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Assessing economic impacts of biological control of weeds: The case of leafy spurge in the northern Great Plains of the United States
Journal of Environmental Management (1999) 56, 35–43 Article No. jema.1999.0269, available online at http://www.idealibrary.com on
Assessing economic impacts of biological control of weeds: The case of leafy spurge in the northern Great Plains of the United States1 D. A. Bangsund, F. L. Leistritz∗ and J. A. Leitch Leafy spurge (Euphorbia esula L.), a perennial weed native to Europe and Asia, has become a serious problem for ranchers and land managers in the northern Great Plains region of the United States. Potential economic benefits (i.e. gross benefits, not including the cost of biological control) from biological control of leafy spurge in the four-state region of Montana, North Dakota, South Dakota and Wyoming are estimated. Biological agents were predicted to control about 65% of the region’s leafy spurge infestations—about 1·2 million acres (497 000 ha)—by the year 2025. Direct economic impacts from control were estimated to total about $19·1 million annually, and secondary impacts were estimated at $39·3 million, for a total annual economic impact of $58·4 million. 1999 Academic Press
Keywords: biological control, leafy spurge (Euphorbia esula L.), economic impacts, northern Great Plains.
Introduction A variety of wild plants, especially invasive, exotic species, pose problems for managers of grazing land and/or wildland because they reduce the land’s usefulness for livestock grazing or are detrimental to its other functions (e.g. wildlife habitat, watershed). While some of these plants can be controlled with herbicides, such chemical controls are often prohibitively expensive to apply to extensive grazing lands characterized by low productivity (Bangsund et al., 1996). Use of chemical controls also raises concerns regarding potential hazards to health and the environment (e.g. undesirable residues, contamination of water supplies, impacts on nontarget species) (Rola and Sanchez, 1992; Pannell, 1994). As a result, greater emphasis has been placed on developing biological controls for problem weeds. Classical biological 1
Support by the Animal and Plant Health Inspection Service, US Department of Agriculture is gratefully acknowledged.
0301–4797/99/050035+09 $30.00/0
control of weeds is the deliberate use of natural enemies (i.e. insects, mites or plant pathogens) to reduce the density of a target weed below an economic threshold (Harris et al., 1985). Successful classical biological control programmes can offer attractive benefit-cost ratios, as well as avoid many of the health and environmental concerns associated with chemical controls (Habeck et al., 1993; Cullen and Whitten, 1995). In addition, biological controls can enhance the sustainability of agricultural systems, may lead to a more equitable distribution of income (because the benefits may be available to all producers, not just those who can afford extensive chemical treatments), and may be the only feasible solution to invasive species in wildland settings where chemical control may be incompatible with land management objectives (Cullen and Whitten, 1995). Implementing biological control programmes typically involves an investment of public funds. Many of the most successful biological weed control programmes have involved agents that can survive and spread in the environment, without needing to be
∗ Corresponding author Department of Agricultural Economics, North Dakota State University, Fargo, ND 58105, USA
1999 Academic Press
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D. A. Bangsund et al.
released by individual landowners (Cullen and Whitten, 1995). In such cases, the biological control agents can be characterized as non-rival (as the fact that one landowner benefits from weed control does not reduce the benefit to others) and non-exclusive (as it is not possible to prevent the agent from spreading to a particular property), two characteristics of pure public goods. In such cases, it is generally not feasible for the private sector to develop and release biological control agents on a commercial basis, and so biological control programmes of this type are generally funded largely by the public sector (Pannell, 1994). While past investments in biological control have yielded favourable returns, public decision makers charged with allocating funds for research, development and implementation of biological control must determine which projects to fund next. Further, in an era of fiscal austerity, biological control projects must compete, explicitly or implicitly, with a variety of other demands for public resources. As a result, an evaluation of potential benefits that may result from different projects is an important part of the decision process. This paper estimates the potential gross economic benefits from biological control of leafy spurge in the northern Great Plains of the United States.
Leafy spurge in the northern Great Plains Leafy spurge (Euphorbia esula L.), a perennial weed native to Europe and Asia, was introduced to North America in the nineteenth century. Leafy spurge was first reported in Newbury, Massachusetts, in 1827 (Bitton, 1921). It subsequently spread into a number of areas in North America, and by 1933 leafy spurge was considered a threat to rangeland in the northern Great Plains of the United States (Hanson and Rudd, 1933). Leafy spurge has become widely established in the northern Great Plains region of the United States and the adjacent Prairie Provinces of Canada, and has developed into a serious problem for ranchers and public land managers. Much of the problem stems from the weed’s ability to spread rapidly, displace native vegetation and sustain itself
despite repeated chemical treatments. In 1994, it was estimated to infest about 1·6 million acres (657 000 ha) in the four-state region of Montana, North Dakota, South Dakota and Wyoming (Leitch et al., 1996). Leafy spurge is primarily a problem on untilled lands (e.g. rangeland, wildland and idled cropland) since periodic tillage inhibits the growth of the weed. Nevertheless, leafy spurge infestations are estimated to result in an annual economic loss of $130 million in the four-state region (Leitch et al., 1996).
Biological control of leafy spurge Leafy spurge was chosen as a candidate for biological control, based on observations indicating that a variety of natural enemies appear to keep the plant’s density below the economic threshold in its native habitats in Europe and Asia (Harris, 1979; Carlson and Littlefield, 1983). By the mid-1980s, growing levels of leafy spurge infestation and concern over its future impact in light of the apparent ineffectiveness of chemical control methods led to a concerted effort to establish a biological control programme for leafy spurge in North America. This programme required importing natural enemies of leafy spurge from Europe/ Eurasia, testing their host specificity, checking them for pathogens and subsequently reproducing them for release in North America. By the early 1990s, several insects had been identified that appeared to be effective in reducing leafy spurge density and reclaiming land, at least in some environments. Within the last 5 years, biological control of leafy spurge has expanded beyond the initial research stages to the general collection and release of agents by a variety of entities (e.g. county and township governments, state and federal land management agencies, and individual landowners) (Hansen et al., 1997). At the same time, fiscal pressure at all levels of government has focused debate over the amount of public funds that should be used to facilitate development and implementation of biological control (biocontrol) programmes for problem weeds. The research reported here was undertaken in part to inform decision makers about the benefits to be gained
Economic impacts of biological control of weeds
from full implementation of leafy spurge biocontrol. In addition, information concerning the economic benefits from biocontrol of leafy spurge may help decision makers weigh the merits of developing other biological control programmes.
