Ecological filtering by a dominant herb selects for shade tolerance in the tree seedling community of coastal dune forest

Abstract

The regeneration niche is commonly partitioned along a gradient from shade-tolerant to shade-intolerant species to explain plant community assembly in forests. We examined the shade tolerance of tree seedlings in a subtropical coastal forest to determine whether the ecological filtering effect of a dominant, synchronously monocarpic herb (Isoglossa woodii) selects for species at either end of the light response continuum during the herb's vegetative and reproductive phases. Photosynthetic characteristics of seedlings of 20 common tree species and the herb were measured. Seedlings were grown in the greenhouse at 12-14% irradiance, and their light compensation points measured using an open-flow gas exchange system. The light compensation points for the tree species were low, falling within a narrow range from 2.1 ± 0.8 μmol m(-2) s(-1) in Celtis africana to 6.4 ± 0.7 μmol m(-2) s(-1) in Allophylus natalensis, indicating general shade tolerance, consistent with a high and narrow range of apparent quantum yield among species (0.078 ± 0.002 mol CO(2) mol(-1) photon). Rates of dark respiration were significantly lower in a generalist pioneer species (Acacia karroo) than in a forest pioneer (C. africana), or in late successional phase forest species. We argue that the general shade tolerance, and phenotypic clustering of shade tolerance, in many tree species from several families in this system, is a result of ecological filtering by the prevailing low light levels beneath the I. woodii understorey, which excludes most light-demanding species from the seedling community.

Understory bamboo flowering provides a very narrow light window of opportunity for canopy-tree recruitment in a neotropical forest of Misiones, Argentina

“…Ecological studies in forests have been mostly focused on trees, however understory vegetation can have a significant effect on forest dynamics by inhibiting tree sapling recruitment and ultimately impacting forest productivity (Maguire and Forman, 1983;George and Bazzaz, 1999;Abe et al, 2002;Nilsson and Wardle, 2005;Holz and Veblen, 2006;Tsvuura et al, 2010). Bamboos are very abundant in the understory of some tropical and temperate forests, and some species are well adapted to colonize areas affected by natural and anthropogenic disturbances because of their fast growth rates and clonal reproduction (Judziewicz et al, 1999).…”

Elevational diversity of terrestrial rainforest herbs: when the whole is less than the sum of its parts

“…Although, terrestrial herbs are recognized as an important component in tropical plant communities (Gentry 1995;Gentry and Dodson 1987;LinaresPalomino et al 2009), there are few quantitative studies of the diversity of tropical herbs. The terrestrial layer of herbaceous plant species in tropical forests plays an important role in light limitation and space competition for seedling and juvenile trees (Tsvuura et al 2010), influencing tree regeneration and forest dynamics (Condit et al 2000), but there is very little data on the diversity of terrestrial herb assemblages (e.g., Poulsen and Pendry 1995). Along tropical elevational gradients, for example, there are dozens of studies on the diversity of trees (e.g., Kitayama 1992) and a lesser number on lianas (Homeier et al 2010), ferns (Kluge et al 2006;Kessler 2000, Kessler et al 2011) and epiphytes (Krömer et al 2005;Cardelús et al 2006), but we are aware of only a handful of studies including terrestrial herbs, although none of these specifically focuses on herbs.…”

The role of historical and ecological factors on initial survival of Copaifera langsdorffii Desf. (Fabaceae)

“…Ramirez & Arroyo (1987) also observed less pre-dispersal seed predation by insects in patches with a high density of C. pubiflora seeds. C. langsdorffii is a supra-annual, mass-fruiting species, and this phenological pattern may be an efficient strategy to increase the number of seeds that escape predation due to predator satiation (Shibata et al 1998;Kon et al 2005;Tsvuura et al 2010). Therefore, it is likely that the negative relationship between percentage seed predation and total number of seeds per plant observed in this study can be associated with R. brevicollis satiation (Silvertown 1980;Ramírez & Traveset 2010).…”