tOregon State University, Corvallis, OR 97331-5703, U.S.A.. Abstract--Cumulative effects of forestry operations accumulate over time and space in forested land-.
Pergamon PII:
Biomass and Bioencrgy Vol. 13. Nos. 415, pp. 223-245. 1997 F 1998 Publishedby ElsevierScienceLtd. All rightsreserved Printedin Great Britain 0961-9534/97 $17.00 + 0.00 s0%1-9534(97)10011-3
CUMULATIVE EFFECTS OF FORESTRY PRACTICES: AN EXAMPLE FRAMEWORK FOR EVALUATION FROM OREGON, U.S.A. JAMES R. CAROL
C.
BOYLE*&
JAMES E. WARILA *, ROBERT L. BESCHTA*,
CHAMBERS?,
JOAN C. HACAR?,
WAYNE
P.
GIesoNt,
STANLEY V.
JUDY L. LIT, WILLIAM
MARYANNE
GREGORY?,
C. MccoMBt,
REITER*.
JEFFREY GRIZZEL~,
TYE W. PARZYBOK~ and
GEORGE TAYLOR? *College of Forestry, Oregon State University, tOregon State University, Corvallis,
Corvallis, OR 97331-5703, OR 97331-5703, U.S.A.
U.S.A.
Abstract--Cumulative effects of forestry operations accumulate over time and space in forested landscapes where harvesting and management occur. We review the literature and concepts associated with cumulative effects and propose a framework for evaluating them. In order to evaluate potential adverse effects of forestry on vegetation, soils, streams, aquatic organisms, wildlife and air, baseline conditions and natural variations of resource characteristics must be known. Cause-effect relationships must be documented. Systems of measurements and monitoring must be implemented along with databases and geographic information systems for displaying information at spatial scales from individual sites to landscapes and regions. Systems for decision-making must be implemented. We provide an example of a framework for such a system in a mountainous, forested river basin in northwest Oregon, U.S.A. We conclude that knowledge and technologies for preliminary systems exist now, but that for more refined systems more knowledge of details of cause-effect links and of simulation models should be developed. ‘c 1998 Published by Elsevier Science Ltd. Keywords-Cumulative
effects; forestry
operations;
soils; air; water; aquatic
1. INTRODUCTION
______ to whom correspondence
should
wildlife.
For many years forest scientists have documented for some situations the additive effects of forestry practices on streams, soil properties or other resource values, but in few if any documented instances have effects over both time and space been reported. This report is an outgrowth of a team effort to establish a basis for the Oregon State Department of Forestry to organize a system for evaluating cumulative effects of forestry practices on air, soils, water, aquatic organisms and wildlife. Conceptually, we think it is most useful to envision potential cumulative effects in a readily defined unit of landscape such as a single watershed or catchment in a mountainous region. For broader-scale considerations, adjacent and/or interacting catchments can be ‘aggregated’ as needed for individual cases. As scales of consideration increase, effects of land uses other than forestry will inevitably complicate potential assessments of cumulative effects of forestry practices, and in some locales such complex interactions are the norm. Whatever the case, it is essential for considering cumulative effects to continuously adjust scales of thinking from site-specific effects to broader
As forestry operations are carried out over time and at various places in forested landscapes, the effects of these operations become ‘cumulative’, i.e. effects are added one to another. The most obvious cumulative effect of forestry practices on a local and landscape scale in the Pacific Northwest U.S.A. is the increasing patterns of patches of harvested forest that have accumulated since intensive forest cutting began in the 1950s in Oregon and Washington. Similar alterations of landscapescale patterns of previously natural forests have occurred and are occurring as forests have been and are cut in many regions of the world. Where forest plantations have replaced agricultural land uses, analogous changes in vegetation result. This cumulative effect of forest cutting or planting has, at a minimum, altered potential habitats for wildlife by changing vegetation, and has likely altered foreststream interactions and other hydrology and biogeochemistry of the forested landscapes. $Author
organisms;
be addressed. 223
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J. R. BOYLEet al.