Methods and models Estimating benefits of biological control of leafy spurge required a model that related the biophysical impacts of changing leafy spurge infestations to economic outcomes. This aspect of the project drew heavily from Leitch et al. (1996), who had developed a bioeconomic model to estimate the economic impacts of leafy spurge infestations (Figure 1). Key relationships in the model relate changes in levels of leafy spurge infestation to changes in land output (e.g. carrying capacity for grazing livestock, wildlife supported). The two key components of the bioeconomic model are: (1) estimating rangeland (grazing land) impacts; and (2) estimating wildland impacts. Rangeland impacts were developed by assessing the effects of leafy spurge on livestock carrying capacity and then estimating the economic effects on both livestock producers and the regional economy (Bangsund and Leistritz, 1991). Wildland impacts were developed by estimating the effect on outdoor recreation activities and changes in soil and water conservation benefits (Wallace et al., 1992). Impacts of leafy spurge on rangeland stem from the plant’s ability to reduce livestock carrying capacity. The economic benefits of biological control on rangeland were based on changes (increases) in grazing output. The principal use of rangeland in the northern Great Plains region is for beef cattle production, with cow–calf herds the predominate beef enterprise. Hence, increases in grazing output were assumed to lead to proportionate increases in cow–calf production. These changes were then used to estimate changes in production expenditures and producer net incomes that were the direct economic impacts of biological control of leafy spurge on rangeland. The distribution of leafy spurge between rangeland and wildland had previously been estimated for all counties in the four-state
region (Wallace et al., 1992; Bangsund et al., 1993). These percentage distributions were assumed to hold for future infestation levels. County-specific estimates of rangeland carrying capacity were then used to estimate the pre-infestation productivity of the rangeland in each county. Rangeland output, after biological suppression of leafy spurge infestations, is a function of overall range health, grazing management, amount and type of forage present, density of pre-control leafy spurge infestation, and degree of leafy spurge suppression. While little scientific information exists concerning the amount of grazing output that can be expected from rangeland after biological suppression of leafy spurge, the nature of biological control and characteristics of leafy spurge infestations indicate that a return of rangeland productivity to pre-infestation rates is unlikely. Even when biological control is effective, some leafy spurge remains, which will have some suppressing effect on rangeland productivity. For this analysis, rangeland carrying capacity, after biological control of leafy spurge, was assumed to be 75% of its pre-infestation carrying capacity. Wildland provides a variety of outputs, including both market goods (e.g. grazing, forest products, mineral resources) and nonmarket goods (e.g. recreation, wildlife production and habitat, erosion control, watershed benefits). Previous research has indicated that the most salient effects of leafy spurge on wildland outputs can be expected to occur in the areas of: (1) wildlife habitat productivity; and (2) soil and water conservation values (Wallace et al., 1992; Bangsund et al., 1993). Wildland, like other land types, provides habitat for wildlife. The existence of wildlife (i.e. wildlife habitat and its outputs) is an important part of many outdoor activities. Soil and water conservation benefits on wildland include preserving topsoil and plant nutrients and reducing water runoff. Benefits from reduced water runoff include lower water treatment costs, lower sediment removal costs, decreased flood damage and increased recreational fishing (Ribaudo, 1989). Leafy spurge possesses the ability to literally choke out most existing native vegetation (Messersmith et al., 1985; Watson, 1985;
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D. A. Bangsund et al.
Leafy spurge infestations
Grazing land
Wildland
Biophysical impacts
Biophysical impacts
• Change in grazing capacity (AUMs)
• Change in wildlife populations • Change in watershed benefits
Direct economic impacts
Direct economic impacts
• Change in income of stock growers and landowners
• Change in wildlifeassociated recreation
• Change in production outlays by producers
• Change in soil erosion and water quality
Input–output analysis
Total (direct and secondary) annual economic impacts
Figure 1.
A conceptual bioeconomic model of the economic impacts of leafy spurge infestations in the northern Great Plains.
Belcher and Wilson, 1989). The establishment of leafy spurge can be directly related to a decline in native plants, threatening native and existing wildland vegetation (Belcher and Wilson, 1989). A substantial decrease in plant diversity resulting from leafy spurge infestations decreases wildlife habitat value and negatively impacts wildland soil and water conservation. The acreage of leafy spurge on wildland was estimated for all counties in the fourstate region using the values for the percentages of leafy spurge on wildland and
rangeland that had been developed in previous research (Wallace et al., 1992; Bangsund et al., 1993). These percentages were applied to the estimated future infestation levels to estimate acreages infested in each county. Biological control of leafy spurge is expected to reduce existing densities to a level where the plant no longer has substantial effects on the land’s ability to support indigenous wildlife and retain normal soil and water conservation benefits. Thus, this study assumes a 100% return of pre-infestation
Economic impacts of biological control of weeds
wildland outputs after biological control of leafy spurge. Direct economic impacts from leafy spurge infestation of wildland include: (1) changes in wildlife-associated recreationist expenditures that impact local suppliers of related goods and services; and (2) changes in user expenditures to mitigate damages from runoff and soil erosion. The acreage of leafy spurge controlled with biological agents was used with estimates of the values of soil and water conservation benefits and wildlife-associated recreationist expenditures to estimate the economic impact of reclaimed wildland outputs. Benefits to wildlife habitat value were estimated by calculating the difference between wildlife recreation expenditures without biological control and the estimated impacts after biological control. The increase in wildlife-related recreationist expenditures was the direct impact of improved wildland habitat resulting from biological control of leafy spurge on wildland. Per-acre values for soil and water conservation benefits were multiplied by the acreage of leafy spurge controlled with biological agents to estimate the value of increased soil and water conservation benefits. Regional impacts were estimated using input–output analysis. The input–output model used has 17 sectors and is based on primary (survey) data from firms and households. The model is closed with respect to households (i.e. the household sector is included in the model and estimates of economy-wide personal income are provided). The multipliers associated with the model are type II multipliers (i.e. they include both indirect and induced effects). Empirical testing has shown the model is reliable in estimating gross business volume, personal income, retail sales and economic activity in other major sectors in the four-state region of Montana, North Dakota, South Dakota and Wyoming (Coon and Leistritz, 1995). Using the model to estimate the benefits of biological control required estimates of: (1) the future level of leafy spurge infestation; (2) the amount of the present and future infestations that will eventually be controlled by biological agents; (3) the time required for control to reduce infestations below an economic threshold; and (4) the extent to which rangeland and wildland values will be restored when leafy spurge infestations are
reduced. The principal basis for estimating these key parameters was phone interviews with more than 25 scientists involved in research on leafy spurge and biological control technologies, as well as individuals involved in implementing and tracking biological control activities. As research-based data were not available to empirically estimate these parameters, the values developed for use in this analysis represent a consensus of expert opinion.
