Changes in Snag Populations on National Forest System Lands in Arizona, 1990s to 2000s

• Published in: Journal of forestry 2017-03, Vol.115 (2), p.103-111
• Main Authors: Ganey, Joseph L., Witt, Chris
• Format: Article
• Language: English
• Subjects: Animal behavior; Forests; Mortality; Pinus ponderosa; Regions; Studies; Trees; Trends
• ISSN: 0022-1201; 1938-3746
• DOI: 10.5849/jof.2016-062

Snags receive special management attention as important components of forest systems. We used data from the US Department of Agriculture (USDA) Forest Service Forest Inventory and Analysis Program, collected during two recent time periods (1995 to 1999 and 2001 to 2010), to evaluate trends in snag populations in two forest types in Arizona. Densities of snags ≥4 in. dbh increased by 21 and 72% between these time periods in mixed conifer and ponderosa pine (Pinus ponderosa) forest, respectively. Proportions of plots meeting USDA Forest Service guidelines for density of large snags (defined as snags ≥18 in. dbh and ≥30 ft tall) increased between time periods in both forest types (from 19 to 45% in mixed conifer and from 5 to 17% in ponderosa pine forest), but large snags remained relatively sparse, especially in less productive ponderosa pine forests. More than 50 and 75% of sampled plots lacked large snags entirely in mixed conifer and ponderosa pine forest, respectively. Management and Policy Implications Snags are important components of forest systems, providing resources for numerous wildlife species and contributing to decay dynamics and other ecological processes. Overall, snag numbers are increasing and species composition of snag populations is changing within mixed conifer and ponderosa pine forests in Arizona due to drought-mediated mortality. Despite increases in overall snag numbers, the large snags most important to native wildlife remained relatively sparse, especially in ponderosa pine forest, and large snags generally were most abundant in areas of reduced human access. Managers and interested public groups should recognize that not all areas can or should support high densities of large snags. In other areas, managers should emphasize retention of large snags and recruitment of the large trees that provide a source for large snags, ensure that large snags remain well (but not uniformly) distributed across heterogeneous landscapes, explicitly consider human disturbance in snag management plans, limit salvage logging of larger snags after disturbance events, and incorporate climate-mediated changes in forest composition and structure and adaptive strategies to address those changes in management plans.