RESUMEN
The American Southwest is experiencing drastic increases in aridity and wildfire incidence, triggering conversion of some frequent surface forests to non-forest. Extensive research has focused on these dynamics in regional ponderosa pine forests, but we know much less about Madrean pine-oak forests, which are broadly distributed from the Sierra Madre in Mexico to the Sky Island mountain ranges in the U.S. Increased fire incidence and drought in these forests are limiting pine regeneration and driving conversion of biodiverse forests to oak shrublands. We investigated regeneration patterns in Pinus engelmannii and P. leiophylla during severe drought 10 years after the Horseshoe Two Megafire in the Chiricahua Mountains, Arizona-a follow-up to an assessment five years post-fire. In long-term plots, we examined changes in pine seedling and resprout recruitment. Past research demonstrated that topography and fire severity influenced pine recruitment across environmental gradients. We investigated here whether Landsat-8 normalized difference vegetation index (NDVI) and evapotranspiration estimated by the ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) added explanatory value to our understanding of these patterns. Conversion of Madrean pine-oak forest to oak shrublands continued 6-10 years post-fire. A dense, low oak canopy continued to coalesce in sites subject to severe fire. The importance of resprouts in P. leiophylla regeneration accelerated because these plants outgrew competing oak resprouts. Topography and fire severity (dNBR) were important predictors of 2021 patterns of pine recruitment. NDVI added explanatory value to these models, suggesting its potential in tracking forest dynamics. Evapotranspiration did not add value, likely because ECOSTRESS' larger pixel sizes and moving pixel locations created excessive subpixel heterogeneity in this highly dissected landscape. These models suggest that P. engelmannii is more drought sensitive, was more negatively affected by drought and fire, and is more at risk to shifts in climate and wildfires than P. leiophylla.
Asunto(s)
Monitoreo del Ambiente , Incendios , Pinus , Tecnología de Sensores Remotos , Ecosistema , Bosques , Pinus/crecimiento & desarrollo , Monitoreo del Ambiente/métodosRESUMEN
Much of the western United States is experiencing longer fire seasons with an increased frequency of high-severity fires and fire risk. Fire managers in the southwestern United States have increased efforts to reduce fire risk by managing more fires to meet resource objectives (e.g. thin forests, reduce hazardous fuel loads, and restore the landscape). However, little is known about the situational circumstances and decision space that inform the strategic response to wildland fire. Using generalized and time-to-event modeling techniques, we examined how fire management decisions are reached in a context informed by weather, burning conditions, and subsequent fire behavior. Modeling results captured daily containment probabilities along a gradient from limiting natural conditions to suppression invoked containment. Results inform fire management decisions, future research efforts, and the simulation of wildland fires with resource objectives.