Athabasca Dunes is the province's largest Ecological Reserve. It contains part of Alberta's largest active sand dune system - approximately 8 km from north to south and 1.5 km wide. The active dunes are a series of sand ridges. They are slowly migrating southeast, burying jack pine forests and filling small lakes. There are large areas of kame and kettle. The kames, over 60 metres high, are among the largest in the world. Peatlands range from relatively dry bogs dominated by jack pine, black spruce, Labrador tea and reindeer lichen to wetter peatlands with black spruce, tamarack and peat moss. Shoreline areas include mixed forests of aspen, balsam poplar and white spruce. Arctic terns, not known to nest elsewhere in Alberta, nest in the reserve.