Markus L. Heinrichs

Postglacial paleoecology and inferred paleoclimate in the Engelmann spruce–subalpine fir forest of south-central British Columbia, Canada

Abstract Pollen, charcoal, and plant macrofossil analyses reveal five postglacial vegetation periods at Crater Lake, Crater Mountain, British Columbia. The first period, beginning ca. 11 400 14C yr BP was characterized by Artemisia steppe-tundra. At 9700 14C yr BP, Pinus parkland developed, and by 6700 14C yr BP was replaced by fire-successional Pinus-dominated Engelmann spruce and subalpine fir forest (ESSF). At 3800 14C yr BP, Picea became a more important element of the forest, and modern forest structure and composition developed by 1600 14C yr BP. Comparison of the fossil vegetation and fossil midge data derived from several ESSF sites in the southern interior reveals (1) similar late-Pleistocene vegetation and climate at all sites, (2) three distinct Holocene climatic stages: warm/dry, warm/moist, and cool/moist, (3) confirmation of the warm/moist period as a distinct climatic period, and (4) distinct differences in Holocene vegetation change among the sites. The driest and warmest site was most sensitive to climatic change, whereas cooler, moister sites were less sensitive. The present east–west climate gradient originated with postglacial warming at the beginning of the Holocene. Vegetation response to climate change and natural disturbance in these sites is strongly controlled by local site characteristics. These characteristics may have implications for forest, environment, and resource management.

Abies lasiocarpa (Hook.) Nutt. in the late-glacial and early-Holocene vegetation of British Columbia, Canada, and adjacent regions in Washington, USA

Abstract Abies lasiocarpa is a major element of high elevation forests and parkland of British Columbia, Canada, and adjacent regions, yet its history, especially in the late-glacial, is poorly understood. We present four new pollen and macrofossil records, summarize modern surface spectra and review previous studies to understand the role of A. lasiocarpa during the marked climatic changes of the late-glacial and early-Holocene. Today, in southern British Columbia, A. lasiocarpa reaches between 5 and 20% cover in the vegetation at Crater Lake, Buckbean Bog, and Lake of the Woods, but the 1–5% Abies pollen values under-represent its occurrence in the vegetation. At Sicamous Creek Lake, A. lasiocarpa grows at 50% cover and Pinus is absent locally, but the modern pollen surface spectra under-represent sub-alpine fir at 10% of the pollen rain. Based on these observations, sediments from Sicamous Creek Lake, Crater Lake, Buckbean Bog, and Lake of the Woods reveal that Abies grew locally in the late-glacial period. On southern Vancouver Island, British Columbia, the occurrence of an A. lasiocarpa needle, dated to 11 900±400 14 C yr BP in a lake core, along with only 1–2% Abies pollen, suggests that the tree grew at low elevations where it does not today. These results and a review of regional paleobotanical records suggest that the role of A. lasiocarpa in late-glacial and early-Holocene vegetation communities has been under-estimated. This species was likely a major element of the vegetation during this interval and among the first tree species to colonize deglaciated surfaces. Considering the magnitude of future climate change, a better understanding of the history of A. lasiocarpa during previous climate changes is necessary to project vegetation response and design effective resource management plans.