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Indicators of forest degradation – biodiversity
Ian Thompson, Robert Nasi, Kimiko Okabe, Valerie Kapos, and James Gordon
1.2 Introduction to forest biodiversity indicators:
Forest-associated biodiversity is one of several criteria by whichforest degradation can be assessed. We are not proposing a single ‘biodiversity score’ or cumulative index, rather we suggest that loss of biodiversity needs to be assessed independently for several key indicators. These indicators would be scored against an a prioriexpectation of level or kind of biodiversity (e.g., number of certain species, populations of functional species, numbers of ecosystem types, etc.) to determine a level of degradation for each indicator and for the forest stand or landscape.At the very least, an indicator requires two points in time, or a measure against a control value. The proposed biodiversity indicators would form a common set that could be employed to determine the amount of degradation in a local forest, regardless of the forest type. The actual component, however, (e.g., a species or a forest type) being measured would obviously differ depending on the local forests.
Degradation differs from forest loss but some loss of forests across a landscape can degrade the larger area from a biodiversity perspective. For example, Andren (1994) suggested a threshold of 30-40% forest loss across a landscape resulted in non-linear declines in species occurrence. This threshold value has since been tested for various species and landscapes with the result that generality is difficult and thresholds depend on the species of interest and forest type (e.g., Betts and Villard 2008). Hence, thresholds may need to be determined based on expected range of variation for each ecosystem, community, or species of interest.
Ecologically, biodiversity objectives relate in large part to the functioning of the ecosystem. This includes important ecosystem services provided by biodiversity such as pollination (by bats, birds, andinsects), decomposition (soil arthropods, fungi, or micro-organisms), seed dispersal (insects, birds, mammals, fish), resilience, disease reduction, etc. Such processes are also affected by the scale at which they are assessed. Biodiversity indicators for forest degradation should be assessed for two scales: landscapes (multiple stands) and stands (individual groups of trees distinguishable from other surrounding groups of tree by their species composition). Both scales are important and both require a different, but sometimes overlapping, set of indicators. In many cases, scaling up from stand to landscape will be required for reporting degradation. Indicators must be relatively uncomplicated to use in terms of data collection and easily repeatable, especially for countries with limited resources. The indicators must also be unambiguous and provide quantitative data that can be used to assess trends over time.
2.0 A summary of biodiversity indicators from other forest-related processes:
The following list reflects sustainable forest management (SFM) indicators from indicator processes (Table 1), certification processes, and indicators as suggested in Sheil et al. (2004) and Loh et al. (2005). SFM and forest degradation are not the same consideration and so many of these indicators are not helpful. However, if some of these indicators are useful for both and are possibly being collected for SFM, then it makes sense to use those indicators to suggest degradation as well.
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Table 1. Biodiversity indicators for sustainable management from five different indicator sets or processes. Indicators relevantto indicate degradation are marked with an asterisk.
