Assessing and monitoring forest biodiversity - UCF College of Sciences

Forest Ecology and Management 115 (1999) 135±146

Assessing and monitoring forest biodiversity: A suggested framework and indicators Reed F. Noss1 Conservation Biology Institute, 800 NW Starker Avenue, Suite 31C, Corvallis OR, USA

Abstract Enlightened forest management requires reliable information on the status and condition of each forest ± interpreted from a broad context ± and of change in forest conditions over time. The process of forest planning must begin with a clear statement of goals, from which detailed objectives and management plans follow. Goals and objectives for forest management should re¯ect the conservation value of a forest relative to other forests of the same general type. This paper reviews some recent assessments (with emphasis on North America), presents a framework for forest assessment and monitoring, and suggests some indicators of biodiversity in forests. Among the broad assessments of forest status and conservation value are a global `forest frontiers' assessment by the World Resources Institute, gap analysis projects that assess the level of representation of forests and other communities in protected areas, and ecoregion-based conservation assessments conducted by the World Wildlife Fund. Also important is information on change in forest area and condition over time. Among the common changes in forests over the past two centuries are loss of old forests, simpli®cation of forest structure, decreasing size of forest patches, increasing isolation of patches, disruption of natural ®re regimes, and increased road building, all of which have had negative effects on native biodiversity. These trends can be reversed, or at least slowed, through better management. Progress toward forest recovery can be measured through the use of ecological indicators that correspond to the speci®c conditions and trends of concern. Although there is a wealth of indicators to choose from, most have been poorly tested and require rigorous validation in order to be interpreted with con®dence. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Forests; Biodiversity; Assessment; Monitoring; Indicators

1. Introduction If maintaining the biodiversity and ecological integrity of forests is a goal of management, then it is axiomatic that managers be fully informed about the forests being managed. A primary requirement is to assess the status, condition, and conservation value of the forest in question ± at whatever spatial scale ± 1 Tel.: +1-541-757-0687; fax: +1-541-757-7991; e-mail: [email protected]

relative to other forests. Managers and policy makers need to be cognizant of the biological signi®cance of the forests they manage in a broad context; otherwise they may inadvertently compromise global biodiversity goals by managing their forests inappropriately. The need for assessment applies both to managed natural forests ± for example, those within protected areas ± and to more intensively managed, production forests. (In the temperate zone, at least, I know of few truly unmanaged forests, so I will not consider such forests in this paper.) Assessments of status, condition,

0378-1127/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S0378-1127(98)00394-6

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R.F. Noss / Forest Ecology and Management 115 (1999) 135±146

and conservation value should ideally be made at several spatial scales ± from a broad, global or continental context, to comparisons of forest landscapes within de®ned regions, and to comparisons of stands within and among regions. The historical context is also important. Managers should have some understanding of the forests that occupied their region prior to intensive human activity. They also must have a way of tracking changes in the status and condition of forests over time, extrapolating backward to historic conditions (maybe at several points in time) and forward to a range of potential future conditions. One striking historical trend in temperate forests (e.g. in the US over the past 250 years) has been the loss of primary forests (Noss et al., 1995). Some regions, such as the southern Piedmont and the northeastern states of the US have regained forest area over the past several decades after the abandonment of agricultural land. These secondary forests, however, have not regained the structural qualities of the original old growth (Hunter, 1990; Noss and Cooperrider, 1994; Perry, 1994). Some forest-types have experienced much greater losses and shown less recovery than others (Noss and Peters, 1995; Noss et al., 1995). Predictably, as forest ecosystems decline, so do the species associated with them. Forest-types that have suffered major declines in area or quality or are at high risk of signi®cant losses in the future can be considered `endangered ecosystems,' and are worthy of focused conservation efforts. Given a reasonably clear picture of how forests in a region have changed over time and what the ecological consequences of those changes have been, managers and policy makers must decide what they want their forests to be in the future. Then they must measure their rate of progress toward the future condition deemed desirable and be cognizant of any departures from the desired trajectories. This measurement requires rigorous use of ecological indicators. All of the above may seem logical enough to scientists, but scientists have not presented their case convincingly to policy makers and land managers. Accomplishing the objectives of assessment and monitoring ± being fully cognizant of forest status, conditions, and trends ± is an enormous task. The process I have summarized in a few sentences is, in fact, highly complex and has never been carried through completely for any forest worldwide. Yet, without reliable

