MacMillan Provincial Park is a 301 hectare provincial park in British Columbia, Canada. Located 25 km west of Qualicum Beach and 16 km east of Port Alberni, the park straddles Highway 4 in central Vancouver Island. It is nestled on the western shore of Cameron Lake, and protects the delta of the Cameron River.
The park is home to a famous, 157 hectare stand of ancient Douglas-fir, known as Cathedral Grove, which draws visitors from all over the world. The park provides the only highway-accessible protected old-growth Douglas-fir forest in British Columbia. In 2007 Cathedral Grove made the short list on CBC television's competition, Seven Wonders of Canada.
The forests in the park are transitional between the drier Coastal Douglas-fir Biogeoclimatic Zone (CDF), which characterizes the east coast of Vancouver Island, and the wetter Coastal Western Hemlock Biogeoclimatic Zone (CWH), found along the island's west coast. Some of the trees are more than 800 years old and 9 metres in circumference.
The flora of the park is typical of the region, and includes stands of old-growth tree species including Western Redcedar and Bigleaf Maple (found south of the highway), Western Hemlock, and Grand Fir. The understory (term for the area of the forest that grows in the shade the forest canopy) includes red huckleberry, salal, and Devil's Club.
The name "Cathedral Grove" is reputed to have originated from the Governor General of Canada, Viscount Willingdon in 1928, and appeared in correspondence to the provincial government in the 1920s. Cathedral Grove was a well-known tourist stop in the 1920s and 1930s, long before its protection.