Pioneer species, unsurprisingly, thrived in environments
of high light intensity. Non- pioneer species exhibited
high mortality when young, but the rate of mortality
decreased as they aged, reaching a plateau. As individuals
grew larger, their survivorship increased, but once trees
became very large, survivorship decreased. The pattern
resembles that typical of human populations: infant
mortality may be high, but if one survives infancy the
mortality rate declines until old age, when it accelerates.
The study concluded that a tree requires a minimum
of 60 years to reach the canopy and possibly up to
about 200 years if subjected to shady conditions. But
once in the canopy, trees’ life expectancies reached 300
years or longer.
A study from Amazonia that used carbon dating
along with tree ring counts to age 12 fallen trees
estimated longevity of large canopy trees to be between
500 and 650 years.
At Cocha Cashu Biological Station in southeastern
Peru, set in an Amazonian forest on rich soils, mortalityrate of adult trees (those with a trunk diameter at
breast height, or dbh, of >10 cm/4 in) was 1.58% per
year, implying an average life span of 63.3 years. At San
Carlos de Río Negro in Amazonian Venezuela, mean
annual mortality rates for trees of >10 cm dbh was 1.2%.
Most tree deaths resulted in small gaps (large gaps were
much rarer), and approximately 4– 6% of the forest
area was in gap phase at any given time. At Manaus,
Brazil, mortality was 1.13% for adult trees, indicating
a turnover time of 82 to 89 years for adult trees with a
minimum size of >10 cm dbh. A tree often lives many
years before attaining such a diameter, so the total age,
from seedling to death, would be considerably longer.
In the Manaus study it was learned that the larger a tree
grew to be in diameter, the longer its probable life span
(plate 7- 15). For trees greater than 55 cm (21.5 in) dbh,
the turnover time increases to 204 years.
Mortality rates of seedlings and sapling trees exceed
those of adults. Any recently germinated seedling
stands a fairly high chance of being smashed by aPlate 7- 15. Trees of various ages growing together in an Amazonian floodplain forest. As they age, their survivorship potential
changes. Photo by John Kricher.chapter 7 if a tree falls . . . rain forest disturbance dynamics 105