information on forest status, condition, conservation value, and trends, how can we possibly meet wellaccepted goals such as maintaining viable populations of native species or maintaining the ecological processes that keep forests healthy? How can we determine where our forest is now along the spectrum of forest health, where it has been, and where it is going? There are ways to make the process of assessment and monitoring less daunting and more practical for forest managers. These ways depend on the intelligent selection of measurable indicators that correspond to the elements of forest biodiversity, health, and sustainability that society ®nds valuable. Managers cannot measure everything of potential interest in a forest, so the choice of what to measure is critical. Indicator development is one of the most popular research topics in natural resources management and conservation today, yet few indicators have been adequately tested or validated. We are still a long way from knowing what to measure to give us the answers we need for urgent and long-term management questions. In this paper I attempt to provide an overview of monitoring and assessment as they apply to conservation of forest biodiversity. I will review some forest conservation assessments at fairly broad scales, then progress to a discussion of speci®c indicators that might be used to track change in forests along particular axes of interest, and ways of measuring progress toward the achievement of forest conservation goals. As this paper was presented at a plenary session, my emphasis is on broad frameworks and strategies rather than speci®c research projects. Most of my examples come from North America, as other papers in this special volume provide examples from other regions, especially Europe and Australia. 2. Goals Before moving to the speci®c topics of this paper, it is necessary to consider the issues of goal-setting and the relationships among monitoring, assessment, planning, and research. Forest planning must involve, ®rst of all, the setting of goals. Goals should be established with adequate knowledge of the past, current, and potential future conditions of the forest (i.e. the historical context, as noted above). Some well-accepted general goals for conservation of biodiversity, in


forests or elsewhere, include (1) Represent, in a system of protected areas, all kinds of communities or ecosystems, across their natural range of variation; (2) Maintain or restore viable populations of all native species in natural patterns of abundance and distribution; (3) Sustain key geomorphological, hydrological, ecological, biological, and evolutionary processes within normal ranges of variation, while being adaptable to a changing environment; (4) Encourage human uses that are compatible with the maintenance of ecological integrity, and discourage those that are not (Noss, 1992, 1995). As with all goals, these derive from values. Implicit in these goals is the value judgment that biodiversity and ecological integrity are good and worth maintaining ± or restoring ± for any number of reasons. The goals just stated would apply at landscape, regional, or broader spatial scales. They would be applied or interpreted in very different ways for different stands, land ownerships, or management units within a forest landscape. Similarly, even within an ownership the speci®c objectives and actions that would underlie each of these goals would vary greatly from case to case, depending on site conditions and other ecological as well as social conditions. Flexibility in implementation need not undermine ambitious goals, so long as managers continually evaluate their actions for consistency with the higher goals and purposes of forest conservation and management. I emphasize the importance of goal-setting because goals and objectives create the entire context and sense of purpose for assessment and monitoring. We assess and we monitor to measure our progress toward meeting established goals and objectives ± or at least that is how it should be. In the case of forests in regions with a history of intensive human land use, such as most of the temperate zone, it would make sense to monitor progress toward goals corresponding to forest recovery. Perhaps the need for goals and targets seems so obvious as to not warrant mention, but I have seen many cases of assessment and monitoring ± including multi-million dollar programs of government agencies ± that lack explicit goals for the system being monitored and have no performance standards for those doing the work. Rarely is any mention made in monitoring and assessment programs of underlying value judgments. Hence, it may be

