Assessing Degradation of Forest Goods and ServicesManuel Guariguata (CIFOR), Cesar Sabogal (FAO), Diji Chandrasekharan (WB)

Introduction

Degradation of the provision of forest goods and services means that their supply is reduced permanently or over a long term, as temporary reductions can be part of sustainable management. This is illustrated in Figure 1. Forest goods include timber, fuelwood (including charcoal production), and non-wood forest products (NWFP). Forest services include biological diversity (reference to the respective chapter), mitigation and adaptation of climate change, conservation of soil and water (reference to the respective chapter), recreation and amenity, as well as various cultural and spiritual values which forests provide to local populations. Changes in the supply of forest goods are directly measurable while many services are often subject to indirect measurement. Reduction of the availability of various socio-economic benefits from forest goods and services can therefore be often assessed only based on surveys on their availability and use among local populations.

Long-term reduction in the supply of forest goods is assessed based on whether over-harvesting has occurred. Harvesting of forest goods is not per se degradation unless it leads to permanent significant reduction of their supply. However, the result can be degradation if harvesting levels are higher than what is sustained by the forest in terms of regrowth. In practice, assessment is often made comparing the removal of forest goods with the level which is defined in the a priori management objectives as typically expressed in the forest management plan.

Over-harvesting in a forest area can take different forms such as uncontrolled logging, pervasive collection of non-timber forest products (NWFP) and fuelwood, and excessive production of charcoal. Underlying factors for these activities are short-term economic benefits from the sale of forest goods or meeting subsistence needs which goes beyond the reproductive capacity of the forest. Typical factors in such situations include lack of proper planning and control of the forest utilization, prevalence of illicit activities, weak governance as well as lack of awareness and knowledge among local populations on how forests should be sustainably managed.

Due to wide variation on local forest situations and thereby management objectives, the specificity of forest type, harvesting activities and local conditions should therefore be considered when defining indicators for assessing whether a long-term significant reduction in the supply of forest goods and services has taken place. 1.

In this section the focus is on natural tropical forests in which most of the forest degradation is taking place (ref to chapter 1). When primary natural forest is subject to human intervention, the outcome is typically a change in biomass and species composition. The forest becomes modified2 and it no more contains the same characteristics as before because the combination of forest goods and services is different. Modified forests can be managed sustainably for production purposes while maintaining other values or services even though their combination is different from the primary forest. Such a modified forest cannot therefore be considered a priori degraded. However, if such a forest has e.g. less biodiversity than primary forest, from the biodiversity perspective the forest may be considered “degraded” (reference to the biodiversity chapter) .

1 See further discussion on the issue in Simula (2009).

2 In this connection FRA uses the concept of “modified forest”. The term “secondary forest” is also frequently used for modified natural tropical forest which has been subject to selective logging.

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In the assessment of degradation of forest goods and services a proper understanding of temporal and spatial scales is necessary. In general, assessment should always be over a sufficiently long time period in order not to mix those changes in the forest which are part of its regular sustainable management. This is illustrated in Figure 1 in which the average biomass volume per hectare is used as an indicator and can vary in the short run due to selective cuttings of large commercial trees or thinnings in young stands. What is important is how in this case the biodiversity develops in the long run. Further information on this can be found in the chapter on biodiversity3. Forest degradation is often a slow gradual process which can take long time periods. This kind of change is often difficult to capture even by field observation as it implies a long-term loss of biomass, productivity or changes in species composition that are difficult to assess, especially the impacts on soils, water, nutrients, biodiversity and the landscape. However, degradation can also be abrupt e.g. due to excessive logging in which case, if significant, it is easily detectable by remote sensing (see for instance Gerwing 2002, de Souza 2009). This calls for continuous monitoring to enable fast corrective action and prevent further degradation.

