9. A Comparative Review of Forest Dynamics
183
nonvolcanic mountains of south-central Chile at approximately 41
0
Sand
the island of Chiloe where mass movements are less important, extensive
areas are dominated by the shade-tolerant tree species and forest dynamics
follow a pattern of fine-scale treefall gap dynamics (Armesto & Fuentes,
1988; Veblen et aI., 1981).
In South American temperate rainforests, the pattern of stand development varies according to the type of stand-devastating disturbance. Disturbances that remove nearly all the preexisting vegetation and expose
bare mineral soil (such as mass movements, floods, glaciers, and volcanism) result in stand initiation and stem exclusion stages consisting
solely of even-aged cohorts of shade-intolerant tree species (typically
Nothofagus species). Shade-tolerant tree species and tall understory
Chusquea bamboos typically do not establish in abundance until the
understory reinitiation stage. As the initial cohort of shade-intolerant
species become senescent, die, and create gaps, these gaps are preempted
by the advance regeneration of the shade-tolerant tree species and the
proliferation of bamboos . If the frequency and scale of disturbance are
sufficiently high, the shade-intolerant colonists do not die before the next
stand-devastating disturbance occurs, so a true old-growth stage (or
steady-state stand) is not attained. Where the stand-initiating disturbance
does not remove the understory (e.g., a blowdown), the response is
dominated by the accelerated growth of plants that survive the disturbance
rather than by new establishment. In this case, it is mostly small individuals of shade-tolerant trees and the Chusquea bamboos that increase
their growth rates. Shade-intolerant species such as N . dombeyi may also
regenerate in small numbers following this kind of canopy disturbance
that does not entirely remove the understory. In blowdowns of mixedspecies rainforest, scattered N . dombeyi may establish on nurse logs and
survive to maturity in low numbers in competition with the bamboos and
the released advance regeneration of shade-tolerant species such as
Laureliopsis philippiana.
In the old-growth forests of more stable habitats (e.g. , the coastal
mountains of Chiloe and south-central Chile), forest dynamics are controlled mainly by the occurrence of small treefall gaps (Armesto ,
Figueroa, 1987; Armesto & Fuentes, 1988; Veblen et aI., 1981). The
most shade-tolerant tree species are able to regenerate beneath a continuous canopy cover, but their growth rates are enhanced by the creation
of small canopy gaps (Armesto & Fuentes, 1988; Veblen, 1985b).
Somewhat less shade-tolerant species, both subcanopy and main canopy
in potential stature, are totally dependent on treefall gaps for successful
regeneration (Armesto & Fuentes, 1988). Again , preemption of canopy
gaps by rapidly growing Chusquea bamboos may have a major inhibitory
influence on tree regeneration, even of the most shade-tolerant tree
species. Interference from bamboos sometimes results in a slow rate of
gap filling . Tree species with some mode of vegetative reproduction (e.g.,
183
nonvolcanic mountains of south-central Chile at approximately 41
0
Sand
the island of Chiloe where mass movements are less important, extensive
areas are dominated by the shade-tolerant tree species and forest dynamics
follow a pattern of fine-scale treefall gap dynamics (Armesto & Fuentes,
1988; Veblen et aI., 1981).
In South American temperate rainforests, the pattern of stand development varies according to the type of stand-devastating disturbance. Disturbances that remove nearly all the preexisting vegetation and expose
bare mineral soil (such as mass movements, floods, glaciers, and volcanism) result in stand initiation and stem exclusion stages consisting
solely of even-aged cohorts of shade-intolerant tree species (typically
Nothofagus species). Shade-tolerant tree species and tall understory
Chusquea bamboos typically do not establish in abundance until the
understory reinitiation stage. As the initial cohort of shade-intolerant
species become senescent, die, and create gaps, these gaps are preempted
by the advance regeneration of the shade-tolerant tree species and the
proliferation of bamboos . If the frequency and scale of disturbance are
sufficiently high, the shade-intolerant colonists do not die before the next
stand-devastating disturbance occurs, so a true old-growth stage (or
steady-state stand) is not attained. Where the stand-initiating disturbance
does not remove the understory (e.g., a blowdown), the response is
dominated by the accelerated growth of plants that survive the disturbance
rather than by new establishment. In this case, it is mostly small individuals of shade-tolerant trees and the Chusquea bamboos that increase
their growth rates. Shade-intolerant species such as N . dombeyi may also
regenerate in small numbers following this kind of canopy disturbance
that does not entirely remove the understory. In blowdowns of mixedspecies rainforest, scattered N . dombeyi may establish on nurse logs and
survive to maturity in low numbers in competition with the bamboos and
the released advance regeneration of shade-tolerant species such as
Laureliopsis philippiana.
In the old-growth forests of more stable habitats (e.g. , the coastal
mountains of Chiloe and south-central Chile), forest dynamics are controlled mainly by the occurrence of small treefall gaps (Armesto ,
Figueroa, 1987; Armesto & Fuentes, 1988; Veblen et aI., 1981). The
most shade-tolerant tree species are able to regenerate beneath a continuous canopy cover, but their growth rates are enhanced by the creation
of small canopy gaps (Armesto & Fuentes, 1988; Veblen, 1985b).
Somewhat less shade-tolerant species, both subcanopy and main canopy
in potential stature, are totally dependent on treefall gaps for successful
regeneration (Armesto & Fuentes, 1988). Again , preemption of canopy
gaps by rapidly growing Chusquea bamboos may have a major inhibitory
influence on tree regeneration, even of the most shade-tolerant tree
species. Interference from bamboos sometimes results in a slow rate of
gap filling . Tree species with some mode of vegetative reproduction (e.g.,