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Inventory of Snags on Camp Navajo

Standing dead trees (snags) are considered an integral habitat component of cavity nesting birds and other wildlife in the coniferous forests of the southwestern United States. The species, size, bark retention, and condition influence the value of a snag as wildlife habitat. Removal of snags has been linked to declines in both diversity and density of cavity-nesting birds and tree roosting bats in southwestern forests. Snags also serve as nesting and perching platforms for numerous raptor species. Conversions of forests from old growth to even aged stands shortens the rotation age from centuries to decades, thereby reducing the size and age of the trees left in the forest. This reduction drastically decreases the amount, size and quality of dead and dying trees available for the future. Treatment of ponderosa pine forests on Camp Navajo is ongoing and currently includes thinning, thinning and burning, and burning.  The purpose of these restoration efforts is to restore the structure and function of the forest community to pre-European settlement conditions as well as reduce the risk of catastrophic wildfire.  Forest restoration treatments involve removing accumulated litter and over stocked stands through thinning and burning which may alter the type and density of snags. The purpose of this project is to conduct a survey of snags within the ponderosa pine forest on Camp Navajo and permanently mark benchmark snags for future monitoring.

We inventoried snags throughout the ponderosa pine forest on the western section of Camp Navajo Army National Guard Depot. The area is approximately 10 square miles and is bound on the west by U.S. Forest Service land and on the east by the Camp Navajo Limited Area.

We conducted a complete census of snags within the boundaries measuring snag species composition, size (height and diameter), decay class and density. Snags were considered any standing dead trees greater than 4 inches diameter at breast height (dbh) and greater than 7 feet tall, with an angle greater than 45 degrees from the ground. We recorded woodpecker use, beetle infestation and bark sloughing as a surrogate for bat roost suitability. Each inventoried snag was marked with a uniquely numbered aluminum tag and we permanently marked a representative sample of these for long term monitoring (approx. 50 each) based on size class (4-12, 12-18, 18-24, and > 24 inches dbh) and decay class.  We were able to locate 1398 of the original 1600 potential benchmark snags of which 436 had fallen, 114 exceeded decay class requirements, 3 were not ponderosa pine, 3 were still alive, and 1 had been cut.  The remaining 841 snags were assessed as appropriate benchmarks for long-term monitoring and marked with permanent tags.  For each snag we verified decay class, dbh, location, slope, and aspect as well as whether the snag was present in a treated area or not.  In fall 2010 we will revisit all of the benchmarked snags to characterize snag retention and decay.  We will also resurvey the entire Camp Navajo west buffer for new, unmarked snags to increase our sample of benchmarked snags, and to provide data regarding snag recruitment.   This will continue every other year indefinitely.  The results will be quantified by forest treatments in order to provide insight into the affects of silviculture management on snag recruitment, retention, and decay.

An inventory of currently standing snags will provide biologists with baseline information about snag density and age prior to implementing proposed forest restoration treatments. This study will facilitate the long-term monitoring of snags to assess decay rates and retention rates over time. Through monitoring, we will also gain information about the effects of forest restoration treatments on snag recruitment. This information, combined with wildlife surveys will provide insight to long-term effects that forest restoration may have on wildlife species in the ponderosa pine community.

For more information contact:

Michael Ingraldi, Ph.D
Arizona Game and Fish Department,
5000 W. Carefree Highway, Phoenix, AZ 85086

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