Changes in Heartwood Chemistry of Dead Yellow-Cedar Trees that Remain Standing for 80 Years or More in Southeast Alaska

Abstract

Abstract-We measured the concentrations of extractable bioactive compounds in heartwood of live yellow-cedar (Chamaecyparis noothtensis) trees and five classes of standing snags (1-5, averaging 4, 14,26,5 1, and 81 yearssince-death, respectively) to determine how the concentrations changed in the slowly deteriorating snags. Three individuals from each of these six condition classes were sampled at four sites spanning a 260-km distance across southeast Alaska, and the influence of geographic location on heartwood chemistry was evaluated. Cores of heartwood were collected at breast height and cut into consecutive 5-cm segments starting at the pith. Each segment was extracted with ethyl acetate and analyzed by gas chromatography. Concentrations of carvacrol, nootkatene, nootkatol, nootkatone, nootkatin, and total extractives (a sum of 16 compounds) for the inner (0-5 cm from pith), middle (5-10 cm from pith), and surface (outer 1.1-6.0 cm of heartwood) segments from each core were compared within each tree condition class and within segments across condition classes. Heartwood of class 1 and 2 snags had the same chemical composition as live trees. The first concentration changes begin to appear in class 3 snags, which coincides with greater heartwood exposure to the external environment as decaying sapwood sloughs away, after losing the protective outer bark. Within core segments, the concen-* To whom correspondence should be addressed. E-mail: rke1seyGJfs.fed.u~ trations of all compounds, except nootkatene, decrease between snag classes 2 and 5, resulting in the Ileartwood of class 5 snags having the Iowest quantities of bioactive compounds, although not different t%om the amounts in class 4 snags. This decline in chemical defense is consistent with heartwood of class 5 snags being less decay-resistant than heartwood of live trees, as observed by others. The unique heartwood chemistry of yellow cedar and the slow way it is altered after death allow dead trees to remain standing for up to a century with a profound impact on the ecology of forests in southeast Alaska where these trees are in decline.

Long‐term vegetation changes in a temperate forest impacted by climate change

“…Not all yellow-cedar trees in a forest affected by mortality die at once; mortality is progressive in forests experiencing dieback (Hennon et al 1990a). Highly resistant to decay, these trees remain standing for up to a century after their death (Kelsey et al 2005). As a result, they offer the opportunity to date disturbance, approximately, and to create a long-term chronosequence.…”

Tree-ring investigations into changing climatic responses of yellow-cedar, Glacier Bay, Alaska

“…Its shallow root systems require a deep snowpack to insulate the roots from hard frosts that can damage roots and potentially lead to the death of the tree (Schaberg et al 2008). Yellow-cedar is extremely durable, economically valuable (Kelsey et al 2005), and long-lived, with reports of trees with as many as 1824 annual rings (Pojar and MacKinnon 1994).…”

“…The greatest concentration of yellow-cedar mortality in Southeast Alaska is below 305 m elevation, whereas farther north, the decline is concentrated at lower elevations, up to 150 m (Lamb and Wurtz 2009). Concentrations of dead cedar make up to 70% of the stand's area in some cases (Kelsey et al 2005;Hennon et al 2005).…”

Alternative interpretation and scale-based context for “No evidence of recent (1995–2013) decrease of yellow-cedar in Alaska” (Barrett and Pattison 2017)

“…• Yellow-cedar is extremely decay resistant (Kelsey et al 2005), and snags may stand for 80 or more years following death (Hennon et al 1990b). Applying a species-specific snag classification system developed using plot data allows researchers to reconstruct spatial and temporal patterns of mortality dating back to the early 1900s (Hennon et al 1990a;Oakes et al 2014).…”

“…After 50 years, the distinctive yellow heartwood color and aromatic compounds are diminished (Kelsey et al 2005), both of which are key features for distinguishing yellow-cedar snags from dead trees of other species. Identification of older snags, therefore, can be challenging -even for seasoned field biologistswithout careful and time-intensive examination.…”