Results Results from the analysis include estimates or predictions of: (1) future acreage of leafy spurge; (2) future level of biological control; (3) direct impacts of biological control; and (4) secondary economic impacts.
Future acreage of leafy spurge The acreage infested by leafy spurge in the northern Great Plains region expanded rapidly over time. From 1950 to 1990, the acreage of leafy spurge infestations roughly doubled each decade (Figure 2). From 1990 to 1996 (the last year for which estimates were available), the rate of growth in leafy spurge acreage slowed somewhat, but the total acreage in the four-state region still increased about 24% over the 6-year period. The general consensus of individuals contacted during the study is that the slowing of the rate of growth can be attributed in part to increased use of herbicides to control infestations, but may also reflect the fact that leafy spurge is now occupying most of the environments to which it is best adapted. The acreage of leafy spurge infestations was projected to continue increasing until about the year 2000, at which time the area infested in the four-state region would be about 1·85 million acres (760 000 ha).
Future level of biological control The future level of biological control, measured in terms of acreage of leafy spurge effectively suppressed, is dependent on a number of factors. Based on experiences to
39
D. A. Bangsund et al.
2 000 000 Total acreage Biologically controlled infestation 1 500 000
Acres
40
1 000 000
Uncontrolled infestation
500 000
0 1950
1960
1970
1980
1990
2000
2010
2020
2030
Years
Figure 2.
Historic and projected acreage of leafy spurge in the northern Great Plains.
date, low- to medium-density leafy spurge stands appear best suited to control with biological agents in the United States (McClay et al., 1995; Hansen et al., 1997). Success to date has been poor in riparian or other high moisture areas or infestations in shaded environments. It remains uncertain if: (1) current biological control agents, cleared for use in North America, can adapt to those environments in which control has proven difficult; or (2) new biological agents that may be better suited to these environments will be discovered and cleared for use. Given experience to date, most of the experts contacted believed that about 60–70% of future leafy spurge infestations will eventually be controlled with biological agents. Control was defined as reducing the infestation density below economic thresholds. Estimates of the time needed for biological agents to reach their maximum level of control (acreage) fell in the range of 10–30 years. The acreage of leafy spurge eventually controlled and the time needed to reach maximum control by biological agents were
arrived by modal analysis of the information obtained from experts contacted. Thus, for this analysis, 65% of total future leafy spurge acreage was assumed to be controlled with biological agents by the year 2025.
Direct impacts of biological control Economic impacts of a project, programme or policy can be categorized into direct and secondary impacts. Direct impacts are those changes in output, employment or income that represent the initial or first-round effects. The secondary impacts (sometimes further categorized into indirect and induced effects) result from subsequent rounds of spending and respending within the economy. The direct effects of the leafy spurge biological control programme were categorized into rangeland impacts and wildland impacts. Direct economic impacts to the economy of the northern Great Plains region from biological control of leafy spurge on rangeland include the value of the increase in grazing
Economic impacts of biological control of weeds Table 1. Future annual biological control benefits in rangeland in the northern Great Plains by 2025 Item
Table 2. Future annual benefits of biological control of leafy spurge in wildland in the northern Great Plains by 2025
Totals Item
Future acres controlled AUMsa recovered Value of recovered AUMs (1997 dollars) Increase in beef herds (number of cows) Increase in beef herd expenditures (1997 dollars) Total direct economic impact (1997 dollars)
820 000 320 500 4 980 000 39 400
Totals
Future acres controlled Value of increased wildlife-related expenditures (1997 dollars) Increase in soil and water conservation benefits (1997 dollars)
450 000 1 845 200
Total direct economic impact (1997 dollars)
2 630 500
785 300
11 470 000
16 450 000
a
An animal unit month is an average amount of forage needed to feed one animal unit (AU) for 1 month. An AU is typically considered a mature cow weighing approximately 1000 pounds or an equivalent grazing animal(s) based on an average feed consumption of 26 pounds of dry matter per day.
output and the production expenditures associated with changes in ranchers’ cow–calf herd operations. Biological control was estimated to suppress leafy spurge infestations on about 820 000 acres (337 000 ha) of rangeland in the northern Great Plains by the year 2025 (Table 1). The suppression of leafy spurge was estimated to result in recovery of about 320 000 AUMs of grazing, which was estimated to have a value (based on grazing land rental rates) of $4·98 million in 1997 dollars (Table 1). The recovered grazing capacity would support an increase in the region’s beef cow herds of about 39 400 cows. The increased cow herds were estimated to result in additional production expenditures to the region’s input suppliers of about $11·47 million. Thus, the estimated total annual direct impact of biological control of leafy spurge on rangeland was estimated to be about $16·45 million (i.e. value of recovered AUMs plus increase in beef herd expenditures). Biological control was estimated to suppress leafy spurge on about 450 000 acres (185 000 ha) of wildland in the northern Great Plains by the year 2025 (Table 2). The suppression of leafy spurge is estimated to result in increased annual expenditures for wildlife associated recreation of about $1·8 million (1997 dollars) (Table 2). The total annual increase in soil and water conservation benefits was estimated to be $785 000 (1997 dollars). Thus, the total direct impacts from biological
control of leafy spurge on wildland in the year 2025 was estimated at about $2·6 million (1997 dollars).
