). Revegetation has been a of native warm-season grasses, big and functional processes in which various common component of integrated bluestem (Andropogon gerardii Vitman), species .. are interchangeable." approachesbecause it is essential that desir- indiangrass [Sorghastrum nutans (L.) Mechanical. Mechanical treatments able plant species, ratherthan another inva- Nash], and switchgrass (Panicum virga- involve either removal of the aerial por- sive plant species, fill the niche vacated by tum L.), were established on leafy spurge- tions of the weed or removal of enough of the controlled invader. Herbicides and infested rangeland and increased herbage the root and crown to kill the plant. tillage were used to suppress dalmation yields by more than 40% and reduced Annuals and some biennials and perennials toadflax (Linaria dalmatica Mill.) and St. leafy spurge density and yield (Masters can be suppressed or controlled if mowing Johnswort (Gates and Robocker 1960), and Nissen 1998). The sites were treated occurs before fruits mature and viable cheatgrass (Eckert and Evans et al. 1967), with imazapyr and sulfometuron in the fall seeds form. Mowing in the fall for 3 con- and medusahead (Young et al. 1969) in and burned the following spring before secutive years decreased spotted knapweed early attempts to prepare degraded range- tallgrasses were planted into the herbicide- density about 85% compared to areas that land sites for revegetation with cool-sea- suppressed sod without tillage. were not mowed (Rinella et al. 2001). son grasses. Recent rangeland improvement research Mowing perennial herbaceous or woody Approaches that include herbicide appli- demonstrated an integrated weed manage- cation and establishing monoculture

510 JOURNAL OF RANGE MANAGEMENT 54(5), September 2001 ment strategy, which suppressed leafy tect the site at a minimum." This concept a trajectory that is driven by both naturally spurge and associated vegetation and facil- recognizes that plant community succes- occurring and human-induced processes. A itated planting and establishment of stands sion for a given site can progress along generalized model describes the process of of mixture of native warm-season grass multiple trajectories and result in different managing succession by using various man- and legume species (Masters et al. 2001). outcomes. Factors that influence these out- agement tools in appropriatesequences and These multi-species assemblages may comes include past management, plant and combinations to achieve a desired grassland more fully use resources on degraded animal dispersal from adjacent areas, cli- community structure (Fig. 2) (Masters and rangeland and preempt resource use by matic conditions, disturbance regimes Nissen 1998). less desirable species, including leafy (past, present, and future), and species The restoration ecology discipline pro- spurge. The strategy consisted of herbicide selected for revegetation projects. The vides goals to consider when developing application, burning the herbaceous stand- desired plant community concept is con- and implementing strategies to manipulate ing crop, and planting mixtures of native sistent with prevailing state and transition community succession to meet manage- species without tillage. Glyphosate and (Westoby et al. 1989) and threshold ment objectives. Restoration has been dis- imazapic were the herbicides selected to (Laycock 1991, Friedel 1991) models of tinguished from or referred to interchange- suppress existing resident vegetation, vegetation change. These non-equilibrium ably with rehabilitation, reclamation, while not interfering with establishment of models of succession have superceded the reconstruction, renovation, and other species in the planted mixtures. unidirectional Clementsian climax com- terms (Whisenant 1999). The Society for Glyphosate controlled cool-season grasses munity model (Clements 1916, Weaver Ecological Restoration (1994) defined that were growing at the time of applica- and Clements 1938). restoration as the process of repairing tion, but provided no residual weed con- The desired plant community is an damage caused by humans to the diversity trol. Imazapic provided residual control of appealing concept for rangeland manage- and dynamics of indigenous ecosystems, leafy spurge and annual grass and ment because it empowers land managers and Jackson et al. (1995) provide further broadleaf plants and was tolerated by a to design a plant community that meets elaboration of the definition. Hobbs and number of warm-season grasses (Rivas- management objectives. In the context of Norton (1996) suggest a broader defini- Pantoja et al. 1997, Beran et al. 2000), invasive plant management, resistance to tion, with restoration occurring along a forbs (Beran et al. 1999a) and legumes alien plant invasion would be a key criteri- continuum from rebuilding totally devas- (Beran et al. 1999b). on considered when designing a desired tated sites to maintaining pristine sites plant community. Obtaining the desired with limited management. They indicate plant community involves managing suc- that restoration should be