landscape scales, and from immediate concerns to integrated effects over periods of several years to decades. It is clear that the effects of forestry over time are cumulative. The critical issues are whether such cumulative effects have measurable and meaningful impacts on resource values of concern, and whether such effects can be effectively documented in order to provide frameworks for value assessments. 2. OVERVIEW OF CUMULATIVE EFFECTS LEGISLATION AND DEFINITIONS
In the early history of the United States, extensive harvesting of watersheds led to concerns that such practices would adversely affect streamflow. These concerns were of fundamental importance regarding the creation of Forest Reserves, which later became National Forests.’ The 1897 Organic Act, which created the U.S. Forest Service, treated the production of timber and the maintenance of favorable water flow as equal objectives.2 The Federal government was charged with the protection of navigable waters. Those who favored the creation of a forest reserve system argued that such reserves were needed to protect navigable waters since streamflow was directly related to forest cover and was affected by clearing.’ Some officials in the Army Corps of Engineers and the U.S. Weather Bureau asserted that streamflow is solely controlled by precipitation. The controversy over forests and streamflow eventually led to the initiation of the nation’s first paired watershed study at Wagonwheel Gap, Colorado in the early 1900s. Paired watersheds were selected and calibrated, harvesting treatments were implemented and changes in streamflow monitored. Since then, other experimental forests and watersheds have been established at various locations throughout the United States to conduct research on forest hydrology and related environmental factors. Oregon has had several such sites. However, studies at these sites have generally evaluated no effects other than streamflow, and in some cases water quality. The environmental movement of the 1960s in the U.S.A. focused attention on water pollution and degradation associated with a wide variety of land use practices, including forestry. These growing concerns led to a series of Federal environmental laws in the late 1960s and 1970s. For example, the Multiple
Use Sustained Yield Act (Public Law 86-217) of 1960 served as a precursor to cumulative effects legislation with its guiding principle “the achievement and maintenance in perpetuity of a high-level annual or regular periodic output of the various renewable resources of the national forests without impairment of the productivity of the land”. The National Environmental Policy Act (NEPA; Public Law 91-190) of 1969 requires that projects with the potential for significantly affecting the quality of the environment on Federal lands must undergo a process of environmental impact review leading to an Environmental Impact Statement (EIS).’ By 1975, the courts were grappling with cumulative effects issues since most projects undertaken by Federal agencies rarely occur in isolation. In 1978, the Council on Environmental Quality put forth regulations to implement NEPA which required EISs to consider direct impacts, indirect impacts and cumulative effects. The legislative definitions of direct and indirect effects and of cumulative impacts are as follows: Direct effects are caused by an action and occur at the same time and place. Indirect effects are caused by an action and are later in time or farther removed in distance, but are still reasonably foreseeable. Cumulative impact is the impact on the environment that results from the incremental impact of an action when added to other past, present and reasonably foreseeable future actions regardless of what agency (Federal or non-Federal) or persons undertakes such other actions. Cumulative impacts can result from individually minor but collectively significant actions taking place over a period of time. Other Federal legislation of the 1970s addressed environmental issues, including forests and water. The National Forest Management Act (NFMA) of 1976 (PL 94588) also required cumulative effects to be addressed. This Act directed the Forest Service to protect “streams, stream sidebanks, shorelines, lakes, wetlands, and other bodies of water from detrimental changes in water temperature, blockages of water courses, and deposits of sediment, where harvests are likely to seriously and adversely affect water conditions or fish habitat.“2 However, it was not until passage of the Clean Water Act in 1977
Cumulative effects of forestry practices