Secondary impacts The secondary impacts of the biological control of leafy spurge were estimated using an input–output (I-O) model (Coon et al., 1985). The direct impacts were allocated to the appropriate economic sectors of the I-O model. With respect to rangeland impacts, the retail trade sector, which represents the bulk of livestock production expenses, and the households sector, which includes producer returns, were the two most affected sectors. For wildland impacts, the increased recreation expenditures were allocated to the retail trade sector (67%) and the business and personal services sector (33%). Direct economic impacts associated with increased soil and water conservation benefits were allocated to the government, agriculture-crops and electricity generation sectors. The annual direct impacts of biological control were estimated to total about $19·1 million (Table 3). These generated about $39·3 million in secondary impacts. The economic sectors receiving the largest secondary impacts were the households and retail trade sectors (Table 3). The total (direct plus secondary) economic impacts from biological control of leafy spurge were estimated at $58·4 million annually. About 876 jobs would be supported in the regional economy as a result of biological control of leafy spurge (Coon et al., 1985).
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D. A. Bangsund et al. Table 3. Direct, secondary and total future annual economic impacts of the biological control of leafy spurge in the northern Great Plains by 2025 Economics impacts Economic sector Agriculture-livestock Agriculture-crops Non-metal mining Construction Transportation Communication and public utilities Agricultural processing and miscellaneous manufacturing Retail trade Finance, insurance and real estate Business and personal service Professional and social service Households Government Others Totals Number of jobs supported
Conclusions and implications Invasive weeds constitute a major problem for both public and private land managers and for policymakers. Weed infestations can have detrimental effects on a number of the outputs from rangeland or wildland and hence on local and regional economies. Biological control may offer a cost-effective alternative for controlling some weed species, while avoiding some of the environmental concerns associated with herbicides. However, development and deployment of biological controls may require substantial investments of public funds, which in turn leads to interest in estimates of the benefits that may result from these programmes. The results of this study indicate that, if the level of control postulated is eventually achieved, the stimulus to the regional economy would be considerable. While the costs incurred in developing and implementing the biological control programme have not been estimated, the magnitude of the potential economic benefits suggests that the benefit-cost ratio for this project could be quite favourable. The
Direct
Secondary
––––1997 dollars 829 5385 0 0 351 242 0
Totals
(000s) 1455 1159 100 1334 196 1643 1863
–––– 2284 6544 100 1334 547 1885 1863
3661 574 826 0 6655 550 8
11 982 2602 1000 1279 12 963 1700 1
15 643 3176 1826 1279 19 618 2250 9
19 082
39 276
58 358 876
study results also indicate that, although pasture weeds are commonly regarded as a problem that affects only livestock producers, effective control of leafy spurge will result in direct benefits to other groups as well (e.g. recreationists, water users). Further, the findings indicate that the secondary benefits of leafy spurge control would be substantial for many sectors of the regional economy.
References Bangsund, D. A. and Leistritz, F. L. (1991). Economic Impact of Leafy Spurge in Montana, South Dakota, and Wyoming. Agr. Econ. Report No. 275. Fargo: North Dakota State University. Bangsund, D. A., Baltezore, J. F., Leitch, J. A. and Leistritz, F. L. (1993). Economic Impact of Leafy Spurge on Wildland in Montana, South Dakota, and Wyoming. Agr. Econ. Report No. 304. Fargo: North Dakota State University. Bangsund, D. A., Leitch, J. A. and Leistritz, F. L. (1996). Economics of herbicide control of leafy spurge (Euphorbia esula L.). Journal of Agricultural and Resource Economics 21, 381–395. Belcher, J. W. and Wilson, S. D. (1989). Leafy spurge and the species composition of a mixedgrass prairie. Journal of Range Management 42, 172–175.
Economic impacts of biological control of weeds Bitton, N. L. (1921). The leafy spurge becoming a pest. Journal of New York Botanical Gardeners 22, 73–75. Carlson, R. B. and Littlefield, L. J. (1983). The potential for biological control of leafy spurge. North Dakota Farm Research 40, 14–16. Coon, R. C. and Leistritz, F. L. (1995). An Updated Economic Base Data Set for North Dakota. Agr. Econ. Stat. Series No. 55. Fargo: North Dakota State University. Coon, R. C., Leistritz, F. L., Hertsgaard, T. A. and Leholm, A. G. (1985). The North Dakota InputOutput Model: A Tool for Analyzing Economic Linkages. Agr. Econ. Report No. 187, Fargo, North Dakota State University. Cullen, J. M. and Whitten, M. J. (1995). Economics of classical biological control: a research perspective. Plant and Microbial Biotechnology Research Series 4, 270–276. Habeck, M. H., Lovejoy, S. B. and Lee, J. G. (1993). When does investing in classical biological control research make economic sense? Florida Entomologist 76, 96–101. Hansen, R. W., Richard, R. D., Parker, P. E. and Wendel, L. E. (1997). Distribution of biological control agents of leafy spurge (Euphorbia esula L.) in the United States: 1988–1996. Biological Control 10, 129–142. Hanson, H. C. and Rudd, V. E. (1933). Leafy Spurge Life History and Habits. Ag. Exp. Sta. Bull. No. 226. Fargo: North Dakota Agricultural College. Harris, P. (1979). The Biological Control of Leafy Spurge. Paper presented at the 1979 Leafy Spurge Symposium, Bismarck, ND. Fargo: North Dakota State University. Harris, P., Dunn, P. H., Schroeder, D. and Von Moos, R. (1985). Biological control of leafy spurge
in North America. In Leafy Spurge (A. K. Watson, ed.), pp. 79–92. Champaign, IL: Weed Science Society of America. Leitch, J. A., Leistritz, F. L. and Bangsund, D. A. (1996). Economic effect of leafy spurge in the Upper Great Plains: methods, models, and results. Impact Assessment 14, 419–433. McClay, A. S., Cole, D. E., Harris, P. and Richardson, C. J. (1995). Biological Control of Leafy Spurge in Alberta: Progress and Prospects. Report AECV95-R2. Vegreville, Alberta: Alberta Environmental Centre. Messersmith, C. G., Lym, R. G. and Galitz, D. S. (1985). Biology of leafy spurge. In Leafy Spurge (A. K. Watson, ed.), pp. 42–56. Champaign, IL: Weed Science Society of America. Pannell, D. J. (1994). Economic justification for government involvement in weed management: a catalogue of market failures. Plant Protection Quarterly 9, 131–137. Ribaudo, M. O. (1989). Water Quality Benefits from the Conservation Reserve Program. Agr. Econ. Report No. 606. Washington, DC: USDA, Economic Research Service. Rola, A. C. and Sanchez, F. F. (1992). The economics of integrated pest management: theory and empirical evidence in rice in the Philippines. The Philippine Entomologist 8, 1193–1212. Wallace, N. M., Leitch, J. A. and Leistritz, F. L. (1992). Economic impact of leafy spurge on North Dakota wildland. North Dakota Farm Research 49, 9–13. Watson, A. K. (1985). Integrated management of leafy spurge. In Leafy Spurge (A. K. Watson, ed.). Champaign, IL: Weed Science Society of America.
