Holocene vegetation, climate, and lake-level changes in the Interior Douglas-fir Biogeoclimatic Zone, British Columbia

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Abstract
Chilhil, Phair, Fishblue, and Horseshoe lakes in the southern interior of British Columbia were cored and analyzed for pollen. Phair Lake was also examined for plant macrofossils and aquatic molluscs. Two dated volcanic tephras (Mazama and Bridge River) are present in three of the four lakes and, together with radiocarbon dates, provide an absolute chronology for pollen-influx calculations and stratigraphic correlation. Abrupt changes in sediment type at Phair Lake about 5650 and 2000 years ago correlate with Neoglacial advances near the coast–interior transition. Pollen changes suggestive of moister conditions and the presence of an aquatic mollusc (Valvata sincera helicoidea) at Phair and Chilhil lakes are consistent with the Neoglacial evidence of cooler and wetter conditions after about 2400 years ago. The driest part of the Holocene was the early, pre-Mazama (ca. 6600–6800 years ago) interval, when the vegetation was more open and herb rich and the lake levels were lower than at present. Wetter climatic conditions appear in post-Mazama time, indicated by regional increases in the pollen of Tsuga heterophylla and other coastal and subalpine trees. Pollen-influx values for the Interior Douglas-fir Zone are broadly consistent at all sites, with values of < 2000 –8000 grains cm−2 year−1. Douglas-fir (Pseudotsuga menziesii) has been an important forest species in the study region throughout the Holocene.