that consideration of cumulative effects was required.2 This act requires: “a process to (i) identify, if appropriate, agriculturally and silviculturally related non-point sources of pollution including return flows from irrigated agriculture, and their cumulative effects, and (ii) set forth procedures and methods (including land use requirements) to control to the extent feasible such sources.” In addition to Federal legislation, the Federal courts have given specific rulings in several cases which further consider cumulative effects. Following the lead of the Federal government, states have enacted various types of ‘cumulative effects legislation’. In some instances, legislation was directed at a particular resource within the state. For example, in Florida there is a Wetlands Protection Act (Section 403.919), which directs the Department of Natural Resources to consider cumulative impacts of proposed projects. In Maryland there is State cumulative effects legislation aimed at protecting the Chesapeake Bay (Maryland Chesapeake Bay Cultural Area Law, Section 8-1801). In other states, the legislation is not directed at a particular resource, but instead indicates that cumulative effects must be considered for specific types of projects. The New York Environmental Quality Review Act (Section 8-0101) indicates that cumulative impacts must be considered for proposed or pending developments undertaken by the government. In the western United States, the development of cumulative effects legislation parallels Federal legislation. In 1970, California passed the California Environmental Quality Act (CEQA), which required all projects which may have significant environmental impacts to disclose an Environmental Impact Report. A project may have significant impact if “the possible effects of a project are individually cumulatively considerable” limited but (Section 21083 of CEQA).2 The 1983 guidelines of CEQA define cumulative effects similar to the NEPA definition. In forestry, both the California Department of Forestry (CDF) and the U.S. Forest Service share responsibility for protecting waters of the State since many watersheds have mixed ownerships. Thus, cumulative effects assessment methodologies for both agencies must be compatible. In addition, court decisions in California have indicated that the forest industry must con-
225
sider cumulative effects as required under both State and Federal regulations. In the State of Washington the 1974 State Forest Practices Act provided authority to the State for regulating forest practices on State forest land. In recent years, there has been greater emphasis on creating a systematic way to evaluate and prevent cumulative effects on streams. The Timber/Fish/Wildlife (TFW) program, comprising representatives from forest industries, State agencies, environmental groups and tribes, identified an approach to cumulative effects in 1987. The recommended approach included provisions for state, regional and basin goal setting, monitoring to determine if goals are being met, use of risk assessments for problem identification, implementation of an adaptive management process and re-evaluation of goals as new information becomes available. In 1991, the Cooperative Monitoring Evaluation and Research Committee of TFW, in cooperation with the Washington Department of Natural Resources, developed a methodology for watershed analysis on forest lands which focuses on a series of resource assessments, including mass wasting, surface erosion, hydrology, riparian, stream channel, fish habitat, water quality, water supply and public works and the routing of materials downstream. The methodology (which currently does not address wildlife assessments) was adopted by the Forest Practices Board in 1992.3 This approach to assessing cumulative effects for forested lands in Washington represents a significant departure from the traditional approach of simply utilizing forest practice regulations that tend to be uniform across a wide range of ecosystems. The Watershed Analysis approach is a sciencebased assessment of the conditions and characteristics of specific watersheds and allows for the identification of prescriptions based on the sensitivity of the land to management activities. The 1991 revised Oregon Forest Practices Act contains rules which provide for the overall maintenance or restoration of air, water, soil, fish and wildlife resources. In addition, the legislation indicates that the State Board of Forestry shall adopt forest practices rules that “minimize adverse impacts of cumulative effects of forest practices on air and water quality, soil productivity, fish and wildlife resources, and watersheds” (Section 12 ORS
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527.710). These rules also require that a process be used for determining areas where adverse impacts from cumulative effects have occurred or are likely to occur and that these areas require a written plan. These actions were the basis for our work. The development of terminology has been an evolving and important component of cumulative effects concepts and programs. A modified version of the Federal definition of cumulative effects was included in the 1991 Oregon Senate Bill (1125) revising the Oregon Forest Practices Act: cumulative effects means the impact on the environment which results from the incremental impact of the forest practice when added to other past, present and reasonably foreseeable future forest practices regardless of what governmental agency or person undertakes such other actions.[ORS 527.620(3)].
