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Incorporating water goals into forest management decisions at a local level
Forest Ecology and Management 143 (2001) 87±93
Incorporating water goals into forest management decisions at a local level Mark J. Twerya,*, James W. Hornbeckb a
USDA Forest Service, Northeastern Research Station, PO Box 968, Burlington, VT 05402-0968, USA b USDA Forest Service, Northeastern Research Station, Durham, NH 03824, USA
Abstract Silvicultural practices are important factors in determining water yield and quality from forested watersheds. Similarly, goals for water yield and quality signi®cantly in¯uence the acceptability of various silvicultural practices. Developed through a process of consulting experts in various subspecialties of natural resource management, the NED1 decision support software is designed to provide a structure for project-level analysis of management alternatives based on identi®ed goals. Using this software, one can analyze forest conditions in the northeastern United States with respect to water, wildlife, timber production, visual quality, and general ecological goals. Water quantity goals include increasing water ¯ow, maintaining a minimum ¯ow, and limiting peak ¯ow. Water quality goals include intensive watercourse protection, wetlands protection, riparian area management, cold-water ®sh habitat, and warm-water ®sh habitat. In all cases, a minimum goal of obeying the law by following statutory best management practices (BMPs) is implied, whether or not one selects another water goal. Given a set of goals, a user of the NED system can analyze which goals are met under alternative silvicultural prescriptions or other activities and resolve which goals may or may not be compatible with each other. Published by Elsevier Science B.V. Keywords: Water quality; Water yield; Decision-support systems; Forest management
1. NED background Forestry is a social activity in which people interact with ecological processes to ful®ll social goals. Some of these goals are related to ecosystem functions, forest products, community vitality, recreational
* Corresponding author. Tel.: 1-802-951-6771, ext. 1040; fax: 1-802-951-6368. E-mail address: [email protected] (M.J. Twery). 1 NED is a simple, easy-to-remember name for a group of software products. Originally it was used as an acronym for the northeast decision model. However, since the software is no longer restricted to the northeast and is not truly a model, the name is technically no longer an acronym, but has been retained as a mnemonic device because of its simplicity and name recognition.
0378-1127/01/$ ± see front matter Published by Elsevier Science B.V. PII: S 0 3 7 8 - 1 1 2 7 ( 0 0 ) 0 0 5 0 8 - 9
activities, aesthetic and spiritual values and experiences, and cultural and historical values; some of these goals are those of an individual landowner; and some are interpreted by public land managers for society as a whole. Goals must be de®ned before appropriate actions can be determined. From this premise NED focuses on goal de®nition as the organizing principle of analysis and management recommendations. Helping people understand the consequences of their activities on the land is an important part of improving decisions they make with respect to natural resource management. Although there is extensive information on the effects of various management actions on ecological systems, often it is scattered in scienti®c literature, single-resource oriented, and dif®cult to understand. Decision-support software
88
M.J. Twery, J.W. Hornbeck / Forest Ecology and Management 143 (2001) 87±93
such as NED is one approach to making this vast store of knowledge available, accessible, and useful to people managing natural resources (Oliver and Twery, 1999). NED is a collection of software products intended to help resource managers develop goals, assess current and future conditions, and produce sustainable management plans for forest properties (Twery et al., 2000). NED includes specialized programs that help landowners identify and articulate management goals, help foresters evaluate a timber inventory and estimate future growth, or help anyone interested to understand the relationships between wildlife species and their habitats. NED also includes an integrated program that allows evaluation of multiple management goals and identi®es tradeoffs among potentially incompatible goals or activities. Silviculture often heads the list of tools used by resource managers to achieve their goals. In its broadest sense, silviculture includes any manipulation of forest vegetation, either direct or indirect. The most direct and most traditional method familiar to foresters is cutting trees, but planting, burning, and other activities also are part of silviculture. NED attempts to provide as much information as possible to a user about possible management goals for a particular property, the conditions necessary to meet those goals, and possible silvicultural activities that can help move conditions in the forest closer to the desired ones (Twery et al., 2000). The NED concept is to use an original prescription design system to incorporate management goals for multiple objectives, analyze current forest conditions, recommend management alternatives, and predict future conditions under different alternatives. NED is designed to include a long-term, landscape-level view of the forest as an interconnected ecosystem that is too complex to understand at every level but which still requires management. Recommendations for potential treatments involve information on all resources affected and provide plausible options from which a manager may choose. The technique involves de®ning a management area of interest, establishing goals for the area, identifying conditions necessary to meet each goal, and identifying conditions that can be met in conjunction with others, from most restrictive to least restrictive. The process begins with the selection of management goals, for any or all of ®ve resources: visual
quality, wildlife, water, wood production, and general ecological objectives. These goals are de®ned for a management unit at a scale from one to many stands, generally within the range 5±5000 ha. Committees of experts in each of the speci®c resources have de®ned the conditions necessary to meet the speci®ed goals, and have determined common variables to allow consistent evaluation of the conditions across goals. This integrated evaluation is a key element in the process of determining acceptable prescriptions and evaluating whether different alternative actions across the entire area will provide the desired conditions. This paper focuses on speci®c goals for water quality and quantity in NED and the process by which they were developed. The rules are not comprehensive and all-inclusive, but they do represent the best estimation by watershed management experts in the northeastern United States of what water goals can be described clearly and how they can be achieved in eastern forests. 1.1. Expert committees Committees of experts in each of the resource specialties to be addressed in NED were organized to develop the information necessary for a multipleresource system (Rauscher et al., 1995). These committees consist of 8±20 well-established professionals in a particular discipline such as wildlife management, silviculture, or watershed management. Each committee included a mix of research scientists and practitioners. Each committee also had a speci®c individual charged with coordinating the work of the committee, either a postdoctoral associate, a cooperating university researcher, or a Forest Service scientist. The coordinators of the NED project participated in all meetings. Within each of the committees a series of meetings and correspondences led to the de®nition of potential desirable goals for that particular resource, plus a description of conditions necessary to achieve each goal. This process was considerably easier for some resources than others. For example, silviculturists de®ning timber goals were very comfortable specifying measures of conditions that would meet the needs for growing wood ®ber, but wildlife biologists had a much more dif®cult time de®ning measures of habitat quality for particular desired species.
