Fn. Scatena et Ae. Lugo, GEOMORPHOLOGY, DISTURBANCE, AND THE SOIL AND VEGETATION OF 2 SUBTROPICAL WET STEEPLAND WATERSHEDS OF PUERTO-RICO, Geomorphology, 13(1-4), 1995, pp. 199-213
Relationships between landforms, soil nutrients, forest structure, and
the relative importance of different disturbances were quantified in
two subtropical wet steepland watersheds in Puerto Rico. Ridges had fe
wer landslides and treefall gaps, more above-ground biomass, older age
d stands, and greater species richness than other landscape positions.
Ridge soils had relatively low quantities of exchangeable bases but h
igh soil organic matter, acidity and exchangeable iron. Valley sites h
ad higher frequencies of disturbance, less biomass, younger aged stand
s, lower species richness and soils with more exchangeable bases. Soil
N, P, and K were distributed relatively independently of geomorphic s
etting, but were significantly related to the composition and age of v
egetation.On a watershed basis, hurricanes were the dominant natural d
isturbance in the turnover of individuals, biomass, and forest canopy.
However, turnover by the mortality of individuals that die without cr
eating canopy openings was faster than the turnover by any natural dis
turbance. Only in riparian areas was forest turnover by treefall gaps
faster than turnover by hurricanes. The same downslope mass transfer t
hat links soil forming processes across the landscape also influences
the distribution of landslides, treefall gaps, and the structure and c
omposition of the forest. One consequence of these interactions is tha
t the greatest aboveground biomass occurs on ridges where the soil nut
rient pools are the smallest. Geomorphic stability, edaphic conditions
, and biotic adaptations apparently override the importance of spatial
variations in soil nutrients in the accumulation of above-ground biom
ass at this site.