The large forest fires in and around Yellowstone National Park in 1988 bring up many ecologial questions, including the role of bark beetles. Bark beetles may contribute to fuel buildup over the years preceding a fire, resulting in stand replacement fires. Fire is important to the survival of seral tree species and bark beetles that reproduce them. Without fire, seral species are ultimately replaced by climax species. Following fire, bark-and wood-boring beetles respond to fire-injured trees. Because of synchrony of the fires and life cycles of the beetles, beetle infestation in 1988 was not observed in fire-injured trees. However, endemic populations of beetles, upon emergence in 1989, infested large numbers of fire-injured trees. Of the trees examined in each species, 28 to 65 percent were infested by bark beetles: Pinus contorta (28 percent by Ips pini: Pseudotsuga menziesii (32 percent) by Dendroctonus pseudotsugae; Picea engelmannii (65 percent) by Dendroctonus rufipennis; and Abies lasiocarpa (35 percent) by Buprestidae and Cerambycidae. Most trees infested by bark beetles had 50 percent or more of their basal circumference killed by fire. Bark beetle populations probably will increase in the remaining fire-injured trees.

This book is a printed edition of the Special Issue "Wildland Fire, Forest Dynamics, and Their Interactions" that was published in Forests

Consequences of bark beetle outbreaks for forest wildfire potential are receiving heightened attention, but little research has considered ecosystems with mixed-severity fire regimes. Such forests are widespread, variable in stand structure, and often fuel limited, suggesting that beetle outbreaks could substantially alter fire potentials. We studied canopy and surface fuels in interior Douglas-fir (Pseudotsuga menziesii v. glauca) forests in Greater Yellowstone, Wyoming, USA, to determine how fuel characteristics varied with time since outbreak of the Douglas-fir beetle (Dendroctonus pseudotsugae). We sampled five stands in each of four outbreak stages, validated for pre-outbreak similarity: green (undisturbed), red (1?3 yr), gray (4?14 yr), and silver (25?30 yr). General linear models were used to compare variation in fuel profiles associated with outbreak to variation associated with the range of stand structures (dense mesic forest to open xeric parkland) characteristic of interior Douglas-fir forest. Beetle outbreak killed 38?83% of basal area within stands, generating a mix of live trees and snags over several years. Canopy fuel load and bulk density began declining in the red stage via needle drop and decreased by 50% by the silver stage. The dead portion of available canopy fuels peaked in the red stage at 41%. After accounting for background variation, there was little effect of beetle outbreak on surface fuels, with differences mainly in herbaceous biomass (50% greater in red stands) and coarse woody fuels (doubled in silver stands). Within-stand spatial heterogeneity of fuels increased with time since outbreak, and surface-to-crown continuity decreased and remained low because of slow/sparse regeneration. Collectively, results suggest reduced fire potentials in post-outbreak stands, particularly for crown fire after the red stage, although abundant coarse fuels in silver stands may increase burn residence time and heat release. Outbreak effects on fuels were comparable to background variation in stand structure. The net effect of beetle outbreak was to shift the structure of mesic closed-canopy stands toward that of parklands, and to shift xeric parklands toward very sparse woodlands. This study highlights the importance of evaluating outbreak effects in the context of the wide structural variation inherent to many forest types in the absence of beetle disturbance.

"The compilation of papers in this proceedings is based on a symposium sponsored by the Insect and Diseases Working Group (D5) at the 2007 Society of American Foresters (SAF) convention in Portland, Oregon. The selection of topics parallels the research priorities of the Western Bark Beetle Research Group (WBBRG) (USDA Forest Service, Research and Development), which had been recently formed at the time of the symposium. Reflecting a unique partnership within the Forest Service, each paper was jointly prepared by a research scientist with the WBBRG and one or more entomologists with Forest Health Protection (USDA Forest Service, State and Private Forestry). Among these papers is a description of the currently elevated impacts of bark beetles in the Western United States; descriptions of the current state of knowledge of bark beetle response to vegetation management and also to climate change; discussions of the complex interactions of bark beetles and fire and of the complex ecological and socioeconomic impacts of infestations; an overview of the use of semiochemical (behavioral chemicals)-based technology for conifer protection; and a case study exemplifying efforts to assess risks posed by nonnative invasive bark beetles." --