The short-term view among many stakeholders on forest changes due to harvesting as degradation derives from the misperception that a forest stand is the basic unit of decision-making in conserving or enhancing productive capacity or provision of forest services such as carbon sequestration or conservation of biodiversity. However, forest management decisions are based on planning which concerns a territorially designated forest management unit (FMU) which may be a holding, a forest estate or another type of forest management unit (watershed, landscape etc.). Depending on their size, these management units typically consist of at least dozens of stands or management compartments with different species compositions, ages or other structural characteristics. The mixture of individual stands in the management unit is under a constant change due to biological processes and management interventions. For instance, carbon stock reduction in a year may take place in some stands while in the others the stock is increased as a result of biological growth. It is the territorial entity for which management objectives are set and which as a whole should be managed and assessed for such objectives as supply of forest goods and services in appropriate combinations in the local conditions. This principle is graphically illustrated in Figure 2 where the average growing stock (m3/ha) is used as an indicator.

In forest management prescriptions, it is probably useful to set thresholds for “degraded” and “non-degraded” on the basis of some measurable indicators such as the mean annual increment (MAI), canopy cover, or stocking density which is often used to identify whether a forest should be considered “degraded”, i.e. the productivity is less than expected on the site. Another option is to relate the productivity indicator value to that of sustainable harvesting levels.

Indicators of over-harvesting include declined yields, reduced or altered population densities, diminished reproductive capacity both at the (commercial) species and targeted population levels (as evidenced e.g. by abandoned or exhausted coppices in certain forest types), and deterioration of the soil quality (due to harvesting damage or inappropriate forest road construction). While most of these indicators are assessed at the stand level, others related to environmental aspects such as changes in animal and plant population structures and densities need to be assessed on a broader level. This is also the case with assessment of carbon stored in the forest. In addition to reducing the carbon stored in aboveground biomass, forest degradation may also reduce future biomass (i.e., the growth and accumulation of carbon in woody biomass) owing to a shift in species composition or tree size structure from mature forest trees to pioneer tree species and woody vines (lianas).

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In the case of informal/subsistence management, evidence of degradation of the resource can be assessed by monitoring sequential reductions in the abundance, density, and/or size class distribution in a forest either over time or distance from a defined point4. It is also possible to use social and socio-economic indicators as proxies for degradation of sustainable use with the caveat that these social variables would need to be adjusted for other factors that may influence their change. Social indicators can help in triangulating/validating information on e.g., non-timber forest products5.

Assessing degradation of forest goods Table 1 lists some indicators of degradation of the provision of forest goods (timber, NWFP and fuelwood). The table also includes potential sources of information and limitations of measuring degradation of the corresponding forest good

Over-harvesting of timber

Considering a formal management (i.e. following an approved forest management plan or a similar document), the main task consists of comparing the actual level of harvesting against what was planned or authorized assuming that the plan was based on sustainability. Over-harvesting occurs if the actual harvest intensity per unit area is higher than the allowable harvest intensity (assuming no changes in cutting cycles). The measurement of harvest intensity should also include the losses resulting from felling damage.

For sustainable timber harvesting in natural (tropical) forest (yield regulation – see Box 1), the essential information needed to assess over-harvesting of timber includes: (i) the annual allowable cut (AAC, measured as total m3 harvested in a designated area) or allowable harvest intensity (m3/ha), (ii) the minimum diameter at DBH commercial size), and (iii) the net periodic mean annual increment or net annual commercial increment (m3/ha/yr) – the total change in volume over the measurement period including growth and recruitment and deducting losses from mortality, averaged as an annual value. The main limitation of using any yield regulation method is the availability of reliable growth information, ie. historical measurement data on the growing stock. Indicators that can be used as proxies are discussed below. BOX 1. Yield regulation* Yield regulation is the means to achieving sustained yield. Sustained yield itself implies that products removed from the forest are replaced by growth, with or without management interventions such as enrichment replanting, liberation thinning, etc. The annual allowable cut (AAC) is the practical measure of the sustained yield for a period and can be used to monitor forest production and set limits for forest use. It is usually quoted as an aggregate figure, for all commercial species, but in forest management planning it is often broken down by species/species group and stands or harvesting compartments. It will definitely relate to commercial yield and size limits.The mean annual increment (MAI) is calculated using tree-specific growth functions or derived from the data on successive inventories. In tropical natural forests MAI for the commercial species must be corrected for expected logging damage in the calculation of AAC. In practical terms, AAC should be about 50-70% of the estimated commercial MAI, depending on observed levels of logging damage but the share can be higher if Reduced Impact Logging (RIL) is practised. In the estimation of the commercial volume that can be extracted an allowance for within tree wastage and degrade is needed. The latter is necessary if AAC is monitored and controlled based on

