Long-term empirical evidence shows post-disturbance climate controls post-fire regeneration

Abstract

Increased wildfire activity and climate change have intensified disturbance regimes globally and have raised concern among scientists and land managers about the resilience of disturbed landscapes. Here we test the effects of climate, topographic variation and pre-fire stand structure on regeneration in lodgepole pine (Pinus contorta var. latifolia) forests following high-severity fire over the past seven decades. We surveyed lodgepole pine regeneration 8–67 years after eight high-severity fires in western Colorado and southern Wyoming. We used dendroecological methods and machine learning to (a) identify temporal trends in post-fire regeneration and (b) examine influences of climate on post-fire regeneration, with focus on post-fire establishment, initial post-fire density and radial growth. All burned sites reached a median stocking density of ≥150 seedlings/ ha, but there was a large range of spatial heterogeneity, with regeneration being absent or scarce in many plots, implying a trend of increasing patchiness with likely cascading effects on subsequent patterns and processes. Our analysis indicated that (a) post-fire regeneration is influenced by pre-fire stand structure (stand age and density), elevation and post-fire minimum temperature; (b) pre-fire densities of >14,000 stems/ha promoted successful stocking (≥150 seedlings/ha) and reduced lag between the disturbance and initial regeneration; and (c) minimum post-fire temperatures >−1.6°C reduced lag of initial regeneration and promoted initial radial growth. Synthesis. Our study demonstrates that lodgepole pine in high-elevation forests are regenerating following fires under recent climatic trends, but that regeneration is affected by post-fire climatic conditions. Importantly, forest patchiness may be increasing in a way that affects future ecological dynamics and may compromise the resilience of these systems.