Earth Almanac: May/June 2008

In ponderosa pine forests of the southern Rockies and the Colorado Plateau, Abert’s squirrels, also called tassel-eared squirrels for the jaunty ear tufts they sport in winter, are engaged in madcap games of tag that often last 11 hours. Several males race after a female, chasing her along branches, between trees, and up trunks. The darker-bellied Kaibab squirrel, isolated on the Kaibab Plateau north of the Grand Canyon and formerly thought to be a separate species, is now recognized as an Abert’s subspecies. Abert’s squirrels are used by the U.S. Forest Service as a health indicator for ponderosa pine because they have a complex and mostly symbiotic relationship with these trees. While Abert’s squirrels weaken individual pines by severing needle-bearing shoots from the crowns to get at the nutritious phloem within, they also eat a species of false truffle (itself symbiotic with ponderosa pines) and, through their feces, distribute the spores throughout the forest. The fungi act as root extensions, drawing water and nutrients to the tree which, in turn, provides the fungi with carbohydrates.