Climate and vegetation change during the twentieth century in the lower Peace River district, northern Alberta, Canada

Abstract

A 96-yr climate record (1908—2004), historical descriptions, multiyear (1950, 1964, 1978, 1994) lake-surface area measurements, and 1950 and 2004 physiognomically based vegetation maps were compiled to assess vegetation change in the Fox Lake area (4248 ha) within the lower Peace River district of northern Alberta. A climatic warming trend ( r = 0.615, P < 0.001; 0.35°C/decade) was evident during the twentieth century, with peak precipitation occurring from 1970 to 1990. Five major wet—dry cycles, based on net water balance values (precipitation minus potential evaporation), were evident with peaks occurring at about 17(±3) year intervals. Each cycle became slightly less arid than the previous until the mid-1990s. Deciduous forests dominated upland sites in 2004, whereas deciduous shrub and juvenile tree stands comprised 78% in 1950. Total wetland area remained relatively constant between 1950 and 2004, but less meadow and more standing water were present in 2004. Lake-surface area changes suggested that wetlands were recharged by precipitation rather than floodwaters from the nearby Peace River. Low water availability and historical descriptions suggest grassland-dominated parkland-like vegetation occurred in the study area during the early part of the twentieth century, with upland shrubs replacing grasslands by 1950. Increased atmospheric water availability rather than cessation of aboriginal burning or natural fires was considered responsible for increased forest abundance after 1945. Greater aridity in response to future global warming could reduce the abundance of forests in the lower Peace River district, and shift the regional climate from a boreal to a grassland-dominated parkland climatic regime.

Climate change is the primary driver of white‐tailed deer (Odocoileus virginianus) range expansion at the northern extent of its range; land use is secondary

“…; Strong et al. ). Snow melt is occurring 8 days earlier in northern Alaska compared to pre‐1960 periods due to decreased snow fall and warmer springs, a trend that has likely occurred across northwestern North America (Stone et al.…”

“…Mean temperatures from the warmest and coldest month are 15.7 and À19.2°C, respectively, and mean annual precipitation is 469 mm (Downing and Pettepiece 2006). Both temperature and precipitation have changed in northwestern North America since 1908 (Jarvis and Linder 2000;Stone et al 2002;Nemani et al 2003;Lemke et al 2007;Strong et al 2009). Snow melt is occurring 8 days earlier in northern Alaska compared to pre-1960 periods due to decreased snow fall and warmer springs, a trend that has likely occurred across northwestern North America (Stone et al 2002;Lemke et al 2007).…”

Tree and forest encroachment into fescue grasslands on the Cypress Hills plateau, southeast Alberta, Canada

“…The general consensus is that fire suppression has permitted tree encroachment (Strauss, 2001;O 2 Planning, unpublished), as postulated in other studies (e.g., Burkhardt and Tisdale, 1976;Briggs et al, 2002). In contrast, several other studies in western North America and elsewhere identified climate change as the likely cause for tree encroachment (Wearne and Morgan, 2001;Kennedy and Sousa, 2006;Zier and Baker, 2006;Coop and Givnish, 2007;Strong et al, 2009).…”

Recent advance of forest–grassland ecotones in southwestern Yukon

“…Similarly, herbivores influence grassland dynamics directly by grazing and indirectly from trampling, as woody seedling establishment has been recorded when grazing pressure decreases (Norman and Taylor 2005). Lastly, recent changes in climate, notably increases in temperature and precipitation, have been linked to forest encroachment (Strong et al 2009). The sensitivity of grasslands to climate has significant implications in light of future global climate scenarios (Prowse et al 2009).…”