Long-term growth rates of two caulescent rosette species, Coespeletia timotensis (Cuatrec.) Cuatrec., and Espeletia schultzii Wedd., in an Andean páramo

Abstract

Growth rates of two caulescent rosette species, Coespeletia timotensis and Espeletia schultzii, were estimated in Piedras Blancas, an Andean páramo, on 4 sites at 4270–4525 m, near their upper elevation limits. Stem and crown height were measured at the start and end of the study periods, and differences in plant stature divided by number of years to obtain annual growth rates. An isolated C. timotensis on a granite outcrop at 4525 m grew 1.08 cm/yr average for 19.5 yrs, but its elongation rate dropped gradually with time. 60 C. timotensis on a dense valley-floor stand at ≤4285 m showed an average rate of 1.34 ± 0.59 cm/yr for >10 yrs; growth varied between −0.2 and 3.16 cm/yr and was not associated with initial plant height. 31 E. schultzii rosettes on a basal slope stand at ≤4300 m grew 1.15 ± 0.51 cm/yr during >10 yrs; growth ranged from 0.44 to 2.37 cm/yr and appeared to be inversely correlated with plant stature. Each stand exhibited fairly uniform aspect, gradient, slope position, and groundcover, but microsite differences, including soil nutrient and moisture content, proximity to rocks, and competitive plant interactions, may have affected rosette development. Mortality was similar for both species (18.4–18.9%) but was higher for C. timotensis seedlings and taller plants, which tilted and toppled, presumably due to ground frost disturbance. Mortality was also concentrated on larger E. schultzii plants, but these remained standing and did not topple. Due to extreme growth variation, use of average rates to calculate ages of individual rosettes is not recommended.