By the late Holocene, when climate favoured succession of oak savannah to forest, many generations of people over thousands of years would have observed the role and importance of fire in maintaining savannah and woodland structure. Historical accounts indicate that Garry oak ecosystems were ignited in late summer and fall (Boyd 1986; Fuchs 2001; Turner 1999). By the mid-1800s, however, find more as Europeans began clearing portions of Selleckchem NCT-501 southeastern Vancouver Island for agriculture, large fires were commonly observed (Grant 1857; Maslovat 2002). It is unclear whether the constant veil of summer smoke reported
during this time originated from lightning strikes, from fires lit by aboriginal peoples, or from the settlers themselves who burned for cultivation and after logging. Europeans restricted cultural burning in southwestern BC through the Bush Fire Act of 1874 (MacDonald 1929). In less than 100 years, European settlement, followed by fire exclusion, disrupted the fire regime in virtually all western North American oak ecosystems that have been studied (Pyne 1982). Palaeoecological context Early to mid-Holocene The Holocene climate along south coastal British Columbia has varied considerably over the last 12,000 years (Mathewes 1985;Hebda 1995; Walker and Pellatt 2003). After deglaciation, warm dry conditions occurred on southeastern Vancouver Blasticidin S Island (11,450–8,300 BP) and were typical of climate throughout the coast
of BC at the time (Walker and Pellatt 2003), with frequent fires also occurring in the Fraser Valley (Mathewes 1973). These conditions supported Douglas-fir (Pseudotsuga menziesii) parkland with abundant grasses (Poaceae) and bracken fern (Pterdium) (Pellatt et al. 2001) (Fig. 2). These and other species present in the pollen record indicate a relatively warm/dry climate with frequent disturbance, likely fire. Garry oak arrives curiously late along the south BC coast (~8300 BP), before but quickly increases in abundance after its arrival (Allen 1995; Heusser 1983; Pellatt et al. 2001). Although
maximum summer temperature for the Holocene occurred between 11,000 to ~8000 BP (Mathewes and Heusser 1981; Rosenberg et al. 2004), oak pollen was rare prior to 8300 BP and peaked at 8000 BP or later on southern Vancouver Island (Allen 1995; Heusser 1983; Pellatt et al. 2001). A slow northward migration across the southern Gulf Islands to Vancouver Island, and thus, a long time lag following climatic change, offers a possible explanation for this species’ late arrival. Fig. 2 Simplified Pollen Accumulation Rate (grains/cm/year) Diagram from Saanich Inlet, BC. Red (Zones 1a and 1b) represents conditions that are warmer, dryer and more continental than present, yellow (Zone 2) is warmer and wetter, green (Zone 3) is a transitional cooling phase, and blue (Zone 4a and 4b) represents the establishment of conditions more typical of the present day.