PHYTOLITHS IN PALEOECOLOGY: A TOOL FOR RECONSTRUCTING HABITAT STRUCTURE, AND HETEROGENEITY

Phytoliths, microscopic plant silica bodies often preserved in soils and sediment, have been used extensively in paleoenvironmental reconstruction in the Quaternary. More recently they have also been applied in deep-time paleoecology to shed light on the evolution of grasses and spread of grasslands, plant-animal coevolution, and animal paleo-diets. It has long been known that phytolith assemblages typically reflect more local vegetation than the pollen/spore record, suggesting that phytoliths could be especially useful for reconstructing vegetation heterogeneity across the landscape, in particular in well-oxidized terrestrial Cenozoic sediments. By inferring spatial variability in vegetation, paleontologists can establish (or test) relationships between faunal diversity, climate, and habitat structure and use that to understand ecosystem assembly in deep-time. However, very little work that specifically addresses phytolith spatial resolution exists. The available studies differ in methodology (including sampling scheme, extraction protocol, counting/analysis methods, and phytolith classification) making it difficult to synthesize results into general analytical rules for use in paleoecology.

To address this issue, we designed a study to test what the spatial resolution of the phytolith record is in tropical vegetation (rainforest-woodland??). Specifically, we collected soil samples in several quadrants along two vegetation transects in Costa Rica, in order to: 1) determine the most appropriate phytolith sampling strategy for accurate paleoenvironmental reconstructions, and 2) to test for the spatial resolution of the phytolith record as an indicator of vegetation composition and canopy openness, and as a tool to detect habitat heterogeneity. We used both phytolith assemblage composition analysis and a new proxy for vegetation openness developed by Dunn and colleagues using epidermal phytolith shape. Here, we present preliminary results that will help refine the use of phytolith analysis in paleoecology.