Life History Diversity of Canopy and Emergent Trees in a Neotropical Rain Forest

Abstract

To assess the diversity of tropical tree life histories, a conceptual framework is needed to guide quantitative comparative study of many species. We propose one such framework, which focuses on long-term performance through ontogeny and over the natural range of microsites. For 6 yr we annually evaluated survival, growth, and microsite conditions of six non-pioneer tree species in primary tropical wet forest at the La Selva Biological Station, Costa Rica. The species were: Lecythis amp/a, Hymenolobium mesoamericanum, Dipteryx panamensis, Pithecellobium elegans, Hyeronima alchorneoides (all emergents), and Minquartia guianensis (a canopy species). The study was based on long-term measurement of individuals from all post-seedling size classes. Trees were sampled from 150 ha of primary forest spanning several watersheds and soil types. To evaluate individuals' microsites we recorded the number of overtopping crowns, forest phase (gap, building, mature), and crown illumination index (an estimate of the tree's light environment). For comparison, we also evaluated the microsites of three species that have been categorized as pioneers (Cecropia ins ignis, C. obtusifolia) or high-light demanders (Simarouba amara).For the six species of non-pioneers, mortality rates declined with increasing juvenile size class. As a group, these emergent and canopy trees showed a much lower exponential annual mortality rate (0.44%/yr at> 10 em diameter) than has been found for the La Selva forest as a whole. Growth rates increased with juvenile size class for all six species. As adults (trees > 30 em in diameter), all five emergent species showed substantial annual diameter increments (medians of 5-14 mm/yr). Small saplings and adults of all species had significant year-to-year variation in diameter growth, with much greater growth occurring in the year of lowest rainfall. Passage time analysis suggests that all six species require> 150 yr for growth from small saplings to the canopy.Evaluation of all nine species revealed four patterns of microsite occupancy by juveniles. Among the non-pioneers, one species pair (Lecythis and Minquartia: Group A) was associated with low crown illumination and mature-phase forest in all juvenile stages. For two species (Dipteryx and Hymenolobium: Group B) the smallest saplings were in predominantly low-light, mature-forest sites, but crown illumination and association with gapor building-phase sites increased with juvenile size (Simarouba also showed this pattern). Two species (Pithecel/obium and Hyeronima: Group C) were strongly associated with gap or building phase as small juveniles (~4 em diameter) and again as subcanopy trees(> 10-20 em diameter), but were predominantly in mature-phase sites at intermediate sizes.Juveniles of the two pioneer species (Cecropia: Group D) showed the highest crown illumination and association with gap or building sites.Among the six non-pioneer species, only one aspect of juvenile performance clearly varied according to microsite group. The smallest saplings ( ~ 1 em di...

Patterns of tree growth in relation to environmental variability in the tropical dry deciduous forest at Mudumalai, southern India

“…Harper (1977) described such plant populations as being largely composed of "suppressed weaklings", implying that only a few individuals exhibited much greater than average growth while most individuals tended to cluster around low growth values, especially under density stress. Similar effects were found in a Costa Rican rain forest (Clark and Clark 1992), and in Sarawak, Malaysia (Primack et al 1985). Interestingly, in 1992-1996 skewness and kurtosis values were reduced, suggesting less competitive interactions under unfavourable growth conditions (although this effect was not obvious with conservative cutoffs).…”

“…However, longer term studies (without dendrometers) have suggested that on an annual basis the relationship between rainfall and growth might become negative as the average annual rainfall increases. Thus, a four year study in a dry evergreen rainforest of Ghana (Swaine et al 1990;annual rainfall: 570-910 mm, at least eight months with less than 100 mm) found that faster growth occurred during higher rainfall years as expected based on seasonal patterns, whereas studies lasting up to eight years in moist forest sites of Panama (Condit et al 1993a(Condit et al , 2004annual rainfall: 2030-2892.5 to 4.5 months with less rainfall than potential evapotranspiration) found higher growth rates in saplings and several large trees during a drought year, and similarly a six-year study in a wet forest of Costa Rica (Clark and Clark 1992; annual rainfall: 3859 mm, no months with less than 100 mm) found highest median annual growth rates in the smallest and largest size classes during the lowest rainfall years and lowest growth during the highest rainfall years in most of the species studied. Similarly, a short twoyear dendrometer study in a wet evergreen forest of India (Pelissier and Pascal 2000; annual rainfall >4000 mm, five months with less than 100 mm) also showed higher average annual growth during the relatively drier year.…”

Seedling growth of fifteen Brazilian tropical tree species differing in successional status

“…Kitajima (1994) points out that these traits are better correlated with survivorship in shade and not just with the reputed successional class of species. It is possible that the lack of a consistent trend of variation of these parameters may have emerged here because of the attempt to correlate them with the successional position of the species at adult stage, as species requirements and even growth responses may change with ontogeny (Clark & Clark 1992). Despite these considerations, the RGR still seems to vary consistently with the successional ranking, as discussed above.…”

Structure and dynamics of a woody plant community of a tropical semi-deciduous seasonal forest in the "Estação Ecológica do Panga", municipality of Uberlândia, Minas Gerais, Brazil

“…Uhl et al (1988) and Clark & Clark (1992) found higher mortality among individuals of less than 10 cm diameter. According to Felfili (1995b), the greater mortality among individuals belonging to the smallest diameter classes should result from the lower competition capacity in relation to the larger trees, which occupy the upper strata.…”