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• We present an index-based assessment of ecological condition (IBECA). • We test the methodology using a regional case study in central Norway. • We investigate how IBECA aligns with two international frameworks. • We discuss challenges in indicator development and ecological condition assessments. • IBECA provides a transparent, flexible, cost-effective and management relevant tool. Sustainable nature management and ecosystem conservation depends critically on scientifically sound and stakeholder-relevant analytical frameworks for monitoring and assessing ecological condition. Several general frameworks are currently being developed internationally, including the Essential Biodiversity Variables (EBV), and the UN's SEEA EEA Ecosystem Condition Typology (ECT). However, there has so far been few attempts to develop empirical implementations of these general frameworks, or to assess their applicability for environmental decision-making at national or regional scales. In this paper, we aim to fill this implementation gap by demonstrating a practical application of an empirically-based ecological condition assessment framework, the Index-Based Ecological Condition Assessment (IBECA). IBECA defines seven major classes of indicators of ecological condition, representing distinct ecosystem characteristics, and empirically synthesizes indicators for each of these characteristics from various monitoring data. We exemplify and explore the utility and robustness of IBECA using a case study from forest and alpine ecosystems in central Norway, and we investigate how IBECA aligns with the two international frameworks EBV and ECT. In particular, we analyze how the different approaches to categorize indicators into classes affect the assessment of ecological condition, both conceptually and using the case study indicators. We used eleven indicators for each of the two ecosystems and assessed the ecological condition according to IBECA for i) each individual indicator, ii) the seven ecosystem characteristics (indicator classes), and iii) a synthetic ecological condition value for the whole ecosystem. IBECA challenges key concepts of the international frameworks and illustrates practical challenges for national or regional level implementation. We identify three main strengths with the IBECA approach: i) it provides a transparent and management-relevant quantitative approach allowing assessment of spatio-temporal variation in ecological condition across indicators, characteristics and ecosystems, ii) the high degree of flexibility and transparency facilitates updating the ecological condition assessments, also back in time, as improved data and knowledge of indicators emerge, and iii) the quantitative and flexible procedure makes it a cost-effective approach suitable for fast management implementations. More generally, we stress the need for carefully choosing appropriate classification and aggregation approaches in ecological condition assessments, and for transparent and data-driven analytical approaches that can be adjusted as knowledge improves. [ABSTRACT FROM AUTHOR]

• We present five conceptual approaches for setting indicator reference values. • We present four conceptual approaches for setting indicator limit values. • The choice of approach depends on data availability, coverage and type. • We discuss practical considerations and possible solutions to setting these values. • We aim to contribute to development and practical use of this type of value setting. Effective evidence-based nature conservation and habitat management relies on developing and refining our methodological toolbox for detecting critical ecological changes at an early stage. This requires not only optimizing the use and integration of evidence from available data, but also optimizing methods for dealing with imperfect knowledge and data deficiencies. For policy and management relevance, ecological data are often synthesized into indicators, which are assessed against reference levels and limit values. Here we explore challenges and opportunities in defining ecological condition in relation to a reference condition reflecting intact ecosystems, as well as setting limit values for good ecological condition , linked to critical ecological thresholds in dose–response relationships between pressures and condition variables. These two concepts have been widely studied and implemented in aquatic sciences, but rarely in terrestrial systems. In this paper, we address practical considerations, theoretical challenges and possible solutions using different approaches to determine reference and limit values for good ecological condition in terrestrial ecosystems, based on empirical experiences from a case study in central Norway. We present five approaches for setting indicator reference values for intact ecosystems : absolute biophysical boundaries, reference areas, reference communities, ecosystem dynamics based models, and habitat availability based models. We further present four approaches for identifying indicator limit values for good ecological condition : empirically estimated values, statistical distributions, assumed linear relationships, and expert judgement-based limits. This exercise highlights the versatile and robust nature of ecological condition assessments based on reference and limit values for different management purposes, for situations where knowledge of the underlying relationships is lacking, and for situations limited by data availability. [ABSTRACT FROM AUTHOR]