Data from: Resource acquisition strategies facilitate Gilbertiodendron dewevrei monodominance in African lowland forests

1. Tropical forests are hyperdiverse, yet extensive areas of monodominant
forest occur in the tropics worldwide. Most long-lived and persistent
monodominant tree species form ectomycorrhizal fungi symbioses, allowing
them to obtain nutrients directly from soil organic matter. This might
promote monodominance by reducing nutrient availability to co-occurring
species, the majority of which form associations with arbuscular
mycorrhizal fungi. 2. Gilbertiodendron dewevrei forest is the most
widespread monodominant forest in tropical Africa. Its distribution
appears determined in part by moisture availability, but its monodominance
is not thought to be driven by its fungal partner or soil fertility. 3.
Here we compare soil fertility of twenty G. dewevrei stands to mixed
forest from three sites across an 8,400 km2 region of the Central African
Republic and the Republic of Congo. In contrast to previous studies, we
find monodominant G. dewevrei stands associated with infertile soils, as
base cations (calcium, magnesium, total exchangeable bases) and
extractable manganese are extremely low, and significantly lower in soils
under G. dewevrei forest compared to mixed forest. Further, and consistent
with ectomycorrhizal forests globally, soil carbon to nitrogen and carbon
to phosphorus ratios are significantly higher in G. dewevrei stands than
in mixed forest stands, providing evidence in support of direct
acquisition of nitrogen and phosphorus from soil organic matter by
ectomycorrhizal fungi. 4. Gilbertiodendron dewevrei recruits from the
seedling bank, with its large seedlings surviving in high densities for
over a decade. We tested whether light plasticity could facilitate
monodominance by growing seedlings of G. dewevrei under controlled light
conditions. We found that its seedlings grow well under a wide range of
irradiance levels and conclude that this plasticity affords a competitive
advantage. 5. Synthesis: We reframe the discussion of factors contributing
to monodominance of G. dewevrei into one of resource acquisition and use
efficiency. In particular, G. dewevrei is associated with moist and
infertile soils and competes well under a variety of light conditions. Our
data is consistent with a model where root associations with
ectomycorrhizal fungi drive monodominance through the direct acquisition
of nutrients from soil organic matter, promoting nutrient limitation of
co-occurring species.