742 J. R. Ferrer‐Paris et al.


TABLE 2 Summary of the IUCN Red List of Ecosystems assessment of the tropical glacier ecosystem of the Cordillera de Mérida, Venezuela. The first column indicates the sub-criteria assessed under each criterion.Amore detailed report is available in the SupplementaryMaterial. The categories of ecosystem risk are: Collapsed (CO), Critically Endangered (CR), Endangered (EN), Vulnerable (VU), Near Threatened (NT), Least Concern (LC) and Data Deficient (DD). A threat defined location is ‘a geographically or ecologically distinct area in which a single threatening event can rapidly affect all occurrences of an ecosystem type’ (Bland et al., 2017).


Indicator data & analysis applied


Criterion A A1 Cartographic estimates of glacier ex- tent for three peaks (La Concha, Bolívar & Humboldt) in the Cordillera de Mérida (Ramírez et al., 2020)


A2b Data fromRamírez et al. (2020) used to estimate proportional rates of decline for the last remaining patch (Humboldt) & comparison with recently collapsed patch (Bolívar)


A3 Cartographic estimates of glacier extent for three peaks (La Concha, Bolívar & Humboldt) in the Cordillera de Mérida (Ramírez et al., 2020)


Criterion B B1 Data fromRamírez et al. (2020), Braun & Bezada (2013) & RGI 6.0 database (Randolph Glacier Inventory Consortium, 2017)


B2 Same as B1


Criterion C C1 Freezing level height (in metres) from climate reanalysis data for the period 1948–2011 (Braun & Bezada, 2013), with a local polynomial regression


C2a Estimated change in suitability of bio- climatic conditions using a Gradient Boosting Machine model fitted to cur- rent climate (1980–2010)&projected to future timeframes (2010–2040 & 2040– 2070) considering uncertainty


C3 Equilibrium-line altitude estimated from reconstructed palaeo-glacier topography & elevation profiles of ex- isting glaciers (Polissar et al., 2006)


Criterion D We considered prospective samples of the supraglacial microbiota & postgla- cial chronosequence of the glacier forefield (Ball et al., 2014; Rondón et al., 2016; Llambí et al., 2021)


Estimates & uncertainty


Plausible bounds of decline in extent: 89–98%


Best estimates of decline based on alternative proportional rate of decline estimates are .94%. Assuming a similar trajectory be- tween both patches, it is expected to reach 100% decline within the next 20 years


Best estimate of decline in extent: 99 ± SE 0.1%


Rationale


There is no direct estimate of decline in extent for the last 50 years, but calculations of rates of decline be- tween 1952–2019 & 1998–2019 used as minimum & maximum bounds


Recent acceleration of the rate of de- cline suggests that the higher propor- tional rate of decline is more likely; this is consistent with the observed timeframe of collapse in Bolívar Peak (Ramírez et al., 2020)


Reconstruction of the historical evolu- tion of glaciers suggests that the max- imumglacial extent during the Little Ice Age occurred c. 1730 (Jomelli et al., 2009;Rabatel et al., 2013).The observed decline during 1910–2019 represents a lower bound of the total decline


Extent of occurrence,20,000 km2 Restricted to one threat defined loca- tion, with evidence of continuing de- cline & inferred threatening processes


All occurrences (extant & col- lapsed) occupy one 10 × 10 km cell


Averaged relative severity of deg- radation considering two collapse thresholds: 84% (plausible bounds 48–100%)


Best estimate of mean relative severity: 97% (95% CI 63–100%)


Restricted to one threat defined loca- tion, with evidence of continuing de- cline & inferred threatening processes


We used the values of the smoothed freezing level height to calculate initial & final values & assumed that the collapse value is 4,920–4,970 m


Predicted suitability represents the initial & final values; different cut-off values represent potential collapse thresholds. We considered uncer- tainty in climate models, scenarios & cut-off values


Best estimate of relative severity of degradation considering three probable values: 72% (plausible bounds 54–90%)


No measure of relative severity could be calculated from the avail- able data


Change in equilibrium-line altitude was calculated for a historical time- frame (1820–1972) & an extended timeframe (1820–2006). This last value is considered to be near to the collapse threshold


The biota of this assessment unit is poorly known; there is no direct in- formation on temporal changes in microbial communities in the differ- ent habitats after the loss of the ice substrate, but studies investigating this are underway


Category of risk


CR


CR (CR-CO)


CR (CR-CO)


CR CR CR (VU-CO) CR (EN-CO)


EN (VU-CR)


DD


Oryx, 2024, 58(6), 735–745 © The Author(s), 2024. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605323001771


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