Abstract

www.PosterPresentations.co m The American Southwest is experiencing increased aridity and wildfire incidence, triggering conversion of some frequent-fire forests to non-forest. These dynamics are well-established in ponderosa pine forests, but we know far less about Madrean pine-oak forests in the Sky Islands of Mexico and USA. We have documented scarce pine regeneration and vigorous post-fire oak resprouting in these forests over 27 yrs. We investigated pine regeneration patterns in long-term plots during severe drought, 10 yrs after the Horseshoe 2 Megafire in the Chiricahua Mountains, AZ-a follow-up to a 5-yr assessment. Our goals were to (1) document changes in pine regeneration and (2) develop remote-sensing tools to identify pine refugia across landscapes. For (2), we tested whether two remotely-sensed predictors-Landsat NDVI & ECOSTRESS evapotranspiration-provided predictive power beyond indices of fire severity and topographic moisture. INTRODUCTION The reliability of projections and restoration under intensifying drought and wildfire depends on a fine-grained understanding of refugia for at-risk tree populations. Fire Severity: Landsat differenced Normalized Burn Ratio (dNBR; 30-m resolution): • NBR = (NIR-SWIR) / (NIR + SWIR), dNBR = Pre-fire NBR-Post-fire NBR Topography: • elevation • topo relative moisture index (TRMI) = aspect + position + % slope + surface shape Landsat Normalized Difference Vegetation Index (NDVI; 30-m resolution): • vegetation greenness: NDVI = (NIR-R) / (NIR+ R) ECOSTRESS evapotranspiration (70-m resolution): • land surface temperature + other inputs à Priestly-Taylor algorithm à ET • Conversion of pine-oak forest to oak shrublands continued 6-10 yrs post-fire. Few pine recruits were found in a matrix of dense, oak sprouts, especially after severe fire (FIG 1) • Fewer large pine seedlings in 2021 (a dry season of record aridity) than 2016 • P. leiophylla post-fire resprouts continue to survive and, unlike seedlings, are beginning to overtop the oak resprout canopy (FIG 2) CONCLUSIONS • Nearly three decades of conversion of pine-oak forest to oak shrublands after high-severity wildfire. • Post-fire resprouting, unusual in pines, may be a lifeline for P. leiophylla. • Remotely-sensed Landsat NDVI, combined with topography and fire severity, do a good job of predicting the locations of pine refugia. • ECOSTRESS ET does not help, likely due to larger, less stationary pixels than NDVI • Field data and models suggest P. engelmannii is more drought sensitive and at risk to climate change and wildfires than P. leiophylla. REFERENCES ACKNOWLEDGEMENTS