Persistence of fire-killed conifer snags in California, USA

Abstract

BackgroundCoarse woody debris has numerous functions in forest ecosystems, including wildlife habitat, fuel loading, and nutrient cycling. Standing dead trees, or snags, are particularly important resources for wildlife, and guidelines for snag recruitment and retention are integral parts of forest management. However, snag persistence is not well understood and existing models are poorly validated. We monitored fire-killed conifer snag persistence after four California wildfires and one prescribed fire. Species sampled included white fir (Abies concolor [Gord. & Glend.] Lindl. ex Hildebr.), incense-cedar (Calocedrus decurrens [Torr.] Florin), Jeffrey pine (Pinus jeffreyi [Balf.]), sugar pine (Pinus lambertiana Douglas), and ponderosa pine (Pinus ponderosa Lawson & C. Lawson var. ponderosa C. Lawson).ResultsFire-injured trees that survived at least one year post fire were monitored for 10 years after they died. We developed two sets of species-specific snag persistence rates: a simplified model based only on time since death, and a full model that included tree characteristics. The primary factors affecting persistence rates in all models were snag age (years since death) and species. Secondary factors included diameter at breast height, time between fire and tree death, and crown injury. Snag persistence rates decreased with snag age. Yellow pine snags (a combined group of ponderosa pine and Jeffrey pine) fell significantly faster than any other species. Larger-diameter snags persisted longer than smaller-diameter snags for all species. Incense-cedar trees that survived longer post fire persisted longer as snags.ConclusionsThis study provides land managers with guidance on snag longevity, which can aid in planning for long-term wildlife habitat, fuel loading estimates, and forest structural diversity.