POLLEN AND NON-POLLEN PALYNOMORPH ANALYSES OF PEAT: INFERRING HOLOCENE VEGETATION CHANGE AND BOG DEVELOPMENT ON NORTHERN VANCOUVER ISLAND

Wetlands occupy 50 to 75% of the British Columbia coast. Despite the widespread occurrence of bogs in the region, few palynological studies have investigated the effects of long-term environmental change on these ecosystems. A 3.24 m peat core was collected from a flat bog in advanced succession near Port McNeill on northern Vancouver Island. A chronology based on seven AMS radiocarbon ages indicates a basal age of 10,400 cal yr BP for the peat core. Fossil pollen and non-pollen palynomorphs (NPPs), including remains of testate amoebae, aquatic plants and fungi, were used to determine both local and regional changes in vegetation as well as local hydrological changes at the bog.

An abundance of Nuphar pollen, sclereids and leaf hair basal cells indicates the presence of a wetland with standing water and/or bog pools in the earliest Holocene. A decreasing water table, inferred from testate amoebae and fungal remains, enabled a Sphagnum-dominated peat bog to develop by 7500 cal yr BP with abundant ericaceous shrubs after 4000 cal yr BP. On a regional scale, pollen assemblages indicate that early Holocene vegetation was mixed coniferous forest of Tsuga heterophylla, Picea sitchensis and Alnus rubra. Pseudotsuga menziesii, which is rare on northern Vancouver Island today, was also present, suggesting that warm early Holocene summers facilitated its northward expansion. By 8000 cal yr BP, regional forests transitioned to Tsuga heterophylla-dominated rainforests similar to today.

This study demonstrates the value of combining pollen analysis with NPPs in paleoenvironmental studies and, specifically, for understanding the paleoecological history of British Columbia wetlands. As a next step, we will compare changes in vegetation and hydrological conditions with long-term rates of carbon accumulation to clarify the links between plant communities, water table depth and carbon accumulation as well as the impacts of climate change on these important carbon sinks.