Response of understory vegetation to salvage logging following a high‐severity wildfire

Abstract

Citation: Knapp, E. E., and M. W. Ritchie. 2016. Response of understory vegetation to salvage logging following a high-severity wildfire. Ecosphere 7(11):e01550. 10.1002/ecs2.1550Abstract. Timber is frequently salvage-logged following high-severity stand-replacing wildfire, but the practice is controversial. One concern is that compound disturbances could result in more deleterious impacts than either disturbance individually, with mechanical operations having the potential to set back recovering native species and increase invasion by non-native species. Following the 2002 Cone Fire on the Lassen National Forest, three replicates of five salvage treatments were applied to 15 units formerly dominated by ponderosa pine, covering a range of disturbance intensities from unsalvaged to 100% salvaged. Understory species richness and cover data were collected every two years between 2006 and 2012. Richness of both native and non-native species did not differ among salvage treatments, but both showed strong changes over time. While cover of forbs and graminoids did not differ with salvage treatment, cover of shrubs was significantly reduced at the higher salvage intensities. The three main shrub species are all stimulated to germinate by fire, potentially leaving seedlings vulnerable to any mechanical disturbance occurring immediately postgermination. Many other native perennial species emerge from rhizomes or other deeply buried underground structures and appear to be less affected by salvage harvest. Over time, the plant community in all salvage treatments shifted from dominance by shrubs and forbs to shrubs and grasses. Most of the grasses were native, except Bromus tectorum (cheatgrass), which was found in 4% of measurement quadrats in 2006 and 52% in 2012. Our results indicated that understory vegetation change 4-10 years posthigh-severity wildfire appeared to be influenced more strongly by factors other than salvage logging.

Ecological consequences of compound disturbances in forest ecosystems: a systematic review

“…Deadwood extraction yielded suitable conditions for early-successional species associated with open habitats, thereby delaying bryophyte recovery (Hern andez-Hern andez et al 2017) and reducing the compositional variability of ground beetles (Cobb et al 2007). Similarly, Knapp and Ritchie (2016) attributed reduced shrub cover and richness to mechanical impacts of salvage logging, but noted that, of the multiple functional groups and life-history categories assessed, only shrubs were significantly impacted. However, foliar nutrition and regeneration growth converged, reinforcing that the detection of compound interactions can depend on the response variables assessed.…”

“…These distinctions most commonly involved differential recovery related to the expression of speciesspecific life-history strategies (Buma and Wessman 2012, Knapp and Ritchie 2016, Bowd et al 2018, but also involved a distinction between recovery time and trajectory (Lang et al 2009, White et al 2014) and forest succession and development (Bonilla-Moheno 2012, Matusick et al 2016, Sass et al 2018. These distinctions most commonly involved differential recovery related to the expression of speciesspecific life-history strategies (Buma and Wessman 2012, Knapp and Ritchie 2016, Bowd et al 2018, but also involved a distinction between recovery time and trajectory (Lang et al 2009, White et al 2014) and forest succession and development (Bonilla-Moheno 2012, Matusick et al 2016, Sass et al 2018.…”

“…However, foliar nutrition and regeneration growth converged, reinforcing that the detection of compound interactions can depend on the response variables assessed. Similarly, Knapp and Ritchie (2016) attributed reduced shrub cover and richness to mechanical impacts of salvage logging, but noted that, of the multiple functional groups and life-history categories assessed, only shrubs were significantly impacted. Bowd et al (2018) reported that, although on-site seeders persisted in salvaged sites, resprouting species exhibited significant reductions.…”

“…Indeed, the response variables used to assess forest recovery often determined whether a compound interaction was detected. These distinctions most commonly involved differential recovery related to the expression of speciesspecific life-history strategies (Buma and Wessman 2012, Knapp and Ritchie 2016, Bowd et al 2018, but also involved a distinction between recovery time and trajectory (Lang et al 2009, White et al 2014) and forest succession and development (Bonilla-Moheno 2012, Matusick et al 2016, Sass et al 2018. Other disturbance combinations only exhibited compound interactions at specific forest strata (Bradford et al 2012, Mitchell et al 2012 or scales, such as changes in individual species but not overall communities (Coleman et al 2008).…”

Salvage logging in the world’s forests: Interactions between natural disturbance and logging need recognition

“…A study with five experimental salvage logging intensities (with 0%, 25%, 50%, 75%, and 100% retention) was established after the 2002 Cone Fire in California. Although nonlinear behaviour was not specifically addressed, the results of that study suggest that some response variables—such as shrub cover— may show nonlinear effects of salvage logging intensity, and that some others —fine woody debris in this case—can show nonlinear interactions between salvage intensity and time (Knapp & Ritchie, ). Conversely, the sampling of 255 stands across Oregon and Washington showed that the response of woody fuels to post‐fire salvage logging was a nonlinear function of time (Peterson, Dodson, & Harrod, ).…”