A broad transition from cloud forest to paramo characterizes an undisturbed treeline in Parque Nacional Llanganates, Ecuador

作者：Hofstede Robert G M^*; Dickinson Katharine J M; Mark Alan F; Narvaez Edwin

来源：Arctic Antarctic and Alpine Research, 2014, 46(4): 975-986.

DOI：10.1657/1938-4246-46.4.975

This study aimed at investigating the vegetation pattern associated with the transition from upper northern Andean cloud forest to paramo grassland in a relatively unmodified area in Ecuador%26apos;s Eastern Cordillera. Single 20 x 10 m plots were randomly placed in representative sites along an altitudinal gradient from continuously wet Andean montane cloud forest at 3400-3700 m to paramo grassland at 3900-4000 m. Also sampled was a disjunct stand of the stem-rosette Espeletia pycnophylla var. llanganatensis, some 200 km south of the limit of the otherwise continuous distribution of this genus. Several physical and chemical soil factors, including temperature at 30 cm, were determined. Visual estimates of cover in four life-form classes (trees, shrubs, herbs, ground cover) at each site revealed similarities related to their relative proximity along an elevation gradient. Stands with a tree cover were more species-rich than those without, due largely to the differential distribution of the woody flora. No abrupt discontinuity occurred in the mix of species along this gradient. Soil temperature and altitude were the most important factors of those measured to explain the variability in plant community structure and composition. There was no clear zonation evident along the altitudinal gradient, with vegetation structure and fioristics displaying continuous variation. No clear upper forest limit was differentiated. The isolated presence of Espeletia in the area is discussed, but the theory about its origin remains speculative.

• 出版日期2014-11