《森林生态学》课程教学资源（生态学热点）Issues in ecology - 06 运用生态学原理管理森林 Applying Ecological Principles to Management of the U.S. National Forests

Applying Ecological Principles to Management of the U.S.National Forests

Published by the Ecological Society of America Number 6, Spring 2000 Applying Ecological Principles to Management of the U.S. National Forests Issues in Eco logy

Issues in Ecology Number 6 Spring 2000 Applying Ecological Principles to Management of the U.S.National Forests SUMMARY The U..National Forest System is a diverse and unique resource that must be managed within the cntextf competing and shifting socil expectations.The policies under which the system operates have changed over the century. along with the values wood production. tion.Proposals nagemer orests are once g debated. h among ecologists is that nd on an unde managed as orest management practices erstanding of how natural forest ecosys- ems wo We have identified majorc niderations that should be in sound forest managemen policy nc cks that hold the fture forest sit. 9 t es al d le ore large cutover quality and yield na pre an ides call for greater attention to the ative mpacts logging roads ne value o undis urbe zones along streams and rivers Conservation of forest bic iversity will often require reducing forest fragmentation by clearcuts and roads iding harvest in vulnerable areas such as hardwood or old growth stands and riparian zones,and restoring atural struct ural complexity to cutover sites Planning at the landscape level is needed to address ecological conce ns such as biodiversity.water flows,and ntatio Repeated overcutting of National Forests lands in the past has been linked to lack of planning at the landscape scale Increasing pressures on forests due to human population growth and global change oblige land managers to be alert for climate-related stresses as well as damage from ground-level ozone,acid rain,and acidification of soils and watersheds. This pane as analyzed assumptins.both explicit and implicit,that underlie a number of curent es in National Forest management.Key assumptions i some of these proposals are unsupported or irradicted by current knowledge of forest ec We are confident that Despite natural disturbance and successional change.forest reserves are much more likely to sustain the full biological diversity of forests than lands managed primarily for timber production. No evidence supports the view that natural forests or reserves are more vulnerable to disturbances such as wildfire,windthrow,and pests than intensively managed forests.Indeed,there is evidence natural systems may be more resistant in many cases. Traditional beliefs that timber harvesting can duplicate and fully substitute for the ecological effects of natural disturbance are incorrect.although newer techniques such as retaining trees and large woody debris on harvest sites can more closely mimic natural processes. There is no scientific basis for asserting that silvicultural practices can create forests that are ecologically equivalent to natural old-growth forests.although we can certainly use our understanding of forest ecology to help restore managed forests to more natural conditions. Proposals to ban all timber harvesting on National Forests would leave managers without a valuable tool that can be used selectively to restore early successional habitat,reduce fuel loads.and contain pest and pathogen outbreaks in some forests. Creativity is needed in designing forest management policies for the future.but simple solutions are almost never adequate for sustaining a complex system that must fulfill diverse expectations.Sustainable management policies must make full use of current ecological knowledge.The goal of our policy efforts today should be to design forest manage- ment practices that assure the value of our forest resources for future generations

1 Issues in Ecology Number 6 Spring 2000 Applying Ecological Principles to Management of the U.S. National Forests SUMMARY The U.S. National Forest System is a diverse and unique resource that must be managed within the context of competing and shifting social expectations. The policies under which the system operates have changed over the century, along with the values society places on wood production, wilderness protection, recreation, and biodiversity conserva￾tion. Proposals for major changes in the management of the National Forests are once again being debated. The consensus among forest ecologists is that all forests, despite their complexity and variability, should be managed as ecosystems. Sustainable forest management practices must be based on an understanding of how natural forest ecosys￾tems work. We have identified major ecological considerations that should be incorporated in sound forest management policy and their potential impacts on current practice: • Maintenance of soil quality and nutrient stocks that hold the key to current and future forest productivity may necessitate adjusting timber harvest rates and leaving more large woody debris on cutover sites. • Protection of water quality and yield and prevention