Wildfire extends the shelf-life of elk nutritional resources regardless of fire severity

Large-scale, high severity wildfires are increasingly frequent across the western United States. Fire severity affects the amount of vegetation removed and helps dictate what, where, and how many plants regenerate postfire, potentially altering the available habitat and nutritional landscape for wildlife. To evaluate the effects of fire severity on summer nutritional resources for elk (Cervus canadensis), we collected field data and remotely sensed information in years two and three after a large-scale wildfire to compare forage quality and quantity across forest types and fire severities within the summer range of one elk population in west-central Montana. To understand the landscape level effects of fire severity on nutritional resources, we developed predictive forage quality and quantity models. We used these models to predict nutritional resources across the landscape for four scenarios representing different fire severity patterns (i.e., an unburned landscape, a landscape burned only at low severity, a landscape burned only at high severity, and the observed landscape burned at a mixed severity). Shortly after the wildfire, summer forage quality and herbaceous forage quantity increased in both mesic and dry mixed conifer forests regardless of fire severity. Summer shrub forage quantity was greater in unburned mesic and dry forests, and there was no difference between fire severities in dry forests. Low severity burned mesic forests had significantly greater shrub forage quantity compared to high severity burned mesic forests. The three predicted fire scenarios had the highest percentage of the summer range with adequate forage quality which increased throughout the summer. In contrast, the predicted unburned landscape had the lowest percentage of adequate forage quality which decreased throughout the summer. Wildfire extended the duration in which elk can access high quality forage in the summer in years two and three postfire. Therefore, shortly after a large-scale wildfire, elk may be better able to meet their nutritional requirements which may positively impact elk body condition, reproductive performance, and survival.

美国西部各地的大规模高烈度野火愈发频发。野火烈度会影响植被移除量，并决定火灾后植被的恢复种类、分布格局与恢复规模，进而可能改变野生动物的可用栖息地与营养供给格局。为评估野火烈度对北美马鹿（Cervus canadensis）夏季营养资源的影响，我们在蒙大拿州中西部某马鹿种群的夏季活动范围内，于一场大规模野火发生后的第2、3年采集野外数据与遥感信息，以对比不同林型与野火烈度下的饲草质量与产量。为阐明野火烈度对营养资源的景观尺度影响，我们构建了饲草质量与产量的预测模型，并利用该模型针对四种不同野火烈度格局的场景开展营养资源预测：即未烧景观、仅发生低烈度火烧的景观、仅发生高烈度火烧的景观，以及实际发生混合烈度火烧的观测景观。野火发生后不久，无论野火烈度如何，中生与旱生混合针叶林（mesic and dry mixed conifer forests）的夏季饲草质量与草本饲草（herbaceous forage）产量均有所提升。未受火烧的中生与旱生林内，夏季灌丛饲草（shrub forage）产量更高；而旱生林内不同烈度火烧间的灌丛饲草产量无显著差异。低烈度火烧的中生林内，灌丛饲草产量显著高于高烈度火烧的中生林。三种预设火烧场景下，夏季活动范围内具备充足饲草质量的区域占比最高，且该占比随夏季进程持续提升。与之形成对比的是，预设未烧景观中具备充足饲草质量的区域占比最低，且该占比随夏季进程逐渐下降。野火可延长火后第2、3年夏季马鹿获取高品质饲草的时长。因此，大规模野火发生后不久，马鹿或可更易满足自身营养需求，进而可能对其体况、繁殖表现与存活率产生积极影响。