It is important to know whether forests are being degraded and, if so, what the causes are, so that steps can be taken to arrest and reverse the process.

Collecting and analysing information on forest condition and the extent of forest degradation will help in prioritizing resources and measures to prevent further degradation, address the root causes, and restore and rehabilitate degraded forest landscapes. It will also allow countries to fulfil their commitments on international reporting.

Quantifying the scale of the problem is difficult, however. Different stakeholders perceive forest degradation differently – one person’s degraded forest may be another’s livelihood – and it can be difficult to find a common approach to defining it. Various criteria may be applied, such as health and vitality, species diversity, production capacity, protection capacity and aesthetic value, but the weighting given to such criteria will influence the perception of degradation. For example, a planted forest may be regarded as “degraded” if consideration is based only on the criterion of biodiversity.

The definition of degradation should be linked to the objectives of forest management and ultimately to society’s goals – “degradation” is thus defined by the capacity of a forest to produce the products and services wanted by stakeholders.

Another issue in monitoring degradation is the potential difficulty in differentiating between natural variations and degradation. A reference state is required for comparing changes in a forest at a given temporal scale.

The SFM thematic elements enumerated in the UN Forest Instrument (and listed in the table) may provide a suitable framework for choosing indicators of forest degradation.

The assessment of forest degradation implies the selection of a spatial scale (e.g. global, national, subnational, landscape/watershed, forest management unit –FMU, or stand/site), and an assessment methodology. These are discussed further below.

Assessing forest degradation at each site or FMU enables forest owners and managers to decide on corrective actions at the local scale.

Forest managers should decide on the degradation indicators to be measured in their regular forest monitoring (see Forest Management Monitoring module). The early identification of local problems can guide the revision of forest management plans so as to prevent further degradation, address the root causes of degradation, take action to restore the damage already done, and invest in rehabilitation.

Forest managers should bear in mind that many indicators of a forest’s capacity to provide goods and services vary over time within a stand without implying forest degradation. Short-term fluctuations may be part of natural cycles or the result of planned human interventions (see Figure 1 in “basic knowledge”).

Forest degradation is normally estimated at larger scales to assist in policy and programme design and implementation, including payment mechanisms or other incentive schemes aimed at preventing degradation (e.g. payments for environmental services). Such larger-scale monitoring is also need for national reporting to international processes, such as those related to GHG emissions and biodiversity.

Measuring and monitoring forest degradation at the subnational or national scale is a challenge, and it can be more time-consuming and costly than assessing deforestation. A combination of on-the-ground forest inventories and remotely sensed data will provide the most reliable estimates. Remote sensing can be used as a cost-efficient option for assessing degradation through proxies – such as canopy-cover percentage (with a decreasing trend implying degradation). Focused field surveys (e.g. biometric field observations, biodiversity assessments and rapid rural assessments) can be undertaken in areas where remote sensing has detected degradation to obtain a more nuanced understanding of degradation trends and their causes and possible solutions.

The most suitable monitoring approach should be determined depending on parameters such as vegetation type, climate and degradation dynamic (e.g. is degradation occurring at a small or large scale? Is it concentrated or diffuse?). Sometimes, degradation may be the direct result of management, and differences in forest condition may be observable on different sides of management boundaries. In other cases, time-series observations may be required to detect change.

In some countries, existing national forest monitoring systems may be suitable – if adapted and expanded – for monitoring forest degradation.

Monitoring forest degradation with a high level of certainty is time-consuming and costly; it should only be considered in the context of REDD+ if forest degradation is likely to be a major contributor to GHG emissions. If such monitoring is considered necessary, it should focus on those areas most likely to be subject to degradation. 

Estimates of degradation are likely to be imprecise (i.e. with wide confidence intervals) because of the large number of variables and the difficulty in measuring many of these. Even with the best measurement and monitoring systems, it may be difficult to estimate degradation rates from year to year, so a long-term approach is required.

Sources of remotely sensed data that can be used in monitoring forest degradation include high-spatial-resolution optical methods (e.g. RapidEye) and active sensors such as radar and lidar. 

Forest degradation is a complex, highly location-specific phenomenon, and understanding it requires the analysis of both direct and indirect causes. When the scale and areas of forest degradation have been identified, a comprehensive assessment of the drivers of degradation should be undertaken in each area. It is desirable that the key stakeholders associated with degradation drivers participate in such assessments and assist in analysing data to understand the dynamics of change.

Degradation can be – but is not necessarily – a precursor to deforestation. Forests may remain degraded for a long time but never become completely deforested. Moreover, forest degradation can be halted or reversed at many points on the degradation pathway (see Figure 1 in “basic knowledge”) by forest management interventions. In many other cases, however, forest degradation is a precursor to deforestation: for example, selectively logged areas may become deforested within a few years of logging in the absence of SFM and the presence of deforestation pressures.

Actions and strategies to address forest degradation drivers should take into account the potential impacts on food security, local livelihoods, and climate-change mitigation and adaptation. Priority should be given to improving governance; increasing transparency, capacity and law enforcement; providing secure, equitable tenure; and combating illegal activities.

Interventions should consider both direct and underlying drivers and scale (e.g. local, national or global) and include a mix of measures. Forest managers are mainly responsible for actions at the local level, but viewing forest degradation in the context of larger scales may be beneficial. The time needed to design programmes to address drivers and reconcile the interests of multiple stakeholders should not be underestimated.

Actions should be selected and ranked according to agreed criteria (e.g. objectives, estimated costs and potential for funding, and existing implementation capacities) through consultation with local stakeholders. The consultation process can be used to determine which drivers should be addressed first, the most suitable actions for addressing them, and the rationale for the choices.