Functional community structure of African monodominant Gilbertiodendron dewevrei forest influenced by local environmental filtering

Abstract

Monodominant patches of forest dominated by Gilbertiodendron dewevrei are commonly found in central African tropical forests, alongside forests with high species diversity. Although these forests are generally found sparsely distributed along rivers, their occurrence is not thought to be (clearly) driven by edaphic conditions but rather by trait combinations of G. dewevrei that aid in achieving monodominance. Functional community structure between these monodominant and mixed forests has, however, not yet been compared. Additionally, little is known about nondominant species in the monodominant forest community. These two topics are addressed in this study. We investigate the functional community structure of 10 one‐hectare plots of monodominant and mixed forests in a central region of the Congo basin, in DR Congo. Thirteen leaf and wood traits are measured, covering 95% (basal area weighted) of all species present in the plots, including leaf nutrient contents, leaf isotopic compositions, specific leaf area, wood density, and vessel anatomy. The trait‐based assessment of G. dewevrei shows an ensemble of traits related to water use and transport that could be favorable for its location near forest rivers. Moreover, indications have been found for N and P limitations in the monodominant forest, possibly related to ectomycorrhizal associations formed with G. dewevrei. Reduced leaf N and P contents are found at the community level for the monodominant forest and for different nondominant groups, as compared to those in the mixed forest. In summary, this work shows that environmental filtering does prevail in the monodominant G. dewevrei forest, leading to lower functional diversity in this forest type, with the dominant species showing beneficial traits related to its common riverine locations and with reduced soil N and P availability found in this environment, both coregulating the tree community assembly.

Resource acquisition strategies facilitate Gilbertiodendron dewevrei monodominance in African lowland forests

“…Our results therefore indicate that a similar advantage might apply to P as for N in promoting nutrient limitation in Gilbertiodendron and other ectomycorrhizal forests. Similarly, Kearsley et al () report lower bioavailable P in soil at 0–30 cm depth in Gilbertiodendron as compared to mixed forest for their DRC study site, and suggest that low concentrations of N and P in Gilbertiodendron leaves point to ectomycorrhizal‐mediated N and P limitation.…”

“…Plasticity in light acquisition provides seedlings competitive advantage to recruit and release at different light levels; abundant large seedlings in the seedling bank help shape the light environment of smaller competitors. Citations in Figure: 1 Vierling and Wessman (); 2 Torti et al (), 3 Hart (); 4 Makana and Thomas (); 5 This study; 6 Newbery et al (); 7 Blake and Fay (); 8 Makana et al (); 9 Kearsley et al (); 10 Gérard (); 11 Cassart et al (); 12 Corrales et al (); 13 Phillips et al (); 14 Lin et al (); 15 Zhu et al (); 16 Averill and Hawkes () [Proposed mechanisms that have not been supported in studies: Makana and Thomas () found no evidence to support dense leaf litter preventing seedlings of other species to establish. Ebenye et al () found no evidence that EM hyphal networks facilitate nutrient exchange between adults and seedlings.…”

“…When corrected for pseudo‐replication, Hart et al () and Conway () compared only three mixed and three monodominant sites. Peh, Sonké, et al (), Kearsley et al (), and Lokonda et al () compared three, five, and nine sites of each forest type, respectively. Taking samples from 20 cm and 150 cm depth, Hart et al () arguably ignored the most important soil horizon (i.e.…”

“…Tovar et al () and Tovar et al () showed that both mixed and Gilbertiodendron forest types have persisted in the region for thousands of years. Recent research on functional traits suggests G. dewevrei has a poor ability to regulate water use (Kearsley et al, ), helping to explain its occurrence near rivers and streams (e.g. Blake & Fay, ).…”

“…Research assessing the role of the association between G. dewevrei and ectomycorrhizal fungi has been inconclusive (e.g. Bauters et al, ; Kearsley et al, ; Peh, Lewis, et al, ; Peh, Sonké, et al, ; Torti et al, ). We hypothesized that (2) soils below G. dewevrei have higher carbon to nitrogen (C:N) and carbon to phosphorus (C:P) ratios than mixed species forest soils, indicators of ectomycorrhizal fungi facilitating its ability to uptake organic forms of these nutrients (Averill, Turner, & Finzi, ; Corrales et al, ; Zhu, McCormack, Lankau, Egan, & Wurzburger, ).…”