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dif®cult to distinguish arguments over philosophy from arguments over technique. Many ecologists have pointed out that far too little effort and funding have been devoted to assessment and monitoring of natural resources. When agency budgets are tight, monitoring is often the ®rst program to be cut. This is partly because monitoring is a longterm process, without immediate results to show decision makers who make budgetary and programmatic decisions. But it is also because monitoring can be incredibly boring. Research, in contrast, is perceived as exciting ± as a vigorous and stimulating intellectual activity. Why can assessment and monitoring not be intellectually stimulating, too? As I have argued previously (Noss, 1990), monitoring will be most useful and productive when it is goaloriented and conceptually, organizationally, and physically linked to research. Ideally, monitoring should have similarly rigorous standards as research. It is often useful, however, to complement monitoring with focused research ± for example, population, genetic, or demographic research on rare species ± which tests explicit hypotheses, many of which may have arisen from observations made while monitoring. Assessments, on the other hand, provide a snapshot of a forest at a single point in time. They also provide a statement or performance review of how successful managers have been in guiding a forest toward desired goals. This information should constantly feed back to the forest planning process in the broad sense. Thus, monitoring, assessment, research, and planning should be in continual interplay, with information from one always informing the others. When placed within the context of adaptive management, where management treatments are tested and objectives and practices are adjusted based on information obtained through periodic measurement of indicators (Holling, 1978; Walters, 1986; Noss and Cooperrider, 1994; Noss et al., 1997), uni®cation of planning, assessment, monitoring, and research is possible. Without such a uni®cation, forest biodiversity is unlikely to be conserved, except by accident. 3. Forest assessments Often neglected by forest managers is an objective evaluation of how unique or important their forest is

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biologically, compared to other forests. In the past the information required to make such determinations has not been widely available. Recently, however, several conservation organizations and government agencies have conducted assessments of forest conditions on broad scales, in North America and elsewhere, using defensible methods. I provide a brief review of three of these assessments and refer the reader to the speci®c reports related to these efforts. One broad assessment of forest conditions, recently completed, is the forest frontiers study of the World Resources Institute (Bryant et al., 1997). In this study, frontier forests were de®ned as contiguous blocks of native forest large and intact enough to sustain natural disturbance regimes and, at least for a few decades, viable populations of all native species. Starting with remote-sensing data on current forest coverage worldwide, candidate frontier forests were identi®ed as large forest blocks with few roads or modern human settlements. Next, experts in forest ecology in various regions of each continent were asked to con®rm or reject candidate sites and to redraw boundaries to meet the criteria for frontier forests. They also were asked to assess the current threats to these forests. From this information the World Resources Institute was able to produce maps of each continent depicting forests in three categories: (1) extant forests that consist of patches too small, fragmented, or degraded to meet criteria for frontier forests, (2) frontier forests that are currently under little threat of modi®cation, and (3) frontier forests that are at risk of modi®cation in the near future if not protected. According to this study 46% of the world's forests have been converted to nonforest uses; 22% of the original forest or 40% of the remaining forest worldwide quali®es as intact, frontier forest; and, of the remaining frontier forest, nearly half is boreal forest (Bryant et al., 1997). Few conservationists would disagree that the last intact forests of the world deserve special consideration in forestry programs. As much as possible of these forests should be encompassed in protected areas, especially in regions with little intact forest remaining. Another broad assessment program that has been going on for several years in North America is gap analysis (GAP). Although this effort is not focused speci®cally on forests, the results are offering many insights about the conservation status of native foresttypes. In the US, GAP has been directed by the federal

Department of Interior in collaboration with state agencies, university researchers, and others. GAP is a complex, geographic information system-based program with many potential applications (see Scott et al., 1993, 1996). From the standpoint of forest conservation and management, the most useful information produced by GAP is the analysis of the level of representation of forest-types in protected areas. Beginning with LANDSAT Thematic Mapper scenes, supplemented by ancillary information such as soil maps and aerial photographs, a map of current vegetation is produced for a state or other region. The boundaries of protected areas and other lands managed for their natural values are overlaid on the vegetation map, producing an assessment of how well the various vegetation-types are currently protected. For example, the GAP project for Idaho identi®ed 29 out of 71 vegetation-types that were either not represented in protected areas or had less than 10 000 ha represented (Caicco et al., 1995). The forest-types with no representation were limber pine/ greasewood (Pinus ¯exilis/Sarcobatus vermiculatus), lodgepole (Pinus contorta) ¯oodplain riparian, subalpine ®r±mountain hemlock (Abies lasiocarpa/Tsuga mertensiana), western juniper/mountain sagebrush (Juniperus occidentalis/Artemisia sp.), Douglas-®r (Pseudotsuga menziesii)±limber pine/mountain brush mosaic, and western juniper/low sagebrush (Artemisia sp.) mosaic. It is noteworthy that these types are not presently under intense pressure for timber harvest, yet they may be vulnerable to other human activities, including livestock grazing, mining, and residential development. Forest-types with less than 10 000 ha protected in Idaho include several types with high timber values that are threatened by logging: western redcedar±western hemlock (Thuja plicata±Tsuga heterophylla), grand ®r (Abies grandis)±western redcedar, western larch (Larix occidentalis)±Douglas-®r, Douglas ®r±Engelmann spruce (Picea engelmannii), ponderosa pine (Pinus ponderosa)±lodgepole pine, grand ®r±Douglas ®r, and lodgepole pine±mixed conifer (Caicco et al., 1995). On public lands, at least, there is a strong case to be made for a moratorium on timber sales in these forest-types until viable examples of each type are included in protected areas. World Wildlife Fund-US (WWF) has recently been engaged in conservation assessments for several regions of the world, including Latin America, Asia,


