Effects of Subzero Temperatures on Populations of Western Pine Beetle1Dendroctonus brevicomis Lec.

Geographically variable response of Dendroctonus ponderosae to winter warming in the western United States

“…Others have noted warming of average winter temperatures (Alward et al 1999;Luterbacher et al 2004;Vose et al 2005), but examination of trends in minimum annual temperatures are rare (but see Edgell 1994;Jung et al 2002;Macias Fauria and Johnson 2009). It would be useful to know if patterns in the US are representative of other mid to high latitude ecosystems because winter warming has broad relevance to biodiversity and natural resource management (Keen and Furniss 1937;Coulson et al 2001;Saether et al 2002;Crozier 2004;Altwegg et al 2006). Some notable emerging threats to forest health management are associated with the diminishing likelihood of winter kill of pest insects due to climate change (Weed et al 2013).…”

Forest Insect Populations

“…This relation has been almost universally observed, and as a result a strong feeling has developed that insect outbreaks are the direct result of weather fluctuations. Keen (1937), Craighead (1925), Miller (1933, and other workers have shown definite correlation between Dendroctonus outbreaks and weather. Spruce budworm outbreaks on pine are usually associated with drought.…”

“…On the other hand, adverse weather conditions may temporarily reduce insect populations, but usually these effects are short-lived when conditions return to normal. For instance, very cold weather may destroy barkbeetle broods, but seldom brings outbreaks under control because after such decimations the insects breed up rapidly (Keen and Furniss, 1937). Although it is dangerous to generalize from limited evidence, it appears that on the whole the effects of favorable weather influence insect populations more than do the unfavorable variations.…”

Low Temperature Differentials in One Forest Drainage

“…In cold periods previously studied in eastern Oregon (Keen and Furniss 1937) and in nortbeastern California (Miller 1933), quite different conditions prevailed. In Oregon, during the cold period from December 7 to 17, 1932, "a strong wind blew more or less constantly, resulting in a thorough agitation of the air so that similar temperatures prevailed over wide areas" (Keen and Furniss 1937). Thus, under conditions of a freeze when great polar air masses sweep across the country, the differentials between forest temperatures and nearby standard weather stations are likely to be negligible.…”

“…Beal (1934) determined the modifying effect of bark of different thicknesses in protecting broods during periods of low temperature. Keen and Furniss (1937) determined the average precentage of brood mortality that can be expected from different low winter temperatures experienced in the ponderosa pine forests of eastern Oregon and northeastern California ; for temperatures, they used weather records available from standard weather stations near the forested areas. The need to use such records raised questions as to how well temperature readings taken at standard weather stations, usually in towns near the forest, actually represented temperatures prevailing under forest conditions.…”