An outbreak of the Douglas-fir tussock moth, Orgyia pseudotsugata McDunnough, occurred in the South Platte River drainage on the Pike-San Isabel National Forest in the Colorado Front Range attacking Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco. Stocking levels, species composition, and tree size in heavily and lightly defoliated stands were similar. Douglas-fir tussock moth defoliation resulted in significant Douglas-fir mortality in the heavily defoliated stands, leading to a change in dominance to ponderosa pine, Pinus ponderosa Lawson. Douglas-fir beetle, Dendroctonus pseudotsuqae Hopkins, populations increased following the defoliation event but caused less mortality, and did not differ between heavily and lightly defoliated stands. Douglas-fir tussock moth-related mortality was greatest in trees less than 15 cm dbh (diameter at 1.4 m above the ground) that grew in suppressed and intermediate canopy positions. Douglas-fir beetle-related mortality was greatest in trees larger than 15 cm dbh that grew in the dominant and co-dominant crown positions. Although both insects utilize Douglas-fir as its primary host, stand response to infestation is different. The extensive outbreak of the Douglas-fir tussock moth followed by Douglas-fir beetle activity may be associated with a legacy of increased host type growing in overstocked conditions as a result of fire exclusion.

Multiple high-severity insect outbreaks and wildfires dramatically altered the character of the Pinaleño high-elevation forests with notable impacts on ecosystem services. The Pinaleños are a small mountain range positioned close to large population centers, but not so close that any large industry is dependent on their resources, so regional and local impacts of the insect outbreaks to provisional resources were minor. There were qualitative impacts to cultural services, particularly to recreation, but no documented economic impacts. Effects on carbon and fuels were significant, but affected firefighting operations more than wildfire severity. The Pinaleños are positioned in an area of high biodiversity, and impacts on habitats of unique species were sometimes positive but also sometimes severely negative, especially on a relict population of Engelmann spruce and the critically endangered Mount Graham red squirrel. The Pinaleño situation illustrates how ecological disturbances can have a minor immediate economic impact but severe impacts on ecosystems and ecosystem services.

Nepytia janetae is a previously innocuous non-eruptive species that has recently incurred multiple devastating outbreaks in the American Southwest. We report information on the life cycle, biology, and impact of this species learned during the first 3 known outbreaks in spruce-fir and mixed-conifer forests of the Pinaleño Mountains and White Mountains of Arizona and the Sacramento Mountains of New Mexico. N. janetae is a univoltine, autumn- and winter-feeding wasteful defoliator with 3-yr eruptive outbreaks. Outbreaks terminate with parasitism, viral infection, starvation, and in one outbreak with heavy rainfall during egg deposition. Conifer mortality varied between outbreaks but approached 100% in some stands in all three study areas. Only severely defoliated trees died. Mortality was associated with defoliation severity, moisture availability in the last growing season of the outbreak and/or in the first post-outbreak growing season, and bark beetle activity. Other site and stand variables associated with defoliation and mortality varied between outbreaks, highlighting the need to evaluate multiple outbreaks before identifying factors related to susceptibility and vulnerability to a new pest species. The emergence of this insect as a serious pest is probably related to warming climate but the mechanisms are unclear; the only consistent pattern is an association with low or early loss of snowpack in either the year immediately preceding or the first year of the outbreaks. Differences in host specificity and larval coloration between the distant mountain ranges indicate that N. janetae may be a complex of multiple species or subspecies.