4 An useful model is presented in: Ahrends, A. et al. 2010. Predictable waves of sequential forest degradation and biodiversity loss spreading from an African city. PNAS 107 (33): 14556-14561. 5 Kleine et al. (2009), mention that local knowledge about the absence/ lack of desirable products and services from the forest assisted in describing the level of forest degradation in India, where unregulated and unsustainable exploitation for fuel wood and other wood and non-wood products caused forest degradation.

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extracted volumes, and is likely to be an additional 50-70% reduction factor. Thus Dawkins’ (1964) pan-tropical mean estimate of commercial MAI of 1 m3 ha-1 yr-1 amounts in practice to pan-tropical AACs of around 0.25-0.5 m3

ha- yr-1 measured as logs at the landing or roadside. There is however a wide variation by geographic zones and forest type. According to Whitmore (1998) natural lowland rain forest commonly adds 2-3 tonne/year of dry weight of bole timber which may increase to 3.6-12 tons/year in forest under good silvicultural management. Growth rates vary with the phase of the forest growth cycle and therefore care must be taken in obtaining or interpreting biomass increment figures from natural tropical forests. Failure to allow for varying growth rate with forest phase is a major weakness of productivity studies on natural tropical forests. -----------------------------------------------------------------------------* Source: Alder D. 1999. Some issues in the yield regulation of moist tropical forests. Paper presented at the Workshop on humid and semi-humid tropical forest yield regulation with minimal data. CATIE, Turrialba, Costa Rica. July 5-9, 1999. 14 p. Whitmore, T.C. 1998. An Introduction to Tropical Rain Forests. Oxford University Press. Second Edition. New York.

Timber removals

This indicator corresponds to the volume of timber removed from a given forest area6. In production forests this volume can be compared with the authorized volume to be extracted according to the management plan to measure whether there has been over-harvesting. The comparison is based on the extracted commercial volume, and can be done at the level of annual harvesting by compartment and for the entire FMU and by species. The information refers to the recorded volume of legally harvested timber which in some instances can represent only a fraction of the total removals if illegal logging is significant. The volume of illegally extracted timber should be estimated to be verified through successive forest inventories. See Table 2 for further reference on scale, data and method for this indicator.

Growing stock

The growing stock refers to the standing volume of all trees above a selected minimum diameter (DBH) growing on a designated forest area. It can be measured in terms of stocking density (m3/ha), basal area (m2/ha) or total volume (m3 over a designated area). The measurement of growing stock is based on forest inventory. The growing stock estimates always include a margin of error and they can be prepared for commercial/potentially commercial species or for all species. In particular, the latter indicator is necessary for the quantification of carbon pools in the forest. Box 2 explains how growing stock is reported in FRA, highlighting the limitations of this indicator alone to provide information on forest degradation.

Box 2. Growing stock in FRAThe FRA 2010 report provides estimations of growing stock per hectare as an indicator of how well or poorly stocked the forests are in a particular country. It also provides information of the growing stock for the 10 most common species. The information usually comes from available inventory data with total and per-hectare figures of growing stock for each broad class of forest type. Included are all trees of commercial species within the threshold limits given for growing stock, regardless whether they have reached commercial dimensions or not and regardless of whether or not they are growing on areas available for wood supply7. Also each species should be identified in the reporting table by both scientific name and common name. Comparative periodic data on the average growing stock estimates at national level (as reported in national forest inventories and FRA) can provide indications on the trends in the quality of the forest resource but they alone cannot be used for assessing forest degradation. Complementary information is therefore necessary.