of flooding and landslides call for greater attention to the negative impacts of logging roads and the value of undisturbed buffer zones along streams and rivers. • Conservation of forest biodiversity will often require reducing forest fragmentation by clearcuts and roads, avoiding harvest in vulnerable areas such as hardwood or old growth stands and riparian zones, and restoring natural structural complexity to cutover sites. • Planning at the landscape level is needed to address ecological concerns such as biodiversity, water flows, and forest fragmentation. Repeated overcutting of National Forests lands in the past has been linked to lack of planning at the landscape scale. • Increasing pressures on forests due to human population growth and global change oblige land managers to be alert for climate-related stresses as well as damage from ground-level ozone, acid rain, and acidification of soils and watersheds. This panel also analyzed the ecological assumptions, both explicit and implicit, that underlie a number of current proposals for changes in National Forest management. Key assumptions in some of these proposals are unsupported or directly contradicted by current knowledge of forest ecology. We are confident that: • Despite natural disturbance and successional change, forest reserves are much more likely to sustain the full biological diversity of forests than lands managed primarily for timber production. • No evidence supports the view that natural forests or reserves are more vulnerable to disturbances such as wildfire, windthrow, and pests than intensively managed forests. Indeed, there is evidence natural systems may be more resistant in many cases. • Traditional beliefs that timber harvesting can duplicate and fully substitute for the ecological effects of natural disturbance are incorrect, although newer techniques such as retaining trees and large woody debris on harvest sites can more closely mimic natural processes. • There is no scientific basis for asserting that silvicultural practices can create forests that are ecologically equivalent to natural old-growth forests, although we can certainly use our understanding of forest ecology to help restore managed forests to more natural conditions. • Proposals to ban all timber harvesting on National Forests would leave managers without a valuable tool that can be used selectively to restore early successional habitat, reduce fuel loads, and contain pest and pathogen outbreaks in some forests. Creativity is needed in designing forest management policies for the future, but simple solutions are almost never adequate for sustaining a complex system that must fulfill diverse expectations. Sustainable management policies must make full use of current ecological knowledge. The goal of our policy efforts today should be to design forest manage￾ment practices that assure the value of our forest resources for future generations

Issues in Ecology Number 6 Spring 2000 Applying Ecological Principles to Management of the U.S.National Forests by John Aber',Norman Christensen.Ivan Fernandez,Jerry Franklin,Lori Hidinger.Malcolm Hunter. James MacMahon.David Mladenoff,John Pastor.David Perry.Ron Slangen.Helga van Miegroet INTRODUCTION Today we are experiencing another period of shifting values as well as conflicting pr posals for maior changes in The U.S.National Forest System is a diverse and unique the management of the National Forest System.Some seg resource.encompassing approximately 192 million acres and ments of society propose to increase forest harvesting dra representing most of the continent's major forest types.The matically while others want to eliminate harvesting alto system itself is entirely a creation of twentieth century po gether (e.g..Oliver et al.1997.McKinney 1999).Policies litical and social forces.and society's expectations for it have regarding the role of natural disturbances such as fire are changed repeatedly over the century.As the values society also under review.Recently,the U.S.Forest Service began places on timber production.wilderness protection.recre reviewing its mission based on the recommendations of the ation,and cor servation of biological dive ersity have shifted. Committee of Scientists Report(199)commissioned by the so have the policy directives under which the system operates Secretary of Agriculture his committee of 13 academic The various legislative mandates under Mhich the Na and professionals concluded that ecological sustainability and with pubic ownership and ipation are key guiding principles esta the lirst po gemen an Dac drop.the forests them 0estabishnation The act gave chang ing hun on pu selves a dyr onst anging in respon e stress, climate y d spec th.po ange,and extended this b five thi door recreation.range and fodder.and watersheds (Wiersum ina howy the natural systems work and developing manage 1995).The National Forests Manage ent Act of 1976 in ment prescrintions consistent with that knowledge Wher tuspecified that this policy of multipleuse be incorporated political pressures are strong.however.it is all too easy for into a mandated planning process. land managers and decision makers to lose sight of the ex- and providing for well-regulated,high-quality streamflow. Private forest lands,western Washington state

