Integrating plant physiology into simulation of fire behavior and effects.

Wildfires are a global crisis, but current fire models fail to capture vegetation response to changing climate. With drought and elevated temperature increasing the importance of vegetation dynamics to fire behavior, and the advent of next generation models capable of capturing increasingly complex physical processes, we provide a renewed focus on representation of woody vegetation in fire models. Currently, the most advanced representations of fire behavior and biophysical fire effects are found in distinct classes of fine-scale models and do not capture variation in live fuel (i.e. living plant) properties. We demonstrate that plant water and carbon dynamics, which influence combustion and heat transfer into the plant and often dictate plant survival, provide the mechanistic linkage between fire behavior and effects. Our conceptual framework linking remotely sensed estimates of plant water and carbon to fine-scale models of fire behavior and effects could be a critical first step toward improving the fidelity of the coarse scale models that are now relied upon for global fire forecasting. This process-based approach will be essential to capturing the influence of physiological responses to drought and warming on live fuel conditions, strengthening the science needed to guide fire managers in an uncertain future.

Warming increased bark beetle-induced tree mortality by 30% during an extreme drought in California.

Quantifying the responses of forest disturbances to climate warming is critical to our understanding of carbon cycles and energy balances of the Earth system. The impact of warming on bark beetle outbreaks is complex as multiple drivers of these events may respond differently to warming. Using a novel model of bark beetle biology and host tree interactions, we assessed how contemporary warming affected western pine beetle (Dendroctonus brevicomis) populations and mortality of its host, ponderosa pine (Pinus ponderosa), during an extreme drought in the Sierra Nevada, California, United States. When compared with the field data, our model captured the western pine beetle flight timing and rates of ponderosa pine mortality observed during the drought. In assessing the influence of temperature on western pine beetles, we found that contemporary warming increased the development rate of the western pine beetle and decreased the overwinter mortality rate of western pine beetle larvae leading to increased population growth during periods of lowered tree defense. We attribute a 29.9% (95% CI: 29.4%-30.2%) increase in ponderosa pine mortality during drought directly to increases in western pine beetle voltinism (i.e., associated with increased development rates of western pine beetle) and, to a much lesser extent, reductions in overwintering mortality. These findings, along with other studies, suggest each degree (°C) increase in temperature may have increased the number of ponderosa pine killed by upwards of 35%-40% °C-1 if the effects of compromised tree defenses (15%-20%) and increased western pine beetle populations (20%) are additive. Due to the warming ability to considerably increase mortality through the mechanism of bark beetle populations, models need to consider climate's influence on both host tree stress and the bark beetle population dynamics when determining future levels of tree mortality.

Forecasting the influence of conservation strategies on landscape connectivity.

Maintaining and enhancing landscape connectivity reduces biodiversity declines due to habitat fragmentation. Uncertainty remains, however, about the effectiveness of conservation for enhancing connectivity for multiple species on dynamic landscapes, especially over long time horizons. We forecasted landscape connectivity from 2020 to 2100 under four common conservation land-acquisition strategies: acquiring the lowest cost land, acquiring land clustered around already established conservation areas, acquiring land with high geodiversity characteristics, and acquiring land opportunistically. We used graph theoretic metrics to quantify landscape connectivity across these four strategies, evaluating connectivity for four ecologically relevant species guilds that represent endpoints along a spectrum of vagility and habitat specificity: long- versus short-distance dispersal ability and habitat specialists versus generalists. We applied our method to central North Carolina and incorporated landscape dynamics, including forest growth, succession, disturbance, and management. Landscape connectivity improved for specialist species under all conservation strategies employed, although increases were highly variable across strategies. For generalist species, connectivity improvements were negligible. Overall, clustering the development of new protected areas around land already designated for conservation yielded the largest improvements in connectivity; increases were several orders of magnitude beyond current landscape connectivity for long- and short-distance dispersing specialist species. Conserving the lowest cost land contributed the least to connectivity. Our approach provides insight into the connectivity contributions of a suite of conservation alternatives prior to on-the-ground implementation and, therefore, can inform connectivity planning to maximize conservation benefit.

Pronóstico de la Influencia de las Estrategias de Conservación sobre la Conectividad del Paisaje Resumen El mantenimiento y la mejora de la conectividad de paisaje reduce las declinaciones de biodiversidad causadas por la fragmentación del hábitat. Sin embargo, todavía existe incertidumbre sobre lo efectiva que es la conservación para la mejora de la conectividad para múltiples especies en paisajes dinámicos, especialmente durante periodos largos. Pronosticamos la conectividad de paisaje desde el 2020 hasta el 2100 bajo cuatro estrategias comunes de adquisición de tierras para conservación: adquisición de las tierras más baratas, adquisición de conjuntos de tierras adyacentes a áreas de conservación ya establecidas, adquisición de tierras con una gran diversidad de características geográficas, y adquisición oportunista de tierras. Después usamos medidas de teoría de grafos para cuantificar la conectividad de paisaje en estas cuatro estrategias y para evaluar la conectividad de cuatro gremios de especies con relevancia ecológica que representan los puntos finales en un espectro de movilidad y especificidad de hábitat: habilidad de dispersión de distancia corta versus larga y especialistas versus generalistas de hábitat. Aplicamos nuestro método en el centro de Carolina del Norte e incorporamos las dinámicas de paisaje, incluyendo el crecimiento, sucesión, alteración y gestión forestales. La conectividad del paisaje mejoró para las especies especialistas bajo todas las estrategias de conservación que se usaron, aunque los incrementos fueron muy variables según la estrategia. Para las especies generalistas, las mejoras en la conectividad fueron insignificantes. En general, agrupar al desarrollo de nuevas áreas protegidas alrededor de tierras ya designadas a la conservación produjo la mayor cantidad de mejoras en la conectividad; los incrementos estuvieron varias magnitudes más allá de la conectividad actual del paisaje para las especies especialistas con dispersión de corta y larga distancia. La conservación de las tierras más baratas contribuyó a la menor conectividad. Nuestra estrategia proporciona información sobre las contribuciones de conectividad de un conjunto de alternativas de conservación previas la implementación in situ y por lo tanto puede servir para orientar la planeación y maximizar el beneficio de conservación.