Operationalising the concept of ecosystem collapse for conservation practice

Highlights

• Ecosystem collapse presents a major challenge to conservation practice.

• Ecosystem collapse is defined to support operationalization of the concept.

• Management responses to collapse should address causal mechanisms.

• Management guidance is provided in the form of a decision tree.

• Application of the decision tree is illustrated with case studies.

Abstract

Concern is growing about ecosystem collapse, namely the abrupt decline or loss of an ecosystem resulting from human activities. While efforts to assess the risk of ecosystem collapse have developed at large spatial scales, less attention has been given to the local scales at which conservation management decisions are typically made. Development of appropriate management responses to ecosystem collapse has been limited by uncertainty regarding how collapse may best be identified, together with its underlying causes. Here we operationalise ecosystem collapse for conservation practice by providing a robust definition of collapse, in a form that is relevant to the scale of conservation decision-making. We provide an overview of different causes of collapse, and then explore the implications of this understanding for conservation practice, by examining potential management responses. This is achieved through development of a decision tree, which we illustrate through a series of case studies. We also explore the role of indicators for the early detection of collapse and for monitoring the effectiveness of management responses. Ecosystem collapse represents a significant challenge to conservation practice, as abrupt changes in ecosystem structure, function and composition can occur with little warning, leading to profound impacts on both biodiversity and human society. The risks of ecosystem collapse are likely to increase in future, as multiple forms of environmental change continue to intensify. We suggest that selection of management responses should be based on an understanding of the causal mechanisms responsible for collapse, which can be identified through appropriate monitoring and research activities.

Introduction

Recent events such as the mass bleaching of the Great Barrier Reef, unprecedented fires in regions including California, southern Australia, Indonesia and the Amazon, and the sudden loss of ice habitat in polar regions, have increased international concerns about ecosystem collapse (Vincent and Mueller, 2020). The phenomenon is increasingly being referred to in the international media, partly as a result of advocacy by high-profile individuals such as Greta Thunberg and David Attenborough (Dasgupta, 2021; Newton, 2021). At the same time, ecosystem collapse is receiving increasing attention from conservation researchers, as illustrated by a rapid recent increase in the number of publications on the topic (Bergstrom et al., 2021; MacDougall et al., 2013; Newton, 2021; Sato and Lindenmayer, 2017). This growth in interest reflects a number of intensifying concerns: the scale of the ecological changes that are currently occurring in the world's ecosystems; the fact that these changes can sometimes occur rapidly, with little warning; and the magnitude of the potential impacts on both biodiversity and human society.

Trends towards increased recognition of ecosystem collapse have been given particular impetus by the recent development of the IUCN Red List of Ecosystems (RLE), which represents the first systematic attempt to assess the conservation status of different ecosystem types that is appropriate for use at the global scale. The RLE specifies collapse as the endpoint of the process of ecosystem degradation, and employs “Collapsed” as a category in the assessment, in an analogous way to which the IUCN Red List of Threatened Species (RLTS) includes “Extinct” as a category for species (Bland et al., 2017a; IUCN, 2012). While the RLTS has had a major influence on the identification of priorities for conservation action and protection, and has been widely incorporated into policy, the RLE of ecosystems is currently at a much earlier stage of implementation. To date, around 60 assessments have been published, drawn from more than 20 countries or regions. One ecosystem, the Aral Sea, has been classified as ‘Collapsed’, whereas a number of others have been assessed as ‘Critically Endangered’ such as the gnarled mossy cloud forest on Lord Howe Island of Australia, the Coorong lagoons of Australia, and the Gonakier forests of Senegal and Mauritania (RLE, 2021). These initial outputs of the RLE are already informing global environmental assessments, such as the Global Biodiversity Outlook (Secretariat of the Convention on Biological Diversity, 2020) and the Global Environment Outlook (GEO-6, UN Environment, 2019), together with their associated policy initiatives. Such global assessments have been further supported by development of the IUCN Global Ecosystem Typology (Keith et al., 2020).

The primary focus of the RLE is to assess risk of collapse throughout the entire geographic range of an ecosystem, to support conservation prioritisation (Bland et al., 2017a, Bland et al., 2017b, Bland et al., 2018; Keith et al., 2013, Keith et al., 2015). However, there is also a need to consider ecosystem collapse at the more local scales at which conservation management decisions are typically made. The RLE guidelines note that an ecosystem may undergo a transition to a collapsed state in some parts of its distribution before others; such areas might be described as ‘locally collapsed’ (Bland et al., 2017a). Despite this, the assessment and analysis of local-scale collapse was not explicitly considered by the RLE. Such collapse may be widespread. For example, in their assessment of 19 Australian ecosystems, Bergstrom et al. (2021) found evidence of local-scale collapse in every ecosystem type, although none had collapsed throughout their entire distribution. In his review of the links between biodiversity and economic development, Dasgupta (2021) notes that the local collapse of an ecosystem can be catastrophic for the human communities that are dependent on it. Furthermore, the impacts are likely to be unequal across different income groups owing to variation in dependence on natural assets and ecosystem services. This highlights the need for actions to reduce the risk of ecosystem collapse at the local scale, both to protect human livelihoods and to benefit wildlife.

Identification of appropriate conservation management interventions to reduce the risk of ecosystem collapse requires an understanding of how and why it occurs, and what the potential consequences of it might be. Development of this understanding has been limited to date, reflecting a lack of consensus regarding the scientific foundations on which the RLE is based. Specifically, Boitani et al. (2015) highlighted a number of problems with the concept of ecosystem collapse presented by Keith et al. (2013), as the definition of an ecosystem might vary dependent on scale or ecological context, and according to the specific features under consideration. Further, Boitani et al. (2015) noted that the collapse of an ecosystem is not equivalent to the extinction of a species; while the latter has a clear theoretical endpoint, the endpoints for an ecosystem can be far more ambiguous. An ecosystem undergoing degradation might exhibit a range of different endpoints, and there may be no consensus on which are desirable or undesirable (Boitani et al., 2015). Progress in developing an understanding of the mechanisms responsible for ecosystem collapse has also been limited to date. Various elements of dynamical systems theory have dominated the literature on ecosystem collapse and on related phenomena such as tipping points, critical transitions, resilience, regime shifts and alternative stable states (Andersen et al., 2009; Bland et al., 2017a, Bland et al., 2018; Keith et al., 2013, Keith et al., 2015; Scheffer, 2009). While there has been substantial theoretical development in this area, not all of these ideas are accessible in a form that can be readily used by conservation practitioners. In addition, theoretical predictions relating to ecosystem collapse have not always been supported by empirical evidence (Hillebrand et al., 2020; Newton, 2021). Consequently there is a need to understand under which situations different theoretical ideas are likely to apply, and therefore which mechanisms are likely to be responsible for causing the collapse, so that appropriate management responses can be identified.

In this paper, we examine how the concept of ecosystem collapse might be operationalised for use by conservation practitioners. Firstly we consider how ecosystem collapse might best be defined in a way that is relevant to the scale of conservation decision-making. Secondly we provide an overview of current understanding of the mechanisms of collapse in relation to some of the theoretical ideas that have been proposed, and with reference to available empirical data. Thirdly we explore the practical implications of this understanding for conservation practice, by examining potential management options and responses. This is achieved through development of a decision tree and by consideration of a series of case studies.