Process or attribution / Landscape / Ecosystem / Species / Genetic / Health / OtherITTO / 5.1 Forest protected area / *5.4 Number of listed species
*5.6 Measures in place to protect listed species, species of interest, keystone species, and seed trees. / 5.5 Measures for protection of genetic diversity of commercial species or listed species
Montreal Process / *1.1.c Fragmentation of forests / *1.1.aArea and percent of forest by forest ecosystem type, successional stage, age class, and forest ownership or tenure
1.1.bArea and percent of forest in protected areas by forest ecosystem type, and by age class or successional stage / 1.2.a Number of native forest associated species
*1.2.b Number and status of native forest associated species at risk, as determined by legislation or scientific assessment
1.2.c Status of on site and off site efforts focused on conservation of species diversity / *1.3.a Number and geographic distribution of forest associated species at risk of losing genetic variation and locally adapted genotypes
*1.3.b Population levels of selected representative forest associated species to describe genetic diversity
1.3.c Status of on site and off site efforts focused on conservation of genetic diversity / *3.a Area and percent of forest affected by biotic processes and agents (e.g. disease, insects, invasive species) beyond reference conditions
*3.b Area and percent of forest affected by abiotic agents (e.g. fire, storm, land clearance) beyond reference conditions / 2.a Area and percent of forest land and net area of forest land available for wood production
Convention on Biological Diversity / *7.1 Patch size distribution, connectivity and fragmentation
*7.2 Area burned
*5.1 Change in forest area / 1.1 Percentage area of forest protected by forest type
*1.2 Percentage of threatened or vulnerable ecosystems protected
*5.2 Forest areas by class: primary, modified natural, semi-natural, plantation / *2.1 Changes in abundance of populations of selected species
2.2 Changes in distribution of selected species
*2.3 Number of listed species by category
*2.4 Changes in status of individual listed species / 3.1 Area managed for ex situ conservation of forest genetic resources
3.2 Area
managed for in situ conservation of forest genetic resources / *6.1 Number of invasive species in forests
6.2 Number of invasive species controlled
*6.3 Area of forest affected by IAS
*7.2 Area burned / *4.1 Percentage of forest area under management that is certified
*5.3 Area of degraded forest
Biodiversity Indicators Partnership / *9.3 Forest fragmentation / *1.1 Extent of forests and forest types
1.2 Extent of selected habitats / 2.1 Living planet index
2.2 Global wild bird indicator
*4.1 Change in the status of listed species / 5.1 Ex situ collections / *8.2 Number and trends of AIS / 6.1 Area managed and certified
6.2 Area managed that has been degraded and deforested
MCPFE
ForestEurope Indicators / *4.7 Landscape
-level spatial pattern of forest cover / *4.3 Area of forest and other wooded land, classified by “undisturbed by man”, “semi-natural” or by “plantations, each by forest type
*4.4 Area of forest and other wooded land dominated by introduced tree species
*4.5 Volume of standing deadwood and of lying deadwood on forest and other wooded land classified by forest type
*4.9 Area of forest and other wooded land protected to conserve biodiversity, landscapes and specific natural elements, according to MCPFE Assessment Guidelines / *4.8 Number of threatened forest species, classified according to IUCN Red List categories in relation to total number of forest species / *4.6 Area managed for conservation and utilisation of forest tree genetic resources (in situ and ex situ gene conservation) and area managed for seed production
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3.0 Indicators of degradation based on maintaining biological diversity
The proposed biodiversity indicators would apply forall forest types for managed (includingagro-forests, which are not classified as forests in FRA), used but unmanaged, and primary forests. For managed forests, the management objectives might be related to any goods and services, such as game animals (bushmeat), other NWFP production such as certain tree species used for carving or crafts, other foods, wildlife viewing possibilities, etc., or they could relate to maintaining all species in time and space. The criteria for indicator selection included: sufficiently generic to apply globally, techniques available to allow measurement, possible existing data sources, reflect a change of biodiversity, potential to be scaled up, and indicates a change in ecosystem goods and services. Ideally, it would be advantageous if indicators could be sensed remotely, but for biodiversity this is not possible for most because many indicators relate to species or structures that must be found on the ground. Hence, not all of the proposed indicators can be sensed remotely and the ones that are ground-based could be viewed as correction factors for forests reported as ‘not degraded’ or ‘possibly degraded’ based on satellite or other imagery. To that end, a stratified sample will be required for each forest typeto at least the level of sub-biomes for ground sampling.
From among the proposed biodiversity indicators, the minimum indicator set that should be used to assess forest degradation from a biodiversity perspective is ‘ecosystem state’ and‘forest fragmentation’. Both these indicators can be determined through remote sensing. Ground-based indicators are more difficult and labour-intensive for data collection, but are necessary to obtain a full understanding of the possible degradation condition. The technical rationale for the suite of selected biodiversity indicators of forest degradation (Table 2) follows below.
Table 2. Proposed biodiversity indicators of forest degradation.
