Twenty years of drought?mediated change in snag populations in mixed?conifer and ponderosa pine forests in Northern Arizona

Abstract Background Snags (standing dead trees) are important biological legacies in forest systems, providing numerous resources as well a record of recent tree mortality. From 1997 to 2017, we monitored snag populations drought-influenced mixed-conifer and ponderosa pine ( Pinus ) forests northern Arizona. Results Snag density increased significantly both types. This increase was driven largely by pulse recruitment that occurred between 2002 2007, following an extreme drought year 2002, with returning pre-pulse levels subsequent time periods. Some later years during the study also were warmer and/or drier than average, but these not did trigger same level recruitment. equal across species size classes, resulting significant changes composition size-class distributions Because trees far more abundant snags forests, effect this mortality on smaller its populations. loss rates over study, even though many newly recruited. may reflect increasing prevalence white fir which generally decay faster other or larger snags. Thus, although total numbers increased, recruited persist long enough be valuable nesting substrates for native wildlife. Conclusions Increases abundance appeared due short-term “event” rather longer-term pattern elevated event followed dry extremely warm (2002) embedded within megadrought. Climate models suggest like occur frequency southwestern U.S. Such result additional pulses, turn strongly affect trajectories abundance, structure, Relative effects likely will smaller, but, time, could significant.