M.J. Twery, J.W. Hornbeck / Forest Ecology and Management 143 (2001) 87±93
Initial development of the water component is described by Hornbeck and Smith (1997). After several rounds of discussion within the expert committees, initial de®nition of the particular resource goals was suf®cient to begin ®tting them together. The identi®cation of common terms with which to de®ne conditions was an important step in the process, and is still undergoing re®nement. For this step, we have created a collaborative group, known as the NED core team, with at least one representative from each resource committee. In regular meetings and correspondence over several years this group has de®ned the structure of the NED analysis approach. 1.2. Integration Integration of the varying resource goals is accomplished by functionally de®ning conditions required in the forest to meet each speci®ed goal and requiring conditions to be de®ned with common, measurable values. These speci®ed conditions, labeled in the system as ``desired future conditions'' or DFCs, provide a basis for analysis that can determine which goals may be compatible or in con¯ict. Because conditions can vary through both time and space independent of management activities, the ranges of acceptable conditions need to be speci®ed across time and space. An iterative process of comparing conditions speci®ed by each of several goals may be needed to arrive at a set of achievable conditions that will satisfy the full set, or to clarify that some speci®c goals may simply be incompatible. The integrative process of DFC de®nition and resolution of compatibility is ongoing and involves representatives from multiple disciplines. For example, the goals of increasing water yield and maintaining a closed, high forest canopy are not possible to maintain simultaneously in one location. The initial approach to identi®cation of goal compatibility and con¯ict is represented in the goal comparison matrix contained in the Forest Stewardship Planning Guide (Alban et al., 1995), one of the early NED software products. 2. Water goals Forests play an important role in the quantity and quality of surface and ground water systems. The United States Clean Water Act (1948, 1972, 1987)
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requires that all forest management activities comply with regulations developed at state levels to protect the quality of forest streams. Beyond this mandated protection of water quality, some landowners may have more speci®c objectives for water resources. For example, managers of municipal watersheds may want to increase low ¯ow volumes by reducing vegetative cover, or forest managers in ¯ood prone areas may want to minimize changes in peak ¯ows. Others may want to give special consideration to managing wetlands and streamside (riparian) zones or enhancing ®sh habitat. NED provides several water quantity and water quality objectives to address these and other water goals. 2.1. Water quality goals 2.1.1. Do nothing except obey the law This and all other choices will provide a contact for obtaining assistance and information, and a listing of state and/or local best management practices (BMPs) or other forms of regulation that must be followed to protect water quality and wetlands during forest use. If this goal is selected, there will be no limitations generated by the model on choice of silvicultural systems or treatments that may be recommended for other resource goals. However, limitations may be imposed external to the model for the purpose of complying with BMPs of a speci®c locality. BMPs generally include maintaining buffer strips along streams and around bodies of water; minimizing overland ¯ow and sedimentation; minimizing changes in water temperature; and minimizing nutrients leached from soil into water. 2.1.2. Provide intensive protection for wetlands as required by law Forest managers are required by law to follow special precautions on wetlands, but compliance is challenging. De®nitions of wetlands are not always consistent and delineation of wetlands can be subjective (National Research Council, 1995; Welsch et al., 1995). For example, some states use wetland plants, while others use soils to delineate wetlands. Information provided regarding this goal will help a manager determine if a wetland is included in the management unit and will provide guidelines for managing wetlands in compliance with laws and
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regulations. Wetland silviculture is subject to regulations under the Federal Clean Water Act. Selection of this goal will provide information to help the landowner determine if their management unit has a wetland, and will also provide guidelines for managing wetlands to comply with laws and regulations, and for protecting both the site and water quality. Within the NED-1 program (Twery et al., 2000), conditions are evaluated in two steps. First, a stand will be considered a wetland stand if one or more of the following conditions exist: (1) at least 20% of the area is identi®ed by ®eld survey as within a riparian zone; (2) at least 50% of the area is identi®ed by ®eld survey as wetland; (3) plants identi®ed as obligate wetland species are present on two or more sample plots within the stand; or (4) two or more sample plots are identi®ed by survey as being within a riparian zone. Second, to satisfy the goal of protecting wetlands, wetland stands must meet all of the following conditions: (1) Relative density of overstory trees must be at least 70%. Relative density (Stout and Nyland, 1986) is a measure of stocking that estimates the ``crowdedness'' of overstory trees such that a fully stocked stand is considered to be at 100% relative density.; (2) no more than 10% of sample plots can be classi®ed as open; (3) coarse woody debris must be present; and (4) canopy closure must be at least 25%. Special treatments that may be called for by this goal include maintaining buffer strips; maintaining at least 70% stocking in the buffer strips; allowing a few mature trees per hectare to die in place; and creating small openings less than 0.1 ha in size. 2.1.3. Enhance habitat for warm-water or cold-water fish Selecting one of these goals will lead to special recommendations for treatment of the vegetation along streams and around lakes, ponds, and wetlands. Depending on whether the goal is warm- or cold-water ®sh, recommendations will address compatibility with other uses, retention or removal of trees to obtain desired levels of shade, restrictions on harvesting methods in the riparian zone to control erosion and sedimentation, prescriptions to optimize growth and maturation of selected trees, and options for achieving desired levels of organic matter and woody debris in streams. These goals are best addressed on a watershed rather than a management unit basis. The
special recommendations primarily affect riparian zones and not the silvicultural systems selected for the remainder of the management unit. To achieve the goal of enhancing habitat for warmwater ®sh, all stands identi®ed as containing riparian zones must satisfy the following conditions: (1) sources of coarse woody debris must be present; (2) coarse woody debris must be present in the water; (3) canopy closure in the riparian area must be below 70%; (4) no more than 10% of sample plots can be classi®ed as open; and (5) relative density of the overstory within the riparian area must be below 70%. Treatments for enhancing warm-water ®sh habitat may include: (1) maintaining buffer strips; (2) removing some trees to allow more sunlight to reach the water surface; (3) allowing a few mature trees to die in place; and (4) prohibiting livestock from entering the buffer strip. To achieve the goal of enhancing habitat for coldwater ®sh, all stands containing streams or riparian zones must satisfy the following conditions: (1) sources of coarse woody debris must be present; (2) coarse woody debris must be present in the water; (3) canopy closure in the riparian area must be above 25%; (4) no more than 10% of sample plots can be classi®ed as open; and (5) relative density of the overstory within the riparian area must be at least 70%. Treatments for enhancing cold-water ®sh habitat may include: (1) maintaining buffer strips with at least 70% relative density; (2) allowing a few mature trees to die in place; and (3) creating small openings less than 0.1 ha in size. 2.1.4. Provide intensive protection for riparian areas The riparian area is the transition between aquatic and terrestrial characteristics of soil, water, vegetation, and landform. As such, they contain unique species associations and are especially important to protecting water quality as well as the food chain and physical structure of aquatic habitats. State BMPs normally require buffer strips of one or more tree heights on both sides of perennial stream channels to protect the stream and riparian area. NED users selecting a riparian area management goal for streams and lakes will be given more detailed information and recommendations for designing riparian stands or buffer strips and managing within them. Selection of this goal will not affect the silvicultural system selected for the management unit as a whole, but may result in the delineation
