Emissions of BVOC from lodgepole pine in response to mountain pine beetle attack in high and low mortality forest stands

T R Duhl,S Ferrenberg,E Pendall,A Guenther,D Gochis

doi:10.5194/bg-10-483-2013

Abstract

Abstract. In this screening study, biogenic volatile organic compound (BVOC) emissions from intact branches of lodgepole pine (Pinus contorta) trees were measured from trees at two forested sites that have been impacted differently by the mountain pine beetle (MPB), with one having higher mortality and the other with lower mortality. Differences in the amounts and chemical diversity of BVOC between the two sites and from apparently healthy trees versus trees in different stages of MPB attack are presented, as well as (for one site) observed seasonal variability in emissions. A brief comparison is made of geological and climatic characteristics as well as prior disturbances (both natural and man-made) at each site. Trees sampled at the site experiencing high MPB-related tree mortality had lower chemodiversity in terms of monoterpene (MT) emission profiles, while profiles were more diverse at the lower-mortality site. Also at the higher-mortality site, MPB-infested trees in various stages of decline had lower emissions of sesquiterpenes (SQTs) compared to healthy trees, while at the site with lower mortality, MPB-survivors had significantly higher SQT emissions during part of the growing season when compared to both uninfested and newly infested trees. SQT profiles differed between the two sites and, like monoterpene and oxygenated VOC profiles, varied through the season. For the low-mortality site in which repeated measurements were made over the course of the early summer–late fall, higher chemical diversity was observed in early- compared to late-season measurements for all compound classes investigated (MT, oxygenated VOC, and SQT), with the amount of change appearing to correlate to the MPB status of the trees studied. Emissions of 2-methyl-3-buten-2-ol (MBO) had a distinct seasonal signal but were not much different between healthy or infested trees, except in trees with dead needles, from which emissions of this compound were negligible, and in late-season MPB survivors, in which they were higher than in newly infested or uninfested trees. Emissions of SQT were significantly higher in the MPB survivors during both mid- and late-season sampling at the low-mortality site. The changes in emissions could have implications for regional air quality and climate through changes in ozone and aerosol distributions, although this study was designed as a preliminary screening effort and not enough individuals were sampled for all of the observed differences to be statistically demonstrated. Despite this, the compelling differences in emissions observed between the sites and individual trees with differing MPB-infestation statuses and the potential impacts these have on regional atmospheric chemistry argue for further research in this topic.

Highlights

The vast pine forests of western North America have recently been the stage for an unprecedented epidemic of mountain pine beetle (MPB; Dendroctonus ponderosae) infestation, with the latitudinal extent of the attack spanning from Canada to Mexico and extending westward from Nebraska to the Pacific coast
This screening study highlights differences in the chemical diversity of emissions from lodgepole pines in two forest sites impacted differently by the MPB, and presents the seasonal variation observed in biogenic volatile organic compound (BVOC) emissions from apparently healthy trees versus trees in different stages of MPB attack
Whether the relatively high degree of variability in monoterpene profiles observed in lodgepole pine trees growing at the Mountain Research Station (MRS) site is related to the MPB resistance observed there remains uncertain

Summary

Introduction

The vast pine forests of western North America have recently been the stage for an unprecedented epidemic of mountain pine beetle (MPB; Dendroctonus ponderosae) infestation, with the latitudinal extent of the attack spanning from Canada to Mexico and extending westward from Nebraska to the Pacific coast. Warmer temperatures experienced in recent decades over much of the region have resulted in fewer beetle kill events, which usually occur during early and late freezes, as it is during these times when the insects are in their most vulnerable developmental stages (Raffa et al, 2008; Robbins, 2010). Milder temperatures have created longer growing seasons, which may have allowed more than one generation of MPB to propagate each year (Mitton and Ferrenberg, 2012). Mature forests are known to be more vulnerable to MPB, while varying forest management strategies (clearcutting, thinning, fire suppression, etc.) may heighten vulnerabilities (e.g., Pendall et al, 2010; USDA Forest Service, 2011)

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