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Assessing economic impacts of biological control of weeds: The case of leafy spurge in the northern Great Plains of the United States1 D. A. Bangsund, F. L. Leistritz∗ and J. A. Leitch Leafy spurge (Euphorbia esula L.), a perennial weed native to Europe and Asia, has become a serious problem for ranchers and land managers in the northern Great Plains region of the United States. Potential economic benefits (i.e. gross benefits, not including the cost of biological control) from biological control of leafy spurge in the four-state region of Montana, North Dakota, South Dakota and Wyoming are estimated. Biological agents were predicted to control about 65% of the region’s leafy spurge infestations—about 1·2 million acres (497 000 ha)—by the year 2025. Direct economic impacts from control were estimated to total about $19·1 million annually, and secondary impacts were estimated at $39·3 million, for a total annual economic impact of $58·4 million. 1999 Academic Press
Keywords: biological control, leafy spurge (Euphorbia esula L.), economic impacts, northern Great Plains.
Introduction A variety of wild plants, especially invasive, exotic species, pose problems for managers of grazing land and/or wildland because they reduce the land’s usefulness for livestock grazing or are detrimental to its other functions (e.g. wildlife habitat, watershed). While some of these plants can be controlled with herbicides, such chemical controls are often prohibitively expensive to apply to extensive grazing lands characterized by low productivity (Bangsund et al., 1996). Use of chemical controls also raises concerns regarding potential hazards to health and the environment (e.g. undesirable residues, contamination of water supplies, impacts on nontarget species) (Rola and Sanchez, 1992; Pannell, 1994). As a result, greater emphasis has been placed on developing biological controls for problem weeds. Classical biological 1
Support by the Animal and Plant Health Inspection Service, US Department of Agriculture is gratefully acknowledged.
0301–4797/99/050035+09 $30.00/0
control of weeds is the deliberate use of natural enemies (i.e. insects, mites or plant pathogens) to reduce the density of a target weed below an economic threshold (Harris et al., 1985). Successful classical biological control programmes can offer attractive benefit-cost ratios, as well as avoid many of the health and environmental concerns associated with chemical controls (Habeck et al., 1993; Cullen and Whitten, 1995). In addition, biological controls can enhance the sustainability of agricultural systems, may lead to a more equitable distribution of income (because the benefits may be available to all producers, not just those who can afford extensive chemical treatments), and may be the only feasible solution to invasive species in wildland settings where chemical control may be incompatible with land management objectives (Cullen and Whitten, 1995). Implementing biological control programmes typically involves an investment of public funds. Many of the most successful biological weed control programmes have involved agents that can survive and spread in the environment, without needing to be
∗ Corresponding author Department of Agricultural Economics, North Dakota State University, Fargo, ND 58105, USA
1999 Academic Press
36
D. A. Bangsund et al.
released by individual landowners (Cullen and Whitten, 1995). In such cases, the biological control agents can be characterized as non-rival (as the fact that one landowner benefits from weed control does not reduce the benefit to others) and non-exclusive (as it is not possible to prevent the agent from spreading to a particular property), two characteristics of pure public goods. In such cases, it is generally not feasible for the private sector to develop and release biological control agents on a commercial basis, and so biological control programmes of this type are generally funded largely by the public sector (Pannell, 1994). While past investments in biological control have yielded favourable returns, public decision makers charged with allocating funds for research, development and implementation of biological control must determine which projects to fund next. Further, in an era of fiscal austerity, biological control projects must compete, explicitly or implicitly, with a variety of other demands for public resources. As a result, an evaluation of potential benefits that may result from different projects is an important part of the decision process. This paper estimates the potential gross economic benefits from biological control of leafy spurge in the northern Great Plains of the United States.
Leafy spurge in the northern Great Plains Leafy spurge (Euphorbia esula L.), a perennial weed native to Europe and Asia, was introduced to North America in the nineteenth century. Leafy spurge was first reported in Newbury, Massachusetts, in 1827 (Bitton, 1921). It subsequently spread into a number of areas in North America, and by 1933 leafy spurge was considered a threat to rangeland in the northern Great Plains of the United States (Hanson and Rudd, 1933). Leafy spurge has become widely established in the northern Great Plains region of the United States and the adjacent Prairie Provinces of Canada, and has developed into a serious problem for ranchers and public land managers. Much of the problem stems from the weed’s ability to spread rapidly, displace native vegetation and sustain itself
despite repeated chemical treatments. In 1994, it was estimated to infest about 1·6 million acres (657 000 ha) in the four-state region of Montana, North Dakota, South Dakota and Wyoming (Leitch et al., 1996). Leafy spurge is primarily a problem on untilled lands (e.g. rangeland, wildland and idled cropland) since periodic tillage inhibits the growth of the weed. Nevertheless, leafy spurge infestations are estimated to result in an annual economic loss of $130 million in the four-state region (Leitch et al., 1996).
Biological control of leafy spurge Leafy spurge was chosen as a candidate for biological control, based on observations indicating that a variety of natural enemies appear to keep the plant’s density below the economic threshold in its native habitats in Europe and Asia (Harris, 1979; Carlson and Littlefield, 1983). By the mid-1980s, growing levels of leafy spurge infestation and concern over its future impact in light of the apparent ineffectiveness of chemical control methods led to a concerted effort to establish a biological control programme for leafy spurge in North America. This programme required importing natural enemies of leafy spurge from Europe/ Eurasia, testing their host specificity, checking them for pathogens and subsequently reproducing them for release in North America. By the early 1990s, several insects had been identified that appeared to be effective in reducing leafy spurge density and reclaiming land, at least in some environments. Within the last 5 years, biological control of leafy spurge has expanded beyond the initial research stages to the general collection and release of agents by a variety of entities (e.g. county and township governments, state and federal land management agencies, and individual landowners) (Hansen et al., 1997). At the same time, fiscal pressure at all levels of government has focused debate over the amount of public funds that should be used to facilitate development and implementation of biological control (biocontrol) programmes for problem weeds. The research reported here was undertaken in part to inform decision makers about the benefits to be gained
Economic impacts of biological control of weeds
from full implementation of leafy spurge biocontrol. In addition, information concerning the economic benefits from biocontrol of leafy spurge may help decision makers weigh the merits of developing other biological control programmes.
