You can’t understand the global carbon cycle without understanding the activities of leaves. Leaves turn CO2 into sugar during photosynthesis, emits it during respiration and releases it when it rots. Leaf shape, size and structure is influenced tradeoffs between how many resources you spend to build the leaf, how quickly the leaf turns CO2 into sugar, and how long the leaf operates. Pluck a leaf from a tree and examine its underside. The central vein branches, and these branches branch. But the density of leaf veins varies considerably from species to species and even within species. Benjamin Blonder, an ecologist at the University of Arizona in Tucson working with Brian Enquist, assumed that were many factors affecting vein density, but he set out to make a model that would capture as much of the variation as possible. He collected leaves from about 65 species from temperate North America. His preliminary models suggest that vein density can predict with a surprising degree of accuracy climatic factors temperature and precipitation.
That means that fossils of leaves, which often capture fine detail of tiny veins, may contain information about past climates. “A fossil is very localized in time and space. So if you are trying to understand something about a very particular time and place—something about, how plants have reacted to climate change in a particular time and place, you want such a fine scale record.”
Blonder next wants to check his models in other parts of the world. If he can show that his method would work in a broader range of climates, he might be ready to start looking at some fossils. Blonder might miss clambering up trees to gather his data, but he’d happily spend weeks indoors looking at fossil leaves, if the method pans out.