Crown Illumination Index (CII) Values for Light on Tree Crowns at Harvard Forest LTER

Patterns of biodiversity, such as the increase toward the tropics and the peaked curve during ecological succession, are fundamental phenomena for ecology. Such patterns have multiple, interacting causes, but temperature emerges as a dominant factor across organisms from microbes to trees and mammals, and across terrestrial, marine, and freshwater environments. However, there is little consensus on the underlying mechanisms, even as global temperatures increase and the need to predict their effects becomes more pressing. The purpose of this project is to generate and test theory for how temperature impacts biodiversity through its effect on biochemical processes and metabolic rate. A combination of standardized surveys in the field and controlled experiments in the field and laboratory measure diversity of three taxa -- trees, invertebrates, and microbes -- and key biogeochemical processes of decomposition in seven forests distributed along a geographic gradient of increasing temperature from cold temperate to warm tropical. This dataset was based on trees contained in five Gentry plots set up at Harvard Forest by the Enquist Lab (PI, Brian Enquist) from the University of Arizona as part of a macrosystems biodiversity and latitude project supported by the National Science Foundation under Cooperative Agreement DEB#1065836. The CII stands for Crown Illumination Index, which is a ranked measure of how closed or open a canopy is. It was developed by Clark and Clark (1992), and focuses on the extent to which the crown of any sized tree receives overhead vertical light (directly above) and lateral light coming from the sides. For instance, a '5' corresponds to an exposed tree, a '1' to a completely shaded tree. Trees were classified by CII at Harvard Forest LTER by John Grady of the University of New Mexico.