A. Relevance and sustainability context
A.1 Policy relevance
The tree mortality indicator measures the volume or share of trees that die due to natural disturbances, climate-related stress, pests, diseases or other causes. It provides important information on forest health, resilience and the impacts of environmental change on forest ecosystems. The indicator is highly relevant for forest policy, climate adaptation policy and national greenhouse gas reporting, particularly in light of increasing disturbance events such as droughts, storms and bark beetle outbreaks.
A.2 Sustainability and / or comparative evaluation options
Sustainability perspective: Tree mortality can be evaluated relative to gross increment and growing stock to assess whether mortality levels threaten long-term forest productivity and ecosystem resilience. Disturbance-related mortality indicators (e.g. bark beetle damage, storm damage or fire impacts) can serve as complementary benchmarks.
Bioeconomy perspective: The indicator can be related to salvage logging volumes, economic losses and forest-sector performance. It helps assess the implications of increasing mortality for biomass availability, wood quality and future resource supply for the bioeconomy.
B. Data availability
B.1 Stage of development
It is a semi-established indicator. The indicator is already monitored through existing forest monitoring systems but is less standardized than traditional forest resource indicators such as harvest or growing stock.
B.2 Data sources
Historical data: National Forest Inventory (Bundeswaldinventur) and Forest Condition Survey (Waldzustandserhebung, WZE), coordinated by the Thünen Institute and related forest monitoring institutions.
Future projections: German Projection Report and scenario studies such as the DIFENs project (Dealing with Impacts on Forests under changing End-use demand, climate change, Natural disturbances and Policy goals). Future estimates may require additional modelling of climate impacts and forest disturbances.
B.3 Coverage over time and replicability
Historical data are available from the National Forest Inventory and Carbon Inventory at approximately five-year intervals (2002, 2007, 2012, 2017 and 2022) and annually on a coarse-scale sampling resolution through the Forest Condition Survey (“Waldzustandserhebung”).
Future projections may be available at annual or five-year intervals up to 2050. Replicability is generally high, although future disturbance dynamics remain uncertain.
B.4 Coverage across scales and sectors; compatibility
The indicator is available at national level for the German forestry sector and may also be disaggregated to the federal-state level. It aligns with forest monitoring systems, climate adaptation monitoring and greenhouse gas reporting activities.
C. Considerations for operationalization
C.1 Feasibility: Fit for monitoring
Robustness ranking: very robust. Historical observations are based on established monitoring systems. However, projections of future mortality may involve considerable uncertainty due to the increasing influence of climate change and disturbance events.
C.2 Institutions
Historical monitoring is primarily conducted by the Thünen Institute and associated forest monitoring authorities. Future projections may involve the Thünen Institute, Öko-Institut and other research institutions working on forest and climate scenarios.
C.3 Future prospects
The continuation of monitoring is considered highly likely. Given the growing importance of climate-change impacts on forests, the indicator is expected to gain further relevance in future monitoring systems.
C.4 Costs, considerations and reproducibility
Costs mainly arise from ongoing forest monitoring, inventory campaigns, disturbance assessments, scenario modelling and data visualization. The indicator benefits from existing monitoring infrastructures and therefore has good reproducibility.
C.5 Potential for automation
Data processing, indicator calculation and visualization can be partially automated. Expert assessment remains important, particularly when attributing mortality to specific causes and interpreting future disturbance risks.
C.6 Presentation options and breakdown / sub-indicator needs
The indicator can be presented as:
- Long-term trends in mortality rates or mortality volume;
- Mortality expressed in m³, carbon or CO₂ equivalents;
- Breakdown by coniferous and broadleaved species; alternatively main species groups as reported in the Forest Condition Survey;
- Differentiation by mortality causes (e.g. drought, storm, bark beetle, fire);
- Comparison of historical observations and future projections.
C.7 Potential for scenario integration
The indicator has high potential for integration into forest and climate scenarios. Mortality dynamics are increasingly considered in forest growth models and are essential for assessing future forest resilience, carbon balances and biomass availability.
C.8 Interlinkages and alignment with other monitoring activities
The indicator is closely linked to:
- National greenhouse gas reporting;
- Forest condition monitoring;
- Climate adaptation monitoring;
- Forest resilience assessments;
- Forest resource and biomass monitoring;
- Bioeconomy monitoring related to future biomass supply and disturbance risks.
Further Comments:
The tree mortality indicator should be interpreted together with gross increment, harvest, growing stock and net stock change indicators. The relationship between mortality and increment is particularly important for assessing whether forests maintain their productive capacity and carbon sink function. Distinguishing between regular mortality and disturbance-related mortality is crucial for understanding emerging risks associated with climate change and their implications for the bioeconomy.