Rickbeil Gregory J M, Hermosilla Txomin, Coops Nicholas C, White Joanne C, Wulder Michael A
Faculty of Forestry, University of British Columbia, Vancouver, British Columbia, Canada.
Canadian Forest Service (Pacific Forestry Centre), Natural Resources Canada, Victoria, British Columbia, Canada.
PLoS One. 2017 Mar 22;12(3):e0172669. doi: 10.1371/journal.pone.0172669. eCollection 2017.
Lichens form a critical portion of barren ground caribou (Rangifer tarandus groenlandicus) diets, especially during winter months. Here, we assess lichen mat volume across five herd ranges in the Northwest Territories and Nunavut, Canada, using newly developed composite Landsat imagery. The lichen volume estimator (LVE) was adapted for use across 700 000 km2 of barren ground caribou habitat annually from 1984-2012. We subsequently assessed how LVE changed temporally throughout the time series for each pixel using Theil-Sen's slopes, and spatially by assessing whether slope values were centered in local clusters of similar values. Additionally, we assessed how LVE estimates resulted in changes in barren ground caribou movement rates using an extensive telemetry data set from 2006-2011. The Ahiak/Beverly herd had the largest overall increase in LVE (median = 0.033), while the more western herds had the least (median slopes below zero in all cases). LVE slope pixels were arranged in significant clusters across the study area, with the Cape Bathurst, Bathurst, and Bluenose East herds having the most significant clusters of negative slopes (more than 20% of vegetated land in each case). The Ahiak/Beverly and Bluenose West had the most significant positive clusters (16.3% and 18.5% of vegetated land respectively). Barren ground caribou displayed complex reactions to changing lichen conditions depending on season; the majority of detected associations with movement data agreed with current understanding of barren ground caribou foraging behavior (the exception was an increase in movement velocity at high lichen volume estimates in Fall). The temporal assessment of LVE identified areas where shifts in ecological conditions may have resulted in changing lichen mat conditions, while assessing the slope estimates for clustering identified zones beyond the pixel scale where forage conditions may be changing. Lichen volume estimates associated with barren ground caribou movement metrics in an expected manner and, as such, show value for future habitat assessments.
地衣是北极驯鹿（Rangifer tarandus groenlandicus）贫瘠土地冬季饮食的重要组成部分。在此，我们使用新开发的Landsat合成图像，评估了加拿大西北地区和努纳武特地区五个鹿群活动范围内的地衣垫体积。从1984年到2012年，每年有70万平方公里的北极驯鹿栖息地使用地衣体积估算器（LVE）。随后，我们使用泰尔-森斜率评估了每个像素在整个时间序列中LVE的时间变化，并通过评估斜率值是否集中在相似值的局部聚类中来评估其空间变化。此外，我们使用2006年至2011年的大量遥测数据集，评估了LVE估计如何导致北极驯鹿活动率的变化。阿希亚克/贝弗利鹿群的LVE总体增幅最大（中位数=0.033），而西部的鹿群增幅最小（所有情况下中位数斜率均低于零）。LVE斜率像素在整个研究区域排列成显著的聚类，巴瑟斯特角、巴瑟斯特和蓝鼻子东部鹿群的负斜率聚类最为显著（每种情况下超过20%的植被土地）。阿希亚克/贝弗利和蓝鼻子西部的正聚类最为显著（分别占植被土地的16.3%和18.5%）。北极驯鹿根据季节对变化的地衣条件表现出复杂的反应；与移动数据检测到的大多数关联与目前对北极驯鹿觅食行为的理解一致（例外情况是秋季地衣体积估计值高时移动速度增加）。LVE的时间评估确定了生态条件变化可能导致地衣垫条件变化的区域，而评估聚类的斜率估计确定了像素尺度以外饲料条件可能变化的区域。地衣体积估计与北极驯鹿移动指标以预期方式相关，因此对未来栖息地评估具有价值。
