DOI: 10.5061/dryad.0cfxpnwd1
title: The higher species richness of calcareous than siliceous communities is explained by lower competition in grasslands but higher facilitation in forests

description: We aim (i) at testing the hypothesis that higher species richness of
 calcareous than siliceous communities is due to lower competition in open
 habitats but to higher facilitation in forests, (ii) at disentangling the
 direct drivers of the higher facilitation of calcareous than siliceous
 forest canopies. To address these two aims, we conducted two transplant
 experiments on the two rock types in the South-west of France. In the
 first experiment, we transplanted, in dry and wet years, six understory
 species of contrasting light requirements, with and without neighbors in
 gaps and forest understories. In the second experiment, we transplanted
 six understory species of the two bedrock origins, in calcareous closed
 and semi-closed forests, in siliceous control and fertilized forests, and
 in calcareous and siliceous gaps. In the first experiment, competition was
 higher in gaps of siliceous than calcareous bedrocks during wet years, and
 facilitation by canopy trees was higher on calcareous than siliceous
 bedrocks during dry years. In addition, facilitation in calcareous forests
 was very intense for species from the shadiest origins, while competition
 was less intense and only significant for species from the sunniest
 origins. In the second, experiment we found that both higher microclimates
 buffering ability of forest canopies and higher soil fertility explained
 the higher facilitation found in calcareous forests. Synthesis:
 The higher species richness of calcareous than siliceous communities might
 be explained by lower competition in open calcareous habitats and higher
 facilitation in calcareous forests. The higher facilitation in calcareous
 forests appeared to be due to higher buffering effect of tree canopies and
 higher soil fertility in calcareous than siliceous soils. The major role
 of facilitation in forest communities from favorable conditions has been
 strongly overlooked in the literature, although it might explain the
 higher species richness of calcareous than siliceous forests.
description: # The higher species richness of calcareous than siliceous communities is
 explained by lower competition in grasslands but higher facilitation in
 forests **Date of data collection:** 2016, 2018, 2019, 2020, 2023
 **Information about geographic location of data collection:** Gironde
 department, France **The file (Data.xlsx), created in 2025, includes 3
 sheets:** * Experiment 1:  RII values of the first experiment (Fig. 1). *
 Experiment 2–Targets: Target responses in experiment 2 (Fig. 2-4). *
 Experiment 2-Light: Light transmission in experiment 2 (Fig. 5). *
 Experiment 2-Litterbags: Litter decay in experiment 2 (Fig. 7). *
 Experiment 2–Temp–VPD: Temperature et VPD in experiment 2 (Fig. 6).
 **There are no restrictions on the data.** **Description of methods for
 data collection or generation**: Target responses were collected in the
 field one year after each experiment. Light transmission and T and VPD
 were collected one day in the early summer. Litter decay was assessed
 using litterbags during the winter season. **Description of methods used
 for data processing (describe how the data were generated from the raw or
 collected data):** We used GLM and ANOVAs. **Variable list, units of
 measurement**, **Sheet 1 (Experiment 1):** * RII type: forest canopy or in
 gap. * Year: dry or wet. * Rock: calcareous or siliceous. * Target light
 requirement: grassland targets or hedgerow targets, or understory targets.
 * RII: RII values (no unit). **Sheet 2 (Experiment 2-Targets):** * Rock:
 calcareous or siliceous. * Treatment: closed, semi-closed, or gaps for
 calcareous; control, fertilized, or gaps for siliceous. * Species origin:
 calcareous or siliceous. * Survival: survival values. * RGRheight:
 RGRheight values (%). * RGRLeaf number: RGR leaf number values (%). *
 Biomass: Biomass values (g). **Sheet 3 (Experiment 2-Light):** * Rock:
 calcareous or siliceous. * Treatment: closed, semi-closed, or gaps for
 calcareous; control, fertilized, or gaps for siliceous. * Light
 transmission: light transmission values (%). **Sheet 4 (Experiment
 2–Litterbags):** * Rock: calcareous or siliceous. * Treatment: closed,
 semi-closed, or gaps for calcareous; control, fertilized, or gaps for
 siliceous. * Residual litter mass: Residual litter mass values (g).
 **Sheet 4 (Experiment 2–Temp-VPD):** * Rock: calcareous or siliceous. *
 Treatment: closed, semi-closed, or gaps for calcareous; control,
 fertilized or gaps for siliceous. * T: temperature values (°C). * VPD: VPD
 values (MP). **Definitions for codes or symbols used to record missing
 data:** n/a.