title: Contrasting structure and composition of the understory in species-rich tropical rain forests.
abstract: In large samples of trees > or = 1 cm dbh (more than 1 million trees and 3000 species), in six lowland tropical forests on three continents, we assigned species with >30 individuals to one of six classes of stature at maturity (SAM). We then compared the proportional representation of understory trees (1-2 cm dbh) among these classes. The understory of the three Asian sites was predominantly composed of the saplings of large-canopy trees whereas the African and American sites were more richly stocked with trees of the smaller SAM classes. Differences in class representation were related to taxonomic families that were present exclusively in one continent or another. Families found in the Asian plots but not in the American plot (e.g., Dipterocarpaceae, Fagaceae) were predominantly species of the largest SAM classes, whereas families exclusive to the American plots (e.g., Melastomataceae sensu stricto, Piperaceae, and Malvaceae [Bombacacoidea]) were predominantly species of small classes. The African plot was similar to Asia in the absence of those American families rich in understory species, while similar to America in lacking the Asian families rich in canopy species. The numerous understory species of Africa were chiefly derived from families shared with Asia and/or America. The ratio of saplings (1-2 cm dbh) to conspecific canopy trees (>40 cm dbh) was lower in American plots than in the Asian plots. Possible explanations for these differences include phenology, moisture and soil fertility regimes, phyletic constraints, and the role of early successional plants in forest development. These results demonstrate that tropical forests that appear similar in tree number, basal area, and the family taxonomy of canopy trees nonetheless differ in ecological structure in ways that may impact the ecology of pollinators, dispersers, and herbivores and might reflect fundamental differences in canopy tree regeneration.
authors.affiliation: Smithsonian Tropical Research Institute, c/o National Institute of Education, 1 Nanyang Walk, 637616 Singapore. jlafrankie@yahoo.com
authors.forename: James V
authors.initials: JV
authors.lastname: LaFrankie
authors.forename: Peter S
authors.initials: PS
authors.lastname: Ashton
authors.forename: George B
authors.initials: GB
authors.lastname: Chuyong
authors.forename: Leonardo
authors.initials: L
authors.lastname: Co
authors.forename: Richard
authors.initials: R
authors.lastname: Condit
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Davies
authors.forename: Robin
authors.initials: R
authors.lastname: Foster
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Hubbell
authors.forename: David
authors.initials: D
authors.lastname: Kenfack
authors.forename: Daniel
authors.initials: D
authors.lastname: Lagunzad
authors.forename: Elizabeth C
authors.initials: EC
authors.lastname: Losos
authors.forename: Noor Supardi Md
authors.initials: NS
authors.lastname: Nor
authors.forename: Sylvester
authors.initials: S
authors.lastname: Tan
authors.forename: Duncan W
authors.initials: DW
authors.lastname: Thomas
authors.forename: Renato
authors.initials: R
authors.lastname: Valencia
authors.forename: Gorky
authors.initials: G
authors.lastname: Villa
mesh_terms: D044822:Biodiversity; D017753:Ecosystem; D011156:Population Density; D011891:Rain; D012044:Regression Analysis; D014197:Trees / Q000145:classification* / Q000502:physiology*; D014329:Tropical Climate