Abstract:

Objective: The aim of this paper is to provide scientific reference on fuel management by analyzing the effect of the fuel treatments on fire behavior of the main forest types in Daxing'anling. Method: In this study, three 20 m×20 m plots were set in each forest type during fire season of 2019, and four 10 m×10 m sub-plots were further divided in each plot. The forest types included natural forests of Larix gmelinii (Larch natural forest), Betula platyphylla (Birch natural forest), and coniferous and broad-leaf mixed forest (Larch and birch natural mixed forest), and plantations of L. gmelinii (Larch plantation) and Pinus sylvestris var. mongolica (Mongolian Scots pine plantation). The forest structure of each plot was investigated, and then four sub-plots were treated with combustible materials, including cutting dead shrubs and herbs, clearing dead branches and surface litter. The combustible materials in sub-plot were treated with four intensities (untreated, low, mid, and high intensive treatment) respectively. After low intensity treatment, there were no inflammable and dead shrubs and grass in the forest and large combustible materials on the surface (> 10 h). After medium intensity treatment, all fallen trees, shrubs and small trees were removed. After high intensity treatment, the combustible materials on the surface would not support the continuous combustion and spreading of fire. The Fuel Characteristic Classification System (FCCS) was used to simulate fire behaviors for each plot under the ordinary weather scenario and drought scenario. Result: The simulation results showed that the surface fire spread decreased by 51.6% and 42.8% for Larch natural forest and plantation under the ordinary weather scenario after fuel treatments in low intensity, respectively. The flame length dropped by 33.6% and 39.4%, and the fire intensity decreased by 33.6% and 39.4%. However, the surface fire behavior did not change significantly after the low intensity treatment in larch and birch natural mixed forest, birch natural forest, and Mongolian Scots pine plantation. The surface fire spread rate decreased by 29.4%, 37.1%, 79.1%, 83.3%, and 19.7% after mid intensity treatment in mixed forest, birch forest, larch natural forest, larch plantation, and Mongolian Scots pine plantation, respectively, and flame length decreased by 33.3%, 29.8%, 67.2%, 69.7% and 38.1%. The surface fire spread rate decreased by 95.3%, 97.6%, 85.7%, 88.9%, and 77.6% after high intensity treatment in larch natural forest, larch plantation, larch and birch natural mixed forest, birch natural forest, and Mongolian Scots pine plantation, and flame length dropped by 93.1%, 93.9%, 92.6%, 87.6%, and 87.3%, respectively. The surface fire behavior under the drought scenario in all forest types decreased significantly with the increasing intensity of fuel treatment (P < 0.01). The crown fire behavior under the drought scenario decreased significantly after fuel treatments for larch natural forest and plantation, larch and birch natural mixed forest, and Mongolian Scots pine plantation (P < 0.01). Conclusion: The surface fire spread rate is less than 1 m·min^-1, and flame length below 1 m under ordinary weather scenario after mid-intensity treatment in mixed forest, birch forest, larch natural forest, and Mongolian Scots pine plantation. The surface fire spread rate and flame length are less than 0.1 m·min^-1 and 0.1 m in larch plantation, respectively. Those fires can be suppressed directly. Crown fires may drop by more than 20% and fire spread rate decreases more than 40% under drought scenario after mid-intensity treatment in mixed forest, Mongolian Scots pine plantation, larch natural forest, and larch plantation. High intensity treatment might affect the forest structure and environment. We recommend the mid-intensity treatment on fuel management for the region.

Key words: fuel characteristic classification system, fuel treatment, fire behavior