Methods and models Estimating benefits of biological control of leafy spurge required a model that related the biophysical impacts of changing leafy spurge infestations to economic outcomes. This aspect of the project drew heavily from Leitch et al. (1996), who had developed a bioeconomic model to estimate the economic impacts of leafy spurge infestations (Figure 1). Key relationships in the model relate changes in levels of leafy spurge infestation to changes in land output (e.g. carrying capacity for grazing livestock, wildlife supported). The two key components of the bioeconomic model are: (1) estimating rangeland (grazing land) impacts; and (2) estimating wildland impacts. Rangeland impacts were developed by assessing the effects of leafy spurge on livestock carrying capacity and then estimating the economic effects on both livestock producers and the regional economy (Bangsund and Leistritz, 1991). Wildland impacts were developed by estimating the effect on outdoor recreation activities and changes in soil and water conservation benefits (Wallace et al., 1992). Impacts of leafy spurge on rangeland stem from the plant’s ability to reduce livestock carrying capacity. The economic benefits of biological control on rangeland were based on changes (increases) in grazing output. The principal use of rangeland in the northern Great Plains region is for beef cattle production, with cow–calf herds the predominate beef enterprise. Hence, increases in grazing output were assumed to lead to proportionate increases in cow–calf production. These changes were then used to estimate changes in production expenditures and producer net incomes that were the direct economic impacts of biological control of leafy spurge on rangeland. The distribution of leafy spurge between rangeland and wildland had previously been estimated for all counties in the four-state
region (Wallace et al., 1992; Bangsund et al., 1993). These percentage distributions were assumed to hold for future infestation levels. County-specific estimates of rangeland carrying capacity were then used to estimate the pre-infestation productivity of the rangeland in each county. Rangeland output, after biological suppression of leafy spurge infestations, is a function of overall range health, grazing management, amount and type of forage present, density of pre-control leafy spurge infestation, and degree of leafy spurge suppression. While little scientific information exists concerning the amount of grazing output that can be expected from rangeland after biological suppression of leafy spurge, the nature of biological control and characteristics of leafy spurge infestations indicate that a return of rangeland productivity to pre-infestation rates is unlikely. Even when biological control is effective, some leafy spurge remains, which will have some suppressing effect on rangeland productivity. For this analysis, rangeland carrying capacity, after biological control of leafy spurge, was assumed to be 75% of its pre-infestation carrying capacity. Wildland provides a variety of outputs, including both market goods (e.g. grazing, forest products, mineral resources) and nonmarket goods (e.g. recreation, wildlife production and habitat, erosion control, watershed benefits). Previous research has indicated that the most salient effects of leafy spurge on wildland outputs can be expected to occur in the areas of: (1) wildlife habitat productivity; and (2) soil and water conservation values (Wallace et al., 1992; Bangsund et al., 1993). Wildland, like other land types, provides habitat for wildlife. The existence of wildlife (i.e. wildlife habitat and its outputs) is an important part of many outdoor activities. Soil and water conservation benefits on wildland include preserving topsoil and plant nutrients and reducing water runoff. Benefits from reduced water runoff include lower water treatment costs, lower sediment removal costs, decreased flood damage and increased recreational fishing (Ribaudo, 1989). Leafy spurge possesses the ability to literally choke out most existing native vegetation (Messersmith et al., 1985; Watson, 1985;
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D. A. Bangsund et al.
Leafy spurge infestations
Grazing land
Wildland
Biophysical impacts
Biophysical impacts
• Change in grazing capacity (AUMs)
• Change in wildlife populations • Change in watershed benefits
Direct economic impacts
Direct economic impacts
• Change in income of stock growers and landowners
• Change in wildlifeassociated recreation
• Change in production outlays by producers
• Change in soil erosion and water quality
Input–output analysis
Total (direct and secondary) annual economic impacts
Figure 1.
A conceptual bioeconomic model of the economic impacts of leafy spurge infestations in the northern Great Plains.
Belcher and Wilson, 1989). The establishment of leafy spurge can be directly related to a decline in native plants, threatening native and existing wildland vegetation (Belcher and Wilson, 1989). A substantial decrease in plant diversity resulting from leafy spurge infestations decreases wildlife habitat value and negatively impacts wildland soil and water conservation. The acreage of leafy spurge on wildland was estimated for all counties in the fourstate region using the values for the percentages of leafy spurge on wildland and
rangeland that had been developed in previous research (Wallace et al., 1992; Bangsund et al., 1993). These percentages were applied to the estimated future infestation levels to estimate acreages infested in each county. Biological control of leafy spurge is expected to reduce existing densities to a level where the plant no longer has substantial effects on the land’s ability to support indigenous wildlife and retain normal soil and water conservation benefits. Thus, this study assumes a 100% return of pre-infestation
Economic impacts of biological control of weeds
wildland outputs after biological control of leafy spurge. Direct economic impacts from leafy spurge infestation of wildland include: (1) changes in wildlife-associated recreationist expenditures that impact local suppliers of related goods and services; and (2) changes in user expenditures to mitigate damages from runoff and soil erosion. The acreage of leafy spurge controlled with biological agents was used with estimates of the values of soil and water conservation benefits and wildlife-associated recreationist expenditures to estimate the economic impact of reclaimed wildland outputs. Benefits to wildlife habitat value were estimated by calculating the difference between wildlife recreation expenditures without biological control and the estimated impacts after biological control. The increase in wildlife-related recreationist expenditures was the direct impact of improved wildland habitat resulting from biological control of leafy spurge on wildland. Per-acre values for soil and water conservation benefits were multiplied by the acreage of leafy spurge controlled with biological agents to estimate the value of increased soil and water conservation benefits. Regional impacts were estimated using input–output analysis. The input–output model used has 17 sectors and is based on primary (survey) data from firms and households. The model is closed with respect to households (i.e. the household sector is included in the model and estimates of economy-wide personal income are provided). The multipliers associated with the model are type II multipliers (i.e. they include both indirect and induced effects). Empirical testing has shown the model is reliable in estimating gross business volume, personal income, retail sales and economic activity in other major sectors in the four-state region of Montana, North Dakota, South Dakota and Wyoming (Coon and Leistritz, 1995). Using the model to estimate the benefits of biological control required estimates of: (1) the future level of leafy spurge infestation; (2) the amount of the present and future infestations that will eventually be controlled by biological agents; (3) the time required for control to reduce infestations below an economic threshold; and (4) the extent to which rangeland and wildland values will be restored when leafy spurge infestations are
reduced. The principal basis for estimating these key parameters was phone interviews with more than 25 scientists involved in research on leafy spurge and biological control technologies, as well as individuals involved in implementing and tracking biological control activities. As research-based data were not available to empirically estimate these parameters, the values developed for use in this analysis represent a consensus of expert opinion.