M.J. Twery, J.W. Hornbeck / Forest Ecology and Management 143 (2001) 87±93
of a riparian management unit. Such units also may incorporate land areas surrounding intermittent streams. To achieve the goal of intensive protection for riparian areas, all stands identi®ed as containing riparian zones must satisfy the following conditions: (1) relative density of the overstory within the riparian area must be at least 70%; (2) no more than 10% of sample plots can be classi®ed as open; (3) coarse woody debris must be present; and canopy closure in the riparian area must be above 25%. Treatments for protecting riparian areas may include: (1) maintaining buffer strips with at least 70% relative density; (2) allowing a few mature trees to die in place; and (3) creating small openings less than 0.1 ha in size. 2.1.5. Provide intensive protection for water quality beyond BMPs This goal could be selected by municipal watershed managers or for sites receiving water-based recreational use. Added precautions in the form of more rigorous applications of BMPs will be recommended. Examples would be applying gravel to all roads left open to the public, locating all roads and skid trails farther from streams than might normally be recommended, and mulching and seeding all exposed soil at stream crossings as soon as crossing structures are installed and also immediately upon their removal. This goal is likely to add to short-term costs of operations on the management unit. To achieve the goal of intensive water quality protection, all stands containing water or riparian areas must maintain relative density of the overstory at 70% or higher throughout the stand, including the riparian zone. Additional requirements applied to treatment areas include (1) maintaining extra wide buffer strips; (2) maintaining plant cover at all times; (3) encouraging rapid establishment of regeneration following treatments; (4) minimizing disturbance, erosion, and sedimentation; (5) restricting use of chemicals; (6) restricting road building or use; and (7) restricting beaver activity. 2.2. Water quantity goals 2.2.1. Do nothing except obey the law Just as in the water quality goal set, the water quantity goal set includes the possibility that a
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manager may not have any speci®c goals for water production. Thus, the minimum water quantity goal is to stay within the limits of conditions and practices required by law as de®ned by the BMPs for each state. 2.2.2. Increase water yields This goal is designed for managers who desire to increase water yield to streams and reservoirs during periods of low ¯ows. Increases during low ¯ow periods will lead to greater overall water yield and also may increase the magnitude of high-frequency ¯ood events. This occurs because soil water content in recently harvested areas is higher than in fully stocked stands. The treatment effect tends to be short-lived (Satterlund and Adams, 1992) and as storm size or snowmelt volume increases, this difference is less important (Verry, 1986). In the absence of other management goals, the recommended silvicultural systems will provide optimum reduction in evapotranspiration. Generally this choice will be short-rotation, even-age silviculture with clearcutting as the harvest method. All harvesting operations must comply with BMPs. If other resource goals are selected, the silvicultural system will be a compromise, but must include clearcut openings on short harvest cycles. To achieve the goal of increasing water yield, a management unit must contain a minimum of 20 ha and all stands contained in the management unit and identi®ed as adjacent to water, wetlands, or buffers must meet the following stand-level requirements: (1) evergreen species should comprise less than 30% of the basal area; (2) relative density of the overstory should be less than 70%; and (3) if the stand is in the seedling size class, relative density should be not more than 30% and sprouts should comprise less than 30% of the stand. Treatments may include: (1) reducing stand stocking to below 70% relative density; (2) using short rotations; (3) encouraging hardwood species; and (4) encouraging regeneration from seedlings. 2.2.3. Maintain or exceed existing low flows Selection of this goal implies that the manager desires to protect against reductions in low ¯ow levels during the next rotation. Changes in species, such as converting hardwoods to softwoods, can reduce water yield, especially during periods of low ¯ow. Silvicultural systems and treatments that would ultimately result in reduced ¯ow, especially at low ¯ow levels,
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will be recommended against if this goal is selected. To satisfy the goal of maintaining minimum ¯ows, the following conditions must be met on all stands containing or adjacent to water: (1) evergreen species should comprise less than 30% of the basal area; (2) relative density of the overstory should be less than 70%; and (3) if the stand is in the seedling size class, relative density should be not more than 30% and sprouts should comprise less than 30% of the stand. Treatments may include: (1) reducing stand stocking to below 70% relative density; (2) using short cutting cycles; (3) using short rotations; (4) encouraging hardwood species; (5) encouraging regeneration from seedlings rather than sprouts; and avoiding conversion to softwood species from hardwood species. 2.2.4. Limit peak (flood) flows Selection of this goal implies that the manager wants to minimize the volume and rate of ¯ow during peak periods. Forests are the best vegetative cover in the northeastern United States to maximize soil water de®cits and minimize peak ¯ows. Timber harvesting affects peak ¯ows in several ways. There is less opportunity for storage of precipitation in the years immediately after harvest, so peak ¯ows may be increased. Also, compaction and careless layout of roads and skid trails can increase overland ¯ow and add volume to peak ¯ows. On the other hand, where snowpacks occur, harvesting can actually reduce peak ¯ows by causing earlier snowmelt and associated stream¯ow compared to uncut areas. In the absence of other management goals, this choice recommends against cutting. If other resource goals also are selected, the silvicultural system will be a compromise, weighted toward less intensive harvests. To achieve the goal of limiting peak ¯ows, the overall proportion of area in the management unit classi®ed as non-forest or forest openings must be less than 25% and all stands within the unit must meet the following conditions: (1) maintain overstory relative density of at least 70%; (2) maintain canopy closure of at least 25%, and (3) at least some evergreen tree species must be present. Treatments may include: (1) maximizing stand stocking and maintaining it above 70% relative density; (2) using long cutting cycles; (3) using long rotations; (4) encouraging conifer species; and maintaining less than 25% of the area in openings or trees less than 10 years old.
