The New Neotropical Companion

frequency of disturbance may be at least partly
responsible for why there are so many coexisting species
of trees in tropical forests. Heavy rainfalls, landslides,
hurricanes, fires, occasional lightning strikes, and high
winds typical of rainstorms destroy individual or groups
of canopy trees, create forest gaps, and sometimes level
whole forest tracts. Isolated branches, often densely
laden with epiphytes, break off and crash down through
the canopy. This is normal in tropical forests.

How Does Succession Work?

Studies conducted by Chris Uhl and others and by
James Dalling and colleagues have shown that within
Amazonia, a typical square meter (10.75 ft^2 ) of soil is
estimated to contain between 500 and 1,000 seeds, the
seed bank. Think about that: when you are anywhere
in the forest you are standing on future generations

of trees and other plants. All that is needed is some

light for germination. Seeds of some species of pioneer

plants, which are plant species that are first to occupy

disturbed sites, may remain dormant in soil for nearly

40 years and still germinate after a disturbance occurs.

Other seeds have far shorter residence time in the seed

bank. But it is not just the seed bank that is important

for regeneration after disturbance. Seeds transported

either by wind or animals also reach disturbed areas

and germinate.

Now look closely at the shaded floor of a closed

moist forest. Notice the shoots of trees? Observe the

seedlings and saplings (plate 7- 8). Once you start to

really look, you are likely to see many small tree stems

per square meter. Their growth is typically suppressed

in the dense forest shade. Many of these will not grow

further until a gap forms, providing sunlight.

In Amazonia, between 10 and 20 seedlings and

small saplings (<2 m/6.5 ft tall) typically occur within

every square meter of forest floor. Most of these

Plate 7- 8. Seedlings of potential canopy trees abound on the well- shaded floor of closed forest. Photo by John Kricher.

98 chapter 7 if a tree falls . . . rain forest disturbance dynamics