Reduced growth of Alaskan white spruce in the twentieth century from temperature-induced drought stress

Abstract

The extension of growing season at high northern latitudes seems increasingly clear from satellite observations of vegetation extent and duration. This extension is also thought to explain the observed increase in amplitude of seasonal variations in atmospheric CO2 concentration. Increased plant respiration and photosynthesis both correlate well with increases in temperature this century and are therefore the most probable link between the vegetation and CO2 observations. From these observations, it has been suggested that increases in temperature have stimulated carbon uptake in high latitudes and for the boreal forest system as a whole. Here we present multi-proxy tree-ring data (ring width, maximum late-wood density and carbon-isotope composition) from 20 productive stands of white spruce in the interior of Alaska. The tree-ring records show a strong and consistent relationship over the past 90 years and indicate that, in contrast with earlier predictions, radial growth has decreased with increasing temperature. Our data show that temperature-induced drought stress has disproportionately affected the most rapidly growing white spruce, suggesting that, under recent climate warming, drought may have been an important factor limiting carbon uptake in a large portion of the North American boreal forest. If this limitation in growth due to drought stress is sustained, the future capacity of northern latitudes to sequester carbon may be less than currently expected.

Late Quaternary environmental and landscape dynamics revealed by a pingo sequence on the northern Seward Peninsula, Alaska

“…This may have been because the populations were overtaken by the transgression and the major climate changes (especially cooler summers) that would have occurred with coastal retreat across the land bridge, before they were able to expand further inland. One feature of the early Holocene climate was high seasonality, and, until the transgression, the region was also highly continental, making the survival of evergreen conifers more difficult, as lack of available moisture may have been a major stress (Hogg, 1994;Barber et al, 2000). Subsequently, spruce populations in central Alaska expanded in a westerly direction during moister but cooler conditions, reaching the current treeline, which still lies to the east of the Kitluk site.…”

Temperature and Snow-Mediated Moisture Controls of Summer Photosynthetic Activity in Northern Terrestrial Ecosystems between 1982 and 2011

“…Most of these regional reductions in summer NDVI have been attributed to increasing drought stress with hotter summers, an extended period of evaporation and enhanced atmospheric evapotranspiration demand associated with rising temperatures [15,16,21,22]. This effect is referred to as "temperature-induced drought stress" [16,23].…”

“…A number of causal factors have been proposed and are still being debated though one suggestion is that the recent warming has invoked increasing drought stress [26]. A consistent long-term control of boreal forest growth by summer moisture availability has been observed in the drier continental interiors of Alaska and North-Western Canada where increased tree growth is stimulated by cooler and wetter growing seasons [23,27,28]. Hence, warming in these boreal regions has often been associated with tree growth declines rather than with increases [23], consistent in cases with co-located NDVI browning trends [18].…”

“…Local and regional responses of boreal vegetation to moisture variability have typically been inferred indirectly from correlations with soil moisture forcings, such as precipitation and temperature (e.g., [23,39,40]). In other cases, comparisons have been made with simple meteorological drought indices that often neglect soil properties, snow dynamics and vegetation (e.g., [21,35,41]).…”

Macroscale intraspecific variation and environmental heterogeneity: analysis of cold and warm zone abundance, mortality, and regeneration distributions of four eastern US tree species

“…Gsai gives a measure of growing season moisture stress that is predicted to become increasingly important in the future because evapotranspiration is forecast to increase more than precipitation in some regions, increasing moisture stress of various ecosystems (Barber et al. 2000; Breshears et al. 2005; McDowell et al.…”