How Do We Know When We Achieve Land Degradation Neutrality in Forests? A Systematic Review

Abstract

This systematic review develops a comprehensive understanding of how land degradation is measured with respect to forests, and what qualitative and quantitative methods are being utilised in the pursuit of land degradation neutrality (LDN) generally. Scopus and Environmental Abstracts (EVA) databases were searched for peer-reviewed studies from 1998–2021 using key search terms including ‘land degradation neutrality’, ‘soil’ and ‘forest’. Of the 53 included studies, most articles (n = 25) are experimental reports, and the next most common classification (n = 14) is literature reviews. Studies tended to be longitudinal (mean length of 15.4 years) and Eurasia-centric. Almost all extant research focuses on the indicators rather than the drivers of land degradation. Choosing indicators to measure remains contentious; however, most research uses those prescribed by the United Nations Convention to Combat Desertification: land cover, net primary productivity and soil organic carbon. Despite this convergence around which indicators to monitor, there is no standardisation in the methods used to do so. Therefore, no meaningful comparison between countries or even studies can be made. This lack of standardisation and bias towards indicators instead of drivers is important because, under the current paradigm, land managers seeking to prevent or offset forest degradation cannot do so with any certainty. Until these issues are addressed, it will be impossible to track progress towards the United Nations Sustainable Development Goal 15.3 for global LDN, and large-scale conservation work in this area is based on guesswork. How will we know when we achieve LDN in forests, globally? Based on current research, we will not. Future research must seek standardised ways to quantify land degradation based on its drivers: erosion, urbanisation and human activity, drought and desertification, and pollution.