and North America (the latter with the assistance of WWF Canada). The assessment for the terrestrial ecoregions of North America (Ricketts et al., 1997) had several goals: (1) Identify ecoregions that support globally outstanding biodiversity and emphasize the global responsibility to protect or restore them; (2) Assess the types and immediacy of threats to North American ecoregions; (3) Identify appropriate conservation activities for each ecoregion based on its particular biological and ecological characteristics, conservation status, and threats; (4) Encourage decision makers, conservation planners, and the public to adopt an ecoregion-based approach to conservation; and (5) Provide a broad scale framework so that conservation agencies and groups can position their activities within a continental and global context, resulting in more effective allocation of limited conservation resources. Regional and taxonomic experts assessed the biological distinctiveness and conservation status of each of 116 ecoregions in North America (52 of which are forest ecoregions) at a WWF-sponsored workshop in August 1996. Biological distinctiveness was determined through an analysis of species richness, endemism, distinctiveness of higher taxa, unusual ecological or evolutionary phenomena, and global rarity. Conservation status was based on an assessment of landscape and ecosystem-level features such as habitat loss, habitat fragmentation, the size and number of large blocks of habitat, the degree of protection, and current and potential threats. For status assessments ecoregions were grouped into major habitattypes (e.g. temperate deciduous forests), and each ecoregion was assessed in terms of biological distinctiveness and threat only in comparison with other ecoregions of the same major habitat, thus avoiding biases related to latitudinal species richness gradients and other geographic variation. Different combinations of biological distinctiveness and conservation status were used to prioritize ecoregions for conservation action and identify the most appropriate suite of conservation activities to be undertaken within them. A matrix (Fig. 1) was constructed to facilitate this classi®cation. Further analysis of the 52 forest ecoregions in the WWF study (DellaSala et al., 1997) found one-third of the forest ecoregions to have extraordinary levels of biodiversity when compared to similar forests around

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the world. Fully three-quarters of the forest ecoregions in North America were considered critical or endangered because of past, present, or imminent threats to their integrity. In accordance with the recognized importance of these biologically distinctive and imperiled ecoregions at national and continental scales, forest management in these ecoregions arguably should be subject to more intense scrutiny, and standards for such processes as forest certi®cation should be stricter than in regions with lower biological and ecological values. Simply put, these regions have more to lose if managed unsustainably. In order to maintain the biodiversity of these regions, a higher proportion of the forested landscape probably needs to be included within protected areas. This may be especially true for the Appalachian Mixed Mesophytic Forests, Southeastern Conifer Forests, and Klamath± Siskiyou Forests ecoregions in the US, all of which have high levels of endemism and are considered globally outstanding (Ricketts et al., 1997). Endemic species, by de®nition, have narrow and localized distributions, the sites where they occur are irreplaceable, and quite a bit of land may be necessary to represent all these species adequately in protected areas. The current level of protection of forests, in North America and elsewhere, is clearly inadequate ± less than 5% of the forest ecoregions in North America is in protected areas (DellaSala et al., 1997). Forest managers should be made aware of the immense values of protected areas as refugia for species acutely sensitive to human activities and as control areas for forest management experiments. Even if they fail to qualify as controls in a rigorous, experimental sense, natural areas still provide important standards of reference. As we are conducting landscape-scale experiments in forestry, at least some reserves also need to span entire landscapes (i.e. thousands of hectares or larger). 4. Goal-oriented monitoring and management Although this paper has pointed out a variety of deleterious trends and threats to forests related to human activities, the effects of management on forests are not necessarily bad ± nor are they necessarily good. Rather, the impact of management on forest