The Oregon definition incorporates several of the complex and perplexing aspects of cumulative effects, including recognition that: ??effects
tend to accumulate incrementally, no single one of which may necessarily appear significant; ?? effects may combine or accumulate through time and/or space; ?? cumulative effects can result from the dissociated and unrelated activities of various landowners. Researchers and scientists working on cumulative effects have devised additional definitions that emphasize or de-emphasize vareffects ious components of cumulative processes or responses. For example, for evaluating certain types of resource changes it may be desirable to subdivide cumulative effects into several classes, such as temporary and persistent or direct and indirect (e.g. Geppert et ~1.~). If on-site recovery from a specific forest practice has occurred before the onset of the following rotation or sequence of practices, such effects would fall under the category of temporary cumulative effects. If natural recovery did not occur before the onset of the next practice (release, thinning, fertilization) or sequence of practices (harvest, site preparation, reforestation), the resulting combination of effects would fall under the category of persistent cumulative effects, because their duration would be indefinite, and recovery to the previous baseline condition not foreseeable. The distinction between direct and indirect cumulative effects can be defined as
follows: direct cumulative effects result from the combination of direct individual effects of two or more forest practices, whereas indirect cumulative effects result from the combination of a prior cumulative effect or two or more indirect individual effects. Other considerations of cumulative effects, focused on stream systems, are provided by MacDonald et a1.5T6. A cumulative effects definition developed by Sidle7 clearly links human activities and natural processes: changes to the environment caused by the interaction of natural ecosystem processes with the effects of land use, distributed through time or space, or both.
The definitions of Geppert et al4 and Sidle’ have another important aspect in common, which is not included in the CEQ definition; it is explicitly recognized that cumulative effects result not only from the combined effects of human activities, but from the interacting effects of human activities with natural processes. These various definitions recognize that natural systems are dynamic, that natural processes are constantly inducing changes or ‘effects’, and that human-caused changes or effects are in constant interaction with natural processes. Additionally, the individual effects of individual actions, uses or projects, which are often incremental and appear insignificant when considered in isolation, can acquire significance when considered in combination. The following definitions are broad with regard to the types of land-use considered but emphasize an important facet of the cumulative effects issue addressed in the CEQ definition, i.e. that of ‘incremental effects’: cumulative impacts are those resulting from the interactions of many incremental activities, each of which may have an insignificant effect when viewed alone, but which become significant when seen in the aggregate (Dickert and Tuttle*); the cumulative impact of many individual actions, no single one of which is particularly alarming (Gosselink ef aL9).
None of the preceding cumulative effects definitions distinguish among different ways in which effects might accumulate’O’l’. This implies that additive effects, as well as multiplicative, synergistic or antagonistic effects, are incorporated within various definitions. The NEPA definition is important in expressing an approach to effects assessment, rather than distinguishing between different classes of effects. Knowledge about how individual
Cumulative
effects of forestry
effects combine or accumulate is important for analysing and assessing cumulative effects. With this historic and conceptual background, we undertook the task of developing a framework for personnel of the Oregon Department of Forestry to use as basis for attempting to evaluate cumulative effects of forestry practices on air, soils, water, aquatic organisms and wildlife in Oregon’s forests. For the resources of focus for our study, we organized the following general categories of consideration, in addition to spatial and temporal scales for each resource. For air: ‘airshed’ areas and regions; air quality parameters; temporal changes; interactions with human activities. For water: physical hydrology; riparian functions; water quality; channel complexity; interactions; site-/ morphology; system-/basin-specificity. For aquatic biota: abundance and diversity; life history patterns; food webs; habitat characteristics-physical, chemical, biological, temporal, stability and dynamics. For wildlife: habitats; survival; abundance; distribution; seral/growth stages of forests; physical structures; patch sizes and distribution; edges; key species. For soils: physical, chemical and biological properties and dynamics (Fig. 1). For each of these resources, we did extensive and intensive reviews of relevant scientific literature and concluded some basic considerations for establishing systems of baseline measurements and monitoring. We report here only the integrated overview of our proposed framework for establishing a system for evaluating cumulative effects of forestry practices. Details for evaluation of effects on each resource are beyond the present scope, and will be presented in part only as examples for the overall scheme.