applied at the Invasive Plant Management cession, which requires knowledge of the landscape scale and the goal should be to Systems as a Component of 3 general causes of succession: site avail- return degraded ecosystems to conditions Rangeland Resource Management ability; differential species availability; that meet conservation and production To be successful, invasive plant man- and species performance (Table 1) (Pickett objectives in a sustainable manner. agement programs must be compatible et al. 1987, Luken 1990). Within the limits with and integrated into overall rangeland of knowledge about the conditions, mech- Decision Support Systems resource management objectives and anisms, and processes controlling plant Invasive plant management is complex, plans. Effective invasive plant manage- community dynamics, these 3 components thus all applicable information should be ment programs cannot be developed with- can be modified to manage succession by synthesized and presented in a way that is out considering other management compo- using designed disturbance, controlled col- useful to managers. Decision support sys- nents that impinge upon the rangeland onization, and controlled species perfor- tems offer an approach to improve deci- resource. Integrating all components with- mance (Pickett et al. 1987). Designed dis- sion making when complex interactions in the rangeland resource management turbances include activities that create or are involved (Stuth and Smith 1993). program is essential because interactions eliminate site availability and control suc- Expert systems, a form of decision support among the components determine the eco- cession such as tillage or herbicide sup- systems, can improve decision making by nomic and ecological sustainability of the pression of sod. In successional manage- using knowledge and experience of program. For example, altering grazing ment, designed disturbances are used to experts to provide users a means to assess management or fire regimes impact site alter successional trajectories and to mini- alternative management outcomes based invasibility since the invasion process can mize continual reliance on external inputs. on specific information about the situation be influenced by disturbance. Controlled colonization is the intentional (Barrett and Jones 1989). Many decision What is the appropriate goal when alteration of availability and establishment support systems use heuristic ("rule of developing rangeland resource manage- of plant species by influencing seed banks, thumb") approaches to problem-solving ment programs? The "desired plant com- vegetative propagule pools, and regulation that blend hard data with semi-structured munity" could serve as the goal for range- of safe sites for germination and establish- procedures and expertise to provide infor- land resource management. The desired ment of desirable species. Invasive plant mation required to define a problem and plant community concept originated with seed banks can be depleted through attri- possible solutions (Scifres 1987, Stuth and the USDI-Bureau of Land Management tion if seed production is prevented or Smith 1993). The integrated brush man- and was defined by the Society for Range reduced. Controlled species performance agement system concept developed by Management, Task Group on Unity in involves manipulating growth and repro- Scifres et al. (1983) provides a system to Concepts and Terminology (1995) as, "of duction of plant species to redirect succes- evaluate integrated management with mul- the several plant communities that may sion. Biological and chemical weed control, tiple objectives and components. These occupy a site, the one that has been identi- grazing, mowing, fertilization, and planting models could be of great benefit in devel- fied through a management plan to best competitive species can create differential oping decision support systems for inva- meet the plan's objectives for the site. It species performance. Management of suc- sive plant management programs. (the desired plant community) must pro- cession is an ongoing process moving along

JOURNAL OF RANGE MANAGEMENT54(5), September 2001 511 Literature Cited Factors Overgrazing Andres, L. A. 1985. Interactionsof Chrysolina quadrigemina and Hypericum spp. in Fireexclusion California.p. 235-239. In: E. S. Delfosse, IConversion to Tools (ed.), Proceedings.of the VIth International cropland Chemical Symposium. on the biological control of Fig.PM General Weed invasion Cultural weeds. Agr. Canada,Ottawa. Auld, B.A. and C.A. Tisdell. 1986. Impact in snrii Mechanical a assessmentof biologicalinvasions. p. 79-88. Biologtical (e r In: R.H. Groves and J.J. Burdon (eds.), Ecology of biological invasions. Cambridge Univ. Press,Cambridge, England. Baker, H.G. 1965. Characteristicsand modes of origin of weeds, p. 147-169. In: H.G. and Nissen1998). 0 Baker and C.L. Stebbins (eds). The genetics o~~~~~~~~~~~~~~0Pof colonizing species. AcademicPress, New York. state Baker, H.G. 1986. Patterns of invasions in Steady NorthAmerica, p. 44-57. In: H.A. Mooney and J.A. 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