Influence of simulated snow cover on the cold tolerance and freezing injury of yellow‐cedar seedlings

Abstract

It has been hypothesized that yellow-cedar [Chamaecyparis nootkatensis (D. Don) Spachl decline may result from root freezing injury following climate change-induced reductions in protective snow cover. To test this hypothesis, we measured the freezing tolerance and injury expression of yellow-cedar seedlings in three treatments that differed in the insulative protection they provided to soils during winter and spring: (1) full exposure to ambient temperatures (exposed treatment), (2) continuous protection from ambient temperatures via addition of perlite over pots (full protection), and (3) perlite protection only during winter and exposure to ambient temperatures during spring (partial protection). Foliage from all treatments was cold tolerant enough to prevent foliar freezing injury throughout the study period. However, on all sample dates, roots of seedlings from all treatments were only tolerant to about -5 "C -a level considerably warmer than the reported maximum cold tolerance for the species and well above the soil temperature recorded in the exposed treatment. As a result of this limited root cold tolerance, visibly uninjured roots of seedlings from the exposed treatment had significantly higher relative electrolyte leakage (REL) throughout the winter and early spring than seedlings in soil protection treatments. Seedlings from the exposed treatment also had significantly higher foliar REL values and greater visual foliar injury than seedlings from the other treatments starting in early spring. For both roots and foliage, REL measurements consistently detected tissue damage before visual injury was evident. Patterns of injury from both REL and visual injury assessments showed the same pattern: damage began with freezing injury to roots and subsequently became evident as foliar browning after spring temperatures increased. All seedlings in the exposed treatment eventually had 100% fine root damage and died. This progression of initial root damage followed by foliar browning and mortality after the onset of warming conditions is consistent with reports of yellow-cedar decline symptom development in the field.

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

“…Thus, together with seasonal warming, declining snow cover appears to be playing an important role in driving the well-documented contrast between forest browning and tundra greening trends in North America [15,16,18]. Reduced peak snow accumulation can extend the short northern growing seasons and stimulate earlier and faster vegetation greening in some cool Arctic regions [34,90], but it may have an adverse impact in the boreal forests due to reduced water availability during summer [84] and soil insulation during the cold season [92,93].…”

Evidence and implications of recent and projected climate change in Alaska's forest ecosystems

“…The cause is complex and includes a number of cascading landscape, site, and stand factors ) that interact with the physiological susceptibility of yellow-cedar's fine roots to spring freezing injury (Schaberg et al 2008). Although yellow-cedar trees are tolerant of cold temperatures in fall and early winter (Schaberg et al 2005), its roots are dehardened in late winter and early spring, at which time soil temperatures below À58C are lethal (Schaberg et al 2008). When snow is present, this temperature threshold is not crossed (Hennon et al 2010), due to the insulative effect of snow.…”

Forest health and climate change: A British Columbia perspective

“…Recent assessments along the coast indicate that over 40 000 ha of decline have been mapped in the province and this may affect the future range of this species (Hennon et al 2005). Yellow-cedar decline is considered to be a result of longterm climate change (Schaberg et al 2008). Declining snow depths at lower elevations of the species range has led to increased susceptibility of fine roots to late-season frost events (Hennon and Shaw 1994).…”

“…The interaction and ultimate impacts of declines will increase in importance as climate change puts additional stresses on forests. Occurrences of decline syndromes have increased in many of the world's forests, including those of western North America such as western boreal aspen forests (Hogg et al 2008), coastal yellow-cedar (Callitropsis nootkatensis [D. Don] Florin) forests (Hennon et al 2005, Schaberg et al 2008 and BC interior birch stands (Betula papyrifera Marsh.) (Westfall and Ebata 2009).…”