for the most part, gradually replaced by slower- growing
more shade- tolerant species as the once open gap regains
a closed canopy and shade predominates at ground
level. This successional process is characteristically
viewed as one of interspecific competition among plants
for light and soil resources. Ecologists sometimes use
the term recovery when describing the pattern of how
ecosystems respond to natural disturbances. This term
is inappropriate, as it suggests that the ecosystem was
somehow wounded and that time heals the wound. It
is important to realize that the species colonizing and
thriving after the disturbance are specifically adapted to
just such conditions, and so they represent part of the
continuum of evolved species adaptations characteristic
of that ecosystem. Their very existence as species clearly
adapted to disturbance sites speaks to the routine nature
of periodic natural disturbance events.
Succession in the Neotropics: A
Closer Look
Astute naturalists should enjoy perusing gaps and
successional areas. These sunlit habitats, which may
include large roadside fields, are ideal for encountering
species of plants and animals that are not seen nearly as
frequently in closed forests.
Tropical succession typically begins with the
appearance of rapidly growing sun- demanding plant
species, some of which germinated from the soil seed
bank, others of which arrived by natural seed dispersal,
and still others that were present as seedlings (plate 7- 3).
Many are herbaceous and many are vines, both woody
and nonwoody. Some shrubs and small trees are readily
evident too. Seedlings of trees, some typical of closed
forest, begin to grow into saplings. Growth rates are fast
because light is abundant. Biomass increases. Sometimes
vine growth is sufficiently dense as to envelop the brushy
growth of other species, and a blanket of vines may
cover the trees. Spindly trees and feathery palms push
aggressively upward above the tangled mass. Biomass
and the richness of plant and animal species continue
to increase over time. Clumps of huge- leaved plants,
typical sun- demanding species, are sometimes evident.
One such group is Heliconia, its name derived from
the Greek word helikonios (plate 7- 4). The canopy is a
dense, low, irregular, tangled assemblage of competing
plants. Eventually more shade- tolerant tree species
appear. Many of these may have been present from the
Plate 7- 3. Early succession in the tropics is characterized by
dense growth of sun- demanding plant species. Photo by John
Kricher.Plate 7- 4. This disturbed gap in Ecuador experiences an
abundance of sunlight (note the shiny leaves), ideal for species
such as this flowering heliconia. Photo by John Kricher.Plate 7- 5. This field adjacent to a rural village in Belize, now
abandoned, is undergoing early succession. The large- leaved
plants are bananas grown by the former inhabitants. Photo by
John Kricher.96 chapter 7 if a tree falls . . . rain forest disturbance dynamics