Microhabitat associations and seedling bank dynamics in a neotropical forest

Abstract

We conducted a rigorous test of tropical tree seedling microhabitat differentiation by examining microhabitat associations, survival and growth of established seedlings of ten tropical tree species representing a four-factor gradient in seed size. Eight microhabitat variables describing soil and light conditions were measured directly adjacent to each of 588 seedlings within twelve 10x100 m belt transects at Paracou, French Guiana, and at 264 reference points along the transects. From these measurements, we defined three principal components describing soil richness, soil softness and canopy openness. Six of ten species (in 9 of 30 total cases) were distributed non-randomly with respect to microhabitat along at least one principal component. However, few species demonstrated clear microhabitat specialization. All shifts in distribution relative to reference points were in the same direction (richer, softer soil). Furthermore, of 135 pairwise comparisons among the species, only 7 were significantly different. More than three-fourths of all seedlings (75.3%) survived over the 2-year monitoring period, but survival rates varied widely among species. In no case was the probability of survival influenced by any microhabitat parameter. Relative height growth rates for the seedlings over 2 years varied from -0.031 cm cm(-1) year(-1) (Dicorynia guianensis, Caesalpiniaceae) to 0.088 cm cm(-1) year(-1) (Virola michelii, Myristicaceae). In only 4 of 30 cases was height growth significantly associated with one of the three principal components. Because the conditions in this study were designed to maximize the chance of finding microhabitat differentiation among a group of species differing greatly in life history traits, the lack of microhabitat specialization it uncovered suggests that microhabitat partitioning among tropical tree species at the established seedling stage is unlikely to contribute greatly to coexistence among these species.

Seed mass, seedling size and neotropical tree seedling establishment

“…A final possible explanation for the lack of observed microhabitat partitioning is simply that the null hypothesis is true; that is, performance rankings between species differing in seed mass do not change along environmental gradients. We argue that this may indeed be the case, at least across understorey conditions such as those we measured, noting that our results are consistent with those of habitat association field surveys for tropical tree juveniles, in which few or weak relationships between species and environment have been found (Webb & Peart 2000; Baraloto & Goldberg 2004).…”

“…Although canopy gaps (where light availability is > 6% of full‐sun PAR) represent less than 5% of the ground surface area in many tropical forests (Brokaw 1985; van der Meer & Bongers 1996; C. Baraloto & P. Couteron, unpublished data), it is conceivable that species could partition light gradients that range above that measured in the plots in this study (Rose & Poorter 2003). Nevertheless, the eight species we studied all co‐occur in deeply shaded habitats with light levels < 3% of full‐sun PAR (Baraloto & Goldberg 2004). Furthermore, in a complementary field experiment in which seedlings of nine species, including six of those studied here, were planted in gap and understorey conditions across four soil types, only three of the 36 possible species pairs were found to switch rankings for survival or RGR between any microhabitat type (Baraloto et al .…”

Quantifying micro-environmental variation in tropical rainforest understory at landscape scale by combining airborne LiDAR scanning and a sensor network

“…Light availability is also essential for carbon assimilation and plant growth (Nicotra et al 1999;Dalling and Hubbell 2002;Montgomery and Chazdon 2002). Ground-level light maps derived from LiDAR could be thus of great interest in providing better predictive underpinnings for the demographic studies of understory plants (Ackerly and Bazzaz 1995;Baraloto andGoldberg 2004 Laurans M et al 2012;Vincent G et al 2011). Species composition and vegetation abundance in the understory also vary with differences in micro-environmental conditions (e.g.…”

“…Light is critical to seed germination (Baskin and Baskin 2001;Willis et al 2014) and seedling and sapling growth within tropical forests (Tinoco-Ojanguren and Pearcy 1995; Baraloto and Goldberg 2004;Palomaki et al 2006).…”

Seasonal and spatial variation in water availability drive habitat associations in a tropical forest

“…However, in previous studies, differences in performance did not necessarily coincide with a homesite advantage of habitat specialists in their preferred habitat (Baraloto andGoldberg 2004, Russo et al 2005). In addition, strong habitat associations have been observed in the absence of large, habitat-specific differences in performance (Yamada et al 2007).…”