3. ECOSYSTEM
INTEGRATION
A wide range of ecosystem patterns and processes occur across Oregon’s forested landscapes, with elevations from sea level to 1830 m and annual precipitation from 5080 mm to less than 305 mm. These patterns and processes are naturally dynamic over time *For simplicity of language we use ‘natural’ to refer to conditions not significantly influenced by activities of modern, industrialized humans. The issue of what sort of human activity should be considered ‘natural’ is for another forum.
practices
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Forest Productivity A View from the Bottom
wadyR&hJes & Forest Floor Soil Fauna, Flora, Micmbes
II L
“Mineral Soil” Topsoil, Structure, Subsoil
\r
*’
Soil / Site / Forest Productivity Fig. I. Forest
productivity:
a view from the bottom.
and space and have evolved over long periods of time. Forested landscapes are continually changing as a result of both gradual and catastrophic processes. Forest patterns have been formed by the establishment, growth and decay of vegetation and by landslides, floods, insects and diseases, fires and volcanism. Human activities in the forms of forestry practices and other land uses have been overlain on these ‘natural’* patterns and processes. Where forestry practices occur, they can cause disturbances with a time frequency and spatial pattern that differ from many of the natural disturbance regimes associated with forest ecosystems. For example, in Oregon fire exclusion associated with modern forestry has often lengthened time periods between disturbances rather than shortened them. The cumulative effects of various forestry practices across complex and diverse landscapes must be viewed in the contexts of forest environments, random natural events, social preferences, economic activities, institutional constraints, historic forest operations and current forestry technologies (Fig. 2). Whether such effects are viewed as ‘good’ or ‘bad’ depends on the combination of value systems and ecosystem characteristics being considered. For example, forest roads not only provide a transportation network to move logs to mills, but also allow people to readily access forests for recreation and fire suppression. Yet, measured on a different ledger, these same roads may contribute sediments to
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J. R. SOCIAL PREFERENCES
FOREST ENVIRONMENT
ECONOMICS TECHNOLOGY
Fig.
2. Interactions
RANDOM EVENT!3
Forestry Practices
of forestry values.
BOYLE
practices
and
resource
streams such that water quality and aquatic habitats are adversely altered. Similarly, the harvesting of trees and subsequent regeneration practices can create vegetation structure and composition which may spatially and temporally benefit certain wildlife species while adversely affecting others. Additionally, the effects of forest practices are often intermixed with effects of adjacent lands that are used for grazing, agriculture or other human activities. This intermingling of land uses presents significant challenges in attempts to evaluate any cumulative effects associated with forest practices.
et
al.
the potential of additional effects that are sometimes difficult to measure, characterize or simply display as a function of timber harvest rate. A more comprehensive perspective of current forestry practices is that they alter (or have altered) structure, composition, patch size and distributions of vegetation and affect physical, chemical and biological ecosystem processes. These processes, in turn, control flows of energy, water, nutrients, sediments and other matter into, within and from forests and forested landscapes (Fig. 3). Forest management effects on forests influence and interact with terrestrial wildlife including vertebrate and invertebrate organisms, stream ecosystems and organisms, hydrologic processes, air masses passing over forests, soil properties and processes, as well as trees, shrubs, herbs and other plants and microbes in forest ecosystems. Furthermore, today’s forest operations are overlain on past practices and subsequent ecosystem changes. Thus, forestry practices have influences on individual tree, stand, landscape and regional scales. To effectively consider cumulative effects of forestry practices on air, soils, water, aquatic biota and wildlife, these effects must be addressed at the small patch, stand, watershed, landscape and regional scales over varying time periods and in the context of natural ecosystem dynamics and disturbance patterns. Cumulative effects cannot be dealt with in a
Forestry
I
4. A SYSTEMS
Practices I
I
\
FOREST STAND and LANDSCAPE
PERSPECTIVE
Structure,
CornpositIon,Patch Size, Distribution
\
For a previously unharvested forest area, watershed or site, forest practices in Oregon often begin with location and construction of roads, followed by cutting and removal of trees. These operations change the composition and distribution of vegetation and can alter flows of water, energy and material within forest ecosystems and across landscapes. Changes to forest composition and age classes are readily obvious to most people and represent a fundamental effect of forestry operations on natural forest ecosystems. However, for most harvested sites there exists
J
Ecosystem, Watershed & Landscape Processes Physical, Chemical, Biological
ENERGY, WATER, NUTRIENTS,SEDIMENTS, AIR &ORGANISMS
Fig.