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Fig. 1. Matrix used by World Wildlife Fund to integrate biological distinctiveness (rows) and conservation status (columns) indices to determine recommended conservation actions and priorities for the terrestrial ecoregions of North America. Adapted from Ricketts et al. (1997).

biodiversity is likely to depend on how different the disturbances caused by humans are from the disturbances to which species have adapted over evolutionary time. Human activities that represent novel disturbances to the species in a given forest are likely to have the most deleterious effects; human activities that effectively mimic natural disturbance± recovery processes may have little effect; and human activities that help restore forests abused by past management may have positive effects on native biodiversity. In probably most of the temperate zone, the major threat to forests today is not outright deforestation. Rather, forests and their biota are suffering from two main processes: (1) simpli®cation, where structurally rich native forests are converted to simpli®ed second-

ary stands or plantations, and (2) fragmentation, where remaining tracts of native forest are small and separated by terrain that is hostile to many species and poses barriers to movement. Both simpli®cation (Norse et al., 1986; Hunter, 1990; Noss and Cooperrider, 1994; Perry, 1994) and fragmentation (Harris, 1984; Wilcove et al., 1986; Saunders et al., 1991; Noss and Csuti, 1997) have been well discussed elsewhere and need not be reviewed here. Suf®ce it to say that these threats remain severe in many regions. Nevertheless, most of the new developments in ecosystembased forest management (e.g. partial cutting systems, retention of woody debris, clustering of harvest units) are aimed precisely at reducing these threats. Whether these practices will succeed in reducing threats to biodiversity to an acceptable level remains to be seen,


Fig. 2. The shift from a natural condition to the present condition for a generalized forest landscape, as exemplified by seven trends. Dashed arrows in reverse direction to trends indicate the potential for restoration. From Noss (1993b).

but some experiments are fairly promising (Kohm and Franklin, 1997). In forging a strategy to restore forests and manage them sustainably, it is helpful to identify the speci®c structural and functional changes that have led to unacceptable conditions. From this knowledge speci®c objectives for reversing ± or at least slowing ± undesirable changes can be devised, and monitoring can be implemented to track progress toward attaining objectives. Fig. 2 provides a simple framework for goal-oriented monitoring and management in a forest landscape that has experienced several degenerative trends: old forests have been replaced by younger forests and plantations; structurally complex forests of all ages have been replaced by simpli®ed stands; large, well-connected patches have been replaced by smaller, more isolated patches; thousands of miles of roads have been built in what once were roadless landscapes; and natural ®res have been suppressed. Many forests in North America and elsewhere have experienced these kinds of changes, with a concomitant loss of native biodiversity and ecological integrity, (Noss, 1993a, b; Noss and Cooperrider, 1994). These trends can, to some extent, be reversed through a combined strategy of protection, restoration, and management of forests, a strategy that includes opportunities for sustainable production of forest products. Progress toward forest recovery can be tracked by selecting speci®c indicators that correspond to each of these axes (Table 1).

