Seasonal Water Stress Tolerance and Habitat Associations Within Four Neotropical Tree Genera

Abstract

We investigated the relationship between habitat association and physiological performance in four congeneric species pairs exhibiting contrasting distributions between seasonally flooded and terra firme habitats in lowland tropical rain forests of French Guiana, including Virola and Iryanthera (Myristicaceae), Symphonia (Clusiaceae), and Eperua (Caesalpiniaceae). We analyzed 10-year data sets of mapped and measured saplings (stems >150 cm in height and <10 cm diameter at breast height [dbh]) and trees (stems > or =10 cm dbh) across 37.5 ha of permanent plots covering a 300-ha zone, within which seasonally flooded areas (where the water table never descends below 1 m) have been mapped. Additionally, we tested the response of growth, survival, and leaf functional traits of these species to drought and flood stress in a controlled experiment. We tested for habitat preference using a modification of the torus translation method. Strong contrasting associations of the species pairs of Iryanthera, Virola, and Symphonia were observed at the sapling stage, and these associations strengthened for the tree stage. Neither species of Eperua was significantly associated with flooded habitats at the sapling stage, but E. falcata was significantly and positively associated with flooded forests at the tree stage, and trees of E. grandiflora were found almost exclusively in nonflooded habitats. Differential performance provided limited explanatory support for the observed habitat associations, with only congeners of Iryanthera exhibiting divergent sapling survival and tree growth. Seedlings of species associated with flooded forest tended to have higher photosynthetic capacity than their congeners at field capacity. In addition, they tended to have the largest reductions in leaf gas exchange and growth rate in response to experimental drought stress and the least reductions in response to experimental inundation. The corroboration of habitat association with differences in functional traits and, to a lesser extent, measures of performance provides an explanation for the regional coexistence of these species pairs. We suggest that specialization to seasonally flooded habitats may explain patterns of adaptive radiation in many tropical tree genera and thereby provide a substantial contribution to regional tree diversity.

Seedling recruitment factors in low‐diversity Hawaiian wet forest: towards global comparisons among tropical forests

“…Another explanation may relate to the particular limitations of our study design. Plants respond to many resources and we might have found niche differentiation had we measured species associations with, for example, soil moisture or nutrients (Baltzer et al 2005, Baraloto et al 2006, Baraloto et al 2007, Comita and Engelbrecht 2009. Indeed, while light adaptation is generally a major axis of variation among species in most forests (Augspurger 1984, Denslow 1987, Poorter 1999, Hubbell 2006, plants tend to show the strongest differentiation in relative performance at very low irradiances (Kobe 1999), and the Laupahoehoe FDP had relatively high understory irradiance (6.4% transmitted irradiance versus 0.01-3.0% in other evergreen rainforests; Coomes and Grubb 2000).…”

Does ontogeny modulate irradiance-elicited plasticity of leaf traits in saplings of rain-forest tree species? A test with Dicorynia guianensis and Tachigali melinonii (Fabaceae, Caesalpinioideae)

“…The climate is characterised by a wet season from December to August, interrupted during February by a short dry season, and followed by a long dry season from September to November. Average annual precipitation is 2875 ± 540 mm (mean ± SD from 1986 to 2005) with nearly two-third received between mid-March and mid-June (Baraloto et al, 2007;Bonal et al, 2000).…”

Herbivory, growth rates, and habitat specialization in tropical tree lineages: implications for Amazonian beta‐diversity

“…In the mega-diverse Amazonian lowlands there are three well-defined habitats: (1) white-sand forest habitat islands (WS) that are surrounded by (2) terra firme clay forests with higher nutrient availabilities (TF; see Plate 1); and, in low-lying areas near rivers and streams (3) seasonally flooded forests (SF) in which the water table never descends below 50 cm depth and where surface soils often remain submerged during periods of high precipitation. Each of these three habitat types harbors a unique floristic composition (Fine et al 2010, Wittmann et al 2010, and there is high beta-diversity among these three habitats due to the high propensity of habitat specialist species (Baraloto et al 2007, Fine et al 2010. Notably, many of the same lineages (i.e., genera) have representative habitat specialist species that occur in each of these habitats.…”