3. Pathways
of cumulative .. aces.
effects
of forestry
prac-
Cumulative
effects of forestry
simple ‘linear’ context. They cannot be distilled into one or two equations, relationships or box-and-arrow diagrams that suggest simple, static conditions. They cannot be evaluated with a simple check list or form. Although some of the elements and components of cumulative effects evaluations can be simplified, each must be integrated into dynamic ecosystem- and landscape-scale considerations. While some effects are additive, some synergistic and some probably ‘subtractive’, others are too complicated to simply characterize. Interactions among forest practices and other resources depend not only on the resources of interest but also on magnitude and timing of effects and ecosystem context. Furthermore, significant temporal and spatial scales may vary from effect to effect and from resource to resource. For example, effects of slash burning on air quality are important for short time scales and over both local and regional space scales. Effects on hydrologic processes, however, may be delayed until the next rainstorm, or perhaps the next rainy season, and may have relatively local consequences. There may also be a ‘ripple’ or ‘domino’ effect transmitted through a series of ecosystem components (resources). Again using slash burning as an example, burning may change soil porosity, biology and chemistry which, in turn, may impede regrowth of vegetation and alter the successional sequence of wildlife habitats. Similarly, depending on burn intensity, infiltration and evapotranspiration may be reduced, causing increased surface runoff and sediment flows which alter stream habitats, fish populations and terrestrial vertebrates which feed on fish-a complex chain of events spread over space and time. Although high temperatures during slash disposal (i.e. a hot burn) may help to minimize particulate emissions to overlying air masses, such a burn may have a more adverse effect on soils and successional vegetation than would a cooler burn. Thus, the answer to the simple question, “Are the cumulative effects of burning good or bad?” is not necessarily simple to address or easy to answer. Given the wide range of forest practices that can occur across the diverse landscapes of Oregon, the types of effects can be similarly diverse. These could include: single resource effects; multi-resource effects ‘fixed’ in space and time; multi-resource effects fixed in space
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but varying in time; multi-resource effects fixed in time but varying in space; multiresource effects varying in both space and time. Other descriptors of cumulative effects that occur in the scientific literature include direct, indirect, primary, secondary, antagonistic, synergistic, linear, nonlinear, ratcheted, cascading, time-lagged, time-crowded, spacecrowded, etc. While such a listing may intuitively seem to reflect a wealth of understanding, it more likely indicates the complexity of cumulative effects issues. Throughout much of Oregon the effects of forestry practices on various watersheds are often intermixed and integrated with effects of other land use activities such as grazing, farming, recreation and urbanization on nearby or adjacent lands. This intermingling of land uses and ecosystem responses can provide significant challenges for those attempting to separately evaluate potential cumulative effects associated with forestry practices. A starting point for integrative consideration of cumulative effects of forestry is to consider fundamental forest ecosystem characteristics within watershed, landscape and reAn ecosystem may be gional contexts. considered to have the following attributes:12 structure-the organization of biotic and abiotic components; functions-the processes of exchange of matter and energy between the physical environment and living community; multiple-factor determicomplexity-the nation of system properties and processes; interactions and interdependencies among living and non living components; temporal changes in dynamics of organisms, non-living matter and energy; no inherent spatial dimensions-boundaries are defined for human convenience. Based on these considerations, a given forest stand may be considered an ecosystem, or it may be a part of a larger ecosystem. In similar fashion, an assessment of cumulative effects may consider the effects of an individual practice or set of practices on attributes of individual ecosystems, or on the collection of forest stands or ecosystems that comprise a significant landscape unit (e.g. watershed, forested region, ecoregion) or that includes several landscape units or watersheds. When attempting to assess the cumulative effects of forest practices and land uses on air resources or on
