A case study of forest decline in Western Canada and the adjacent United States

Abstract

A comparison of declining forests in Alaska, British columbia, and the Pacific Northwest United States to forest declines in eastern North America indicated that strong similarities existed and justified the use of the western forest region as an 'acid rain' control. The current level of wet acidic deposition over the western region was one-quarter that of eastern Canada and the United States. The onset of crown dieback on Chamaecyparis nootkatensis (1900) and Pinus monticola (1936) did not relate to the incidence of regional air pollution but to extreme climatic variation. The injury mechanism differentiating persistent decline on Pinus monticola from sporadic but transient dieback, which was observed on a larger number of conifer and deciduous tree species, was believed to be cavitation. This dysfunction of the xylem was induced by anomalous winter thaw-freeze conditions in 1936 followed by high summer temperatures and evapotranspiration stress in that and subsequent years. Similar extreme climatic conditions were present at the onset of forest declines in eastern North America and central Europe which suggests that the climate-cavitation-forest decline mechanism may be universal.

The potential effects of climate change on U.S. forests: a review

“…Large-scale incidents of forest dieback have been positively correlated with extreme weather events (Auclair et al 1990(Auclair et al , 1996. Declines observed in various forest ecosystems have corresponded to repeated freeze-thaw events in the winter, followed by severe droughts in the summer.…”

“…Declines observed in various forest ecosystems have corresponded to repeated freeze-thaw events in the winter, followed by severe droughts in the summer. Some of these studies have also described the processes causing the physiological damage which leads to the diebacks (Auclair et al 1990). Should climatic changes lead to periods of significant warming within the winter period, or extreme heating, cooling, or drought during the summer, more such large-scale events are possible.…”

Impacts of Climate Change on Vegetation Distribution No. 1 -- Climate Change Induced Vegetation Shifts in the Palearctic Region

“…When including agriculture in the simulations, fewer changes are expected in natural vegetation (due to less area), but these are considered to be fast. Just like Köhler et al (2005), Kirilenko and Solomon (1998) also predict the dieback of trees (across large regions within a decade) and refer to recent forest diebacks in Europe, the Pacific Rim and northeastern North America (Mueller-Dombois, 1987; Auclair et al, 1990;Auclair, 1992). Regrowth by trees more suitable for new climates is doubtful and may take a century or more.…”

Effects of Climate Change on Forest Insect and Disease Outbreaks

“…Climatic records indicated that in areas with pole blight there was a period of low precipitation and high temperature from 19 17 to 1940 (Leaphart, 1958). Subsequent research (Leaphart and Stage, 1971) indicated that pole blight was triggered by the severe drought of 1936, though more recent research has disputed this claim and proposed that winter thaw-freeze events were the likely triggering factors for the decline (Auclair et al, 1990).…”

“…The initiation of both the warming period and the extensive mortality associated with the decline occur around 1880 (Hennon and Shaw, 1994). Other research implicates the role of extreme freeze-thaw events in this decline (Auclair et al, 1990). Dieback is usually associated with extreme episodes of winter drying, unseasonable frost, summer drought, and heat stress (Auclair et al, 1990).…”