Linking vegetation to ecosystem function through plant paleo-traits

Plants are a key interface in the Earth system, modulating hydrology, nutrient cycles, and surface properties such as albedo through their physiological activity, growth, and development. Because evolution has shaped these plant properties, the representation of geological-age-appropriate vegetation in ecosystem and climate models is critically important for the examination of environmental change over geologic time. The last >400 million years of plant evolution has recorded paradigm shifts in plant anatomical traits in response to adaptation to environmental conditions. The disparity between extinct traits and living traits challenges the validity of extrapolating past ecosystem function from observations made using living plants. Major plant environmental resistances (i.e., to drought and frost) can be opaque to reconstruct in deep-time ecosystems because extinct organisms contained anatomical features with no living analog, but these properties are related to plant traits and can be derived directly from fossilized plant anatomy.

Recent advances integrate measurements of plant fossils containing anatomical detail with process-based ecosystem models. This approach allows quantitative plant traits to be derived for extinct plants and the effects of these paleo-traits to be simulated in the context of age-appropriate environments. Key measurements of plant vascular anatomy from fossilized wood, branches, and leaves are made from field-collected plant fossils or material already present in museum collections using minimally destructive techniques. These measurements are transformed using biophysical, biochemical, or statistical models of plant function into quantitative or qualitative traits, or are used directly as parameters in the process-based ecosystem model Paleo-BGC.

Application of this linked anatomy-trait-model approach across Earth history shows that appropriate modeling of traits may have profound effects on simulated biogeochemical cycles. For example, the replacement of one plant type—a sphenopsid—by another closely related plant within the same taxonomic group with different traits likely had significant effects on the collapse of the Carboniferous rainforest during the Carboniferous-Permian transition (~303 Ma). Likewise, exploring the effect of ecosystem replacement across a singular environmental event (the Triassic-Jurassic mass extinction, ~201 Ma) illustrates how changes in plant community composition, by modifying vegetation traits present in ecosystems, transformed the relative magnitude of plant carbon and water cycle effects in response to Earth system events. Linking deep-time plant anatomy to ecosystem function through quantitative and qualitative paleo-traits is an underutilized, accessible, and informative approach to identifying vegetation response through time. Applying these methods across the evolutionary history of land plants, as recorded in the fossil record, will yield a better understanding of the feedbacks between vegetation and climate and a more complete picture of how the evolution of plant traits influenced plant-environment feedbacks through time.