Figure 9.7. Gap 206, in the taller cloud
forest in the upper portion of the ravine
of the Cerros Centinelas study watershed. A
Dendropanaxgonatopodus (35 cm DBH)
snapped 9 m above the ground. The large tree
in the upper profile is Ficus crassiuscula. In the
upper profile, the azimuth from left to right is
270°. In the lower profile the azimuth from left
to right is 180°. Isoclines of photosynthetic
photon flux density as in Fig. 9.5.mostly litter-covered soil, which covered 87% of the
gaps. The group that colonized the disturbed soil of
pits and mounds included Guettarda poasana, which
has a local center of distribution downslope of the
most exposed ridgecrests, and Cecropia polyphebia
and Tetrorchidium sp., which are most abundant in
the taller, more sheltered forests of ravine bottoms.
All of these species contribute to the soil seed bank;
G. poasana contributes 220 seeds/m^2 (SE = 73), which
comprises 54% of the elfin forest seed bank. The
group of species occupying nurse logs is larger; seven
species are more abundant as saplings than expected
on nurse logs, including the dominant pioneer of the
elfin forest, Didymopanax pittieri, and the dominant
end member of gap-phase regeneration, Clusia sp.
Nurse logs and pits and mounds provide open
space, which is a rare commodity in the dense under-
story of the elfin forest (Putz 1983). Vertical gradients
in light availability can be steep in the dense thickets
of elfin forest gap-phase regeneration (Lawton 1990),
so establishment on nurse logs may offer a head start
in competition for light. Saplings of species on nurse
logs arrive by two routes. Species of Conostegia and
Miconia (Melastomataceae) commonly establish on
nurse logs, but seldom grow on living trees (although
"accidental" epiphytism is common in the very wet
conditions of Monteverde cloud forests; Williams-
Linera and Lawton 1995). This pattern suggests that
saplings only become established near the ground,
perhaps because of limitations on root growth and
water or nutrient acquisition. In contrast, Didy-
mopanax pittieri, Oreopanaxnubigenus, Cosmibuena
valerii, Blakea chlorantha, and Clusia sp. are com-
monly found both as elfin forest canopy trees estab-
lished on nurse logs and in taller cloud forest as hemi-
epiphytes. Epiphytic seedlings and saplings of the
these species often survive host tree collapse; they re-
orient and become vigorous components of gap-phase
regeneration (Lawton and Putz 1988, Williams-Linera
and Lawton 1995; see Putz, "Trees on Trees" p. 70).The rate of gap-phase regeneration. The height and
compositition of the vegetation in gaps change
quickly during regrowth (Lawton and Putz 1988). Bare
ground and wood are covered within 2—3 years as the
thicket of regrowth reaches 1—4 m in height. The con-
tribution of canopy tree species to the regrowing
canopy increases from around 10% at 8 months to
around 50% at 78 months. The rate of height growth
is slow compared to lowland forests, which may be
due to differences in patterns of biomass allocation.
Trees in the elfin forest tend to have dense wood
(Lawton 1984) and thick trunks and limbs relative to
their height (Shreve 1914, Brown 1919, Lawton 1982).
These patterns are presumably adaptive responses to
high wind stress. The rate of regrowth relative to mean
canopy height and to the height of emergent trees is
similar to that in lowland settings. Regrowth of pio-
neers to 50% of canopy height (3-4 m in the elfin
forest, 12-15 m in lowland forest) requires about 6
years in each setting (Brokaw 1985, Lawton and Putz
1988).
Leaf area also recovers rapidly following distur-
bance. Leaf area increases logarithmically with gap312 Ecosystem Ecology and Forest Dynamics