A Dendrochronological Method of Studying Tree Mortality Patterns

This study examines the use of dendrochronological crossdating to determine the dates of death of dead-standing coniferous trees in subalpine forests in the Colorado Rocky Mountains. We cored approximately 800 dead-standing Engelmann spruce (Picea engelmannii Parry ex Engelm.) and subalpine fir (Abies lasiocarpa [Hook.] Nutt.) in two stands and classified them into decay classes. We quantitatively and visually crossdated samples from the dead-standing trees against master chronologies derived from live trees of each species in each stand. The outermost ring on crossdated samples served as an estimate of the year in which a tree died. Seventy percent of the dead-standing trees crossdated successfully. The crossdating technique clearly identified a period of massive mortality of Engelmann spruce attributable to a spruce beetle infestation in the 1940s. This procedure effectively distinguishes between continuous and episodic patterns of tree mortality and compares the relative mortality rates of these coniferous species. Dendrochronological dating of tree deaths is a useful way of providing historical contexts for interpreting tree mortality data derived from short-term monitoring of permanent plots.