2.2.5. Restore hydrologic function to previously disturbed lands This goal can be applied to lands that have impaired soil properties or erosion problems due to ®re or other disturbances such as mining, tilling, or grazing. The objective is to improve soil structure, in®ltration capacity, and moisture storage through reforestation. To begin to restore the hydrologic function of the soil it is important to maximize leaf litter and coarse woody debris, and to slow the decomposition rate. Therefore, no cutting, burning, or disturbing of the litter layer is preferred through the ®rst 100 years after disturbance. High stocking, long rotations, and long cutting cycles are also recommended. The current software is not able to address this goal directly because the standard inventory of vegetation and site conditions does not produce appropriate measures to evaluate hydrologic function. Future development will address this issue. 2.3. Goal integration Integration of the water goals with the other goals identi®ed by a NED user is accomplished through use of the commonly developed and de®ned variables computed from inventories on the property. Variables such as relative density, percent canopy closure, presence of coarse woody debris, for example, are the same ones used to evaluate timber production, wildlife habitat, and visual qualities. This commonality enables the computer program to evaluate the con¯ict or compatibility between any two goals. 3. Conclusion NED provides an extensive set of decision-support tools for forest management for multiple values and purposes. By doing so, we hope to improve the integration and synthesis of information for people making forest management decisions. We are not attempting to provide tools for regional or national policy makers, but rather are focusing on a more local context Ð deciding how best to manage a particular piece of forest. Comprehensiveness is achieved through the development and distribution of a variety of different tools, each of which has a speci®c range of applicability. The water quality and quantity goals
M.J. Twery, J.W. Hornbeck / Forest Ecology and Management 143 (2001) 87±93
provide information that can be used as part of a comprehensive analysis of a management area and may improve the likelihood that a land manager's decisions and subsequent actions will produce the desired results. NED programs are not designed to automate management prescriptions, but to shed light on complex problems and encourage the user's own capabilities and judgment. The water goal portion of the programs will enable managers to understand the consequences of their planned actions better and to use that information to improve actual conditions. It also fosters improved communication among managers and their clients or constituents about the values that may be traded away to meet higher priority needs. Acknowledgements Many people have contributed to the development of NED software, through direct development efforts, participation on committees, testing of preliminary versions, or providing ®nancial or moral support. Laura M. Alban and Deborah J. Bennett assisted with synthesis and organization of material used in this paper. We are also indebted to R. Peter Kollasch, Scott A. Thomasma, Susan L. Stout, David S. deCalesta, J. Morgan Grove, H. Michael Rauscher, Eric Gustafson, Helene Cleveland, Robert Smith, James F. Palmer, Robin E. Hoffman, Barbara McGuinness, Neil Lamson, Linda E. Thomasma, Ralph Nyland, Ningyu Chen, Geneho Kim, Donald Nute, and especially to David A. Marquis, whose vision and energy conceived the project and sustained its early development.
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References Alban, L.M., Thomasma, S.A., Twery, M.J., 1995. Forest Stewardship Planning Guide User's Manual (Version 1.00) (Computer program). USDA Forest Service General Technical Report NE203. Northeastern Forest Experiment Station, Radnor, PA, 15 pp. (Computer disk). Hornbeck, J.W., Smith, R.B., 1997. A water resource decision model for forest managers. Agri. For. Meteorol. 84, 83±88. National Research Council, 1995. Wetlands: Characteristics and Boundaries. National Academic Press, Washington, DC, p. 306. Oliver, C.D., Twery, M.J., 1999. Decision support systems/models and analyses. In: Johnson, N.C., Malk, A.J., Sexton, W.T., Szaro, R. (Eds.), Ecological Stewardship: A Common Reference For Ecosystem Management, Vol. 3. Elsevier, Oxford, pp. 661±685. Rauscher, H.M., Twery, M., Palmer, J., Hoffman, R., Stout, S., Steinman, J., Kollasch, P., Bennett, D., Thomasma, L., Hornbeck, J., Worth, C.V., 1995. Northeast decision model design document. AI Appl. (Electronic insert) 9 (3), 85±86. Satterlund, D.R., Adams, P.W., 1992. Wildland Watershed Management, 2nd Edition. Wiley, New York, 436 pp. Stout, S.L., Nyland, R.D., 1986. Role of species composition in relative density measurements in Allegheny hardwoods. Can. J. For. Res. 16, 574±579. Twery, M. J., Rauscher, H.M., Bennett, D.J., Thomasma, S.A., Stout, S.L., Palmer, J.F., Hoffman, R.E., DeCalesta, D.S., Gustafson, E., Cleveland, H. et al., 2000. NED-1: integrated analyses for forest stewardship decisions. Comput. Elect. Agric. (27) 1±3, 167±193. United States Clean Water Act of 1948, 1972, and 1987, P.L. 80845, P.L. 92-500, P.L. 100-4, 33 USC 1251, 1254, 1323, 1324, 1329, 1342, 1344. Verry, E.S., 1986. Forest harvesting and water: the Lake States experience. Water Resour. Bull. 22 (6), 1039±1047. Welsch, D.J., Smart, D.L., Boyer, J.N., Minkin, P., Smith, H.C., McCandless, T.L., 1995. Forested wetlands: functions, benefits, and the use of best management practices. Bull. NA-PR-01-95. USDA Forest Service, Northeastern Area State and Private Forestry, Radnor, PA, 62 pp.
