| This paper deals with natural disturbances and their impact on vascular
plant enrichment at two climatically contrasting Andean ranges, i.e. the
perhumid Cordillera Real in southern Ecuador and the arid Cordillera de
Atacama in northern Chile. In the first case, main triggers for an
additional input of pioneer species during succession stages initiated by
perturbations are landslides, mudflows, and, to a lesser extent, cohort
mortality, floods, and wildlife damages. Droughts and wind are stressors,
which reduce plant growth but hardly plant diversity, in contrast to
enhanced UV radiation with its mutagen effect. Though stress effects are
similar in the Atacama, disturbance regimes differ considerably in this dry
mountain environment. Here, most perturbations are of small dimension such
as nitrogen inputs by feces of Lamoids and burrow activities of tuco-tuco
mice, both of them fostering nitrophilous plant communities. Flooding,
gelifluction, and other denudation processes such as sheet wash occur too,
however, do not charge species enrichment in the dry Andes. Although the
perhumid study site represents one of the world's plant diversity
"hotspots" and, by contrast, the arid one a comparatively "coldspot",
pioneer species during successive stages after natural disturbances
contribute in a similar percentage to the total plant inventories (appr.
10% of the species numbers). Relatively seen, natural disturbances are
most important for species enrichment in the Atacama (200–500 species per
10 000 km2), while most other ecological factors delimit plant survival.
Instead, plant life at the Ecuadorian study area benefits from many climatic
and edaphic site conditions, and consequently, disturbances are considered
only one of many driving forces for its hotspot status (>5000 species per
10 000 km2). |