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RMRS-RP-66WWW: Modeling snag dynamics in northern Arizona mixed-conifer and ponderosa pine forests


Ganey, Joseph L.; Vojta, Scott C. 2007. Modeling snag dynamics in northern Arizona mixed-conifer and ponderosa pine forests. Res. Pap. RMRS-RP-66WWW. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 15 p.

Snags (standing dead trees) are important components of forested habitats that contribute to ecological decay and recycling processes as well as providing habitat for many life forms. As such, snags are of special interest to land managers, but information on dynamics of snag populations is lacking. We modeled trends in snag populations in mixed-conifer and ponderosa pine (Pinus ponderosa) forests in northern Arizona using a Leslie matrix model developed by Raphael and Morrison (1987). Models were parameterized using data on snag abundance in five decay classes in 2002, transition rates of snags among decay classes from 1997 to 2002, and recruitment of snags into these decay classes from 1997 to 2002. Snags were sampled on randomly located, 1-ha plots (n = 52 and 58 plots in mixedconifer and ponderosa pine, respectively). These plots covered the entire elevational gradient occupied by these forest types and a wide range of stand conditions in both forest types. Trends were modeled separately for each forest type over a 30-yr time horizon. The models predicted that over this period: 1) overall snag densities would increase in both forest types, 2) densities of large snags would increase in both forest types, 3) despite these increases, densities of large snags would remain below target densities in both forest types, and 4) species composition and decay-class distributions would change only slightly in both forest types. The models described here were derived from snag data averaged over large landscapes and a wide range of stand conditions within forest types. These models thus are not suitable for modeling snag dynamics at the stand level, but rather provide a means for coarse-scale modeling of snag dynamics over large landscapes. Future inventories of snags on these plots (planned at five-year intervals) will provide a means to both test and improve model predictions.

Keywords: snags, forest habitats, mixed-conifer forest, ponderosa pine, Pinus ponderosa, matrix model


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Title: RMRS-RP-66WWW: Modeling snag dynamics in northern Arizona mixed-conifer and ponderosa pine forests
Electronic Publish Date: June 29, 2007
Last Update:
June 29, 2007

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