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INTRODUCTION
Conservation planning usually combines general principles with
site-specific rules (Groom et al . 2005). In our review
(Arroyo-Rodríguez et al . 2020), we combined empirically-supported
general principles to describe biodiversity-friendly scenarios in
human-dominated landscapes. One such principle is based on extinction
thresholds: as most species require 10–30% forest cover in a landscape
for population persistence (Andrén 1994; Swift & Hannon 2010), we
suggest that a conservative general guideline would be to
maintain ≥40% forest cover in landscapes to ensure persistence ofmost forest species (“40% criterion” hereafter).
Banks-Leite et al . argued that the 40% criterion lacks evidence
and is problematic, and advocated for using regionally-defined
thresholds to guide conservation and restoration. As discussed below, we
found their criticisms unfounded, and the idea of basing conservation
actions on unique, regionally-defined thresholds impractical and
potentially harmful.
VALUE OF THE 40% CRITERION
We are in a state of planetary emergency, with forests increasingly lost
and degraded by human activities. Therefore, identifying general
conservation guidelines such as the 40% criterion has never been so
urgent and valuable. Banks-Leite et al . argue that applying a
“fixed ” threshold to “any given landscape ” is
“unhelpful and potentially dangerous ” because extinction
thresholds vary among species and regions. These claims are misleading,
as we specify in our paper that the 40% criterion is not fixed, and
should be adapted to some contexts, such as in tropical regions with low
matrix quality (p. 1410 and Fig. 1b in Arroyo-Rodríguez et al .
2020). However, the 40% criterion is adequate for most species
in most landscapes.
Banks-Leite et al . also raised concerns regarding the lack of
social and economic considerations in our guidelines. However, the
stated aim of our review was to illustrate an optimal human-modified
landscape for biodiversity conservation . We agree that
alternative scenarios may optimize other outcomes. Ideally, a
multicriteria planning process would evaluate tradeoffs among different
scenarios (e.g. Neugarten et al . 2016; Vollmer et al .
2016), and we see great potential for future research to inform such
planning.
SUPPORT FOR THE 40% CRITERION
We disagree that the 40% criterion lacks evidence. We cited two global
reviews of dozens of studies indicating that most species have
extinction thresholds at 30% habitat amount (Andrén 1994; Swift &
Hannon 2010). By suggesting 40% (and not 30%), we attempt to be more
conservative, and compensate for variation and uncertainties associated
with the estimation of habitat thresholds (Rompré et al . 2010).
Interestingly, two of the studies we ‘ignored ’ also support a
40% criterion: Macchi et al . (2019) demonstrate that most (71%)
forest birds in the Chaco region have extinction thresholds at
>38% woody cover, and Melo et al . (2018) found that
extinction thresholds average 34% for birds at tropical latitudes.
Although Banks-Leite et al . (2014) found that 30% forest cover
would safeguard Brazilian Atlantic forest vertebrates, other studies in
the same biome document higher thresholds for woody plants (40%,
Rigueira et al . 2013) and forest-specialist birds (46%,
Morante-Filho et al . 2015). Therefore, a 40% general target is
more consistent with the evidence than the 30% preferred by Banks-Leiteet al .
FEASIBILITY OF THE 40% CRITERION
Banks-Leite et al . suggest that economic constraints in regions
requiring massive restoration efforts make the 40% criterion
unfeasible. We disagree. In 50% of Earth’s forested biomes we have
already reached the criterion or have sufficient unaltered forest to
meet the criterion, and 27% more biomes have sufficient forest cover to
reach the 40% target with restoration (Dinerstein et al . 2017).
In the 23% of biomes in which forest cover is < 20%
(Dinerstein et al . 2017), we agree that a lower threshold is
likely a more feasible target.
Banks-Leite et al . also argue that the 40% criterion creates
confusion among policy makers and undermines public trust in science.
This speculation is baseless, as the scientific discussion about
extinction thresholds is not under public dispute. We rather suggest the
opposite: scientists, as members of society, have a responsibility to
inform policy makers and the general public on appropriate use of
science in addressing societal issues and concerns (Lees et al .
2020).
ON THE USE OF REGIONALLY-DEFINED THRESHOLDS
Banks-Leite et al . advocate for regionally-defined thresholds,
because we have the “technical capacity ” to determine optimal
regional forest cover scenarios. We found this suggestion unfeasible and
potentially harmful for conservation, as it would require information on
extinction thresholds of a wide variety of taxonomic groups, each of
which will likely have a different threshold. As this information is
absent in most regions, we simply do not have the time and resources to
identify taxon- and region-specific extinction thresholds across the
globe. We agree that, when available, regionally-defined thresholds
might be more appealing to decision-makers, but if we insist on using
region-specific thresholds everywhere, then deforestation and lack of
restoration will continue, and species will go extinct while we spend
decades collecting data.