Ecol Appl. 2014;24(8):2089-106. doi: 10.1890/13-2192.1.
Management of many North American forests is challenged by the need to balance the potentially competing objectives of reducing risks posed by high-severity wildfires and protecting threatened species. In the Sierra Nevada, California, concern about high-severity fires has increased in recent decades but uncertainty exists over the effects of fuel-reduction treatments on species associated with older forests, such as the California Spotted Owl (Strix occidentalis occidentalis). Here, we assessed the effects of forest conditions, fuel reductions, and wildfire on a declining population of Spotted Owls in the central Sierra Nevada using 20 years of demographic data collected at 74 Spotted Owl territories. Adult survival and territory colonization probabilities were relatively high, while territory extinction probability was relatively low, especially in territories that had relatively large amounts of high canopy cover (≥70%) forest. Reproduction was negatively associated with the area of medium-intensity timber harvests characteristic of proposed fuel treatments. Our results also suggested that the amount of edge between older forests and shrub/sapling vegetation and increased habitat heterogeneity may positively influence demographic rates of Spotted Owls. Finally, high-severity fire negatively influenced the probability of territory colonization. Despite correlations between owl demographic rates and several habitat variables, life stage simulation (sensitivity) analyses indicated that the amount of forest with high canopy cover was the primary driver of population growth and equilibrium occupancy at the scale of individual territories. Greater than 90% of medium-intensity harvests converted high-canopy-cover forests into lower-canopy-cover vegetation classes, suggesting that landscape-scale fuel treatments in such stands could have short-term negative impacts on populations of California Spotted Owls. Moreover, high-canopy-cover forests declined by an average of 7.4% across territories during our study, suggesting that habitat loss could have contributed to declines in abundance and territory occupancy. We recommend that managers consider the existing amount and spatial distribution of high-canopy forest before implementing fuel treatments within an owl territory, and that treatments be accompanied by a rigorous monitoring program.
许多北美的森林管理面临着平衡减少高强度野火风险和保护受威胁物种这两个潜在竞争目标的挑战。在加利福尼亚州的内华达山脉，近几十年来，人们对高强度野火的担忧有所增加，但对于减少燃料处理对与较老森林相关的物种（如加利福尼亚斑点猫头鹰（Strix occidentalis occidentalis））的影响仍存在不确定性。在这里，我们使用在 74 个斑点猫头鹰领地收集的 20 年人口数据，评估了森林条件、燃料减少和野火对中央内华达山脉斑点猫头鹰数量下降的影响。成年个体的存活率和领地殖民概率相对较高，而领地灭绝概率相对较低，特别是在那些拥有相对较大比例高冠层覆盖（≥70%）森林的领地。繁殖与拟议燃料处理中典型的中等强度木材采伐面积呈负相关。我们的结果还表明，较老森林与灌木/幼树植被之间的边缘面积增加和栖息地异质性增加可能会对斑点猫头鹰的人口增长率和个体领地的平衡占有产生积极影响。最后，高强度野火对领地殖民的概率有负面影响。尽管猫头鹰人口增长率与几个栖息地变量之间存在相关性，但生命阶段模拟（敏感性）分析表明，高冠层覆盖的森林面积是个体领地内种群增长和平衡占有率的主要驱动因素。超过 90%的中等强度采伐将高冠层覆盖的森林转化为低冠层覆盖的植被类型，这表明在这些林分中进行景观尺度的燃料处理可能会对加利福尼亚斑点猫头鹰的种群产生短期的负面影响。此外，在我们的研究期间，整个领地的高冠层森林平均减少了 7.4%，这表明栖息地的丧失可能导致数量和领地占有量的下降。我们建议管理者在实施猫头鹰领地内的燃料处理之前，考虑现有的高冠层森林数量和空间分布情况，并在处理过程中配合严格的监测计划。