Incorporating water goals into forest management decisions at a local level Mark J. Twerya,*, James W. Hornbeckb a
USDA Forest Service, Northeastern Research Station, PO Box 968, Burlington, VT 05402-0968, USA b USDA Forest Service, Northeastern Research Station, Durham, NH 03824, USA
Abstract Silvicultural practices are important factors in determining water yield and quality from forested watersheds. Similarly, goals for water yield and quality signi®cantly in¯uence the acceptability of various silvicultural practices. Developed through a process of consulting experts in various subspecialties of natural resource management, the NED1 decision support software is designed to provide a structure for project-level analysis of management alternatives based on identi®ed goals. Using this software, one can analyze forest conditions in the northeastern United States with respect to water, wildlife, timber production, visual quality, and general ecological goals. Water quantity goals include increasing water ¯ow, maintaining a minimum ¯ow, and limiting peak ¯ow. Water quality goals include intensive watercourse protection, wetlands protection, riparian area management, cold-water ®sh habitat, and warm-water ®sh habitat. In all cases, a minimum goal of obeying the law by following statutory best management practices (BMPs) is implied, whether or not one selects another water goal. Given a set of goals, a user of the NED system can analyze which goals are met under alternative silvicultural prescriptions or other activities and resolve which goals may or may not be compatible with each other. Published by Elsevier Science B.V. Keywords: Water quality; Water yield; Decision-support systems; Forest management
1. NED background Forestry is a social activity in which people interact with ecological processes to ful®ll social goals. Some of these goals are related to ecosystem functions, forest products, community vitality, recreational
* Corresponding author. Tel.: 1-802-951-6771, ext. 1040; fax: 1-802-951-6368. E-mail address: [email protected] (M.J. Twery). 1 NED is a simple, easy-to-remember name for a group of software products. Originally it was used as an acronym for the northeast decision model. However, since the software is no longer restricted to the northeast and is not truly a model, the name is technically no longer an acronym, but has been retained as a mnemonic device because of its simplicity and name recognition.
0378-1127/01/$ ± see front matter Published by Elsevier Science B.V. PII: S 0 3 7 8 - 1 1 2 7 ( 0 0 ) 0 0 5 0 8 - 9
activities, aesthetic and spiritual values and experiences, and cultural and historical values; some of these goals are those of an individual landowner; and some are interpreted by public land managers for society as a whole. Goals must be de®ned before appropriate actions can be determined. From this premise NED focuses on goal de®nition as the organizing principle of analysis and management recommendations. Helping people understand the consequences of their activities on the land is an important part of improving decisions they make with respect to natural resource management. Although there is extensive information on the effects of various management actions on ecological systems, often it is scattered in scienti®c literature, single-resource oriented, and dif®cult to understand. Decision-support software
88
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such as NED is one approach to making this vast store of knowledge available, accessible, and useful to people managing natural resources (Oliver and Twery, 1999). NED is a collection of software products intended to help resource managers develop goals, assess current and future conditions, and produce sustainable management plans for forest properties (Twery et al., 2000). NED includes specialized programs that help landowners identify and articulate management goals, help foresters evaluate a timber inventory and estimate future growth, or help anyone interested to understand the relationships between wildlife species and their habitats. NED also includes an integrated program that allows evaluation of multiple management goals and identi®es tradeoffs among potentially incompatible goals or activities. Silviculture often heads the list of tools used by resource managers to achieve their goals. In its broadest sense, silviculture includes any manipulation of forest vegetation, either direct or indirect. The most direct and most traditional method familiar to foresters is cutting trees, but planting, burning, and other activities also are part of silviculture. NED attempts to provide as much information as possible to a user about possible management goals for a particular property, the conditions necessary to meet those goals, and possible silvicultural activities that can help move conditions in the forest closer to the desired ones (Twery et al., 2000). The NED concept is to use an original prescription design system to incorporate management goals for multiple objectives, analyze current forest conditions, recommend management alternatives, and predict future conditions under different alternatives. NED is designed to include a long-term, landscape-level view of the forest as an interconnected ecosystem that is too complex to understand at every level but which still requires management. Recommendations for potential treatments involve information on all resources affected and provide plausible options from which a manager may choose. The technique involves de®ning a management area of interest, establishing goals for the area, identifying conditions necessary to meet each goal, and identifying conditions that can be met in conjunction with others, from most restrictive to least restrictive. The process begins with the selection of management goals, for any or all of ®ve resources: visual
quality, wildlife, water, wood production, and general ecological objectives. These goals are de®ned for a management unit at a scale from one to many stands, generally within the range 5±5000 ha. Committees of experts in each of the speci®c resources have de®ned the conditions necessary to meet the speci®ed goals, and have determined common variables to allow consistent evaluation of the conditions across goals. This integrated evaluation is a key element in the process of determining acceptable prescriptions and evaluating whether different alternative actions across the entire area will provide the desired conditions. This paper focuses on speci®c goals for water quality and quantity in NED and the process by which they were developed. The rules are not comprehensive and all-inclusive, but they do represent the best estimation by watershed management experts in the northeastern United States of what water goals can be described clearly and how they can be achieved in eastern forests. 1.1. Expert committees Committees of experts in each of the resource specialties to be addressed in NED were organized to develop the information necessary for a multipleresource system (Rauscher et al., 1995). These committees consist of 8±20 well-established professionals in a particular discipline such as wildlife management, silviculture, or watershed management. Each committee included a mix of research scientists and practitioners. Each committee also had a speci®c individual charged with coordinating the work of the committee, either a postdoctoral associate, a cooperating university researcher, or a Forest Service scientist. The coordinators of the NED project participated in all meetings. Within each of the committees a series of meetings and correspondences led to the de®nition of potential desirable goals for that particular resource, plus a description of conditions necessary to achieve each goal. This process was considerably easier for some resources than others. For example, silviculturists de®ning timber goals were very comfortable specifying measures of conditions that would meet the needs for growing wood ®ber, but wildlife biologists had a much more dif®cult time de®ning measures of habitat quality for particular desired species.