Issues in Ecology Number 6 Spring 2000 2 by John Aber* , Norman Christensen, Ivan Fernandez, Jerry Franklin, Lori Hidinger, Malcolm Hunter, James MacMahon, David Mladenoff, John Pastor, David Perry, Ron Slangen, Helga van Miegroet Applying Ecological Principles to Management of the U.S. National Forests INTRODUCTION The U.S. National Forest System is a diverse and unique resource, encompassing approximately 192 million acres and representing most of the continent’s major forest types. The system itself is entirely a creation of twentieth century po￾litical and social forces, and society’s expectations for it have changed repeatedly over the century. As the values society places on timber production, wilderness protection, recre￾ation, and conservation of biological diversity have shifted, so have the policy directives under which the system operates. The various legislative mandates under which the Na￾tional Forest System has operated began with The Organic Administration Act of 1897 that established the first policy for national forest use and management. The act gave the President authority to establish national forests on public lands in order to improve and protect the forest within boundaries, or for the purpose of security, favorable condi￾tions of waterflows, and to furnish a continuous supply of timber for the use and necessities of citizens of the United States (Fedkiw 1999). The 1960 Multiple Use Sustained Yield Act extended this by specifying five things that were to be sustained on public landstimber, fish and wildlife, out￾door recreation, range and fodder, and watersheds (Wiersum 1995). The National Forests Management Act of 1976 in turn specified that this policy of multiple use be incorporated into a mandated planning process. Today we are experiencing another period of shifting values as well as conflicting proposals for major changes in the management of the National Forest System. Some seg￾ments of society propose to increase forest harvesting dra￾matically while others want to eliminate harvesting alto￾gether (e.g., Oliver et al. 1997, McKinney 1999). Policies regarding the role of natural disturbances such as fire are also under review. Recently, the U.S. Forest Service began reviewing its mission based on the recommendations of the Committee of Scientists Report (1999) commissioned by the Secretary of Agriculture. This committee of 13 academics and professionals concluded that ecological sustainability and pubic ownership and participation are key guiding principles for managing the National Forests. Behind this changing human backdrop, the forests them￾selves are also dynamic, constantly changing in response to stress, disturbance, and climate, yet always constrained by their underlying physical, chemical, and biological processes. The stresses on forested ecosystems and the plant and ani￾mal species they harbor are continually increasing because of human population growth, pollution, climate change, and other threats (Figure 1). The key to responsible forest management is understand￾ing how the natural systems work and developing manage￾ment prescriptions consistent with that knowledge. When political pressures are strong, however, it is all too easy for land managers and decision makers to lose sight of the ex￾Figure 1 - Continuous clearcutting of forests can create major environmental problems, such as in maintaining biological diversity and providing for well-regulated, high-quality streamflow. Private forest lands, western Washington state. Photo by Jerry Franklin. * Authors in alphabetical order.

Issues in Ecology Number 6 Spring 2000 tent and value of the knowledge base that has been developed forest ecosystems and also how management practices af on forest ecosystem dynamics and response to disturbance. fect soil quality (eg.Cole 1995 and Perry and rose 1998) The purpose of this report is to outline key ecological Although very little research has been published on systems considerations that should underlie sound forest manage for evaluating or monitoring soil quality.defining it and ini ment.The complexity and variability of forest ecosystems tiating programs to evaluate its maintenance and promo throughout the United States make it difficult to formulate tion are central to achieving demonstrable sustainability in ecological principles that apply uniformly to all.Yet there is our National Forests.The ability to define and measure so consensus among forest ecologists about one generalization: quality is important for applications at a number of scales All forests should be regarded and managed as ecosystems from monitoring soil compaction and nutrient supply at spe ecosystems that represent a variety of resources and val- cific .em est this report we management in tive catego Wha cycles blend of minerals. .living .In n pro of the suppo explicitly a te em propo mite h rests (USDA NRCS 1996) tha Healthy soil e critical ec ical