6 .7 To harmonize data, countries are requested to document the specification of the threshold values that are used for the measurement of growing stock. These values are: (i) Minimum diameter(cm) at breast height (DBH) of trees included in growing stock (ii) minimum diameter at the top end of stem for calculation of growing stock (cm); and iii) minimum diameter of branches included in the growing stock (cm)... (FAO 2010).

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The monitoring of changes in growing stock may indicate improvement of forest state from an over-harvested situation to an adequately stocked forest or vice versa. An advantage of this approach is that the data is usually readily available. However, there is a need to establish minimum values for stock density by forest type and geographic zone to serve as a reference in the assessment whether the actual growing stock can be considered adequate (non-degraded). Setting such minimum values should be based on scientific research data supported by expert views as the results can have strong implications for future management. This approach is based on, and requires data coming from, large-scale forest inventory (see Bahamondez et al. 2009 for an example from Chile).

Stand damage (losses)

Timber harvesting causes some level of damage in the stand, which can be minimized if reduced-impact harvesting techniques are practised (FAO 1996). The degradation impact depends on the extent and duration of such damage as the recovery of the forest re-growth can be fast (as is often the case) or slow. The extent of damage depends more on the number of trees extracted than on the volume. Two indicators of damage caused by harvesting operations are: (i) damage to the residual trees in the forest stand and particularly those of commercial species, and (ii) proportion of ground area disturbed during harvesting by heavy machines. The information to assess these indicators may be required by forest regulation but it should always be considered in the forest management plan and the monitoring of the damage should be part of the annual operational plan of the FMU. Annual harvesting records should provide information based on which levels of degradation caused by timber harvesting operations can be estimated and analyzed. From the perspective of future supply of timber from the forest, the assessment should provide information on how damage may influence the forest re-growth in commercial species.

Depletion of high-value timber

The depletion of a given commercial species (or species group) is the outcome of over-harvesting in particular in tropical forests (see Box 3). Over-harvesting is measured as the ratio of quantity harvested/quantity allowed or authorized). This has been specifically the case for high value mahogany (Swietenia macrophylla) in tropical America. The same approach would be needed in monitoring the rate of depletion of other CITES listed tree species.

In view of the difficulties to obtain adequate data due to lack of proper up-to-date inventories, expert assessments have proved to be cost-effective for well known, commercially valuable species8. Such assessments should be supported by available periodic inventory data which is more accurate but significantly more costly for the establishment of sustainable harvesting volumes on a higher than FMU level which is needed for assessment of allowable harvesting volumes of individual listed species on national or subnational levels. The methodology consists of four phases:

1. Defining “sampling units” at the national level combining the known range of the species of interest (through herbarium data, permanent plot data) with current forest cover obtained from satellite images.

2. Developing of an expert questionnaire to be used in assessment at the sampling unit level (containing several FMUs).

3. For the case of mahogany, the variable used was density of commercial-sized trees stratified by density classes. A forest sampling unit with an average (expert-based) density of zero commercially-sized trees was considered commercially depleted.

8 See (i) Kometter et al. 2004. Impacts of unsustainable mahogany logging in Bolivia and Peru. Ecology and Society. http://www.ecologyandsociety.org/vol9/iss1/art12; and (ii) Grogan et al. 2010. Over-harvesting driven by consumer demand leads to population decline: big-leaf mahogany in South America. Conservation Letters 3: 12-20.

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4. Presenting the results in country maps showing the forest sampling units and highlighting contrasting zones of “commercial viability” and depletion levels.

Necessary sources of information for this kind of approach are: i) reliable images/maps of forest cover, ii) availability of experienced field experts; and iii) knowledge about species ecology and dynamics, with regard to minimum harvesting diameters. .

In addition to expert surveys as described above, national timber inventories can also be used for the same purpose. An example is the assessment of stocking density estimates of commercial populations of high value Tabebuia spp. in the Brazilian Amazon, where forest cover and geographical distribution data were also used as input9The example also shows how over-harvesting of a single species can create a broad degradation impact on forest when new areas are opened up by construction of logging roads for encroachment and thereby for other degradation agents.

