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Limits to ponderosa pine regeneration following large high-severity forest fires in the United States Southwest

August 1, 2018

High-severity fires in dry conifer forests of the United States Southwest have created large (>1000 ha) treeless areas that are unprecedented in the regional historical record. These fires have reset extensive portions of Southwestern ponderosa pine (Pinus ponderosa Lawson & C. Lawson var. scopulorum Engelm.) forest landscapes. At least two recovery options following high-severity fire are emerging. One option is for post-fire successional pathways to move toward a return to the pre-fire forest type. Alternatively, an area may transition to persistent non-forested ecosystems. We studied regeneration patterns of ponderosa pine following eight fires in Arizona and New Mexico, USA, that burned in dry conifer forests dominated by ponderosa pine during a recent 18-year regional drought period, 1996 to 2013. Our a priori hypotheses were: 1) the most xeric areas within these severely burned dry conifer forests are least likely to regenerate to the pre-fire forest type due to persistent post-fire moisture stress; and 2) areas farther away from conifer seed sources have a lower likelihood of regeneration, even if these areas are climatically favorable for post-fire ponderosa pine establishment. We evaluated our hypotheses using empirical data and generalized linear mixed-effects models. We found that low-elevation, xeric sites are more limiting to conifer regeneration than higher-elevation mesic sites. Areas >150 m from a seed source are much less likely to have ponderosa pine regeneration. Spatial interpolations of modeled post-fire regeneration of ponderosa pine across the study landscapes indicate expansive areas with low likelihood of pine regeneration following high-severity fire. We discuss multiple post-fire successional pathways following high-severity fire, including potentially stable transitions to non-forest vegetation types that may represent long-term type conversions. These findings regarding landscape changes in Southwest forests in response to fires and post-fire regeneration patterns during early-stage climate warming contribute to the development of better-informed ecosystem management strategies for forest adaptation or mitigation under projected hotter droughts in this region.

Publication Year 2018
Title Limits to ponderosa pine regeneration following large high-severity forest fires in the United States Southwest
DOI 10.4996/fireecology.140114316
Authors Collin Haffey, Thomas D. Sisk, Craig D. Allen, Andrea E. Thode, Ellis Margolis
Publication Type Article
Publication Subtype Journal Article
Series Title Fire Ecology
Index ID 70198515
Record Source USGS Publications Warehouse
USGS Organization Fort Collins Science Center