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Initial development of the water component is described by Hornbeck and Smith (1997). After several rounds of discussion within the expert committees, initial de®nition of the particular resource goals was suf®cient to begin ®tting them together. The identi®cation of common terms with which to de®ne conditions was an important step in the process, and is still undergoing re®nement. For this step, we have created a collaborative group, known as the NED core team, with at least one representative from each resource committee. In regular meetings and correspondence over several years this group has de®ned the structure of the NED analysis approach. 1.2. Integration Integration of the varying resource goals is accomplished by functionally de®ning conditions required in the forest to meet each speci®ed goal and requiring conditions to be de®ned with common, measurable values. These speci®ed conditions, labeled in the system as ``desired future conditions'' or DFCs, provide a basis for analysis that can determine which goals may be compatible or in con¯ict. Because conditions can vary through both time and space independent of management activities, the ranges of acceptable conditions need to be speci®ed across time and space. An iterative process of comparing conditions speci®ed by each of several goals may be needed to arrive at a set of achievable conditions that will satisfy the full set, or to clarify that some speci®c goals may simply be incompatible. The integrative process of DFC de®nition and resolution of compatibility is ongoing and involves representatives from multiple disciplines. For example, the goals of increasing water yield and maintaining a closed, high forest canopy are not possible to maintain simultaneously in one location. The initial approach to identi®cation of goal compatibility and con¯ict is represented in the goal comparison matrix contained in the Forest Stewardship Planning Guide (Alban et al., 1995), one of the early NED software products. 2. Water goals Forests play an important role in the quantity and quality of surface and ground water systems. The United States Clean Water Act (1948, 1972, 1987)
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requires that all forest management activities comply with regulations developed at state levels to protect the quality of forest streams. Beyond this mandated protection of water quality, some landowners may have more speci®c objectives for water resources. For example, managers of municipal watersheds may want to increase low ¯ow volumes by reducing vegetative cover, or forest managers in ¯ood prone areas may want to minimize changes in peak ¯ows. Others may want to give special consideration to managing wetlands and streamside (riparian) zones or enhancing ®sh habitat. NED provides several water quantity and water quality objectives to address these and other water goals. 2.1. Water quality goals 2.1.1. Do nothing except obey the law This and all other choices will provide a contact for obtaining assistance and information, and a listing of state and/or local best management practices (BMPs) or other forms of regulation that must be followed to protect water quality and wetlands during forest use. If this goal is selected, there will be no limitations generated by the model on choice of silvicultural systems or treatments that may be recommended for other resource goals. However, limitations may be imposed external to the model for the purpose of complying with BMPs of a speci®c locality. BMPs generally include maintaining buffer strips along streams and around bodies of water; minimizing overland ¯ow and sedimentation; minimizing changes in water temperature; and minimizing nutrients leached from soil into water. 2.1.2. Provide intensive protection for wetlands as required by law Forest managers are required by law to follow special precautions on wetlands, but compliance is challenging. De®nitions of wetlands are not always consistent and delineation of wetlands can be subjective (National Research Council, 1995; Welsch et al., 1995). For example, some states use wetland plants, while others use soils to delineate wetlands. Information provided regarding this goal will help a manager determine if a wetland is included in the management unit and will provide guidelines for managing wetlands in compliance with laws and
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regulations. Wetland silviculture is subject to regulations under the Federal Clean Water Act. Selection of this goal will provide information to help the landowner determine if their management unit has a wetland, and will also provide guidelines for managing wetlands to comply with laws and regulations, and for protecting both the site and water quality. Within the NED-1 program (Twery et al., 2000), conditions are evaluated in two steps. First, a stand will be considered a wetland stand if one or more of the following conditions exist: (1) at least 20% of the area is identi®ed by ®eld survey as within a riparian zone; (2) at least 50% of the area is identi®ed by ®eld survey as wetland; (3) plants identi®ed as obligate wetland species are present on two or more sample plots within the stand; or (4) two or more sample plots are identi®ed by survey as being within a riparian zone. Second, to satisfy the goal of protecting wetlands, wetland stands must meet all of the following conditions: (1) Relative density of overstory trees must be at least 70%. Relative density (Stout and Nyland, 1986) is a measure of stocking that estimates the ``crowdedness'' of overstory trees such that a fully stocked stand is considered to be at 100% relative density.; (2) no more than 10% of sample plots can be classi®ed as open; (3) coarse woody debris must be present; and (4) canopy closure must be at least 25%. Special treatments that may be called for by this goal include maintaining buffer strips; maintaining at least 70% stocking in the buffer strips; allowing a few mature trees per hectare to die in place; and creating small openings less than 0.1 ha in size. 2.1.3. Enhance habitat for warm-water or cold-water fish Selecting one of these goals will lead to special recommendations for treatment of the vegetation along streams and around lakes, ponds, and wetlands. Depending on whether the goal is warm- or cold-water ®sh, recommendations will address compatibility with other uses, retention or removal of trees to obtain desired levels of shade, restrictions on harvesting methods in the riparian zone to control erosion and sedimentation, prescriptions to optimize growth and maturation of selected trees, and options for achieving desired levels of organic matter and woody debris in streams. These goals are best addressed on a watershed rather than a management unit basis. The
special recommendations primarily affect riparian zones and not the silvicultural systems selected for the remainder of the management unit. To achieve the goal of enhancing habitat for warmwater ®sh, all stands identi®ed as containing riparian zones must satisfy the following conditions: (1) sources of coarse woody debris must be present; (2) coarse woody debris must be present in the water; (3) canopy closure in the riparian area must be below 70%; (4) no more than 10% of sample plots can be classi®ed as open; and (5) relative density of the overstory within the riparian area must be below 70%. Treatments for enhancing warm-water ®sh habitat may include: (1) maintaining buffer strips; (2) removing some trees to allow more sunlight to reach the water surface; (3) allowing a few mature trees to die in place; and (4) prohibiting livestock from entering the buffer strip. To achieve the goal of enhancing habitat for coldwater ®sh, all stands containing streams or riparian zones must satisfy the following conditions: (1) sources of coarse woody debris must be present; (2) coarse woody debris must be present in the water; (3) canopy closure in the riparian area must be above 25%; (4) no more than 10% of sample plots can be classi®ed as open; and (5) relative density of the overstory within the riparian area must be at least 70%. Treatments for enhancing cold-water ®sh habitat may include: (1) maintaining buffer strips with at least 70% relative density; (2) allowing a few mature trees to die in place; and (3) creating small openings less than 0.1 ha in size. 2.1.4. Provide intensive protection for riparian areas The riparian area is the transition between aquatic and terrestrial characteristics of soil, water, vegetation, and landform. As such, they contain unique species associations and are especially important to protecting water quality as well as the food chain and physical structure of aquatic habitats. State BMPs normally require buffer strips of one or more tree heights on both sides of perennial stream channels to protect the stream and riparian area. NED users selecting a riparian area management goal for streams and lakes will be given more detailed information and recommendations for designing riparian stands or buffer strips and managing within them. Selection of this goal will not affect the silvicultural system selected for the management unit as a whole, but may result in the delineation
