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Dynamics of coarse woody debris in southwestern mixed-conifer and ponderosa pine forests

Status: 
Action
Dates: 
May, 1997

A clump of ponderosa pine snags in northern Arizona.
A clump of ponderosa pine snags in northern Arizona.
Snags (standing dead trees) and logs are important components of forest landscapes. They provide many benefits to wildlife, including homes (cavity-nesting birds, some small mammals), resting sites (bats and other mammals), foraging substrates, and perches, are important to many ecological processes (e.g., nutrient cycling), and also influence fuel loads and fire risk. Snags may be particularly important in the southwestern U. S., where secondary cavity nesters, which are largely dependent on snags, comprise a significant portion of the native avifauna.

Despite their importance, little information exists on composition and density of snag populations in southwestern forests, and no information is available on the dynamics of snags and logs in these forests. To address this information gap, RMRS scientists established a series of fixed plots in 1997 for monitoring snag populations. This research has direct ramifications for 11 national forests throughout the Southwestern Region, as well as for our overall understanding of the ecology of coarse woody debris and effects of climate change on forest structure and composition.

Numbered tags were used to uniquely identify snags and logs.
Numbered tags were used to uniquely identify snags and logs.

Approach

Plots (1 ha in size) were randomly located in the ponderosa pine (n = 60) and mixed-conifer (n = 53) forest types across two national forests. All snags within these plots were individually marked, and plots are re-sampled at 5-yr intervals to assess snag recruitment, mortality, and changes in status of remaining snags. In 2004, the study expanded to include logs, with logs also sampled every five years but on smaller subplots due to greater densities of logs. All live trees on these subplots were sampled in 2004 and 2014 to provide data for comparisons with snag and log populations and a direct estimate of changes in forest composition and structure over this period.

 

Key Findings

A Mexican spotted owl nesting in a broken-topped ponderosa pine snag, Arizona.
A Mexican spotted owl nesting in a broken-topped ponderosa pine snag, Arizona.
This ongoing study has to date documented initial densities of snags and logs, characteristics of snags used by cavity nesting birds, changes in snag and log populations over various time periods, patterns of drought-related tree mortality, density of large snags and logs relative to management recommendations for retention of those structures, and the influence of site characteristics on densities of large snags and logs and on snag standing rates.

Collectively, these results document trends in snag and log populations during a long-term drought, as well as detailed information on patterns of drought-mediated tree mortality and resulting changes in forest composition and structure. This information has been used by managers responding to a lawsuit related to failure to monitor management indicator species, and should prove useful in revising recommendations for retention of large snags and logs and parameterizing models for modeling future trends in snag and log populations.

Publications

Other

Publication Not Currently Available in TreeSearch

Ganey, J. L. 1999. Snag density and composition of snag populations on two national forests in Arizona. Forest Ecology and Management 117(1-3):169-178.



Project Contact: 

Principal Investigators:
Collaborators:
Jeffrey S. Jenness - Jenness Enterprises
Gary C. White - Colorado State Univeristy
Benjamin J. Bird - Rocky Mountain Research Station

Research Staff:
Scott C. Vojta - Rocky Mountain Research Station