intensity, bringing about dramatic changes that were
felt throughout the food web.
Studies by numerous researchers have shown that
plants, including many shade- tolerant species, respond to
gaps with a spurt of growth and that at least a few species
are dependent upon gaps. Gary Hartshorn showed that
of 105 canopy tree species studied as saplings at La Selva,
about 75% are estimated to depend at least in part on gaps
in order to complete their life cycle.
A large gap absorbs up to 50 times as much
solar radiation as interior forest. Furthermore, it is
“high- quality” sunlight, of wavelengths appropriate
for photosynthesis. By contrast, the shaded forest
understory is generally limited not only in totallight intensity but in wavelengths from 400 to 700
nanometers, the red and blue wavelengths most utilized
in photosynthesis. Most high- quality solar radiation
(61– 77%) within a shady rain forest understory is
received in the form of short- duration sun flecks,
many of which are small. The total amount and quality
of solar radiation is the single largest limiting factor to
plant growth inside tropical forests.
For many years it has been known that small but
healthy sapling trees of many species persist in the
understory, continuing their upward growth when
adequate light becomes available. Understory specialists
do not necessarily require gaps, but they utilize them
when the opportunity is presented (plate 7- 12).Plate 7- 12. Palms are a common component of gaps in many tropical areas. Photo by John Kricher.chapter 7 if a tree falls . . . rain forest disturbance dynamics 101