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of a riparian management unit. Such units also may incorporate land areas surrounding intermittent streams. To achieve the goal of intensive protection for riparian areas, all stands identi®ed as containing riparian zones must satisfy the following conditions: (1) relative density of the overstory within the riparian area must be at least 70%; (2) no more than 10% of sample plots can be classi®ed as open; (3) coarse woody debris must be present; and canopy closure in the riparian area must be above 25%. Treatments for protecting riparian areas may include: (1) maintaining buffer strips with at least 70% relative density; (2) allowing a few mature trees to die in place; and (3) creating small openings less than 0.1 ha in size. 2.1.5. Provide intensive protection for water quality beyond BMPs This goal could be selected by municipal watershed managers or for sites receiving water-based recreational use. Added precautions in the form of more rigorous applications of BMPs will be recommended. Examples would be applying gravel to all roads left open to the public, locating all roads and skid trails farther from streams than might normally be recommended, and mulching and seeding all exposed soil at stream crossings as soon as crossing structures are installed and also immediately upon their removal. This goal is likely to add to short-term costs of operations on the management unit. To achieve the goal of intensive water quality protection, all stands containing water or riparian areas must maintain relative density of the overstory at 70% or higher throughout the stand, including the riparian zone. Additional requirements applied to treatment areas include (1) maintaining extra wide buffer strips; (2) maintaining plant cover at all times; (3) encouraging rapid establishment of regeneration following treatments; (4) minimizing disturbance, erosion, and sedimentation; (5) restricting use of chemicals; (6) restricting road building or use; and (7) restricting beaver activity. 2.2. Water quantity goals 2.2.1. Do nothing except obey the law Just as in the water quality goal set, the water quantity goal set includes the possibility that a
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manager may not have any speci®c goals for water production. Thus, the minimum water quantity goal is to stay within the limits of conditions and practices required by law as de®ned by the BMPs for each state. 2.2.2. Increase water yields This goal is designed for managers who desire to increase water yield to streams and reservoirs during periods of low ¯ows. Increases during low ¯ow periods will lead to greater overall water yield and also may increase the magnitude of high-frequency ¯ood events. This occurs because soil water content in recently harvested areas is higher than in fully stocked stands. The treatment effect tends to be short-lived (Satterlund and Adams, 1992) and as storm size or snowmelt volume increases, this difference is less important (Verry, 1986). In the absence of other management goals, the recommended silvicultural systems will provide optimum reduction in evapotranspiration. Generally this choice will be short-rotation, even-age silviculture with clearcutting as the harvest method. All harvesting operations must comply with BMPs. If other resource goals are selected, the silvicultural system will be a compromise, but must include clearcut openings on short harvest cycles. To achieve the goal of increasing water yield, a management unit must contain a minimum of 20 ha and all stands contained in the management unit and identi®ed as adjacent to water, wetlands, or buffers must meet the following stand-level requirements: (1) evergreen species should comprise less than 30% of the basal area; (2) relative density of the overstory should be less than 70%; and (3) if the stand is in the seedling size class, relative density should be not more than 30% and sprouts should comprise less than 30% of the stand. Treatments may include: (1) reducing stand stocking to below 70% relative density; (2) using short rotations; (3) encouraging hardwood species; and (4) encouraging regeneration from seedlings. 2.2.3. Maintain or exceed existing low flows Selection of this goal implies that the manager desires to protect against reductions in low ¯ow levels during the next rotation. Changes in species, such as converting hardwoods to softwoods, can reduce water yield, especially during periods of low ¯ow. Silvicultural systems and treatments that would ultimately result in reduced ¯ow, especially at low ¯ow levels,
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will be recommended against if this goal is selected. To satisfy the goal of maintaining minimum ¯ows, the following conditions must be met on all stands containing or adjacent to water: (1) evergreen species should comprise less than 30% of the basal area; (2) relative density of the overstory should be less than 70%; and (3) if the stand is in the seedling size class, relative density should be not more than 30% and sprouts should comprise less than 30% of the stand. Treatments may include: (1) reducing stand stocking to below 70% relative density; (2) using short cutting cycles; (3) using short rotations; (4) encouraging hardwood species; (5) encouraging regeneration from seedlings rather than sprouts; and avoiding conversion to softwood species from hardwood species. 2.2.4. Limit peak (flood) flows Selection of this goal implies that the manager wants to minimize the volume and rate of ¯ow during peak periods. Forests are the best vegetative cover in the northeastern United States to maximize soil water de®cits and minimize peak ¯ows. Timber harvesting affects peak ¯ows in several ways. There is less opportunity for storage of precipitation in the years immediately after harvest, so peak ¯ows may be increased. Also, compaction and careless layout of roads and skid trails can increase overland ¯ow and add volume to peak ¯ows. On the other hand, where snowpacks occur, harvesting can actually reduce peak ¯ows by causing earlier snowmelt and associated stream¯ow compared to uncut areas. In the absence of other management goals, this choice recommends against cutting. If other resource goals also are selected, the silvicultural system will be a compromise, weighted toward less intensive harvests. To achieve the goal of limiting peak ¯ows, the overall proportion of area in the management unit classi®ed as non-forest or forest openings must be less than 25% and all stands within the unit must meet the following conditions: (1) maintain overstory relative density of at least 70%; (2) maintain canopy closure of at least 25%, and (3) at least some evergreen tree species must be present. Treatments may include: (1) maximizing stand stocking and maintaining it above 70% relative density; (2) using long cutting cycles; (3) using long rotations; (4) encouraging conifer species; and maintaining less than 25% of the area in openings or trees less than 10 years old.
