Long-term climate, vegetation and fire regime change in a managed municipal water supply area, British Columbia, Canada

Abstract

Post-glacial climate, vegetation and fire history were reconstructed from a sediment record from Begbie Lake, British Columbia, Canada, located in a municipal water supply area servicing > 350,000 people. Watershed managers have identified wildfire as a threat to water supply and seek to understand how vegetation and fire have varied through time with climate. In the cold late-glacial, open Pinus woodlands, periodically disturbed by fire, transitioned to mixed conifer forests subject to high-severity fire. The early Holocene is of interest to watershed managers because climate was warmer and drier than present. During this interval, low streamflow, abundant fire-adapted taxa, elevated background charcoal and regional increases in biomass burning indicate that fire seasons were longer and that fire was an important disturbance mechanism. Climate moistened in the mid Holocene, facilitating canopy closure and decreased fire disturbance. However, surface fires prevailed in Quercus ecosystems, which were expanding locally. Charcoal increased between 6180–2500 cal yr BP as climate further cooled and moistened, likely reflecting human activity and/or increased climate variability. Modern conditions arose within the last few millennia, impacted most recently by European settlement. In combination with paleoclimate modelling, modern management practices and forecast simulations, the Begbie Lake record informs about ecosystem changes within the watershed, yielding insights for management.

Holocene fire regimes, fire‐related plant functional types, and climate in south‐coastal British Columbia forests

“…At ~7300 cal yr BP, there is a notable increase in Q. garryana pollen at Roe Lake and by 6500 cal yr BP, Q. garryana accounts for 16% of the pollen assemblages (Figure 5). Nearby pollen records on Vancouver Island (e.g., Brown et al, 2022, 2019; Pellatt et al, 2001) show similar increases in Quercus , reflecting the establishment of Garry oak savanna communities throughout the region. At this time, fires continue to be frequent on Pender Island with fires occurring, on average, every 101 ± 29 years between 7300 and 6000 cal yr BP.…”

“…Previous work has shown that fire was uncommon throughout the region at the start of the Holocene, around 12,000 calendar years before present (cal yr BP), but increased over time as temperatures increased in the early Holocene (Walsh et al, 2015). By 10,000 cal yr BP, fire frequency was high at many sites in the Pacific Northwest (e.g., Brown et al, 2022Brown et al, , 2019Prichard et al, 2009;Walsh et al, 2015Walsh et al, , 2010Walsh et al, , 2008White et al, 2015). Warmer and drier climate in the early Holocene coupled with increased seasonality would have facilitated this period of more frequent fire.…”

“…Map of the Pacific Northwest showing Roe Lake (star) on Pender Island, British Columbia, Canada and other macroscopic charcoal studies (circles) in the region: (A) Langley Lake (Brown et al, 2022), (B) Clayoquot Lake/Valley (Gavin et al, 2003a, 2003b), (C) Enos and Boomerang lakes (Brown & Hebda, 2002a), (D) Shingle Point (Derr, 2014), (E) Porphyry Lake (Brown & Hebda, 2003), (F) Somenos Lake (Murphy et al, 2019), (G) Whyac Lake (Brown & Hebda, 2002b), (H) Pixie Lake (Brown & Hebda, 2002b), (I) Walker Lake (Brown & Hebda, 2003), (J) Begbie Lake (Brown et al, 2019), (K) East Sooke Fen (Brown & Hebda, 2002b), (L) Moran State Park (Sugimura et al, 2008), (M) Frozen Lake (Hallett et al, 2003), (N) Mount Barr Cirque Lake (Hallett et al, 2003), (O) Chadsey Lake (Murphy et al, 2019), (P) Panther Potholes (Prichard et al, 2009), (Q) Kirk Lake (Cwynar, 1987), (R) Fish Lake (Walsh et al, 2018), (S) Moose Lake (Gavin et al, 2001), (T) Martins Lake (Gavin et al, 2001), (U) Yahoo Lake (Gavin et al, 2013), (V) Sunrise and Shadow lakes (Walsh et al, 2017), (W) Taylor Lake (Long et al, 2007), (X) Lost Lake (Long et al, 2007), (Y) Battle Ground Lake (Walsh et al, 2008), (Z) Lake Oswego (Walsh et al, 2018), (AA) Beaver Lake (Walsh et al, 2010), (AB) Little Lake (Long et al, 2007), and (AC) Tumalo Lake (Long et al, 2011). …”

Fifty years of wildland fire science in Canada

“…In addition to spatial variability in fire regimes, paleoecological reconstructions from charcoal, fossil pollen, and plant macrofossils in lake sediments, peat, and soil provided evidence of temporal instability throughout the Holocene (Senici et al 2013;Remy et al 2018) (Hallett et al 2003;Hoffman et al 2016;Brown et al 2017Brown et al , 2019, while fire declined during the Medieval Warm Period along the moisture-limited prairie-forest ecotone due to shifts in species composition to less fire-prone species (Campbell and Campbell 2000). Recent analyses have documented ecologically meaningful human influences on fire regimes over centuries to millennia (Blarquez et al 2018;Hoffman et al 2016Hoffman et al , 2017Murphy et al 2019).…”

Chironomid-based paleotemperature reconstruction of the North Slave Region, Northwest Territories during the Late Holocene

“…Due to the coarse resolution of the age-depth model, the record of North Slave Region fire events only extends back to the late nineteenth century (Pelletier et al, 2020). Previous studies have employed multiple proxies derived from lake sediments to successfully reconstruct Holocene paleofire records and vegetative histories (Brown et al, 2019;Gaboriau et al (2020).…”