Abstract
Abstract 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.
Highlights
Ecological assessment tools and approaches that allow early detection of critical changes in biodiversity and ecosystems are key to effective, evidence-based nature management and policy at local, national and global scales (Tittensor et al 2014)
While this discussion is based on our experiences with developing the Index-Based Ecological Condition Assessment tool (IBECA) approach, we emphasize that all our approaches rely on sound empirical system knowledge and/or empirical data, with relevance more generally for other ecological condition frameworks
In developing IBECA and testing it by means of the case study we explored five broad categories of approaches to estimate empirical reference levels for ecological condition indicators
Summary
Ecological assessment tools and approaches that allow early detection of critical changes in biodiversity and ecosystems are key to effective, evidence-based nature management and policy at local, national and global scales (Tittensor et al 2014). For the purpose of general applications and/or comparative purposes, a quantification of a universally defined desirable ecosystem reference condition is preferable (Scholes & Biggs 2005, Nielsen et al 2007) Such universally-defined reference values may be developed to describe the system in good ecological condition as well as by associated limit values – or tipping points – beyond which the system is no longer considered to be in an acceptable condition This may reflect concerns amongst terrestrial ecologists about over-simplification of nature and, more pragmatically, a lack of data and scientific knowledge about dose–response relationships frustrating attempts to set evidence-based thresholds (cf Lindenmayer & Luck 2005, Johnson 2013) While these concerns are valid and important, notably for avoiding misguided management, the inherent ability of reference-based approaches to assess and compare progress towards predefined goals is attractive due to high policy and management relevance (Rakocinski et al 1997). We first introduce the rationale and the conceptual framework behind IBECA, and discuss practical considerations, theoretical challenges, and possible solutions for setting values for the reference condition and limits for good ecological condition
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