2.2.5. Restore hydrologic function to previously disturbed lands This goal can be applied to lands that have impaired soil properties or erosion problems due to ®re or other disturbances such as mining, tilling, or grazing. The objective is to improve soil structure, in®ltration capacity, and moisture storage through reforestation. To begin to restore the hydrologic function of the soil it is important to maximize leaf litter and coarse woody debris, and to slow the decomposition rate. Therefore, no cutting, burning, or disturbing of the litter layer is preferred through the ®rst 100 years after disturbance. High stocking, long rotations, and long cutting cycles are also recommended. The current software is not able to address this goal directly because the standard inventory of vegetation and site conditions does not produce appropriate measures to evaluate hydrologic function. Future development will address this issue. 2.3. Goal integration Integration of the water goals with the other goals identi®ed by a NED user is accomplished through use of the commonly developed and de®ned variables computed from inventories on the property. Variables such as relative density, percent canopy closure, presence of coarse woody debris, for example, are the same ones used to evaluate timber production, wildlife habitat, and visual qualities. This commonality enables the computer program to evaluate the con¯ict or compatibility between any two goals. 3. Conclusion NED provides an extensive set of decision-support tools for forest management for multiple values and purposes. By doing so, we hope to improve the integration and synthesis of information for people making forest management decisions. We are not attempting to provide tools for regional or national policy makers, but rather are focusing on a more local context Ð deciding how best to manage a particular piece of forest. Comprehensiveness is achieved through the development and distribution of a variety of different tools, each of which has a speci®c range of applicability. The water quality and quantity goals
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provide information that can be used as part of a comprehensive analysis of a management area and may improve the likelihood that a land manager's decisions and subsequent actions will produce the desired results. NED programs are not designed to automate management prescriptions, but to shed light on complex problems and encourage the user's own capabilities and judgment. The water goal portion of the programs will enable managers to understand the consequences of their planned actions better and to use that information to improve actual conditions. It also fosters improved communication among managers and their clients or constituents about the values that may be traded away to meet higher priority needs. Acknowledgements Many people have contributed to the development of NED software, through direct development efforts, participation on committees, testing of preliminary versions, or providing ®nancial or moral support. Laura M. Alban and Deborah J. Bennett assisted with synthesis and organization of material used in this paper. We are also indebted to R. Peter Kollasch, Scott A. Thomasma, Susan L. Stout, David S. deCalesta, J. Morgan Grove, H. Michael Rauscher, Eric Gustafson, Helene Cleveland, Robert Smith, James F. Palmer, Robin E. Hoffman, Barbara McGuinness, Neil Lamson, Linda E. Thomasma, Ralph Nyland, Ningyu Chen, Geneho Kim, Donald Nute, and especially to David A. Marquis, whose vision and energy conceived the project and sustained its early development.
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References Alban, L.M., Thomasma, S.A., Twery, M.J., 1995. Forest Stewardship Planning Guide User's Manual (Version 1.00) (Computer program). USDA Forest Service General Technical Report NE203. Northeastern Forest Experiment Station, Radnor, PA, 15 pp. (Computer disk). Hornbeck, J.W., Smith, R.B., 1997. A water resource decision model for forest managers. Agri. For. Meteorol. 84, 83±88. National Research Council, 1995. Wetlands: Characteristics and Boundaries. National Academic Press, Washington, DC, p. 306. Oliver, C.D., Twery, M.J., 1999. Decision support systems/models and analyses. In: Johnson, N.C., Malk, A.J., Sexton, W.T., Szaro, R. (Eds.), Ecological Stewardship: A Common Reference For Ecosystem Management, Vol. 3. Elsevier, Oxford, pp. 661±685. Rauscher, H.M., Twery, M., Palmer, J., Hoffman, R., Stout, S., Steinman, J., Kollasch, P., Bennett, D., Thomasma, L., Hornbeck, J., Worth, C.V., 1995. Northeast decision model design document. AI Appl. (Electronic insert) 9 (3), 85±86. Satterlund, D.R., Adams, P.W., 1992. Wildland Watershed Management, 2nd Edition. Wiley, New York, 436 pp. Stout, S.L., Nyland, R.D., 1986. Role of species composition in relative density measurements in Allegheny hardwoods. Can. J. For. Res. 16, 574±579. Twery, M. J., Rauscher, H.M., Bennett, D.J., Thomasma, S.A., Stout, S.L., Palmer, J.F., Hoffman, R.E., DeCalesta, D.S., Gustafson, E., Cleveland, H. et al., 2000. NED-1: integrated analyses for forest stewardship decisions. Comput. Elect. Agric. (27) 1±3, 167±193. United States Clean Water Act of 1948, 1972, and 1987, P.L. 80845, P.L. 92-500, P.L. 100-4, 33 USC 1251, 1254, 1323, 1324, 1329, 1342, 1344. Verry, E.S., 1986. Forest harvesting and water: the Lake States experience. Water Resour. Bull. 22 (6), 1039±1047. Welsch, D.J., Smart, D.L., Boyer, J.N., Minkin, P., Smith, H.C., McCandless, T.L., 1995. Forested wetlands: functions, benefits, and the use of best management practices. Bull. NA-PR-01-95. USDA Forest Service, Northeastern Area State and Private Forestry, Radnor, PA, 62 pp.