Results Results from the analysis include estimates or predictions of: (1) future acreage of leafy spurge; (2) future level of biological control; (3) direct impacts of biological control; and (4) secondary economic impacts.
Future acreage of leafy spurge The acreage infested by leafy spurge in the northern Great Plains region expanded rapidly over time. From 1950 to 1990, the acreage of leafy spurge infestations roughly doubled each decade (Figure 2). From 1990 to 1996 (the last year for which estimates were available), the rate of growth in leafy spurge acreage slowed somewhat, but the total acreage in the four-state region still increased about 24% over the 6-year period. The general consensus of individuals contacted during the study is that the slowing of the rate of growth can be attributed in part to increased use of herbicides to control infestations, but may also reflect the fact that leafy spurge is now occupying most of the environments to which it is best adapted. The acreage of leafy spurge infestations was projected to continue increasing until about the year 2000, at which time the area infested in the four-state region would be about 1·85 million acres (760 000 ha).
Future level of biological control The future level of biological control, measured in terms of acreage of leafy spurge effectively suppressed, is dependent on a number of factors. Based on experiences to
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D. A. Bangsund et al.
2 000 000 Total acreage Biologically controlled infestation 1 500 000
Acres
40
1 000 000
Uncontrolled infestation
500 000
0 1950
1960
1970
1980
1990
2000
2010
2020
2030
Years
Figure 2.
Historic and projected acreage of leafy spurge in the northern Great Plains.
date, low- to medium-density leafy spurge stands appear best suited to control with biological agents in the United States (McClay et al., 1995; Hansen et al., 1997). Success to date has been poor in riparian or other high moisture areas or infestations in shaded environments. It remains uncertain if: (1) current biological control agents, cleared for use in North America, can adapt to those environments in which control has proven difficult; or (2) new biological agents that may be better suited to these environments will be discovered and cleared for use. Given experience to date, most of the experts contacted believed that about 60–70% of future leafy spurge infestations will eventually be controlled with biological agents. Control was defined as reducing the infestation density below economic thresholds. Estimates of the time needed for biological agents to reach their maximum level of control (acreage) fell in the range of 10–30 years. The acreage of leafy spurge eventually controlled and the time needed to reach maximum control by biological agents were
arrived by modal analysis of the information obtained from experts contacted. Thus, for this analysis, 65% of total future leafy spurge acreage was assumed to be controlled with biological agents by the year 2025.
Direct impacts of biological control Economic impacts of a project, programme or policy can be categorized into direct and secondary impacts. Direct impacts are those changes in output, employment or income that represent the initial or first-round effects. The secondary impacts (sometimes further categorized into indirect and induced effects) result from subsequent rounds of spending and respending within the economy. The direct effects of the leafy spurge biological control programme were categorized into rangeland impacts and wildland impacts. Direct economic impacts to the economy of the northern Great Plains region from biological control of leafy spurge on rangeland include the value of the increase in grazing
Economic impacts of biological control of weeds Table 1. Future annual biological control benefits in rangeland in the northern Great Plains by 2025 Item
Table 2. Future annual benefits of biological control of leafy spurge in wildland in the northern Great Plains by 2025
Totals Item
Future acres controlled AUMsa recovered Value of recovered AUMs (1997 dollars) Increase in beef herds (number of cows) Increase in beef herd expenditures (1997 dollars) Total direct economic impact (1997 dollars)
820 000 320 500 4 980 000 39 400
Totals
Future acres controlled Value of increased wildlife-related expenditures (1997 dollars) Increase in soil and water conservation benefits (1997 dollars)
450 000 1 845 200
Total direct economic impact (1997 dollars)
2 630 500
785 300
11 470 000
16 450 000
a
An animal unit month is an average amount of forage needed to feed one animal unit (AU) for 1 month. An AU is typically considered a mature cow weighing approximately 1000 pounds or an equivalent grazing animal(s) based on an average feed consumption of 26 pounds of dry matter per day.
output and the production expenditures associated with changes in ranchers’ cow–calf herd operations. Biological control was estimated to suppress leafy spurge infestations on about 820 000 acres (337 000 ha) of rangeland in the northern Great Plains by the year 2025 (Table 1). The suppression of leafy spurge was estimated to result in recovery of about 320 000 AUMs of grazing, which was estimated to have a value (based on grazing land rental rates) of $4·98 million in 1997 dollars (Table 1). The recovered grazing capacity would support an increase in the region’s beef cow herds of about 39 400 cows. The increased cow herds were estimated to result in additional production expenditures to the region’s input suppliers of about $11·47 million. Thus, the estimated total annual direct impact of biological control of leafy spurge on rangeland was estimated to be about $16·45 million (i.e. value of recovered AUMs plus increase in beef herd expenditures). Biological control was estimated to suppress leafy spurge on about 450 000 acres (185 000 ha) of wildland in the northern Great Plains by the year 2025 (Table 2). The suppression of leafy spurge is estimated to result in increased annual expenditures for wildlife associated recreation of about $1·8 million (1997 dollars) (Table 2). The total annual increase in soil and water conservation benefits was estimated to be $785 000 (1997 dollars). Thus, the total direct impacts from biological
control of leafy spurge on wildland in the year 2025 was estimated at about $2·6 million (1997 dollars).