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Since we do not know precisely how to achieve recovery of any forest, an experimental approach (adaptive management) is called for. Prescribing a desired future condition in speci®c terms is always problematic ± especially given uncertainties about future background conditions (e.g. global climate) and species responses ± but in most cases we can de®ne a desired future direction for forest management, i.e. reversing trends that we know have been associated with biotic impoverishment. All that is required to de®ne the direction of forest management is some general agreement on values and goals (albeit this agreement may be dif®cult to achieve when many stakeholders are involved). 5. Ecological indicators Measuring progress or change of any kind requires the use of indicators. When ecological indicators are mentioned, most resource managers think of indicator species. Species, however, are only one kind of indicator, and those wishing to monitor species must select speci®c attributes of species' populations for measurement (Noss, 1990; and see Table 1). Selecting the best indicator species for the purposes at hand is dif®cult and controversial. In many cases attributes (e.g. demographic parameters) of species' populations might be more useful in validating indicators (i.e. determining if they indicate what we think they do) than as indicators themselves. To appreciate this point, consider the issue of species sensitivity to habitat losses. As pointed out by Angelstam (1996), species with different life histories show very different responses to habitat losses (Fig. 3). Which of the hypothetical species in Fig. 3 would be the best indicator of forest conditions? The answer is not straightforward. Species A might be so rare that it is dif®cult to monitor. Perhaps B would be most useful because it shows an intermediate response; it might be measurable over a greater range of forest conditions than A or C. But maybe we have this backwards. Forest cover and pattern (e.g. see Table 1) might be the indicator variables that are easiest and cheapest to monitor ± through remote sensing ± and demographic responses of species (of Types A, B, or C) provide the validation of our indicators and allow us to determine thresholds for management planning. If no strong and consistent

Trend Oldgrowth Shift from older to younger age classes of trees; loss of old growth stands and old individual trees

Large blocks of continuous forest replaced by more, but smaller blocks

Patch Continuous or connected forest blocks replaced by separate, isolated blocks

Other Suppression of natural fires and other alteration of natural disturbance regimes

Scale and type of measurement

Rotation period of stand-replacing disturbances (natural and human-caused); diameter and age class distributions of surviving trees in stand and trees removed from stand; mean and range of tree ages within defined seral stages across landscape; diversity of tree ages or diameters in stand; area of landscape occupied by old growth and other seral stages; amount of late-successional forest habitat in all patches and per patch Abundance and density of key structural features (e.g. snags and down logs in various size and decay classes); spatial dispersion of structural elements within stand; physiognomy, including foliage density and layering (profiles), canopy openness, and horizontal patchiness of profile types; percentage of stand in gaps of various sizes and ages since formation; diameter and age class distributions of surviving trees in stand and trees removed from stand; diversity of tree ages or diameters in stand; abundance of species dependent on particular structural features Forest patch size frequency distribution for each seral stage and community type and across all stages and types; size frequency distribution of late-successional forest interior patches (minus defined edge zone, e.g. 100±200 m); fractal dimension (a measure of boundary length and complexity); patch shape indices (e.g. deviation from roundness); patch density; fragmentation indices (e.g. from FRAGSTATS software); relative abundance and demographic characteristics of species requiring large patches of forest

Landscape (remote sensing) and stand (direct measurements)

patch density; fragmentation and connectivity indices; interpatch distance (mean, median, range) for various patch types; juxtaposition measures (percentage of area within a defined distance from patch occupied by different habitat types, length of patch border adjacent to different habitat types); structural contrast (magnitude of difference between adjacent habitats, measured for various structural attributes); presence of habitat corridors or other movement routes for fragmentation-sensitive species; relative abundance and demographic characteristics of species with poor dispersal abilities or otherwise isolation-sensitive

Landscape-scale measurements using remote sensing (with ground-truthing); surveys of isolation-sensitive species

Frequency, return interval, intensity, timing (seasonality or periodicity), patch size (areal extent), predictability, variability, and other characteristics of fires and disturbances; patch size frequency distribution for each seral stage and community type; abundance and density of key structural features (e.g. snags and down logs in various size and decay classes); physiognomy, including foliage density and layering (profiles), canopy openness, and horizontal patchiness of profile types; percentage of stand in gaps of various sizes and ages since formation; relative abundance and demographic characteristics of species sensitive (either positively or negatively) to fire and other kinds of disturbance

Landscape (remote sensing) and stand-level measurements; surveys of disturbance-sensitive species

Direct stand-level measurements for most indicators; remote sensing for some (e.g. gaps)

Landscape-scale measurements using remote sensing (with ground-truthing); surveys of area-dependent species


Shift from structurally complex, all-aged natural forests to simplified secondary forests and plantations

Indicators

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Table 1 Indicators that might be used to monitor degenerative trends in forest conditions (or their reversal through sustainable and restorative forestry). These are only examples of many potential indicators for monitoring and assessing the biodiversity and ecological integrity of forests. From Noss (1997)

Construction of a vast network of roads to access timber

Invasion of exotic species following road construction, site disturbance, and dispersal by vehicles, other equipment, and humans Increased air pollution, including lowlevel ozone, acid fog, acid precipitation, and particulates

Increasing recreational use of forests (hiking, hunting, fishing, camping, off-road vehicle use, etc.)

