The suggestion that landscapes should contain 40% of forest cover lacks evidence and is problematic

Abstract

A recent review suggests that forest cover needs to be restored or maintained on at least 40% of land area. In the absence of empirical evidence to support this threshold, we discuss how this suggestion is unhelpful and potentially dangerous. We advocate for regionally defined thresholds to inform conservation and restoration.

Detecting ecological thresholds for biodiversity in tropical forests: Knowledge gaps and future directions

“…Finally, as highlighted recently by Banks‐Leite et al, (2021) and others, we agree there is a lack of evidence to support blanket assumptions and statements about the existence of ecological thresholds of forest cover for biodiversity across the tropics. Here, we have attempted to fill some of these data gaps, but have shown that existing evidence is heavily biased toward South America, and is based on a wide range of ecological metrics and species.…”

“…Thus, a forest cover threshold of 30-40% may be too low for some under-studied regions and species, risking the creation of conservation policies which do not protect many large mammals and apex predators. As highlighted by others (Banks-Leite et al, 2021), basing forest conservation and/or restoration targets on the amount of protection in a given landscape can be problematic in terms of implementation and ecological outcomes, and we caution the communication of scientific findings in a way which suggests the existence of general thresholds, and their use in policy-making, as current evidence is not enough to support this beyond context-specific examples.…”

“…Despite support for ecological thresholds as an important tool to link forest cover loss to thresholds of change (“tipping points”) beyond which ecosystem functioning is at risk (Arroyo‐Rodríguez et al, 2020; Banks‐Leite et al, 2014; de Oliveira Roque et al, 2018; Johnson, 2013; Lindenmayer & Luck, 2005; I. Melo et al, 2018), strong scientific debate exists around their existence and use in conservation planning (Brook et al, 2013; Foley et al, 2015; van der Hoek et al, 2015; Lindenmayer & Luck, 2005; Muradian, 2001). Concerns surrounding the threshold concept include criticisms of its use as a “rule of thumb” value applied globally, while based on local or regional evidence (Banks‐Leite et al, 2021), and the risk of publication bias meaning studies with negative results are less likely to be published. In addition, some studies investigating the ecological response to forest cover loss may not identify a specific tipping point or non‐linear change, as changes to metrics such as species abundance often happen non‐linearly in the terrestrial biome (Brook et al, 2013).…”

“…Melo et al, 2018), strong scientific debate exists around their existence and use in conservation planning (Brook et al, 2013;Foley et al, 2015;van der Hoek et al, 2015;Lindenmayer & Luck, 2005;Muradian, 2001). Concerns surrounding the threshold concept include criticisms of its use as a "rule of thumb" value applied globally, while based on local or regional evidence (Banks-Leite et al, 2021), and the risk of publication bias meaning studies with negative results are less likely to be published.…”

Preserving 40% forest cover is a valuable and well‐supported conservation guideline: reply to Banks‐Leite et al

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Banks-Leite et al (2021) claim that our suggestion of preserving ≥ 40% forest cover lacks evidence and can be problematic. We find these claims unfounded, and discuss why conservation planning urgently requires valuable, well-supported and feasible general guidelines like the 40% criterion.

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