Analytic Approximation of Invasion Wave Amplitude Predicts Severity of Insect Outbreaks

Outbreaks of phytophagous forest insects are largely driven by host demographics and spatial effects of dispersal. We develop a structured integrodifference equation (IDE) outbreak model that tracks the demographics of sedentary hosts under insect infestation pressure. The model is appropriate for a spectrum of pests attacking the later age classes of long-lived hosts, including mountain pine beetle (MPB), spruce budworm, and spruce beetle, which, among them are responsible for more forest damage than fire. The model generates a train of periodic waves of infestation. We approximate the IDE with a partial differential equation and search for traveling wave solutions. The resulting ordinary differential equation predicts the shape of an outbreak wave profile and peak infestation as functions of wavefront speed, which can be calculated analytically. This culminates in the derivation of an explicit approximation of invasion wave amplitude based on net reproductive rate of the infesting insect and its host searching efficiency. Results are compared with observations taken during a recent MPB outbreak in the northern US Rocky Mountains

A Spatiotemporal Mountain Pine Beetle Outbreak Model Predicting Severity, Cycle Period, and Invasion Speed

The mountain pine beetle (MPB, Dendroctonus ponderosae), a tree-killing bark beetle, has historically been part of the normal disturbance regime in lodgepole pine (Pinus contorta) forests. In recent years, warm winters and summers have allowed MPB populations to achieve synchronous emergence and successful attacks, resulting in widespread population outbreaks and resultant tree mortality across western North America. We develop an age-structured forest demographic model that incorporates temperature-dependent MPB infestations: the Susceptible-Infested-Juvenile (SIJ) model. Stability of fixed points is analyzed as a function of population growth rates, and indicates the existence of periodic outbreaks that intensify as growth rates increase. We devise analytical methods to predict outbreak severity and duration as well as outbreak return time. To assess the vulnerability of natural resources to climate change, we develop a thermally-driven mechanistic model to predict MPB population growth rates using a distributional model of beetle phenology in conjunction with criteria for successful tree colonization. The model uses projected daily minimum and maximum temperatures for the years 2025 to 2085 generated by three separate global climate models. Growth rates are calculated each year for an area defined by latitude range 42° N to 49° N and longitude range 108° W to 117° W on a Cartesian grid of approximately 4km resolution. Using these growth rates, we analyze how the optimal thermal window for beetle development is changing with respect to elevation as a result of climate change induced warming. We also use our combined model to evaluate if thermal regimes exist that would promote life cycle bivoltinism and discuss how yearly growth rates would change as a result. Outbreaks of MPB are largely driven by host tree stand demographics and spatial effects of beetle dispersal. We augment the SIJ model to account for the spatial effects of MPB dispersal throughout a forest landscape by coupling it with a Gaussian redistribution kernel. The new model generates a train of sustained solitary waves of infestation that move through a forest with constant speed. We convert the resulting integrodifference equation into a partial differential equation and search for travelling wave solutions. The resulting differential equation provides predictions of the shape of an outbreak wave profile and of peak infestation as functions of wave speed, which can be calculated analytically. These results culminate in the derivation of an explicit formula for predicting the severity of an outbreak based on the net reproductive rate of MPB and host searching efficiency

Synthesis and Assessment Product

This document is a part of the Synthesis and Assessment Products described in the U.S. Climate Change Science Program Strategic Plan. The report describes how climate affects the design, construction, safety, operations, and maintenance of transportation infrastructure and systems. The prospect of a changing climate raises critical questions regarding how alterations in temperature, precipitation, storm events, and other aspects of the climate could affect the nation's roads, airports, rail, transit systems, pipelines, ports, and waterways. Phase I of this regional assessment of climate change and its potential impacts on transportation systems addresses these questions for the region of the U.S. central Gulf Coast between Galveston, Texas and Mobile, Alabama

Scientific Assessment of Climate Change and Its Effects in Maine

Climate change has already made its presence known in Maine, from shorter winters and warmer summers with ocean heat waves, to stronger storms, new species showing up in our backyards and the Gulf of Maine, aquatic algal blooms, acidic ocean waters that affect shellfish, and new pests and diseases that harm our iconic forests and fisheries. The health of Maine people is also being affected by climate change, from high heat index days driving increased emergency room visits to the ravages of Lyme and other vector-borne diseases. And our economy is feeling the effects, too — with farmers trying to adapt to longer growing seasons but dealing with severe storms and late frosts, aquaculturists already adapting to a more acidic ocean, and winter sports like skiing and snowmobiling being impacted by our shrinking winter season. This is the first report from the Maine Climate Council’s Scientific and Technical Subcommittee, produced by more than 50 scientists from around the State representing Scientific and Technical Subcommittee members, other co-authors, and contributors. This report is part of the 2020 Maine Climate Action Plan. The report summarizes how climate change has already impacted Maine and how it might continue affecting our State in the future

Scientific Assessment of Climate Change and Its Effects in Maine

Climate change has already made its presence known in Maine, from shorter winters and warmer summers with ocean heat waves, to stronger storms, new species showing up in our backyards and the Gulf of Maine, aquatic algal blooms, acidic ocean waters that affect shellfish, and new pests and diseases that harm our iconic forests and fisheries. The health of Maine people is also being affected by climate change, from high heat index days driving increased emergency room visits to the ravages of Lyme and other vector-borne diseases. And our economy is feeling the effects, too -with farmers trying to adapt to longer growing seasons but dealing with severe storms and late frosts, aquaculturists already adapting to a more acidic ocean, and winter sports like skiing and snowmobiling being impacted by our shrinking winter season. This is the first report from the Maine Climate Council’s Scientific and Technical Subcommittee, produced by more than 50 scientists from around the State representing Scientific and Technical Subcommittee members, other co-authors, and contributors. This report is part of the 2020 Maine Climate Action Plan. The report summarizes how climate change has already impacted Maine and how it might continue affecting our State in the future. The findings from this report inform the ongoing deliberations of the Maine Climate Council and have aided the Maine Climate Council’s six working groups in the development of draft strategies to address climate change by reducing Maine’s greenhouse gas emissions. In addition, the Scientific and Technical Subcommittee identified critical scientific information gaps and needs to better understand and forecast potential future climate change impacts in the State. Key take-aways from this report are listed below, with the full details appearing in each of the twelve chapters