Tropical mountain ecosystems exhibit high endemism rates and are considered hotspots of biodiversity that are among the most vulnerable to climate change. Higher temperatures associated with the El Niño Southern Oscillation (ENSO) may further increase abiotic stress. The Colombian Andean Páramo is a high altitude, seasonally wet and dry, and nocturnally cold ecosystem. Espeletia grandiflora (Asteraceae) is the index species in this Páramo. This slow growing, long-lived, caulescent plant helps regulate the ecosystem's hydrological cycle, providing water for 70% of Colombian urban residents. Here we present evidence that E. grandiflora populations are declining, especially in response to increases in temperature associated with ENSO. During 19 months (February 2014-July 2015), at Chingaza Natural National Park (CNNP), 1856 plants of E. grandiflora from 15 (100m2) plots distributed along an elevational gradient (3100-3700 masl) were monitored in four semiannual censuses, corresponding to two dry (February 2014 and February 2015) and two wet seasons (July 2014 and July 2015).
Results/Conclusions
Espeletia grandiflora exhibited a significant increase in mortality (Tukey post hoc test p<0.001) from July 2014 - July 2015 when local increases in mean temperature associated with ENSO were recorded; mean temperatures rose from 10.5 oC to 11.2 oC , 9.0 oC to 9.8 oC, and , 6.8 oC to 7.7 oC at low (3100-3300 masl), mid (3300-3500 masl) and high (3500-3700 masl) elevations, respectively. (For historical perspective, in 2001 the mean annual temperature at 3200 masl in CNNP was 7 oC.) The average mortality was 2.6% for the July 2014 census, 15.4% for the February 2015 census, and 12.4% for the July 2015 census, for a total of 27.8% mortality during the 19-month period, with no significant difference between juveniles and adults. Overall, mortality was significantly higher, 38.0%, at the low elevation compared to 28.9% in mid and 24.3% at high elevations (Tukey post hoc test p<0.001). The comparative survivorship pattern also reflected the relative plant density along the elevational gradient, being greatest at high elevation. These results provide dramatic evidence of the vulnerability of the Colombian Andean Páramo to global warming and ENSO, which may prove devastating for its species diversity and public services.