Developmental Dynamics of Gilbertiodendron dewevrei (Fabaceae) Drive Forest Structure and Biomass in the Eastern Congo Basin

Henry B Glick,Sean C Thomas,Timothy G Gregoire,Jean-Remy Makana,Jonathan D Reuning-Scherer,Peter M Umunay

doi:10.3390/f12060738

Abstract

Patterns of structural change associated with monodominant tropical forest complexes have remained enigmatic for decades. Here, we extend previous efforts in presenting a longitudinal, local-scale analysis of forest dynamics in central Africa. Using four 10-ha census plots measured across three time periods (959,312 stems ≥1 cm DBH), we analyzed changes in a number of biometrical attributes for four distinct forest types capturing the developmental gradient from mixed species forest to Gilbertiodendron dewevrei-dominated forest. We modeled above-ground biomass (AGB), basal area (BA), and stem density across all species, and diameter at breast height (DBH), recruitment, and mortality for Gilbertiodendron dewevrei. We hypothesized that trends in these attributes are consistent with a slow spread of Gilbertiodendron dewevrei into adjacent mixed species forest. We identified statistically significant increases in AGB and BA across sites and positive, though nonsignificant, increases in AGB and BA for most forest types. DBH and relative recruitment increased significantly for Gilbertiodendron dewevrei stems, while relative mortality did not. When looking from mixed species to transitional to monodominant forest types, we found a statistically significant pattern of developmental aggradation and net expansion of monodominant forest. We do not attribute this to atmospheric forcing but to a combination of (a) landscape-scale recovery or response to widespread disturbance (primarily historical fires), (b) Gilbertiodendron dewevrei’s ectomycorrhizal association, and (c) Gilbertiodendron dewevrei’s exceptional stress tolerance traits.

Highlights

The structural dynamics of tropical forests and their relation to species diversity have been a topic of interest for most of a century [3,4,5,6,7,8]
From 1994–2007, the Ituri Forest dynamics plots exhibited a pattern of increasing above-ground biomass and related forest structural parameters
During the inspection of outlying residual values associated with our regression analyses, we found that unusual values were associated with triplets of records in which above-ground biomass (AGB) dropped substantially relative to a previous benchmark

Summary

Introduction

The structural dynamics of tropical forests and their relation to species diversity have been a topic of interest for most of a century [3,4,5,6,7,8]. Patterns of forest structure vary biogeographically [1,2,7,9,10,11,12,13,14,15,16,17], and an exceptional pattern is the dominance of a particular tree species or cohort of species in lowland tropical rain forests [15,17,18,19]. Gilbertiodendron dewevrei, hereafter Gilbertiodendron, has captured scientific attention for decades [4,10,13,19,27] This is in part because of the spatial extent and completeness of its dominance relative to other species, including other canopy species from Caesalpinioideae, such as Julbernardia seretii and Cynometra alexandri [1,6,7,10,19,27]

Methods

Results

Discussion

Conclusion