David R. Gray

Analysis and use of historical patterns of spruce budworm defoliation to forecast outbreak patterns in Quebec

Abstract Historical records of defoliation by spruce budworm in Quebec from 1965 to 1992 were analyzed to determine the degree of variability in the spatial and temporal patterns of defoliation. Approximately 80% of the provincial variation in the 28-year record could be described by 25 representative defoliation patterns after first removing the geographic trends in onset year of outbreak. The spatial distribution and probable host impact of these geo-referenced representative defoliation patterns are discussed. These patterns can be used in the context of forest protection and resource management decision-making, especially if they are incorporated into a decision support system with a geo-referenced database of stand characteristics and a stand growth model. Such a system can improve estimates of expected losses due to defoliation by spruce budworm and of the potential benefits of foliage protection. The spatial and temporal patterns of defoliation can be used also to investigate the influence of environmental conditions on the characteristics of budworm outbreaks. They also constitute a basis for the validation of spatial patterns predicted by epidemiological models of the insects population dynamics.

Fire regime zonation under current and future climate over eastern Canada

Fire is a major disturbance in Canadian forests. Along with fuel and ignition characteristics, climatic conditions are seen as one of the main drivers of fire regimes. Projected changes in climate are expected to significantly influence fire regimes in Canada. As fire regime greatly shapes large-scale patterns in biodiversity, carbon, and vegetation, as well as forest and fire management strategies, it becomes necessary to define regions where current and future fire regimes are homogeneous. Random Forests (RF) modeling was used to relate fire regime attributes prevailing between 1961 and 1990 in eastern Canada with climatic/fire-weather and environmental variables. Using climatic normals outputs from the Canadian Regional Climate Model (CRCM), we delineated current (1961-1990) and future (2011-2040, 2040-2070, 2071 2100) homogeneous fire regime (HFR) zones. Heterogeneous response of fire regime to climate changes is projected for eastern Canada with some areas (e.g., western Quebec) experiencing very small alterations while others (e.g., southeastern Ontario) are facing great shifts. Overall, models predicted a 2.2- and 2.4-fold increase in the number of fires and the annual area burned respectively mostly as a result of an increase in extreme fire-weather normals and mean drought code. As extreme fire danger would occur later in the fire season on average, the fire season would shift slightly later (5-20 days) in the summer for much of the study area while remaining relatively stable elsewhere. Although fire regime values would change significantly over time, most zone boundaries would remain relatively stable. The information resulting from HFR zonations is clearly of interest for forest and fire management agencies as it reveals zones with peculiar fire regimes that would have been hidden otherwise using predefined administrative or ecological stratifications.

Diapause in the gypsy moth: a model of inhibition and development.

We present here the first recorded age-specific estimates of the developmental response to temperature in diapausing gypsy moth, Lymantria dispar (L.). The effect of temperature on diapause development in gypsy moth eggs was examined by exposing individual eggs to temperature regimes of 5 degrees C interrupted by a single, brief exposure to an experimental temperature. Exposure to each of six experimental temperatures took place at six different times during diapause. The relative effect of the exposure on diapause development was estimated by comparing the duration of diapause in each of the treatments to the duration in a control treatment of constant 5 degrees C. The effect of each temperature did not remain constant throughout the diapause phase and the pattern of change was not uniform among the experimental temperatures. We propose a model of diapause where the developmental phase is controlled by two simultaneous temperature-dependent processes: a typical developmental response to temperature that is inhibited by a temperature-activated biochemical agent, and the temperature-dependent removal of the inhibiting agent. This simple model of two simultaneous and temperature-dependent processes explains 92% of the variability in diapause duration observed in the experimental regimes.

Hitchhikers on trade routes: A phenology model estimates the probabilities of gypsy moth introduction and establishment

As global trade increases so too does the probability of introduction of alien species to new locations. Estimating the probability of an alien species introduction and establishment following introduction is a necessary step in risk estimation (probability of an event times the consequences, in the currency of choice, of the event should it occur); risk estimation is a valuable tool for reducing the risk of biological invasion with limited resources. The Asian gypsy moth, Lymantria dispar (L.), is a pest species whose consequence of introduction and establishment in North America and New Zealand warrants over US

Age-Dependent Postdiapause Development in the Gypsy Moth (Lepidoptera: Lymantriidae) Life Stage Model

2 million per year in surveillance expenditure. This work describes the development of a two-dimensional phenology model (GLS-2d) that simulates insect development from source to destination and estimates: (1) the probability of introduction from the proportion of the source population that would achieve the next developmental stage at the destination and (2) the probability of establishment from the proportion of the introduced population that survives until a stable life cycle is reached at the destination. The effect of shipping schedule on the probabilities of introduction and establishment was examined by varying the departure date from 1 January to 25 December by weekly increments. The effect of port efficiency was examined by varying the length of time that invasion vectors (shipping containers and ship) were available for infection. The application of GLS-2d is demonstrated using three common marine trade routes (to Auckland, New Zealand, from Kobe, Japan, and to Vancouver, Canada, from Kobe and from Vladivostok, Russia).

Model-specification uncertainty in future forest pest outbreak.