functions (An in forested eco ont cy lino.a on the scientific hasis of for de nted by david perry (1998)in the annual reu dead organic matter and release vital nlant nutrients such a and phosphorus for reuse.This activity accounts A single overarching prir nciple sets the context for this for the majority of nutrients taken up by plants in matur report:the national forest system should be viewed as a forests.Second.healthy soil enables a forest to maintain multifaceted resource of continuing value.and current man some productivity (tree srowth)during periods of shortase agement policies and practices should not devalue the re- especially droucht Third.healthy soil is capable of retain source for future generations.Any set of management prac ing fertility and thereby facilitating plant recovery follow tices should therefore be sustainable for the indefinite future ing disturbances such as fire or timber harvesting.The lat ter capability quickly degrades,however.when plant cover ECOLOGICAL CONSIDERATIONS IN is removed and the soil is left bare(Perry 1998). R5MANA Soi Structure and Oranic Matter From the early the.Forest Ser A significant concern in the maintenance of forest soil has had two soil o ing compa wers e expande agency s matter includ sity c m he as catego 180 de signed to the d h ms,many which perform th ersity:(4 scape level iss and (5) As lon of soil car ine lit SOIL AND NUTRIENT CYCLES will be th ofc the st Soil quality is central to sustainable forest tus soil nutrients because it defines the current and future productivity of the More problematic is the replenishment of those co land and promotes the health of its plant and animal com nents of soil carhon that are derived from large wo munities (Doran and Parkin 1994).A great deal is known bris,especially tree stems(Figure 2:Harmon et al.1986) about the importance of soil quality for the functioning of The practice of leaving tree stems on site is not common in

3 Issues in Ecology Number 6 Spring 2000 tent and value of the knowledge base that has been developed on forest ecosystem dynamics and response to disturbance. The purpose of this report is to outline key ecological considerations that should underlie sound forest manage￾ment. The complexity and variability of forest ecosystems throughout the United States make it difficult to formulate ecological principles that apply uniformly to all. Yet there is consensus among forest ecologists about one generalization: All forests should be regarded and managed as ecosystems ecosystems that represent a variety of resources and val￾ues for different forest users. In the first section of this report, we discuss ecological considerations for forest management in five broad catego￾ries: 1) soil and nutrient cycles, 2) hydrology, 3) biodiversity, 4) landscape level issues, and 5) global change. In the sec￾ond section of the report, we examine and critique some of the ecological assumptions that explicitly or implicitly un￾derlie several current forest policy proposals. In particular, we analyze acceptable or desirable levels of direct human manipulation and use of federal forests based on current eco￾logical understanding. Rather than presenting a comprehen￾sive review of the literature, we discuss principles that are generally accepted among ecological scientists. (An excel￾lent review of the literature on the scientific basis of forestry was presented by David Perry (1998) in the Annual Review of Ecology and Systematics.) A single overarching principle sets the context for this report: The National Forest System should be viewed as a multifaceted resource of continuing value, and current man￾agement policies and practices should not devalue the re￾source for future generations. Any set of management prac￾tices should therefore be sustainable for the indefinite future. ECOLOGICAL CONSIDERATIONS IN FOREST MANAGEMENT From the early days of its creation, the U.S. Forest Ser￾vice has had two primary goals: to support local industry and to protect and sustain watersheds. Over time, new laws and policies have expanded the agency’s mission to include recreation, biodiversity conservation, and maintenance of soil quality and natural processes. We examine here five broad categories of ecological considerations that should go into management practices designed to fulfill this complex mis￾sion and to sustain forest resources into the future: (1) soil and nutrient cycles; (2) hydrology; (3) biodiversity; (4) land￾scape level issues; and (5) global change. SOIL AND NUTRIENT CYCLES Soil quality is central to sustainable forest management because it defines the current and future productivity of the land and promotes the health of its plant and animal com￾munities (Doran and Parkin 1994). A great deal is known about the importance of soil quality for the functioning of forest ecosystems and also how management practices af￾fect soil quality (eg., Cole 1995 and Perry and Rose 1998). Although very little research has been published on systems for evaluating or monitoring soil quality, defining it and ini￾tiating programs to evaluate its maintenance and