Direct measures of air and precipitation contents; biomass increment and other measures of tree productivity; input/output budgets of ions (as indicators of change in soil pH and nutrient status and of tree nutrition); level of direct damage to leaves and other tissues; status of pollution-sensitive and pollution tolerant species Changes in biomass, distribution, productivity, and other characteristics of temperatureand moisture-sensitive species; changes in relative abundances of species with C3, C4, and CAM metabolic pathways Access indicators (see roads indicators above; also density of airstrips, boat landings, other access points); size and proportion of area closed to human use; measures of erosion, ground-level vegetation density and condition; measures of exotic species invasion (see above); visitor days for various types of recreation; abundance and demographic characteristics of species sensitive to human harassment or simply human presence; visitor attitudes

Landscape-scale measurements using remote sensing (with ground-truthing); engineering data Stand-level measurements; landscape-level measurements for exotic species that can be sensed remotely Stand-level measurements; remote sensing of patterns of mortality and morbidity Stand and landscape measurements Stand and landscape measurements; surveys of sensitive species and visitor attitudes


Global warming

Road density (mi/mi2 or km/km2) for different classes of road and all road classes combined; percentage of landscape in roadless area (for different size thresholds, e.g. 1000 ha and above, 5000 ha and above); miles or kilometers of roads constructed, reconstructed, and closed (seasonally and permanently) each decade; amount of roadless area restored through permanent road closures and revegetation each decade Ratio of exotic species to native species in community (species richness, cover, and biomass); invasion rates and pattern of spread of exotic species; demographic characteristics of particular exotic species and native species sensitive to predation or competition from exotics

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Fig. 3. Model of how species with different life histories might differ in their response to habitat losses (from Angelstam, 1996). The three curves represent species with different requirements. A, species with narrow habitat and/or large area requirements and which cannot disperse through the matrix; B, species with moderate area requirements and a limited dispersal ability through the matrix; C, generalist species with very small area requirements and which can disperse through the matrix.

relationships between demographic responses and landscape variables are found, it is time to test new indicators. Nevertheless, often it makes sense to monitor species' populations directly, particularly if those species are at high risk of extinction or are considered ecologically, economically, or socially important. Among the kinds of species that might make good targets for monitoring are those listed below (the ®rst four categories are from Lambeck, 1997; the latter three I have added). The objective is to identify a suite of focal species, each of which is used to de®ne different attributes that must be present in a landscape if it is to retain its biota. Within each of the ®rst four categories, at least, the species that is most sensitive would presumably be an umbrella species for the others in its category (Lambeck, 1997; Noss et al., 1997). 1. Area-limited species: Species that require the largest patch sizes to maintain viable populations. These species typically have large home ranges and/or low population densities, such as many mammalian carnivores.

2. Dispersal-limited species: Species that are limited in their ability to move from patch to patch, or that face a high mortality risk in trying to do so. These species require patches in close proximity to one another, movement corridors, or crossings across barriers such as roads. Flightless insects limited to forest interiors, lungless salamanders, small forest mammals, and large mammals subject to roadkill or illegal hunting are among the forest species in this category. 3. Resource-limited species: Species requiring specific resources that are often or at least sometimes in critically short supply. These resources may include large snags, nectar sources, fruits, etc. The number of individuals the region can support is determined by the carrying capacity at the time the critical resource is most limited (Lambeck, 1997). Hummingbirds, frugivorous birds, and cavity-nesting birds and mammals are in this category. 4. Process-limited species: Species sensitive to the level, rate, spatial characteristics, or timing of some ecological process, such as flooding, fire, wind transport of sediments, grazing, competition with exotics, or predation. Plant species that require fire for germination or to escape competition are among the many possible species in this category. 5. Keystone species: Ecologically pivotal species whose impact on a community or ecosystem is large, and disproportionately large for their abundance. Examples in forests include cavity-excavating birds and herbivorous insects subject to outbreaks. 6. Narrow endemic species: Species restricted to a small geographic range (e.g.