Recent climate warming forces contrasting growth responses of white spruce at treeline in Alaska through temperature thresholds

Abstract

Northern and high-latitude alpine treelines are generally thought to be limited by available warmth. Most studies of tree-growth-climate interaction at treeline as well as climate reconstructions using dendrochronology report positive growth response of treeline trees to warmer temperatures. However, population-wide responses of treeline trees to climate remain largely unexamined. We systematically sampled 1558 white spruce at 13 treeline sites in the Brooks Range and Alaska Range. Our findings of both positive and negative growth responses to climate warming at treeline challenge the widespread assumption that arctic treeline trees grow better with warming climate. High mean temperatures in July decreased the growth of 40% of white spruce at treeline areas in Alaska, whereas warm springs enhance growth of additional 36% of trees and 24% show no significant correlation with climate. Even though these opposing growth responses are present in all sampled sites, their relative proportion varies between sites and there is no overall clear relationship between growth response and landscape position within a site. Growth increases and decreases appear in our sample above specific temperature index values (temperature thresholds), which occurred more frequently in the late 20th century. Contrary to previous findings, temperature explained more variability in radial growth after 1950. Without accounting for these opposite responses and temperature thresholds, climate reconstructions based on ring width will miscalibrate past climate, and biogeochemical and dynamic vegetation models will overestimate carbon uptake and treeline advance under future warming scenarios.

Height increment of hybrid aspen <i>Populus tremuloides</i> x <i>P. tremula</i> as a function of weather conditions in central part of Latvia

“…Although this is usual in arid regions (i.e. Mediterranean region) (Rozas 2001;Andreu et al 2007), similar effects have recently been observed also for trees growing in boreal regions (Wilmking et al 2004). Thus, knowledge on climate growth relationships, considering regional variability (Andreu et al 2007), is necessary.…”

“…Although Latvia is located in central part of distribution area of aspen (EUFORGEN 2009), temperature showed strong positive effect on HI (lowest p-values for all equations) (Table 1) as observed for wood increment of trees growing in northern regions of their distribution (Wilmking et al 2004;Salminen and Jalkanen 2007). The effect of temperature on HI might be explained by the direct influence on meristematic activity (i.e.…”

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

“…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]).…”

The role of climate change in the widespread mortality of holm oak in open woodlands of Southwestern Spain

“…The susceptibility of trees to mortality seems to be related to tolerance thresholds in tree physiology in a complex way that is not yet completely understood (Allen et al, 2010;McDowell et al, 2011). Warming and increasing aridity could force trees beyond certain thresholds from which they cannot recover (D'Arrigo et al, 2004;Wilmking et al, 2004;McDowell et al, 2011).…”