promo￾tion are central to achieving demonstrable sustainability in our National Forests. The ability to define and measure soil quality is important for applications at a number of scales, from monitoring soil compaction and nutrient supply at spe￾cific sites to addressing global concerns about the amount of carbon sequestered in the wood of the world’s forests. What is soil? Soil is a unique and complex blend of minerals, living organisms, and the organic products of organisms. It pro￾vides habitat and physical support as well as sustenance for a teeming array of creatures, from bacteria and fungi to mites, earthworms and plants. The soil and its living com￾munity store and cycle nutrients, regulate water flows, and also filter, buffer, degrade, immobilize, or detoxify a myriad organic and inorganic materials (USDA NRCS 1996). Healthy soil performs three critical ecological functions in forested ecosystems. One is nutrient cycling, a process carried out by invertebrates and microbes that decompose dead organic matter and release vital plant nutrients such as nitrogen and phosphorus for reuse. This activity accounts for the majority of nutrients taken up by plants in mature forests. Second, healthy soil enables a forest to maintain some productivity (tree growth) during periods of shortage, especially drought. Third, healthy soil is capable of retain￾ing fertility and thereby facilitating plant recovery follow￾ing disturbances such as fire or timber harvesting. The lat￾ter capability quickly degrades, however, when plant cover is removed and the soil is left bare (Perry 1998). Soil Structure and Organic Matter A significant concern in the maintenance of forest soil quality is assuring the replenishment of surface and soil or￾ganic matter and avoiding compaction of the soil (Powers et al. 1990). Soil organic matter includes highly decomposed material called humus, less decomposed leaf litter and other detritus, and large woody debris such as branches and stems. This organic material stores nutrients and water and sup￾plies the carbon to nourish the myriad belowground organ￾isms, many of which perform the critical tasks of releasing the mineral nutrients necessary for continued plant growth. As long as plant communities regrow vigorously after timber harvesting, losses of soil carbon derived from fine litter will be replenished. Regrowth, of course, depends on the sta￾tus of soil nutrients, soil carbon, and soil biology after harvest. More problematic is the replenishment of those compo￾nents of soil carbon that are derived from large woody de￾bris, especially tree stems (Figure 2; Harmon et al. 1986). The practice of leaving tree stems on site is not common in

Issues in Ecology Number 6 Spring 2000 intensive forestry today.and in fact.doino so has been seer to another flevated nitrate levels in streams followino har as a waste.The question of how many trees to leave to vest or forest disturbance represent a threat to wate r qua nt and will ity hecsuee e nutrient fouline can lead to a wide reguire further research on the ecological functions of large problems from algal blooms,loss of oxygen.and fish kills to dead wood.Yet retaining trees on site as future sources of degradation of drinking water.In general.forest ecosy large woody debris must be a major component of sustain- tems with higher levels of nitrogen mineralization (release o able forest management nitrogen from decomposing soil organic matter)have been shown to exhibit higher rates of nitrate production and loss Nutrient Cycling and these losses are further increased by the removal of trees Another major factor in sus and corresponding elimination o taining soil quality is maintaining nitrogen uptake by the trees pools of essential plant nutrients Hibbert 1969.Likens et al.1970 and assuring these are steadily Hornbeck et al.1996). available in forms that plants can Computer modeling of nutri use.Undisturbed forests seldom ent requirements for forest growth experience significant losses of nu as well as studies on waters trient stocks u an importan and forest ecosystems agree tha b orestry i n principl rvesting whol anagement practice est in the long- those nutrients t Until rec nd oth he tant nutrient limiti in te rate and boreal fo 177 and by far the majority of research al.1986.Johnson and Todd has focu ised on nitrogen losse sociated with timber harvest and nrona site preparation (Johnson 1992) sites for planting signific ntly im Losses from a harvested site take nact soil fertility esne cially the use three forms:removal of the nitro of heavy equipment to push slash gen contained in the harvested and other organic matter into wood.nitrogen leached and oiles.a practice called windrow eroded from disturbed soil.and ni ne(Powers et al.1990).In a sus During the last 30 years it has become appar trogen volatilized and lost to the logs and atmosphere during slash burning oer woody debris fulfill m tainable forest management pro y eco the gram.therefore.rates of tree re The extent and impact of these Note person in red for scale moval and other management ac losses vary depending on numer- by Jerry Franklin tivities should be planned accord ous site-specific factors such as ni ing to nutrient budgeting tech trogen ava limate and also on management prac niques in order to reduceor deter long-term degrada tices (Col 1995).In the n nitrogen-poor tion of soil nutrients. em u.s. for example. dslash burn ing ogen-ricl as have increased of North A meric nts shov of r h gen ecognized that h 05 proc le due to tree ha soils to stre espe able fron ne has bee into the

