Fire deficits have increased drought sensitivity in dry conifer forests: Fire frequency and tree‐ring carbon isotope evidence from Central Oregon

• DOI: 10.1111/gcb.14543
• Publication Date: 2018-12-10T04:28:44Z
• Authors: Steven L. Voelker; Andrew G. Merschel; Frederick C. Meinzer; Danielle E. M. Ul...; Thomas A. Spies; Christopher J. Still
• Keywords: Basal area; Thinning

A century of fire suppression across the Western United States has led to more crowded forests and increased competition for resources. Studies forest thinning or stand conditions after mortality events have provided indirect evidence how can promote drought stress predispose severe and/or bark beetle outbreaks. Here, we demonstrate linkages between deficits increasing through analyses annually resolved tree-ring growth, scars, carbon isotope discrimination (Δ13 C) a dry mixed-conifer landscape. Fire study area sensitivity leaf gas exchange over past >100 years. Since 1910, basal in these than doubled fire-return intervals from 25 140 Meanwhile, portion interannual variation Δ13 C explained by Palmer Drought Severity Index ca. 300-500-year-old Pinus ponderosa as well fire-intolerant, 90-190-year-old Abies grandis. stands with ≥25 m2 /ha indicated negative temporal trends, whereas ≤25 due frequent intense wildfire activity decades beforehand, were initially buffered benefited rising ambient dioxide concentrations, [CO2 ], demonstrated positive trends. Furthermore, average response all P. since 1830 indicates that photosynthetic assimilation rates stomatal conductance been reduced ~10% ~20%, respectively, compared expected trends ]. Although disturbance legacies contribute local-scale intensity stress, resistance made them susceptible challenges pests pathogens other disturbances.