Secondary impacts The secondary impacts of the biological control of leafy spurge were estimated using an input–output (I-O) model (Coon et al., 1985). The direct impacts were allocated to the appropriate economic sectors of the I-O model. With respect to rangeland impacts, the retail trade sector, which represents the bulk of livestock production expenses, and the households sector, which includes producer returns, were the two most affected sectors. For wildland impacts, the increased recreation expenditures were allocated to the retail trade sector (67%) and the business and personal services sector (33%). Direct economic impacts associated with increased soil and water conservation benefits were allocated to the government, agriculture-crops and electricity generation sectors. The annual direct impacts of biological control were estimated to total about $19·1 million (Table 3). These generated about $39·3 million in secondary impacts. The economic sectors receiving the largest secondary impacts were the households and retail trade sectors (Table 3). The total (direct plus secondary) economic impacts from biological control of leafy spurge were estimated at $58·4 million annually. About 876 jobs would be supported in the regional economy as a result of biological control of leafy spurge (Coon et al., 1985).
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D. A. Bangsund et al. Table 3. Direct, secondary and total future annual economic impacts of the biological control of leafy spurge in the northern Great Plains by 2025 Economics impacts Economic sector Agriculture-livestock Agriculture-crops Non-metal mining Construction Transportation Communication and public utilities Agricultural processing and miscellaneous manufacturing Retail trade Finance, insurance and real estate Business and personal service Professional and social service Households Government Others Totals Number of jobs supported
Conclusions and implications Invasive weeds constitute a major problem for both public and private land managers and for policymakers. Weed infestations can have detrimental effects on a number of the outputs from rangeland or wildland and hence on local and regional economies. Biological control may offer a cost-effective alternative for controlling some weed species, while avoiding some of the environmental concerns associated with herbicides. However, development and deployment of biological controls may require substantial investments of public funds, which in turn leads to interest in estimates of the benefits that may result from these programmes. The results of this study indicate that, if the level of control postulated is eventually achieved, the stimulus to the regional economy would be considerable. While the costs incurred in developing and implementing the biological control programme have not been estimated, the magnitude of the potential economic benefits suggests that the benefit-cost ratio for this project could be quite favourable. The
Direct
Secondary
––––1997 dollars 829 5385 0 0 351 242 0
Totals
(000s) 1455 1159 100 1334 196 1643 1863
–––– 2284 6544 100 1334 547 1885 1863
3661 574 826 0 6655 550 8
11 982 2602 1000 1279 12 963 1700 1
15 643 3176 1826 1279 19 618 2250 9
19 082
39 276
58 358 876
study results also indicate that, although pasture weeds are commonly regarded as a problem that affects only livestock producers, effective control of leafy spurge will result in direct benefits to other groups as well (e.g. recreationists, water users). Further, the findings indicate that the secondary benefits of leafy spurge control would be substantial for many sectors of the regional economy.
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Economic impacts of biological control of weeds Bitton, N. L. (1921). The leafy spurge becoming a pest. Journal of New York Botanical Gardeners 22, 73–75. Carlson, R. B. and Littlefield, L. J. (1983). The potential for biological control of leafy spurge. North Dakota Farm Research 40, 14–16. Coon, R. C. and Leistritz, F. L. (1995). An Updated Economic Base Data Set for North Dakota. Agr. Econ. Stat. Series No. 55. Fargo: North Dakota State University. Coon, R. C., Leistritz, F. L., Hertsgaard, T. A. and Leholm, A. G. (1985). The North Dakota InputOutput Model: A Tool for Analyzing Economic Linkages. Agr. Econ. Report No. 187, Fargo, North Dakota State University. Cullen, J. M. and Whitten, M. J. (1995). Economics of classical biological control: a research perspective. Plant and Microbial Biotechnology Research Series 4, 270–276. Habeck, M. H., Lovejoy, S. B. and Lee, J. G. (1993). When does investing in classical biological control research make economic sense? Florida Entomologist 76, 96–101. Hansen, R. W., Richard, R. D., Parker, P. E. and Wendel, L. E. (1997). Distribution of biological control agents of leafy spurge (Euphorbia esula L.) in the United States: 1988–1996. Biological Control 10, 129–142. Hanson, H. C. and Rudd, V. E. (1933). Leafy Spurge Life History and Habits. Ag. Exp. Sta. Bull. No. 226. Fargo: North Dakota Agricultural College. Harris, P. (1979). The Biological Control of Leafy Spurge. Paper presented at the 1979 Leafy Spurge Symposium, Bismarck, ND. Fargo: North Dakota State University. Harris, P., Dunn, P. H., Schroeder, D. and Von Moos, R. (1985). Biological control of leafy spurge
in North America. In Leafy Spurge (A. K. Watson, ed.), pp. 79–92. Champaign, IL: Weed Science Society of America. Leitch, J. A., Leistritz, F. L. and Bangsund, D. A. (1996). Economic effect of leafy spurge in the Upper Great Plains: methods, models, and results. Impact Assessment 14, 419–433. McClay, A. S., Cole, D. E., Harris, P. and Richardson, C. J. (1995). Biological Control of Leafy Spurge in Alberta: Progress and Prospects. Report AECV95-R2. Vegreville, Alberta: Alberta Environmental Centre. Messersmith, C. G., Lym, R. G. and Galitz, D. S. (1985). Biology of leafy spurge. In Leafy Spurge (A. K. Watson, ed.), pp. 42–56. Champaign, IL: Weed Science Society of America. Pannell, D. J. (1994). Economic justification for government involvement in weed management: a catalogue of market failures. Plant Protection Quarterly 9, 131–137. Ribaudo, M. O. (1989). Water Quality Benefits from the Conservation Reserve Program. Agr. Econ. Report No. 606. Washington, DC: USDA, Economic Research Service. Rola, A. C. and Sanchez, F. F. (1992). The economics of integrated pest management: theory and empirical evidence in rice in the Philippines. The Philippine Entomologist 8, 1193–1212. Wallace, N. M., Leitch, J. A. and Leistritz, F. L. (1992). Economic impact of leafy spurge on North Dakota wildland. North Dakota Farm Research 49, 9–13. Watson, A. K. (1985). Integrated management of leafy spurge. In Leafy Spurge (A. K. Watson, ed.). Champaign, IL: Weed Science Society of America.
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