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

Aim: Drastic changes in fire regimes are altering plant communities, inspiring ecologists to better understand the relationship between fire and plant species diversity. We examined the impact of a 2011 megafire on woody plant species diversity in an arid mountain range in southern Arizona, USA. We tested recent fire-diversity hypotheses by addressing the impact of the fire severity, fire variability, historic fire regimes, and topography on diversity. Location: Chiricahua National Monument, Chiricahua Mountains, Arizona. USA., part of the Sky Islands of the US-Mexico borderlands. Taxon: Woody plant species. Methods: We sampled woody plant diversity in 138 plots before (2002-2003) and after (2017-2018) the 2011 Horseshoe Two Megafire in three vegetation types and across fire severity and topographic gradients. We calculated gamma, beta, and alpha diversity and examined changes over time in burned vs. unburned plots and the shapes of the relationships of diversity with fire severity and topography. Results: Alpha species richness declined and beta and gamma diversity increased in burned but not unburned plots. Fire-induced enhancement of gamma diversity was confined to low fire severity plots. Alpha diversity did not exhibit a clear continuous relationship with fire severity. Beta diversity was enhanced by fire severity variation among plots and increased with fire severity up to very high diversity, where it declined slightly. Main Conclusions: The results reject the intermediate disturbance hypothesis for alpha diversity but weakly support it for gamma diversity. Spatial variation in fire severity promoted variation among plant assemblages, supporting the pyrodiversity hypothesis. Long-term drought probably amplified fire-driven diversity changes. Despite the apparent benign impact of the fire on diversity, the replacement of two large conifer species with shrubs signals the potential loss of functional diversity, emphasizing the importance of intervention to direct the transition to a novel vegetation mosaic.