Indicator / Measurement method / Relevant case studies or data source / Scale of measurementRemotely-sensed indicators:
Ecosystem state (resilience) / Satellite or aerial photographs: expected forest type for soil and moisture condition / Surrounding area, PAs etc. / Stand or landscape
Fragmentation/intactness and road density / Satellite or aerial photos: area deforested, roads/km2 / UNEP-WCMC, WRI / Landscape
Ecosystem diversity / Satellite or aerial photography:extent of each ecosystem type / NFI / Landscape (stand)
Species-based indicators:
Species 1: Expected community composition by forest tree species for the ecosystem type / Ground plots: species composition / Individual research, gov’t surveys, expert opinion, IUCN list
Niger WP 168 Ghana WP 160 India WP 157 Nepal WP 163 / Stand and landscape
Species 2: Key indicator species including threatened species, old forest species, and hunted species* / Surveys for change in population size (relative or absolute) / IUCN / Stand, landscape
Species 3: Invasive alien species** / Remote sensing or ground surveys: area of forest affected / Stand, landscape
Species 4: Functional species / Surveys for change in population size, surveys for expected function products (e.g., fruit production) / Stand
*hunted species (bush meat) dealt with under ‘Forest Goods’
**invasive species dealt with under ‘Forest Health’
3. 1Technical rationale for ecosystem state as an indicator of forest degradation
Forest state refers to the ecosystem type expected for a given stand and infers to the long-term resilience of the forest ecosystem. If the resilience is overcome through disturbances, the ecosystem state will change. The main ecosystem states of interest are defined by the dominant floristic (tree) composition and stand structure expected for a given stand. Capacity for resilience and ecosystem stability is required to maintain essential ecosystem goods and services over space and time (Thompson et al. 2009). Loss of resilience may be caused by the loss of functional groups caused by environmental change such as climate change, or a sufficiently large or continual alteration of natural disturbance regimes (Folke et al. 2004). Loss of resilience results in a regime shift, often to a state of the ecosystem that is undesirable and irreversible. Resilience needs to be viewed as the capacity of natural systems to self-repair based on their biodiversity, hence the loss of biodiversity will often mean a reduction of that capacity.
However, some changes in the relative abundance of dominant species may occur following a disturbance with little apparent consequence to the ecosystem. In some cases, functional roles may also change among species but the forest maintains its resiliencewith respect to its capacity to provide certain (most or all) ecosystem goods and services, even if the forest composition and structure are permanently altered by disturbances. This ecological resilience (Gunderson 2000, Walker et al. 2004) is strongly dependent on biodiversity (Thompson et al. 2009), and is the focus of this indicator for management purposes. As noted above, change in ecosystem condition may be best measured using several other indicators: species composition, biomass production, etc. However, a large change in forest state, regardless of cause, will result in a forest that produces different goods and services that might be derived from the expected forest type. A major negative change in state from one forest type to another is a clear indication of degraded forest (Thompson et al. 2009).
A negative change in state refers to a loss of resilience and a shift in the system to a completely different ecosystem, with a consequent reduction and change in goods and services. For example, if a forest is expected to be of mixed species but instead it is actually mostly uniform, or it should be closed canopy but is actually open or savannah etc., then the state has changed. These are negative changes in state that would be reported as degraded forest from a biodiversity perspective. For example, Souza et al. (2003) mapped degraded forest classes in the Amazon, defined as heavily burned or heavily logged and burned using satellite data. A relatively simple index of forest degradation could be a sum of the area of atypical or unexpected forest types on a given landscape, such as area of open canopy forest in a closed canopy landscape. These changes are relative to the forest that would be expected on a given site or landscape. Hence, the indicator is: area of forest that has changed state in a negative fashion.
3.1.1Method for stand and landscape-scale monitoring:
1. Develop or use a forest classification system that reflects the available data: such as for few data, use broad forest type (open, closed, deciduous, mixed species, etc.), or with better data, an ecosystem or forest type classification (e.g., mixedwood forest dominated by Acer sp. on mesic soils, etc.), and apply the system over a landscape based on expectation from local knowledge, soil types, and known moisture regimes.
