Department of Forest Engineering, Resources, and Management, Oregon State University, Corvallis, Oregon, United States of America.
Department of Forest Ecosystems and Society, Oregon State University, Corvallis, Oregon, United States of America.
PLoS One. 2023 Feb 27;18(2):e0281927. doi: 10.1371/journal.pone.0281927. eCollection 2023.
As contemporary wildfire activity intensifies across the western United States, there is increasing recognition that a variety of forest management activities are necessary to restore ecosystem function and reduce wildfire hazard in dry forests. However, the pace and scale of current, active forest management is insufficient to address restoration needs. Managed wildfire and landscape-scale prescribed burns hold potential to achieve broad-scale goals but may not achieve desired outcomes where fire severity is too high or too low. To explore the potential for fire alone to restore dry forests, we developed a novel method to predict the range of fire severities most likely to restore historical forest basal area, density, and species composition in forests across eastern Oregon. First, we developed probabilistic tree mortality models for 24 species based on tree characteristics and remotely sensed fire severity from burned field plots. We applied these estimates to unburned stands in four national forests to predict post-fire conditions using multi-scale modeling in a Monte Carlo framework. We compared these results to historical reconstructions to identify fire severities with the highest restoration potential. Generally, we found basal area and density targets could be achieved by a relatively narrow range of moderate-severity fire (roughly 365-560 RdNBR). However, single fire events did not restore species composition in forests that were historically maintained by frequent, low-severity fire. Restorative fire severity ranges for stand basal area and density were strikingly similar for ponderosa pine (Pinus ponderosa) and dry mixed-conifer forests across a broad geographic range, in part due to relatively high fire tolerance of large grand (Abies grandis) and white fir (Abies concolor). Our results suggest historical forest conditions created by recurrent fire are not readily restored by single fires and landscapes have likely passed thresholds that preclude the effectiveness of managed wildfire alone as a restoration tool.
随着当代野火活动在美国西部加剧，人们越来越认识到，需要进行各种森林管理活动，以恢复生态系统功能并降低干旱森林的野火危害。然而，当前活跃的森林管理的速度和规模不足以满足恢复需求。管理野火和景观尺度的规定火烧有可能实现广泛的目标，但在火烧严重程度过高或过低的情况下，可能无法实现预期的结果。为了探索仅用火来恢复干旱森林的潜力，我们开发了一种新方法来预测最有可能恢复俄勒冈东部森林历史林分基面积、密度和物种组成的火灾严重程度范围。首先，我们根据树木特征和从火烧野外样地获得的遥感火灾严重程度，为 24 个物种开发了概率性树木死亡率模型。我们将这些估计值应用于四个国家森林中的未燃烧林分，以在蒙特卡罗框架内使用多尺度建模来预测火灾后的情况。我们将这些结果与历史重建进行比较，以确定具有最高恢复潜力的火灾严重程度。一般来说，我们发现基面积和密度目标可以通过相对较窄的中等严重程度火灾范围（约 365-560 RdNBR）来实现。然而，在历史上由频繁低严重程度火灾维持的森林中，单次火灾事件并未恢复物种组成。林分基面积和密度的恢复性火灾严重程度范围在广泛的地理范围内，对黄松（Pinus ponderosa）和干旱混合针叶林非常相似，部分原因是大冷杉（Abies grandis）和白云杉（Abies concolor）相对较高的火灾耐受性。我们的结果表明，由反复火灾产生的历史森林条件不易通过单次火灾恢复，而且景观可能已经超过了仅用管理野火作为恢复工具的有效性的阈值。
