Fuel treatments alter the effects of wildfire in a mixed-evergreen forest, Oregon, USA

Abstract

We had the rare opportunity to quantify the relationship between fuels and fire severity using prefire surface and canopy fuel data and fire severity data after a wildfire. The study area is a mixed-evergreen forest of southwestern Oregon with a mixed-severity fire regime. Modeled fire behavior showed that thinning reduced canopy fuels, thereby decreasing the potential for crown fire spread. The potential for crown fire initiation remained fairly constant despite reductions in ladder fuels, because thinning increased surface fuels, which contributed to greater surface fire intensity. Thinning followed by underburning reduced canopy, ladder, and surface fuels, thereby decreasing surface fire intensity and crown fire potential. However, crown fire is not a prerequisite for high fire severity; damage to and mortality of overstory trees in the wildfire were extensive despite the absence of crown fire. Mortality was most severe in thinned treatments (80%-100%), moderate in untreated stands (53%-54%), and least severe in the thinned and underburned treatment (5%). Thinned treatments had higher fine-fuel loading and more extensive crown scorch, suggesting that greater consumption of fine fuels contributed to higher tree mortality. Fuel treatments intended to minimize tree mortality will be most effective if both ladder and surface fuels are treated.Résumé : Les auteurs ont eu une occasion exceptionnelle de quantifier la relation entre les combustibles et la sévérité du feu en utilisant des données récoltées avant un incendie sur les combustibles de surface et dans la canopée ainsi que des données sur l'intensité du feu après un incendie de forêt. L'aire d'étude est une forêt mélangée de conifères du sud-ouest de l'Oregon avec un régime de feux d'intensité mixte. La modélisation du comportement du feu a montré que l'éclaircie a réduit les combustibles dans la canopée, ce qui a diminué le potentiel de propagation d'un feu de cime. Les risques d'initiation d'un feu de cime n'ont pas changé malgré la réduction des combustibles étagés parce que l'éclaircie a augmenté les combustibles de surface, ce qui a contribué à accentuer l'intensité du feu de surface. L'éclaircie suivie d'un brûlage au sol a réduit les combustibles dans la canopée, le long du tronc et en surface, diminuant par conséquent l'intensité du feu de surface et les possibilités d'un feu de cime. Cependant, un feu de cime n'est pas né-cessaire pour avoir un feu de forte intensité; les dommages et la mortalité chez les arbres de l'étage dominant causés par un incendie de forêt ont été importants malgré l'absence d'un feu de cime. La mortalité était la plus élevée dans les peuplements éclaircis (80-100 %), modérée dans les peuplements non traités (53-54 %) et la moins élevée dans les peuplements éclaircis et soumis à un brûlage dirigé (5 %). Les peuplements éclaircis avaient une quantité plus importante de combustibles fins et plus de roussissement des cimes, ce qui indique qu'une plus grande consommation de combustibles fins a contribué à une plus fort...

Long and Short-Term Effects of Fire on Soil Charcoal of a Conifer Forest in Southwest Oregon

“…The unthinned units were unmanaged and contained 80-110-year-old Douglas-fir (~1000 trees ha ; all downed woody material >3 m in length and >5 cm in diameter at the small end was removed, except downed tree tops were retained on units that subsequently underwent prescribed burning. Prescribed burn treatments were fulfilled in the fall of 2001 with light surface fire and no fire reaching into the tree crowns [44]. For this soil charcoal study, two experimental units were evaluated for each of the following categories: unburned, unthinned wildfire, thinned wildfire, and thinned prescribed fire.…”

“…The 2002 Biscuit Wildfire burned a portion of the Siskiyou Long-Term Ecosystem Productivity (LTEP) experiment in the Rogue River-Siskiyou National Forest, OR, [21,22,27]. Pre and post-wildfire soil and fuel sampling at the Siskiyou LTEP site directly quantified how fire-induced losses of soil C and N are related to woody fuels, thinning, fire type, and fire severity [21,22].…”

Quantifying Ladder Fuels: A New Approach Using LiDAR

“…Fuel reduction treatments are often used to mitigate fire hazards in strategic areas to help decrease the risk of harming these assets [3]. These treatments have been shown to be effective in ameliorating fire behavior and reducing tree mortality through both modeled simulations [4,5] and when encountered by real wildfires [3,[6][7][8][9][10][11][12][13]. Recent studies suggest the duration for reduction in potential fire behavior and effects, or treatment longevity, can exist for up to 8-15 years in the Sierra Nevada [14,15].…”

Fuel manipulation with herbicide treatments to reduce fire hazard in young pine (Pinus elliottii × P. caribaea) plantations in south-east Queensland, Australia

“…they make up most of the area), and hence reducing fuel hazard in the inter-rows should help reduce the spread of a wildfire and assist in wildfire suppression. However, this pattern of herbicide application may not be as successful in reducing the potential fire damage to young trees, because significant fuels can accumulate in the tree rows and encourage the vertical spread of fire into the tree canopy (Kilgore and Sando 1975;Raymond and Peterson 2005;Battaglia et al 2008), effectively increasing the probability of scorch and tree mortality.…”

“…Stephens 1998;Brose and Wade 2002;Raymond and Peterson 2005;Stephens and Moghaddas 2005;Battaglia et al 2008). However, there is little published information on the potential changes in fuel biomass, composition and structure following herbicide treatments.…”