Local site conditions drive climate–growth responses ofPicea marianaandPicea glaucain interior Alaska

Abstract

Abstract. The growth response of boreal forest trees to projected changes in climate will have wide ranging and cascading impacts on disturbance regimes, climate feedbacks, carbon storage, and habitat ranges for flora and fauna. Recent findings in Alaska suggest the boreal biome is shifting in response to changes in climate. It is unlikely such a shift will occur in a uniform manner over a landscape variable in topography and site conditions, although there is little consensus of how local site characteristics will interact with climate to alter tree growth patterns. Few studies of tree growth responses to climate in the boreal forest have used randomized study designs encompassing the full range of site conditions, leaving open the question of whether observed patterns in tree growth at local scales are wholly representative of the boreal forest. We addressed these issues using a systematic sampling design to quantify the landscapescale patterns in annual growth for Picea mariana and Picea glauca, the two most abundant tree species in interior Alaska. We used measurements of annual tree growth based on increment cores taken from trees distributed across a 1.28 million-ha study area in Denali National Park and Preserve. We found site-specific variables, namely near-surface permafrost, slope angle, and elevation, strongly modified the magnitude, shape, and, in some cases, the direction of growth response to climatic conditions for both species. With predicted warming, our results suggest both P. mariana and P. glauca will decrease growth in areas underlain by shallow permafrost. P. mariana growth may increase on flat terrain, but decrease on steep slopes, while P. glauca growth will show the greatest increases at high elevations during very warm summers. Our results suggest future shifts in these species distributions in response to a changing climate will be conditional on variation in site factors operating at local scales.

Differential declines in Alaskan boreal forest vitality related to climate and competition

“…Previous site‐level studies have recorded significant growth declines for white spruce trees in interior Alaska (Barber et al., ; Beck et al., ), and tree ring analyses have documented white spruce growth declines in western Canada (Hogg, Michaelian, Hook, & Undershultz, ); however, we did not find significant trends in white spruce growth during the study period (Table ). It is possible that these different results arise from differences in sample location (Hogg et al., ), time period, or spatial scale (Nicklen et al., ). We also found no significant growth or mortality trends for birch species, contrary to an inventory study in central Canada (Zhang et al., ).…”

Can snowshoe hares control treeline expansions?

“…Warmer temperatures may promote establishment and growth (Nicklen et al. ); however, the restriction of spruce to primarily open floodplain sites by hares puts them at greater risk of desiccation as summers become warmer and drier (Fig. ), a trend already occurring at lower elevations (Angell and Kielland , Juday et al.…”

“…, Nicklen et al. ). This range expansion may cause a transition from tundra to boreal forest communities across much of Interior Alaska (Juday et al.…”

Post-1980 shifts in the sensitivity of boreal tree growth to North Atlantic Ocean dynamics and seasonal climate

“…6). This relationship appears to be linked to a significant positive 497 association between tree growth and spring temperature ( climate (Wilmking et al, 2004) and to enhance the control of site factors upon growth 515 (Nicklen et al, 2016). This is particularly true with site factors influencing soil water 516 retention, such as soil type, micro-topography, and vegetation cover (Düthorn et al, 2013).…”