Figure 9.1. The distribution of
forest types along the crest of the
central Cordillera deTilaran.
CO, leeward cove forest; LC,
leeward cloud forest; OR, oak
ridge forest; WC, windward cloud
forest; EL, elfin forest; SW,
swamp forest; U, undetermined.
(From Lawton and Dryer 1980)
overlooking the Penas Blancas valley. Average wind
speeds 0.5m above the forest canopy were twice as high
at a ridgecrest weather station than at a station halfway
down the windward slope (Lawton 1980, 1982). The
drop in windspeed with descent through the canopy is
greater on the ridgecrest as well (Lawton 1982). The
change in windspeed with a change in height is propor-
tional to the momentum transferred from the airstream
to the underlying substrate (i.e., the forest). Thus, the
trees of the dwarfed forest are literally shaken more by
the wind than those in the taller forest below.
The forest displays a variety of adjustments to
wind, ranging from changes in community composi-
tion to phenotypically plastic changes of form within
the crowns of individual trees. For instance, tree spe-
cies that have their centers of distribution in the wind-
sheltered taller forest tend to have less dense wood
(dry weight to wet volume) than those species in more
wind-exposed sites (Lawton 1984). Among the tree
species characteristic of a site, those that are shade
intolerant tend to have less dense wood than those
that are shade tolerant. Since denser wood is gener-
ally stronger and metabolically more expensive to
construct (Kollman and Cote 1968, Panshin and
DeZeeuw 1970, Niklas 1993), tree species of wind-
stressed sites invest more in mechanical support than
those than in more protected places.
The elfin forest is composed of denser woods than
the taller forests below. When species wood densities
are weighted by the species contribution to the basal
area of the stand, the sum gives a stand mean wood
density, which is 0.60, 0.47, and 0.56 g/cm^3 for the306 Ecosystem Ecology and Forest Dynamics