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A mountain pine beetle (Dendroctonus ponderosae Hopkins) epidemic has caused widespread mortality of lodge-pole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) trees across western North America,. We characterized the initial effects of beetle-induced mortality on forest structure and composition in Rocky Mountain National Park, Colorado. In 2008, we surveyed stand structure and tree species composition across lodgepole pine dominated forests in the western portion of the Park. We defined five lodgepole pine forest types to describe variability in pre-epidemic forest conditions. This forested landscape appears to be resilient to the effects of the beetle. Surviving trees, including both canopy trees and saplings, were plentiful in most of the post-epidemic forests, even after accounting for anticipated future mortality. Subalpine fir (Abies lasiocarpa (Hook.) Nutt.), Engelmann spruce (Picea engelmannii Parry ex Engelm.), and aspen (Populus tremu-loides Michx.) had modestly higher relative abundances after the epidemic. Lodgepole pine remained the dominant species on approximately 85% of the landscape. The impact of the outbreak on forest structure and composition varied considerably among the five forest types, suggesting that post-epidemic forest developmental trajectories will vary according to pre-outbreak stand characteristics. Active management efforts to regenerate lodgepole pine forests, e.g., tree planting, will likely not be necessary on this landscape. Resume: Une epidemie de dendroctone du pin ponderosa (Dendroctonus ponderosae Hopkins) a cause beaucoup de mortalite chez le pin tordu latifolie (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) partout dans l'ouest de l'Amerique du nord. Nous avons caracterise les premiers effets de la mortalite causee par le dendroctone sur la structure et la composition de la foret dans le parc national des Montagnes Rocheuses, Colorado. En 2008, nous avons inventorie la structure et la composition en especes d'arbres des peuplements parmi les forets dominees par le pin tordu dans la partie ouest du parc. Nous avons defini cinq types de forets de pin tordu pour decrire la variabilite de la foret qui existait avant l'epidemie. Ce paysage forestier semble resilient aux effets du dendroctone. Les arbres qui ont survecu, incluant des arbres dominants et des gaules, etaient nombreux dans la plupart des forets apres l'epidemie, meme en tenant compte de la mortalite anticipee. Le sapin subalpin (Abies lasiocarpa (Hook.) Nutt.), l'epinette d'Engelmann (Picea engelmannii Parry ex Engelm.) et le peuplier faux-tremble (Populus tremuloides Michx.) avaient une abondance relative legerement plus elevee apres l'epidemie. Le pin tordu demeurait l'espece dominante dans environ 85% du paysage. L'impact de l'epidemie sur la composition et la structure de la foret variait considerablement parmi les cinq types forestiers, ce qui indique que la trajectoire du developpement de la foret apres une epidemie variera en fonction des caracteristiques du peuplement avant une epidemie. Des efforts soutenus d'amenagement pour regenerer les forets de pin tordu, tels que la plantation d'arbres, ne seront probablement pas neces-saires dans ce paysage. [Traduit par la Redaction], Introduction A severe mountain pine beetle (Dendroctonus ponderosae Hopkins) epidemic has severely impacted subalpine forests across much of western North America during the last decade. This recent beetle outbreak has [...]

Warmer temperatures are expected to increase the incidence of Lyme disease through enhanced tick maturation rates and a longer season of transmission. In addition, there could be an increased risk of disease export because of infected mobile hosts, usually birds. A temperature-driven seasonal model of Borrelia burgdorferi (Lyme disease) transmission among four host types is constructed as a system of nonlinear ordinary differential equations. The model is developed and parametrized based on a collection of lab and field studies. The model is shown to produce biologically reasonable results for both the tick vector (Ixodes scapularis) and the hosts when compared to a different set of studies. The model is used to predict the response of Lyme disease risk to a mean annual temperature increase, based on current temperature cycles in Hanover, NH. Many of the risk measures suggested by the literature are shown to change with increased mean annual temperature. The most straightforward measure of disease risk is the abundance of infected questing ticks, averaged over a year. Compared to this measure, which is difficult and resource-intensive to track in the field, all other risk measures considered underestimate the rise of risk with rise in mean annual temperature. The measure coming closest was "degree days above zero." Disease prevalence in ticks and hosts showed less increase with rising temperature. Single field measurements at the height of transmission season did not show much change at all with rising temperature. [ABSTRACT FROM AUTHOR]