J. R. BOYLE et al
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some wildlife populations (e.g. mountain lions, eagles, elk, hummingbirds) the landscape units of concern may extend well beyond watershed boundaries. As a template for understanding cumulative effects of forestry practices, consider the traditional and relatively straightforward sets of practices involving constructing roads, cutting trees, removing limbs and tops and skidding logs to a landing for transport. These elementary practices alter many of the forest ecosystem attributes listed above and the magnitudes of these alterations vary over time and space. These actions can also have cumulative effects when implemented on any significant scale. Constructing, using and maintaining roads over time in a forested landscape have numerous cascading and cumulative effects on forest ecosystem resources, watersheds and landscapes (Fig. 4). Road corridors alter spatial relationships of vegetation, create edges of habitat and microclimate, alter air flows and modify the pathways for organisms, water and sediments. Exposed soil surfaces on road cuts and fill slopes are available for accelerated erosion. Hardened road surfaces and accompanying ditches and culverts may accelerate and channel runoff and any accompanying soil particles or chemicals, and redistribute it to other than natural stream courses or at greater than natural rates to stream courses. Altered flows of water and solids to streams can significantly alter stream habitats and communities of aquatic organisms and may combine with
s? ROADS
Fig.
4. Schematic
of road effects values.
on
selected
resource
flows from other streams in a watershed to have downstream effects. The effects of road corridors will change over time as roadside vegetation changes, as bare soils become vegetated and as road surfaces and ditches change. Road-related changes in spatial patterns and compositions of vegetation on a landscape may alter patterns of distributions of propagules of plants and microbes (e.g. tree and herb seeds and fungal spores) and can provide opportunities and/or obstacles for movements of vertebrate and invertebrate organism (e.g. deer, frogs and insects). These are just some effects of roads. Whether any of these effects are usefully measurable depends on the availability of baseline information, including variations of natural conditions, and on the types of established measurement systems. Whether such effects are deemed undesirable or adverse will depend on the evaluative system used. However, nearly all of these effects are cumulative as a road network expands across a landscape. The felling and de-limbing of trees immediately alters the structure and composition of a forest. Felling, yarding and site preparation practices initiate conditions for successional development of new plant communities. Subsequent forestry practices, in combination with natural disturbances such as disease, fire, blowdown or major rainfall events may further influence plant community development. The development of related animal, insect and microorganism communities and dynamics of energy, water and nutrients are also changed. Depending on the different types of forest practices used on uplands and riparian forest zones, effects on these two subsets of forest ecosystem types will vary, as will consequent effects on stream ecosystems, hydrology and other resources. Altered composition of vegetation in riparian zones will change solar radiation impinging on stream channels and will alter the amounts and compositions of organic residues that enter streams. Streamside invertebrate communities may change, which may affect potential food sources for aquatic organisms, including fish. (Fly anglers may be challenged to match a new hatch!) Cutting and removing trees alters hydrologic processes of interception, evapotranspiration and infiltration. It also alters micro- and meso-climatic conditions that may influence snow accumulation and melt rates. Rates and
Cumulative effects of forestry practices
