Dendroecological reconstruction of mountain pine beetle outbreaks in the chilcotin plateau of British Columbia

The mountain pine beetle (Dendroctonus ponderosae Hopk.) (Coleoptera: Scolytidae) is an aggressive bark beetle that periodically increases to outbreak levels killing thousands of trees. It is considered one of the major natural disturbance agents in North America. In British Columbia, the main host species is lodgepole pine (Pinus contorta var. latifolia Engelm.), but western white pine (Pinus monticola Dougl.), ponderosa pine (Pinus ponderosa Laws.), whitebark pine (Pinus albicaulis Engelm.), and limber pine (Pinus flexilis James) are also attacked. We used dendrochronology to establish the history of canopy disturbances indicative of potential past beetle outbreaks. For this we relied on the fact that beetle outbreaks do not normally kill all the trees in a stand and that trees that survive outbreaks, experience extended periods of increased growth, visible in tree ring series as prolonged periods of release. Increased growth is thus used as a proxy for canopy disturbance. Fifteen chronologies studied in the south central area of British Columbia showed three fairly synchronous large-scale release periods which are proposed as three large outbreaks: 1890s, 1940s and the 1980s. The three releases averaged 13.8 years (Min=5, Max=23 years) in duration and recurred every 42 years (Min=28, Max=53 years), counted from the start of the release.