Ecosystem memory of wildfires affects resilience of boreal mixedwood biodiversity after retention harvest

Abstract

The extent to which past states influence present and future ecosystem characteristics (ecosystem memory (EM)) is challenging to assess because signals of past ecological conditions fade with time. Using data about seven different taxa, we show that ecological gradients initiated by wildfires up to three centuries earlier affect biotic recovery after variable retention harvest in the boreal mixedwood forest. First, we show that fire history over the last 300 years is reflected in pre‐harvest species‐specific stand basal area (BA), with longer times since high severity fire associated with proportionally higher BA of shade‐tolerant softwood species than shade‐intolerant hardwoods. Second, using patterns in the BA of pre‐harvest tree species we link fire history to species composition of pre‐harvest assemblages of bryophytes, herbs, shrubs, regenerated trees, songbirds, spiders and carabid beetles. Finally, we use variance partitioning to compare the importance of species‐specific pre‐ versus post‐harvest BA for explaining the structure of these seven biotic assemblages two, five and ten years after harvest. We detected persistent significant effects of pre‐harvest BA in all post‐harvest biotic assemblages up to ten years after harvest. Pre‐harvest BA was more strongly associated with early post‐harvest understory plant and carabid beetle assemblages than was post‐harvest BA, but the opposite was true for spiders, songbirds and regenerated trees. EM effects were detected two, five and ten years after harvest but temporal patterns varied according to taxa. Thus, EM of fire history can persist at least ten years after variable retention harvest and such effects appear to be stronger for understory plants than for animals. We conclude that management of biological legacies to increase post‐disturbance EM will increase overall resilience and sustainability of these mixedwood forests.

Can retention harvests help conserve wildlife? Evidence for vertebrates in the boreal forest

“…The stands were ~120–180 yr old at the time of sampling as they experienced fires in 1895, 1877, and/or 1837 (Bergeron et al. ).…”

“…Data were collected in stands dominated by conifers, predominantly white spruce (Picea glauca), prior to harvest, and post-harvest regeneration mainly consisted of aspen (Populus tremuloides) and balsam poplar (Populus balsamifera; Gradowski et al 2008Gradowski et al , 2010. The stands were~120-180 yr old at the time of sampling as they experienced fires in 1895, 1877, and/or 1837 (Bergeron et al 2017).…”

Understory vascular plant responses to retention harvesting with and without prescribed fire

“…The EMEND site is comprised of a total of ϳ1000 ha of experimental compartments in the boreal mixedwood forest. When the experiment was established in 1998, the majority of the trees were approximately 103 or 161 years old, having recruited from fires in the years 1895 and 1837 (Bergeron et al 2017). The dominant tree species are Picea glauca (Moench) Voss, Populus balsamifera L., and Populus tremuloides Michx., while the dominant understory shrub species include Viburnum edule (Michx.)…”

“…After wildfire, plant species richness and abundance tend to be high, reflecting rapid establishment of disturbance-adapted species combined with populations of residual species that survived the fire in situ (Liu et al 2017). Over time following wildfire, the understory vegetation redevelops as a function of prior fire history and severity, the prefire community, canopy cover, light, competing vegetation, and time since fire (Wang and Kemball 2005, De Grandpré et al 2014, Bergeron et al 2017, Kumar et al 2018.…”

Recognizing Women Leaders in Fire Science: Revisited

“…Her notable works include an assessment of the impacts of fires on the reduction of organic-layer depth in North American boreal forests [99], and assessments of fire on white spruce regeneration [100,101]. Her recent works include an assessment of resilience in boreal forests following wildfires [102].…”