2. Map forest stands based on their condition using remote sensing or ground surveys and report area of stands in states other than expected.
3. Report area of forest that occurs in an unexpected or undesired state.
3.2Technical rationale for forest fragmentation as an indicator of forest degradation
Land use change and other forms of disturbance often lead not only to a reduction in overall forest area, but also to division of remaining forest into smaller and smaller pieces. A certain amount of fragmentation on a landscape is unlikely to result in loss of biodiversity, but thresholds occur that are system and species specific (e.g., Fahrig 2003).
In some cases fragmentation may have a positive effect on some animals and animal groups, with fragmentation leading to higher levels of biodiversity in a given area. Negative effects tend to depend on the level of fragmentation, the forest type and the animals and plants of interest.
Forest fragmentation poses a substantial threat to global biodiversity and may cause cascading impacts on a wide range of ecosystem functions and services depending on thresholds (Wu et al. 2003, Millennium Ecosystem Assessment 2005). When land-use change breaks tracts of continuous forest into smaller pieces, it also creates new edges between forest and other vegetation types and disconnects patches from adjacent, continuous habitat (Collinge 1996, Fahrig 2003, Saura and Carballal 2004). There is a wealth of information that has been produced regarding forest fragmentation and its impacts on biodiversity (e.g., see reviews by Fahrig 2003, Fisher and Lindenmayer 2007). A review (Fazey el. 2005) of publications of conservation biologists found that habitat fragmentation was the largest single area of study in conservation biology. Large animals and top carnivores, which are well known to require large areas of habitat, are especially vulnerable to the reduction in habitat area caused by forest fragmentation, and they may disappear entirely from forest patches because food or other resources are inadequate to support them. Smaller species are also affected, and disappearance of some species from forest fragments can profoundly affect the forest itself, for example through changes in seed dispersal and regeneration. Even species that persist do so in smaller populations, which may be vulnerable to other ecological changes such as disease, predation, or Allee effects (i.e., reduced breeding because of low population density). Rare species and those that normally occur at low population densities are especially vulnerable to these kinds of effects. The edges of forest patches are associated with environmental gradients that affect ecological processes including weather effects, canopy gap formation, biomass and nutrient cycling changes, regeneration, invasion, and altered levels of predation. For example, invasive species are often favoured by an increased incidence of forest edges within the landscape. The separation of forest fragments from each other and from larger blocks of forest reduces the movement of species that are reluctant or unable to cross non-forest areas and increases the chance of local extinction of individual species. Overall, these area, edge and isolation effects can singly and in combination adversely affect local populations of many organisms and increase their vulnerability to stochastic events, leading to population decline or extinction (Driscoll and Weir 2005, Arroyo-Rodríguez et al. 2007)
Natural ecosystems, especially forests, have become increasingly fragmented on a global scale because of forest development. Increasing universally highlevels of forest fragmentationis a major cause of well-documented reductionsin the distribution and abundance of individual species and on the species composition of many forest communities, especially in temperate and tropical forests (e.g., Laurance et al. 2002, Kupfer et al. 2006, Watling and Donnelly 2006, Ewers et al. 2007, Fischer and Lindenmayer 2007). Empirical evidence shows that fragmentation has significant and largely negative implications for biodiversity through impacts on species composition and stand structure of the altered spatial patterns (e.g. area reduction, reduced interior space, increased edge exposure, isolation) (Fahrig 2003). Alteration of forest spatial patterns affects biodiversity in both tropical and non-tropical forests (Wade et al. 2003). There is also evidence that forest fragmentation may reduce total carbon storage at the landscape scale (Groenveld et al. 2009) and that hydrological cycles are appreciably altered by forest fragmentation causing changes both in evapotranspiration and local climates (REF) and changes in run-off (Ziegler et al 2007). Fragmentation appears, therefore, to be an excellent indicator for biodiversity degradation for all types of forests, except possibly boreal forests where, at least in managed landscapes, fragmentation is ephemeral (Thompson and Welsh 1993).