Figure 9.2. (above) Profile diagram from a representa-
tive 10 x 40 m plot at the foot of the windward slope in
the central part of the Cerros Centinelas study watershed.
Figure 9.3. (left) Profile diagrams from 5 x 20 m plots
on the ridgecrest and middle windward slope of the
Cerros Centinelas study watershed.elfin forest along the ridgecrest, the taller ravine for-
ests, and the windward slope, respectively. The
consequences of these contrasts in investment are par-
ticularly striking in comparing the dominant shade-
intolerant (pioneer) species within the study water-
shed. Didymopanax pittieri, the dominant pioneer
of the elfin forest, has a mean wood density of 0.57
g/cm^3 (SE) = 0.01, N= 5), while Cecropia polyphlebia
the pioneer of the tallest forest in the bottom of the
watershed bowl, has a mean wood density of 0.28
g/cm^3 (SE = 0.012, N= 5). Saplings of both species
commonly establish together in the well-lit gaps in the
forest canopy created by treefalls. In the taller forest
of ravine bottoms, C. polyphlebia invests less in wood
and grows more rapidly than D. pittieri, which even-
tually dies in the shade of its competitors. In treefall
gaps of the windswept elfin forest, however, D. pittieri,
with its denser wood, is more durable; C. polyphlebia
saplings are tattered and broken in storms. These me-
chanically important structural differences vary among
individuals and within species. Trees can respond to
mechanical stresses by increasing growth of the tissues
that deal with such stresses, a widespread form of ac-
climation in plants, termed thig-momorphogenesis.
This produces stouter trunks, branches, and twigs in
trees exposed to greater stresses.307 Ecosystem Ecology and Forest Dynamics