BOX 3. Ipê (Tabebuia spp.) logging as a catalyst for forest degradation and clearing in the Brazilian Amazon*In recent years there has been a clear shift in the geographical range of ipê logging, as stocks in older eastern frontiers were exhausted and logging operations spread to central and western Amazon. Left to market forces, ipê logging will continue to spread to unlogged forest areas wherever these species can be profitably harvested. As logging roads and sawmills penetrate new regions they provide access and incentive for colonists and land speculators to follow. This dynamic has been well documented for Amazon, and in much of the so-called ‘arc of deforestation’ the pursuit of big-leaf mahogany served as the catalyst for the process of land-clearing, serial logging and burning that has resulted in a landscape where islands of degraded forest (heavily logged and in many cases repeatedly burned) persist precariously within a matrix of used and abandoned pastures and agricultural fields. With ipê as a new catalyst, the wave of forest degradation and clearing powered by largely unregulated logging now threatens to wash across the heart of Amazon. The implications of uncontrolled logging of ipê extend well beyond the potential depletion of commercial stocks of Tabebuia species and could undermine government efforts to achieve forest conservation by bringing order to the Amazon frontier.---------------------------------------------------------------------------------------* Schulze, M., et al. 2008. Evaluating ipê (Tabebuia, Bignoniaceae) logging in Amazonia: sustainable management or catalyst for forest degradation? Bio. Cons. 141: 2071-2085.

At the operational level, harvesting intensity of individual species can be managed to avoid over-harvesting based on pre-harvest tree census which is a standard practice in RIL. Enumeration of each tree and its exact location on the tree map provides an additional source of information both for operational planning and degradation assessments. Another source is of course FMU level forest inventories.

Over-harvesting of non-wood forest products

The diversity of species, living forms, distribution patterns or seasonality of plants providing non-timber forest products, used either for local consumption or for commercial purpose, makes the evaluation of their status a highly difficult task as these require specific sampling designs for quantification. However, not all NWFPs are harvested everywhere and therefore assessment can focus on areas where collection for commercial purposes is concentrated or which are under pressure from subsistence consumption.

At the national level, countries have been reporting estimates of consumption of commercially important NWFPs (e.g. FAO-FRA 2010), but the reliability of these estimates is questioned as in many cases most of the consumption is local or is simply not recorded. In addition, it is recognized that it may be difficult to make a distinction on whether the collected product originates from areas classified as forest as many NWFPs originate from trees outside forests (FAO-FRA 2010). Another issue is that national level data can hide extensive variation by geographical zones or forest types.

9 Schulze, M. et al. 2008. Evaluating ipê (Tabebuia, Bignoniaceae) logging in Amazonia: sustainable management or catalyst for forest degradation? Bio. Cons. 141: 2071-2085.

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Harvest intensity vs rate of production

If data is available, for some NWFPs such as bamboo and rattan, over-harvesting at the stand level occurs when annual rate of harvest is higher than the annual rate of production (P), which can be expressed as follows:

P = (X * Y)/r

where: X = abundance of NWFP stratified by size class (minimum harvestable size; Y = average yield per individual of minimum harvestable size; and r = time required to recover to harvestable levels.

This indicator is especially applicable if local statistics are reliable as a result of participatory recording by producers or collectors of harvested volumes and recovery times.10.

Changes in plant population structure

Another way of assessing over-exploitation of NWFPs is to determine the shape of size- class distributions of NWFP plant species at the stand or landscape level (see e.g., Peres et al. 2003 for Brazil nut across Bolivia, Brazil and Peru)11. Such information may be obtained from NWFP collectors/producers or from specific NWFP resource assessments if not part of forest inventory data collection.

The level of over-harvesting can also be deducted based on information on how distances of collection areas from cities/villages/collection or processing centers have evolved over time. Survey data among collectors/producers represents a cross-section in space and, if repeated periodically, also over time.

If a distance-based approach is used as a proxy for indicator of utilization pressure, a negative change in size class distributions of NWFP plants showing fewer or no individuals in juvenile size classes can be taken as an indication of degradation trend in the resource base. It is critical, however, to define the minimum size class cut-off limit12. The main assumption here is that changes in population structure reflect harvesting impacts alone.