ABSTRACT For the last ≈10 yr, the Gypsy Moth Life Stage (GLS) model has been used by pest managers to predict when important events in the gypsy moth, Lymantria dispar L., life cycle will occur (e.g., peak second larval instar population and male moth flight). Although the GLS model has been shown to outperform other gypsy moth phenology models, its predictions have not always been as accurate as desired. Differences between predicted and observed egg hatch phenology prompted a re-examination of the original experimental data that were used in the construction of the egg hatch submodels of the original GLS model, and a data processing error was discovered to have truncated the postdiapause experimental data. Analysis of the complete data set confirmed that developmental rates in the postdiapause phase were age and temperature dependent but that the developmental response to temperature is distinctly nonlinear at postdiapause initiation, in contrast to the indeterminate response previously reported. By incorporating the new estimates of developmental rate patterns and parameters into the GLS model, errors in the GLS-simulated egg hatch period were reduced by 33–71% and error in date of 50% cumulative egg hatch by 25–100%.

Risk analysis of the invasion pathway of the Asian gypsy moth: a known forest invader

Climate change will modify forest pest outbreak characteristics, although there are disagreements regarding the specifics of these changes. A large part of this variability may be attributed to model specifications. As a case study, we developed a consensus model predicting spruce budworm (SBW, Choristoneura fumiferana [Clem.]) outbreak duration using two different predictor data sets and six different correlative methods. The model was used to project outbreak duration and the uncertainty associated with using different data sets and correlative methods (=model-specification uncertainty) for 2011-2040, 2041-2070 and 2071-2100, according to three forcing scenarios (RCP 2.6, RCP 4.5 and RCP 8.5). The consensus model showed very high explanatory power and low bias. The model projected a more important northward shift and decrease in outbreak duration under the RCP 8.5 scenario. However, variation in single-model projections increases with time, making future projections highly uncertain. Notably, the magnitude of the shifts in northward expansion, overall outbreak duration and the patterns of outbreaks duration at the southern edge were highly variable according to the predictor data set and correlative method used. We also demonstrated that variation in forcing scenarios contributed only slightly to the uncertainty of model projections compared with the two sources of model-specification uncertainty. Our approach helped to quantify model-specification uncertainty in future forest pest outbreak characteristics. It may contribute to sounder decision-making by acknowledging the limits of the projections and help to identify areas where model-specification uncertainty is high. As such, we further stress that this uncertainty should be strongly considered when making forest management plans, notably by adopting adaptive management strategies so as to reduce future risks.

Climate change can reduce the risk of biological invasion by reducing propagule size

Abstract Risk is defined with many minor variations in the biological literature. Common to most definitions are the following elements: the probability of a future event; and the consequences of the event, usually with respect to some predefined human value. Risk analysis includes elements of risk assessment (quantification of risk), uncertainty (of the event and its consequences), risk management (reducing risk to an acceptable level), and development of policy to balance finite resources with uncertainty and risk tolerance. When biological invasion and its risk are jointly examined, it is common that the consequences of invasion are not explicitly quantified, but understood to be sufficiently negative that it must be minimized to the extent possible. Risk analysis then becomes quantification of the probabilities of an introduction (event) and that the introduction leads to establishment, and the uncertainty of those probabilities. I describe a risk analysis framework for the Asian gypsy moth—a known invader—in its pathway. The framework uses the available information regarding the transportation route of the vector (ships), and a phenology model that estimates vector contamination (propagule size), the probability of introduction, and the probability of initial establishment given an introduction. Reducing propagule pressure is arguably the most important factor in reducing biological invasion; propagule pressure can be reduced by inspection and sanitation of the pathway vector (e.g., ships, trucks, humans) at the point(s) of departure and at the point of entry. I demonstrate how the risk analysis framework can be used to more efficiently target incoming ships for inspection and propagule pressure reduction.

Future spruce budworm outbreak may create a carbon source in Eastern Canadian forests.

Climate change has been conclusively linked to species extinctions, and to expansion and contractions and shifts of species ranges. Climate change is exerting similarly profound pressures on the individual stages of biological invasion which can significantly impact the biodiversity and ecology of invaded areas. Propagule pressure is perhaps the single most important determinant of invasion success, but the effects of climate change on propagule pressure are still largely uncertain because we have few observations of introduction events (or their size) that can be analyzed together with climate records. The common surrogate variables for propagule pressure do not logically respond to climate. Here I use a process-based simulation model to examine the potential effects of climate change (specifically temperature) on propagule size of a common invading insect species by estimating in-transit survivorship rate of propagules using historical and future (projected) temperatures and two common trade routes between a donor and a recipient location (Yokohama, Japan and Sydney, Australia). Propagule size (=the number of individuals in an introduction event) was lower under climate change temperatures than under historical temperatures in both routes. The route had significant effects on propagule size through its influence on the duration (and also the timing) of exposure to temperature conditions that are of time-sensitive importance to the development of the invasive species. Under historical temperatures propagule size was higher and less variable in the direct than the indirect route in 20 independent iterations. Under the future temperatures propagule size was also higher in the direct route but it was more variable than in the indirect route. Increased trade is increasing the opportunities for introductions, but the results reported here suggest that climate change will have inconsistent effects on biological invasion because of the complex relationship between temperature and insect ontogeny.