Db. Clark et Da. Clark, ABUNDANCE, GROWTH AND MORTALITY OF VERY LARGE TREES IN NEOTROPICAL LOWLAND RAIN-FOREST, Forest ecology and management, 80(1-3), 1996, pp. 235-244
Very large trees, arbitrarily defined as those over 70 cm diameter abo
ve buttresses, account for a major portion of the above-ground biomass
in neotropical rain forests. Owing to the scarcity of individuals of
a given species and the difficulty of accurate measurement, there are
few species-level data on the growth, mortality, and abundance of spec
ies that regularly reach emergent status. We report such data for very
large individuals from old-growth tropical wet forest at the La Selva
Biological Station in the Atlantic lowlands of the Republic of Costa
Rica. The landscape-scale abundance of all species reaching over 70 cm
diameter was assessed using 515 0.01-ha quadrats located at grid poin
ts in a 500 ha area of old-growth forest. In the total sample of 2301
stems 10 cm or more in diameter, very large individuals accounted for
2% of the stems, 23% of the basal area, and 27% of the estimated above
-ground biomass. Growth and survival for five species that regularly a
ttain emergent status were measured in a 150 ha area within the 500 ha
plot. Survival of 282 very large individuals of the five species was
measured over 6 years. The mean annual mortality rate of the total sam
ple was only 0.6% year(-1). Mean annual diameter growth increments var
ied from 1.9 to 5.2 mm year(-1) among species, and were negatively cor
related with diameter in four of the five species. For a sample of 193
individuals measured over 7 years, growth almost exactly equalled los
ses in basal area and biomass due to mortality. Because all of these s
pecies are regularly recruiting new trees into the over 70 cm diameter
class, the amount of biomass in the large-individual size class is in
creasing over the 150 ha old-growth study area. Historic disturbance a
nd/or current climatic change are hypothesized to account for the incr
ease. We identify lack of standard diameter measurement criteria, and
small and potentially unrepresentative plot locations as two problems
in assessing the role of very large trees in other neotropical forests
. Future studies should sample larger areas; this will increase the ge
nerality of the conclusions and will make possible a species-level com
parison of the ecology of very large tropical trees.