To detect the duration and frequency of WSB outbreaks dendrochronological studies commonly remove the climate-driven component of radial growth contributing to inter-annual variation. This variation is ‘corrected’ using a chronology from a non-host tree species, i.e., a tree species that is not defoliated by the budworm, but is sensitive to the same climatic conditions as the host. Periods of sustained growth reduction remaining in the corrected host chronology are inferred to result from NVP-AUY922 order WSB defoliation (Swetnam and Lynch, 1989). The Cariboo Forest Region extends from 51°00′ to 52°30′ north latitude and from 120°30′ to 125°45′

west longitude in the BC central interior (Fig. 1). The Fraser Plateau makes

up a large portion of the region and is characterized by a level to gently rolling landscape incised by river valleys, and local uplands with elevations predominantly ranging from 900 to 1500 metres above sea level (masl). The Chilcotin Plateau extends along the western periphery of the region, beyond which the Coast Mountains rise sharply to elevations up to 4000 masl. This landscape configuration results in a strong rain shadow effect and the western Chilcotin is the driest LY2835219 concentration portion of the study area, with average annual precipitation at Tatla Lake averaging 403 mm/yr. As Pacific air masses move further eastward towards Williams Lake, humidity levels and precipitation increase slightly, with annual precipitation totals averaging 417 mm/yr Coproporphyrinogen III oxidase (Wang et al., 2012). Summer months are typically dry, with most precipitation resulting from numerous convective storms. In the winter months Arctic air masses result in extended periods of extreme cold temperatures (Steen and Coupé, 1997). In BC the biogeoclimatic ecosystem classification

(BEC) uses vegetation, soils, and topography to identify geographic areas, referred to as biogeoclimatic zones, which have a relatively uniform climate. BEC zones are further divided into subzones based on the moisture and temperature regime of the area, respectively and some BEC subzones are further classified into variants based on their location or distribution within a subzone (Meidinger and Pojar, 1991). In the Cariboo Forest Region, the Interior Douglas-fir (IDF) BEC zone makes up approximately 45% (17,000 km2) of the area and is located above the valleys of the Fraser, Chilcotin, and Chilanko rivers (Steen and Coupé, 1997). The very dry-warm (xw) and very dry-mild (xm) subzones are the driest and warmest in the region, and are transitional between grassland and forest (Table 2). The dry-cool (dk) subzone covers the largest area in the Cariboo Forest Region and is comprised of four variants, with the Chilcotin variant (dk4) being the coldest and driest (Steen and Coupé, 1997; Table 2). Herein, we shall refer to BEC subzones (e.g., xm) and BEC variants (e.g., dk4) simply as BEC units.