Changes in production and utilization

In the context of informal/subsistence harvesting, a possible indicator for assessing over-harvesting of the resource base is to use NWFP consumption volumes/yield reported in national statistics and compare these over time. Due to lack of adequate information, this approach can rarely be applied in tropical countries13. Furthermore, when available statistics on NWFPs are confined to export markets, baseline surveys among traders and processing plants of local medicinal plant/wild harvested fruits can provide estimates of traded volumes and changes in demand over time which, if negative trends are observed, can be taken as indications of progressive degradation of the NWFP resource base14.

10 A summary of methods can be found in: Evans, K., Guariguata, M. R. 2008. Participatory monitoring in tropical forest management. A review of tools, concepts and lessons learned. CIFOR, Indonesia. Another useful reference is: Participatory Science for Sustainable Harvest-A methods handbook. 2008. University of Oxford-Forest Action-DFID, by Anna Lawrence et al. 11 Peres, C. et al. 2003. Demographic threats to the sustainability of Brazil nut exploitation. Science 302: 2112–2114.12 For example, Peres et al. (2003) concluded that some Brazil nut populations in parts of the Western Amazon lacked juvenile, pre-reproductive trees (> 10 cm dbh), suggesting that some populations were on the verge of demographic collapse under continued harvesting; yet by including a smaller tree size cutoff (> 1.5 m tall but < 10 cm dbh), other authors reached the opposite conclusion in the same area?. 13 Shackleton, S. et al. 2007. Invisible but viable: recognizing local markets for non-timber forest products. Int. For. Rev. 9: 697-712.

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Change in number of NWFPs consumed

Another indicator is change in number of NWFPs households rely on for subsistence consumption. Such data can be collected using rapid rural assessments such as those specified in the Poverty-Forest Linkages Toolkit (http://www.profor.info/profor/node/103). The methodology requires:

a) Identification of forest dependent households and sampling strategy.b) Using participatory approaches with a random sample of households to ascertain the value

of relevant parameters.c) If necessary, repeating the survey during different seasons to capture seasonal variations

over the course of the year. d) Repeat the procedure at selected intervals to establish the change

This approach can provide information on which NWFPs have been subject to consumption pressure assuming that their supply has been reduced for that reason.

Other social indicators at the local level which could provide indirect information on possible degradation in terms of reduced supply of NWFPs include average revenue from sales of specific NWFPs, average time taken or average distance travelled to collect a specified volume of certain NWFPs, or their importance in household resource portfolios (measured using proxies for NWFP income contribution of the products). Obtaining information on these aspects usually requires either special periodic surveys or participatory recording by the involved households.

Over-harvesting of fuelwood

National level forest statistics attempt to include information on the production and consumption of fuelwood and charcoal. Unfortunately, they tend to be gross estimates based on demographic data and estimated unit consumption of households. Resource assessments are often needed to estimate the current and potential supply of fuelwood from natural forests. This is particularly the case in areas with dry tropical forests where fuelwood and charcoal may be the principal uses of wood.

At local scales, the same approaches for data collection as used for NWFPs may be followed but direct measurement methods on the resource and supply are likely to provide more accurate information. At the level of provinces, municipalities or other administrative units, assessing over-harvesting of wood for fuel can be carried out by quantifying above ground forest biomass and its annual increment. Above ground biomass (AGB) can be assessed based on periodic data on permanent sample plots using allometric models such as:

AGB= SV x WD x BEF

in which SV is Stem Volume, WD is Wood Density, and BEF is Biomass Expansion Factor. Each of these variables changes over time and has a respective increment in the case of non-degradation. A statistically valid relationship needs to be developed between AGB and AGB increments. AGB increment per ha x forest area for each forest type equals annual biomass increment for the designated area (Mg/yr). This value can be compared with annual consumption (Mg/yr) stratified by forest type as appropriate15.

