Late quaternary history of vegetation, climate, and fire on South Central Vancouver Island, British Columbia, Canada
Date
2003
Authors
Fitton, John Richard
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Abstract
Pollen, macrofossils and charcoal from Turtle Lake (80 m above sea level) and Harris Lake Ridge Bog ( 1300 m above sea level) were used to reconstruct the lateĀ Quaternary history of vegetation, climate, and fire disturbance on south central Vancouver Island, British Columbia. A non-arboreal community was present in lowland areas around Turtle Lake before 12, 000 14C ybp, and represents parkland environments growing in the cold conditions near glaciers. From 12,000-11,500 14C ybp open Pinus forests with A/nus grew in lowland areas. A mixed conifer forest of Abies, Tsuga heterophylla and Tsuga mertensiana replaced Pinus from 11,500-10,700 14C ybp. Pinus regained dominance, and T mertensiana increased from I 0, 700-10,200 14C ybp. Open Pseudotsuga menziesii forests with A/nus and Pteridium expanded in lowland areas from 10,200-7,800 14C ybp in response to warm and dry conditions. Later, moistening from 7,800-6300 14C ybp produced a transitional forest with T heterophylla, Cupressaceae and Pseudotsuga menziesii. From 6,300-0 14C ybp forest were similar to modem lowland forests except for a brief rise in Cupressaceae from 3,000-1,900 14C ybp, and climate was like that surrounding Turtle Lake today. Vegetation composition, timing of change, and climatic patterns were similar to other records in the Pacific Northwest. At high elevation around Harris Lake Ridge Bog, Abies and T mertensiana forest characterised the landscape from 10, 270-6,640 14C ybp. T mertensiana and T heterophylla expanded in the mid-late Holocene from 6,640-1,970 14C ybp as moisture increased and temperatures decreased. Abies and Pinus increased from 1,970-1,260 14C ybp, as a result of fire. Phyllodoce empetriformis communities replaced tree cover from 260-520 14C ybp, after which modem subalpine forest developed. Climate during the last 2,000 years at Harris Lake Ridge Bog is interpreted as cool and moist. Plant communities however were strongly shaped by fire. The record from Harris Lake Ridge Bog is unlike other subalpine sites on Vancouver Island and reveals dynamic local changes in subalpine ecosystems. Fire played a role in forest development at both high and low elevations but fire history from Turtle Lake and Harris Lake Ridge Bog is not clearly associated with climate. Paleoecological results from the study have application to forest management on south central Vancouver Island and shed light on biodiversity issues related to Garry Oak ecosystems, and the Vancouver Island marmot (Marmota vancouverensis).