A. Relevance and sustainability context
A.1 Policy relevance
The Volume of Broadleaf Habitat Trees indicator measures the amount of standing broadleaf trees with potential habitat characteristics that provide important ecological functions for biodiversity conservation. Habitat trees serve as nesting, breeding and feeding sites for numerous species and contribute to the structural diversity of forest ecosystems. The indicator is highly relevant for biodiversity policy, sustainable forest management and the implementation of the German National Biodiversity Strategy.
A.2 Sustainability and / or comparative evaluation options
Sustainability perspective: The indicator can be assessed in relation to biodiversity targets, retention forestry objectives and minimum habitat-tree requirements per hectare. It can also be compared to the share of habitat trees in total growing stock and across different forest types.
Bioeconomy perspective: The indicator can be used to illustrate trade-offs between biomass utilization and biodiversity conservation. Habitat trees represent standing timber that is intentionally retained in forests for ecological purposes rather than used for wood production. The indicator therefore provides information on the balance between biodiversity protection and resource mobilization.
B. Data availability
B.1 Stage of development
1 – Established indicator. The indicator is already included in established forest biodiversity monitoring activities.
B.2 Data sources
Historical data: National Forest Inventory (Bundeswaldinventur) and related biodiversity monitoring activities conducted by the Thünen Institute.
Future projections: German Projection Report and scenario studies such as the DIFENs project. Assessment of future developments may require evaluation of scenario model outputs.
B.3 Coverage over time and replicability
Historical observations are available approximately every five years (from NFI and CI in 2002, 2007, 2012, 2017 and 2022). Future projections may be available at annual or five-year intervals up to 2050. Replicability is high due to established inventory methodologies and repeated monitoring.
B.4 Coverage across scales and sectors; compatibility
The indicator is available for the forestry sector at national scale and can potentially be disaggregated to federal-state level. It is compatible with biodiversity monitoring, sustainable forest management indicators and conservation reporting frameworks.
C. Considerations for operationalization
C.1 Feasibility: Fit for monitoring
Robustness ranking:** (very robust). Historical observations are based on established inventory systems. Future developments depend on assumptions regarding forest management, conservation policies and future forest structure.
C.2 Institutions
Historical monitoring is conducted primarily by the Thünen Institute. Future assessments may involve the Thünen Institute, Öko-Institut and other institutions participating in forest and biodiversity scenario development.
C.3 Future prospects
The continuation of monitoring is considered highly likely. The indicator is already established and is expected to remain relevant due to increasing policy attention to biodiversity conservation and multifunctional forest management.
C.4 Costs, considerations and reproducibility
Costs mainly arise from forest inventories, biodiversity monitoring, scenario modelling and graphical presentation. Since the underlying monitoring infrastructure already exists, reproducibility is high.
C.5 Potential for automation
Data processing, indicator calculation and visualization can be partly automated. However, expert judgement remains important, particularly regarding habitat-tree definitions and interpretation of biodiversity implications.
C.6 Presentation options and breakdown / sub-indicator needs
The indicator can be presented as:
- Time series showing changes in habitat-tree volume or tree number;
- Habitat-tree volume expressed in m³, carbon stock or CO₂ equivalents;
- Share of habitat-tree volume relative to total growing stock;
- Breakdown by forest type and tree species groups;
- Comparison with biodiversity targets or retention benchmarks.
C.7 Potential for scenario integration
The indicator has high potential for integration into forest, biodiversity and bioeconomy scenarios. It can be used to assess the consequences of alternative management strategies for biodiversity conservation and biomass availability.
C.8 Interlinkages and alignment with other monitoring activities
The indicator is closely linked to:
- Biodiversity reporting;
- National Biodiversity Strategy monitoring;
- Sustainable forest management monitoring;
- Forest resource assessments;
- Bioeconomy monitoring addressing trade-offs between biomass production and ecosystem services.
Further Comments:
The indicator should ideally be interpreted together with growing stock, deadwood volume and forest habitat quality indicators. Consistent definitions of potential habitat trees across regions and monitoring cycles are important to ensure comparability over time. For bioeconomy assessments, the indicator can help quantify the extent to which forest biomass is retained for biodiversity objectives rather than mobilized for material or energy use.