Editing IPCC:AR6/WGII/Cross-Chapter-Paper-7 (section)

=== CCP7.2.1 Distribution and Biodiversity of Tropical Forest Ecosystems ===

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Tropical forests are indisputably the areas with highest biological diversity on Earth, both in absolute and density (species per area) terms (Plotkin et al., 2000). Estimates account that tropical forests harbour half or even more of world’s biodiversity (Kier et al., 2009; Jenkins et al., 2013), even though this figure is highly uncertain owing to varying estimates of undescribed species (Mora et al., 2011). For example, it is estimated that there are at least 40,000, but possibly more than 53,000 tree species in tropical forests (Slik et al., 2015). A vast majority of this biodiversity and Indigenous knowledge and local knowledge associated with its use remains poorly explored, presenting a vast unlocked genetic reserve at risk of loss, although many of today’s important medicines, foods and ecosystem products originate from tropical forests ( [[#Kouznetsov--2008|Kouznetsov and Amado Torres, 2008]] ; Calderon et al., 2009, [[#Maia--2016|Maia and Mourão, 2016]] ).

Rates of global biodiversity loss in the past few decades have acelerated to levels that are, for some taxa, approaching the estimated rate of 75% of taxa extinction found in Earth’s ‘big five’ mass extinction events (Barnosky et al., 2011; Díaz et al., 2019; [[#Davison--2021|Davison et al., 2021]] ). Even though species–area relationships tend to overestimate extinction rates ( [[#He--2011|He and Hubbell, 2011]] ), there is evidence that species richness in tropical forests is alarmingly approaching or surpassing the taxa extinction value in this period (45% for dung beetles, 51% for lizards, 65% for ants, and 80% for mammals) should deforestation and habitat loss continue at the current pace ( [[#Alroy--2017|Alroy, 2017]] ; Ceballos et al., 2017). Moreover, there is reasonable understanding that these numbers are underestimated and, as such, tropical forest loss and degradation alone will precipitate a sixth mass extinction event ( [[#Giam--2017|Giam, 2017]] ). A total of 13 out of the 25 global biodiversity hotspots for conservation are located in tropical forests, such as Brazil’s Atlantic Forest and India’s Western Ghats/Sri Lanka (Myers et al., 2000). While forest loss and degradation have been the main cause of tropical biodiversity loss in the past, climate change now arises as a major threat not only for individual tropical forest species or taxa—as already observed for frogs (Pounds et al., 2006)—but for whole communities (Esquivel-Muelbert et al., 2019), and even entire tropical forest ecoregions (Lapola et al., 2018).

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