Pando

map

In the 1970s scientists noted the unusual size of some western aspen clones compared to those commonly found in eastern North America. In particular, a large clone near Fish Lake, Utah, was estimated to be approximately 106 acres (43 ha) in size1. Later, a different team came up with a similar size estimate, as well as giving it a weight (13 million lbs/5.8 million kg), and judged what they were now calling the "Pando Clone" to be the largest and heaviest living thing on earth2. In the late 1980s U.S. Forest Service managers began a series of "treatments" to stimulate growth within the giant clone. In 1987-1988 two small clearfell cuts (~ 4 acres/1.6 ha) were completed, then another larger 15 acre (6.1 ha) cut in 1992. Managers noticed that most of the sprouting from the original two cuts was consumed by herbivores (and has never grown back), assumed to be mule deer. Thus, the spring 1992 silviculture treatment was followed by erection of a perimeter fence to prevent further browsing of regeneration. Regrowth of this larger clearfell area has continued to the present with the exclusion fence in place. A dense stand of aspen within this fenced zone is approximately 20-25 ft. (6-7.6 m) in height today.

Within the past decade mature trees within the remaining (unfenced) portions of the Pando clone have begun to die rapidly. This is not uncommon for aspen stems (ramets) which are now between 120-150 years old. What is unusual is the apparent lack of sprouting as mature trees become stressed and die; a natural response of clonal species such as quaking aspen. In fact, it is not for lack of trying that Pando is not reproducing. It appears that there is ample regeneration—though that level of root suckering will diminish as more mature trees die—but nearly all the young suckers are being eaten by a combination of domestic and wild herbivores (likely deer, elk, or cattle). Further research is underway to understand, a.) what species are eating regeneration, b.) how we can better protect the new suckers, c.) what are the most effective means of stimulating additional sprouting (assuming they can be protected, and d.) how do regeneration modes (asexual and sexual) interact over long periods on landscapes such as where Pando resides. One thing seems clear to managers and scientists alike: the large, and likely long-lived, Pando clone's recent troubles can probably be attributed to recent actions by humans. With this viewpoint, it is incumbent upon us to preserve this natural legacy. See "What's Being Done" for ongoing restoration strategies.

1Kemperman, J. A. and B. V. Barnes. 1976. Clone size in American aspens. Canadian Journal of Botany 54:2603-2607.

2Mitton, J. B. and M. C. Grant. 1996. Genetic variation and the natural history of quaking aspen. Bioscience 46:25-31.

NEW Aspen Field Guide

by Paul C. Rogers

May 2017, 98 p.

RESTORING THE WEST

Forest Restoration: what's working, what's not?

Oct. 17-18, 2017

Utah State University, Logan, UT