Dendroecological detection of spruce bark beetle outbreaks in northwestern Colorado

Abstract

Episodic outbreaks of Dendroctonus rufipennis (Kirby), the spruce bark beetle, have greatly influenced the structure of subalpine forests in northern Colorado. During the 1940s, much of the subalpine zone of northwestern Colorado was severely affected by beetle outbreak; also, tree-ring and photographic evidence suggest that large-scale outbreaks occurred in the 19th century. The present study focused on tree-ring methods to examine the regional extent and synchrony of pre-20th-century beetle outbreaks in northwestern Colorado. Results from examination of both live and dead Engelmann spruce (Picea engelmannii Parry ex Engelm.) tree rings in nine stands were compared with results of previous tree-ring studies in the same region. Evidence of past canopy disturbance included episodes of tree mortality in conjunction with sustained increases in radial growth rates. We identified regional outbreaks of spruce beetle by synchronous and sustained growth release in trees from disjunct stands. These new tree-ring records, along with previously published records, indicate that severe and widespread canopy disturbances, probably spruce beetle outbreaks, affected northwestern Colorado in 1716-1750, 1827-1845, 1860-1870, and 1940-1960. These results support earlier findings that large-scale outbreaks of spruce beetle have long been an important component of the dynamics of subalpine forests in Colorado.

Post-fire forest dynamics and climate variability affect spatial and temporal properties of spruce beetle outbreaks on a Sky Island mountain range

“…Bark beetle outbreaks are usually inferred in dendrochronological reconstructions by growth releases in surviving understory trees (Veblen et al, 1991b;Eisenhart and Veblen, 2000;Berg et al, 2006). Raw ring width measurements from individual trees at each plot location were analyzed for growth releases with the program JOLTS (Holmes, 1999).…”

Influence of fire and mountain pine beetle on the dynamics of lodgepole pine stands in British Columbia, Canada

“…There is a delay in growth response of trees to beetle thinning, and as not all trees are killed in 1 year during an outbreak, growth releases are not precisely simultaneous (Eisenhart and Veblen, 2000). For dating these releases we assumed a lag of 3 years between initiation of an outbreak and initiation of a release response (based on Heath and Alfaro, 1990).…”

The pollen record of a 20th century spruce beetle (Dendroctonus rufipennis) outbreak in a Colorado subalpine forest, USA

“…Presently, our research at Antler Pond has been limited to the most recent outbreak in the 20th century, but we expect that outbreaks of greater antiquity could be determined from lake sediment when high-resolution pollen analytical techniques are used. For instance, it may be possible to confirm other events identified from tree-ring studies, such as the 1716-1750 AD, 1827-1845 AD, and 1860-1870 AD events documented from other areas of the White River Plateau (Miller, 1970;Baker and Veblen, 1990;Veblen et al, 1991aVeblen et al, , 1994Eisenhart and Veblen, 2000). However, such events may be obscured in the pollen record, because other factors might be important locally, such as available seed sources (e.g., Turner et al, 2003), or the complexity of successional pathways in subalpine forests (e.g., Kipfmueller and Kupfer, 2005).…”

“…Outbreaks of D. rufipennis (Baker and Veblen, 1990;Veblen et al, 1991a, b;Zhang et al, 1999;Eisenhart and Veblen, 2000), Choristoneura occidentalis (western spruce budworm; Swetnam and Lynch, 1989;Ryerson et al, 2003), and Coloradia pandora (pandora moth; Speer et al, 2001) among others have been documented from tree-ring records. Sediment studies have been instrumental in tracking the chestnut blight, a 20th century decline in Castanea dentata (American chestnut) caused by a fungal pathogen (Cryphonectria parasitica; Anderson, 1974), and the mid-Holocene "hemlock decline", a massive widespread die-off of Tsuga canadensis (eastern hemlock), beginning ca.…”

“…Sedimentary documentation of a known recent D. rufipennis infestation provides a unique opportunity to investigate the history and effect of large outbreaks in the past, important in determining strategies for management of insect populations. GIS techniques (Bebi et al, 2003), stand structure (Veblen et al, 1994) and tree-ring (Eisenhart and Veblen, 2000) evidence are critical to understanding the ecological effects and spatial extent of large outbreaks over the last few hundreds of years. However, by using a paleoecological approach the record could be extended by centuries to millennia.…”