pathways of flow of water to stream courses may be changed, as may water quality parameters of sediment load and elemental and dissolved organic contents. These changes in turn may affect aquatic ecosystems adjacent to cut forests and may combine with changes caused elsewhere in a watershed to alter downstream aquatic systems. Dynamic compositions and patch sizes of forest vegetation created by cutting and removing trees produce new mosaics of wildlife and invertebrate habitats over watersheds and landscapes, leading to numerous effects on population dynamics and organism community structures. Large amounts of logging slash, i.e. limbs and tops of cut trees, will alter amounts and rates of nutrient flows resulting from leaching and decomposition of residues. Numerous soil properties and processes may change, more or less dramatically depending on the characteristics of soils in the systems. Depending on rates of recovery to pre-cutting tree ecosystem conditions, subsequent removal operation or operations may cause further effects that add to those of the first tree removal. As a result, almost any forestry operation can be construed to potentially cause cumulative effects over time and/or space. The difficulty, of course, is knowing which of the effects on air, soils, water, aquatic biota and wildlife are significant and undesirable. A reductionist approach to cumulative effects assessment might simply consider the individual impact of each forestry practice, or a set of practices (few forestry practices are implemented singly) on a particular resource or group of resources; then sum these impacts over space and time to obtain an index of cumulative effects and reach a conclusion. A more integrative approach would be to evaluate the individual effects of a set of practices on ecosystem attributes of structure, functions, complexity, interrelationships and temporal changes, within a variety of appropriate boundaries and simultaneously display these effects in both ecosystem and landscape settings over a time sequence. Not only would such an assessment focus on system characteristics and processes and on individual locations and species of organisms, but also on communities or assemblages of organisms, their compositions and population dynamics and complex aggregates of landscape units.
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5. CUMULATIVE EFFECTS ASSESSMENTS: CONCEPTUAL FRAMEWORK
Assessing the cumulative effects of forestry practices on air, soils, water, aquatic biota and wildlife requires evaluation of effects as they interact and express themselves over time and across landscapes. Our conceptual framework is based on the concepts that individual forest stands and their soils are parts of: larger forests; watersheds of interconnected stream systems; interconnected wildlife habitat areas; medium- and large-scale landscape areas; and airsheds (i.e. areas influenced by air masses moving from forests of concern). Additionally, forest ecosystems, their components and many of their properties are dynamic. Few forest characteristics, if any, are the same from year to year or decade to decade, and many properties vary from hour to hour, day to day and rainstorm to rainstorm. Finally, it must be emphasized that individual forest management activities at the site level are the practices that ultimately cause cumulative effects. Thus, the minimization or prevention of potential cumulative effects from forestry practices must underscore the importance of on-site impacts. Site-specific evaluations, determinations and information are essential. Forested landscapes must be simultaneously viewed at multiple scales of both time and space in order to assess cumulative effects. To develop a system of assessing the combined effects of forestry practices and natural processes on one forest site last year, a second site today, a third next week, a fourth next year, and so on, is complicated and difficult. It requires attention to details at small temporal and spatial scales and relatively sophisticated integration of information at larger scales. To develop a system of assessing potential cumulative impacts on the environment resulting from forestry practices (Fig. 5) several conditions should exist: Definitions and mapping of landscape areas and units (e.g. forest stands, watersheds, wildlife habitat areas, airsheds) for which cumulative effects analyses are desired. Accurate assessments and understandings of the ranges of natural variation and baseline conditions for critical characteristics of each resource (i.e. air, soil, water, aquatic biota and wildlife) in each location and area of interest. Local and regional ‘refer-
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232 FRAMEWORK
FOR
CUMULATIVE
EFFECTS
EVALUATION
MAPPING SYSTEMS \
BASEUNE RESOURCE CHARACTERISTICS
VARIATIONS OF RESOURCE CHARACTERISTICS
\
/
IMPACTS OF PAST PRACTICES
~+~~.IDIDU~LU~ GEOGRAPHIC
INFORMATION
SYSTEM
I
I \