14 Shanley, P. 2003. The impacts of forest degradation on medicinal plant use and implications for health care in Eastern Amazonia. BioScience 53(6). 15 The original AGB vs. AGB increment relationship was first devised by: Clark et al. (2001). Net primary production in tropical forests: an evaluation and synthesis of existing field data. Ecol. Appl. 11: 371-384. The method was applied at the sub-national level by: Top, N. et al., (2004). Estimating forest biomass increment based on permanent sample plots in relation to woodfuel consumption: a case study in Kampong Thom Province, Cambodia. J. For. Res. 9 : 117-123. A re-assessment can be found in: Biomass and Bioenergy (2006) Vol. 30 (2), pp. 134-143.

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Table 2. Measurement of Forest Degradation Based on Supply of GoodsGoods and Services

Scale Unit of measurement

Method Comments

a) Wood removals

Measurement at the stand/FMU/landscape/sub-national/national levels. Reported by forest class or type at the administrative unit level (e.g. province, district, municipality) and at the national level

m3 At the stand level, comparing data from approved management plans versus reported timber removals. At higher levels comparison of removals with AAC.

Illegal is excluded and should be estimated by remote sensing or other data.

b) Growing stock for selected species

m3 Forest inventory, pre-harvest inventory of selected species/tree census

Degradation assessment requires periodic data over time

c) Fuelwood m3 or kg Forest inventory, production and consumption surveys

Illegal is excluded and should be estimated by remote sensing or other data.

d) Non-wood forest production

Measurement at stand level (e.g. for bamboo and rattan), as well as FMU and subnational/national levels

m3, kg, number of products collected, etc.

Resource assessments, production records, production and consumption surveys

Degradation assessment requires periodic data over time

Degradation of forest services

This section may be based on cross-referencing to other relevant chapters in the guidelines. Carbon is covered in the section on historical degradation. A discussion on water is here, but could potentially go with the soil criteria.

Water

The relationship between changes in forest land use and hydrology is very complex. However some patterns are reasonably robust16 and therefore indicators of degradation can be suggested at the local-landscape level.

16 Bruijnzeel et al. (2005). Forests, water and people in the humid tropics: an emerging view. In: Bonnell, M., L. A. Bruijnzeel (eds). Forests, water and people in the humid tropics. Cambridge Univ. Press / UNESCO.

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Removal of forest has an initial short-term effect of increasing annual water yield and stream discharge, with the size of change depending on rainfall and extent of soil disturbance. Subsequent water yields depend on the new type of vegetation cover.

Converting forest to non forest cover increases low (dry season) flows as long as soils are not heavily compacted. This suggests that a degraded watershed in terms of significant loss of forest cover can enhance the supply of water downstream. Here we have a clear example of how the definition of degradation (as used in this Group) is highly context- and variable-dependent.

Converting forest to other uses is likely to lead to reduced low (dry season) flows if soil disturbance/compaction is high. This stage is typically reached after prolonged exposure of bare soil to heavy machinery, extensive grazing or occurrence of impermeable surfaces such as roads.

The short term (c. 30 yr) initial hydrological response to reforestation of bare land is of reduced total water yield and low (dry season) flows vis-a-vis completely deforested land.

The relationship between natural/planted forest cover and maintenance of water quality is clear as the soil is protected, nutrient leaching is minimal, and sedimentation rates are kept within the natural range.

Hence indicators for degradation of forest-related (or lack thereof) water provision would have to focus on water quality and perhaps quantity in well-defined areas (as far as sampling allocation is concerned to avoid confounding), with known histories of land use change and/or clear management objectives (e.g. restoration of degraded watershed soils or maintenance of dry season flows).

Regulation of vector-borne diseases

The extent and pattern of deforestation may degrade the disease regulation services of the forest. Deforestation in many parts of the tropics has preceded a surge in malaria infections and its anopheline vectors. A recent study in Peruvian Amazonia showed that changes in forest cover, through the effects on the distribution pattern of the principal mosquito vector for malaria in South America17. The authors sampled sites with varying degrees of deforestation on a regular basis. Human biting rates of Anopheles darlingi were directly proportional to the amount of non-forest or altered land and inversely proportional to the amount of remaining forest (controlling for human population density). Potential indicators of degradation of disease regulation would include abundance of disease vectors and/or incidence of human cases in recently deforested areas.