Issues in Ecology Number 6 Spring 2000 4 intensive forestry today, and in fact, doing so has been seen as a waste. The question of how many trees to leave to sustain soil quality is not easily answered at present and will require further research on the ecological functions of large dead wood. Yet retaining trees on site as future sources of large woody debris must be a major component of sustain￾able forest management. Nutrient Cycling Another major factor in sus￾taining soil quality is maintaining pools of essential plant nutrients and assuring these are steadily available in forms that plants can use. Undisturbed forests seldom experience significant losses of nu￾trient stocks. Thus an important element in sustainable forestry is taking care that management practices do not result in long￾term reductions in a forest’s nu￾trient capital or in the long-term availability of those nutrients to plants. Until recently, nitrogen has been considered the most impor￾tant nutrient limiting tree growth in temperate and boreal forests, and by far the majority of research has focused on nitrogen losses as￾sociated with timber harvest and site preparation (Johnson 1992). Losses from a harvested site take three forms: removal of the nitro￾gen contained in the harvested wood, nitrogen leached and eroded from disturbed soil, and ni￾trogen volatilized and lost to the atmosphere during slash burning. The extent and impact of these losses vary depending on numer￾ous site-specific factors such as ni￾trogen availability and climate and also on management prac￾tices (Cole 1995). In the nitrogen-poor forests of the west￾ern U.S., for example, losses in wood removal and slash burn￾ing far exceed those in leaching, while in more nitrogen-rich eastern forests, leaching losses can be quite high. Watershed-scale studies and harvesting experiments show that total nitrogen lost from a site after clearcutting varies widely among forest types. Since nitrogen is considered the major nutrient limiting tree growth in most systems, post￾harvest losses are regarded as a long-term threat to forest productivity. Nitrogen losses in the form of nitrate leached from soils to streams are especially variable from one forest to another. Elevated nitrate levels in streams following har￾vest or forest disturbance represent a threat to water qual￾ity because nutrient fouling can lead to a wide range of problems from algal blooms, loss of oxygen, and fish kills to degradation of drinking water. In general, forest ecosys￾tems with higher levels of nitrogen mineralization (release of nitrogen from decomposing soil organic matter) have been shown to exhibit higher rates of nitrate production and loss, and these losses are further increased by the removal of trees and corresponding elimination of nitrogen uptake by the trees. (Hibbert 1969, Likens et al. 1970, Hornbeck et al. 1996). Computer modeling of nutri￾ent requirements for forest growth as well as studies on watersheds and forest ecosystems agree that, in principle, harvesting whole trees and using short intervals be￾tween harvests on a site lead to significant reductions in soil nitro￾gen stocks, nitrogen availability, and productivity. Large losses of phosphorus, calcium, magnesium, potassium, and other nutrients also occur in association with whole-tree harvest and short ro￾tations (Kimmins 1977, Smith et al. 1986, Johnson and Todd 1987). Some practices used to clear logging slash and prepare sites for planting significantly im￾pact soil fertility, especially the use of heavy equipment to push slash and other organic matter into piles, a practice called windrow￾ing (Powers et al. 1990). In a sus￾tainable forest management pro￾gram, therefore, rates of tree re￾moval and other management ac￾tivities should be planned accord￾ing to nutrient budgeting tech￾niques in order to reduce or deter long-term degrada￾tion of soil nutrients. Nitrogen Saturation Concerns have increased across much of North America and Europe about the overabundance of nitrogen entering forests due to the human-driven buildup of airborne nitro￾gen. It is now recognized that human activities such as burn￾ing of fossil fuels and production of nitrogen fertilizers have effectively doubled the supply of biologically available nitro￾gen. Thus, research on nitrogen shortages due to tree har￾vest has been augmented by investigations into the effects of Figure 2 - During the last 30 years it has become appar￾ent that logs and other woody debris fulfill many eco￾logical functions and persist for centuries, as in the case of this giant sequoia log. Note person in red for scale. Photo by Jerry Franklin