Abstract

In tropical semi-deciduous forests, where 20-50 % of canopy trees shed their leaves in the dry season, species with varying degrees of leaf deciduousness share the same space and resources. Here, we describe the tree community in a 10.24-ha plot to assess whether small-scale variation in canopy structure and soil conditions are associated with changes in tree community structure, diversity, and composition. We sampled 11,585 individuals with diameter at breast height ≥ 4.8 cm belonging to 146 species. Plot density (1,129 trees ha-1) and basal area (24.81 m2 ha-1) were smaller than other similar forests, which may be due to an old wind disturbance. For 8.96 ha, we evaluated the relationship between abiotic factors and community descriptors using regression models. Results varied within size classes, but canopy openness was associated with changes in the community structure and diversity, and soil fertility did not affect species diversity. Tree density, basal area, and diversity were smaller in areas with more canopy gaps. Tree density and basal area increase with phosphorus availability, while the density of deciduous trees increased with canopy openness and base saturation. Thus, we found evidence that canopy openness and soil can explain small-scale variations of forest structure and diversity.

Highlights

  • Tropical rain forests are dominated by evergreen tree species in regions with no pronounced dry season

  • General description of forest structure and diversity The 10-ha permanent plot contained more than 11,000 individuals with Diameter at Breast Height (DBH) ≥ 4.8 cm (Tab. 1), belonging to 42 families, 106 genera and 146 species (Tab. 2)

  • We found that small-scale variation of canopy openness and soil conditions did affect the structure and diversity of the tree community both size classes evaluated (i.e., DBH ≥ 4.8 and ≥ 20 cm, Tab. 5)

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Summary

Introduction

Tropical rain forests are dominated by evergreen tree species in regions with no pronounced dry season. Semi-deciduous forests are characterized by the deciduousness of up to 50 % of their trees during the dry season (IBGE 2012). In these forests, one key question is how evergreen, deciduous, and semi-deciduous species can cooccur in the same stand and what abiotic factors determine their dominance (Walters & Reich 1999; Namikawa et al 2000; Niinemets 2010; Pérez-Harguindeguy et al 2013). Evergreen species should be favored by a longer growing season (i.e., greater the leaf longevity) and a higher leaf allocation ratio in comparison to deciduous trees. Deciduous trees have higher photosynthetic rates and hydraulic conductivities (Sobrado 1993; Vico et al 2017)

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