17 Vittor, A. et al. 2006. The effect of deforestation on the human-biting rate of Anopheles darlingi, the primary vector of Falciparum malaria in the Peruvian Amazon. Am. J. Trop. Med. Hyg. 74: 3-11.

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References

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Table 1. Potential indicators of degradation of the provision of forest goods and services

Forest good/ service

Potential indicators of degradation Potential for up-scaling

Potential sources of information

Limitations

Timber Shortened cutting cycles Canopy cover Number of harvested trees below the established

minimum diameter Absence/inadequate number of commercial-sized

individuals in logged forest Inadequate number of adolescent trees of selected

species Absence/inadequate number of designated seed trees

for a given species in a given logging compartment Reduction in timber supply (indirect indicator)

Medium to high. National reporting (e.g. ITTO, FAO) on annual timber production can be used against independently gathered data

Forest inventories at national, subnational and FMU levels

Pre and post-harvest inventories

Forest cover maps Expert assessments Permanent sample plot data

in logging concessions Herbarium data Inspection reports of

enforcement authorities Audit reports from certified

forests Sawmill input statistics

Absence of long term data

Absence of reliable national statistics

Inadequate enforcement activity

Confidentiality of certification audit reports

Inconsistencies in different data sets

Non-wood forest products

Changes in plant population structure over time or space and replenishment of selected species

Decrease in yield/locally gathered volume Reduction in recorded production, consumption and

exports of NWFPs Negative changes in revenue from NWFPs, average time

taken or average distance traveled to collect a specified volume of certain NWFPs, or their importance in household resource portfolios (indirect measurement)

Low to medium Largely locally collected statistics through survey and other methods

National statistics on collected/consumed/traded volumes and NWFP income

Foreign trade statistics for export data

Periodic assessments of NWFP population structures

Comparison of permit data for allowable harvest with local supply and demand surveys and other data

Expert assessments

Largely locally based and intensive; participatory approaches are almost always necessary.

Overall lack of national statistics on NWFPs especially in developing countries.

Lack of enforcement records

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Forest good/ service

Potential indicators of degradation Potential for up-scaling

Potential sources of information

Limitations

Fuelwood Reduction in the supply of fuelwood and charcoal

Reduction in subsistence consumption of fuelwood and charcoal

Negative changes in revenue from NWFPs, average time taken or average distance traveled to collect a specified volume of certain NWFPs, or their importance in household resource portfolios

Low to medium Inventory data on aboveground biomass (AGB) from sample plots and AGB increment data to estimate potential supply

Local and aggregated production and consumption data, including from surveys among users and producers

Data from bioenergy plantations

Comparison of permit data for allowable harvest with local supply and demand surveys and other data

Exclusion of dead wood and fuelwood from non forest areas (trees outside forest) can distort supply estimates

Water regulation

Reduction in water quality: increase in suspended sediments, change in chemical composition

Change in stream discharge Total annual water yield

Low Local water companies Some quality and quantity

parameters empirically assessed

Contingent on scale, land use history and intended watershed use (e.g. conservation vs. restoration)

Disease regulation

Peri-urban changes in forest cover Infection rates Human biting rates

Low Empirically assessed Local health statistics

Specific for certain diseases only

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Figure 1. Harvesting in Sustainable Management of National Tropical Forest (Schematic Illustration at Stand /Compartment Level)

Note: If the harvesting level reduces the growing stock below the minimum limit, degradation occurs. In practice, harvesting level regulation is based on minimum diameter and occurrence of selected species in the stand/compartment.

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Minimum limit of growing stock

Long-term sustainable level of growing stock

Growing stock periodic changes due to harvesting interventions (selective logging)

Growing stock m3/ha

time

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Figure 2. Growing Stock Index (m3/ha) in Forest Management Unit and its Stands

1. Actively managed (not harvested)

2. Actively ma-naged (harvested during the period)

3. Set aside(steady state)

4. Set aside(mortality higher than› growth)

100

0

100

0

100

0

100

0

100

0t

Etc.

FMU

Stand/compartment (examples)

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