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Interactions among climate, wildfire and tree regeneration at lower treeline in the U.S. northern rockies

Author(s): Philip E. Higuera, Kerry Kemp
Year Published: 2015

Recent increases in area burned in the western U.S. have raised concerns about the resilience of forests to large wildfires, particularly in dry mixed-conifer forests, where climate change and 20th-century land management have altered species composition, fuel loads, and fire regimes. To study forest resilience to recent wildfires, we examined patterns of post-fire conifer regeneration across 182 sites in 21 recent large fires in dry-mixed conifer forests of the U.S. northern Rocky Mountains. We used logistic and negative binomial regression to predict the probability of establishment and abundance of conifers 5 to 13 years post-fire, as a function of fire legacies (burn severity, distance to nearest live trees, and time since fire), landscape features (elevation, aspect, and slope), and ecological conditions (vegetation and canopy cover, tree density). Seedling densities varied widely across all sites (0 – 127,500 seedlings ha-1) and were best explained by variability in distance to live seed sources (! = -0.014, p = 0.002) and pre-fire tree basal area (! = 0.072, p = 0.008). The probability of seedling establishment decreased greatly beyond a threshold of 95 m from the nearest live seed source. Across all areas within the fires we studied, 75% of the burned area with high tree mortality was within this 95-m threshold, suggesting the presence of live seed trees to facilitate natural regeneration. Combined with the mix of species present within the burn mosaic, dry mixed-conifer forests appear resilient to recent large fires across our study region. This resilience would be undermined if in the future, shorter fire-return intervals prevented stands from reaching reproductive maturity, if fires were characterized by significantly larger high-severity patches, or if post-fire climate conditions were unsuitable for seedling establishment and survival.

Citation: Higuera, Philip E.; Kemp, Kerry B. 2015. Interactions among climate, wildfire, and forest regeneration at lower treeline in the U.S. northern rockies - Final Report to the Joint Fire Science Program. JFSP Project No. 12-3-01-13. Moscow, ID: University of Idaho, Department of Forest, Rangeland, and Fire Sciences. 27 p.
Topic(s): Fire Ecology, Fire Effects, Ecological - First Order, Ecological - Second Order
Ecosystem(s): None
Document Type: Technical Report or White Paper
NRFSN number: 15564
FRAMES RCS number: 20549
Record updated: Sep 4, 2019