30 Years Later: Comparative demography and biomass dynamics of the Brazil nut family (Lecythidaceae) in mature central Amazon rain forest

Tamara F. Milton, Ecology and Evolution Biology, University of Michigan, Ann Arbor, MI, Alberto Vicentini, Instituto Nacional de Pesquisas da Amazônia, Brazil and Christopher W. Dick, University of Michigan, Ann Arbor, MI

Background/Question/Methods
Baseline demographic data for trees in the Amazon basin is particularly important in light of recent forest destruction and climate change combined with the region’s disproportionately large role in global carbon budgets. The Lecythidaceae family (Ericales) has great economic, cultural, and ecological significance in the Amazon, and is emblematic of old growth Amazon forest.
We report on the dynamics of a large (100-hectare) permanent forest plot north of Manaus, Brazil. All Lecythidaceae individuals (≥10 cm diameter at breast height, dbh) were identified, mapped, tagged, and measured in the late 1980s. The plot is split into six terra firme habitats at the 10x10 subplot level, one of which experienced an anomalous flooding event following the initial census. We performed a second census of the “Lecythidaceae plot,” and present species-level demographic information for the approximately 38 co-occurring species in the family. Additionally, we report Lecythidaceae above ground biomass (ABG) dynamics and ask whether certain lineages and demographic processes are contributing disproportionately to biomass dynamics. Finally, we ask whether density, species richness, demographic rates, and biomass dynamics differ among habitats.
Results/Conclusions
The plot experienced a net loss in both individuals (1023) and ABG (35.47 Mg, or 0.69% of initial AGB). The decrease in abundance was driven by mortality in the canopy height class, while the decrease in biomass can be attributed almost entirely to emergent species; subcanopy species experienced a slight increase in biomass. Probability of survival decreased most dramatically with increasing dbh for subcanopy trees, and almost not at all for emergent species Growth rates averaged only 3.69 cm dbh over 30 years, with subcanopy species growing slowest. All habitats experienced a decrease in density and species richness between the two censuses, and the flooded habitat had the lowest density and richness in both years. Growth, mortality, and recruitment were all significantly higher in the flooded habitat than any other habitat. Additionally, the flooded habitat is the only one to have experienced a significant loss of biomass over the thirty years. This demonstrates that uncommon flooding in a typically unflooded forest can have a significant influence on forest dynamics.
As intended with its establishment, this plot continues to provide integral baseline Lecythidaceae data for a large area of mature, undisturbed forest, that can be used to compare change-over-time dynamics to the near-by fragmented forest, as well as other areas throughout Amazonia that are being impacted by human land use.