Impact of fine‐scale edaphic heterogeneity on tree species assembly in a central African rainforest

Abstract

Questions Soil properties have been shown to partially explain tree species distribution in tropical forests. Locally, species turnover across space can result not only from edaphic heterogeneities but also from limited seed dispersal. To characterize the contribution of each process, contact areas between contrasted soil types offer ideal settings. In the present study, we aimed to test species and species assemblage responses to a sharp edaphic discontinuity in a tropical forest tree community. Location Yoko forest reserve (6975 ha), Democratic Republic of the Congo. Methods We set up four 500–600‐m long parallel transects crossing two contrasted edaphic habitats, one lying on clayey soil and the other on sandy soil. The canopy and subcanopy trees were identified and geo‐referenced along the transects over a width of 50 m and 5 m, respectively, and soil samples were collected every 50 m to characterize each habitat. Results Correspondence analyses indicated a clear differentiation of tree communities between sandy and clayey soils. Using a torus‐translation method combined with Chi‐squared non‐parametric tests, we observed that ca. 40% and 18% of the species represented by at least 12 individuals displayed significant density differences according to habitat in the canopy and subcanopy, respectively, although very few species displayed significant differences in their relative abundance. Nevertheless, whole community tests of differentiation (in species relative abundances) between soil types were significant in both strata, even after removing individual species or families displaying a significant habitat preference. Conclusion While only a minority of species displayed a clear habitat preference, we still observed a community‐wide impact of the edaphic discontinuity on species assemblages at a local scale. Our results provide further evidence for the major contribution of environmental heterogeneity in maintaining biodiversity in tropical forests.

The influence of spatially structured soil properties on tree community assemblages at a landscape scale in the tropical forests of southern Cameroon

“…; Vleminckx et al . ). A more recent approach, the Moran spectral randomization (MSR, Wagner & Dray ) offers the possibility to simulate artificial abundance or environmental data displaying spatial autocorrelation patterns that are identical or nearly identical to the original data.…”

“…; Vleminckx et al . ). Mn availability is strongly inflated at low pH (characterizing all soil samples collected in our plots), reaching toxic levels that may induce multiple kinds of damages on plants (Millaleo et al .…”

“…() emphasized floristic turnover explained by a soil texture gradient at spatial scales reaching up to 100 km, while Vleminckx et al . () found similar patterns at much finer spatial scale (<1 km). Finally, the variation of topographical characteristics across space has also been shown to structure tree community assemblages (Lan et al .…”

Patterns of local species richness and their associations with functional traits in a 60‐ha tropical forest dynamics plot

“…, Vleminckx et al. ), and facilitative interactions are generally considered important mechanisms that contribute to species richness at the community level in relatively harsh and resource‐limited environments (Callaway et al. , Amarasekare , Brooker et al.…”

Local Scale Edaphic Surveys in and out of a &lt;i&gt;Pericopsis elata&lt;/i&gt; (Harms) Meeuwen Natural Forest Stand in East Cameroon

“…Clay is generally considered as the active part of soil because it plays a role in the supply and availability of nutrient elements [35]. The impact of edaphic heterogeneity on species assembly has been reported in rainforests of the Congo Basin, where differences in soil texture (clayey versus sandy soils) considerably influence biodiversity and habitat preference [2] [36] [37]. According to Silver et al [38], soil texture is primarily responsible for nutrient availability in lowland tropical forests.…”