Supplementary materials: Monitoring recovery of overgrazed lichen communities on Hagemeister Island, southwestern Alaska

AbstractUnderstanding the recovery rate of overgrazed lichen communities has value to mangers of lands in northern regions. We describe lichen community composition and present recovery rate measurements for a 12-year period following overgrazing by reindeer (Rangifer tarandus) on Hagemeister Island, Alaska. Reindeer were removed from the island in 1993 following overgrazing and average total lichen biomass increased from 504.2 kg/ha (SD 205.4) in 2003 to 795.3 (SD 489.6) in 2015. We estimate time to recovery with three competing growth curves which estimate grazeable biomass may be reached in 34-41 years. However, estimates of full recovery to climax biomass varied among the models, ranging from 71 to 400 years. In 2015, lichen communities were composed of various mixtures of at least 78 lichen taxa, and were dominated by Cladina stygia and other important reindeer forage species. While reindeer overgrazing diminished forage quantity, it did not extirpate preferred forage taxa.

摘要：探明过度放牧干扰下地衣群落的恢复速率，对北部地区土地管理者具有重要实践价值。本研究以阿拉斯加州哈格迈斯特岛为研究区域，系统记录了驯鹿（Rangifer tarandus）过度放牧后12年监测周期内地衣群落组成与恢复速率的实测数据。该岛于1993年因过度放牧移除所有驯鹿，此间地衣总平均生物量从2003年的504.2 kg/ha（标准差205.4）增长至2015年的795.3 kg/ha（标准差489.6）。本研究采用三种竞争性生长曲线模型估算恢复时长：结果显示，可采食生物量阈值将在34~41年内达成；但针对达到顶极生物量的完全恢复时长，不同模型的估算结果差异显著，区间为71至400年。2015年，该区域地衣群落由至少78种地衣类群混合组成，优势类群为暗石蕊（Cladina stygia）及其他重要的驯鹿饲用地衣物种。尽管驯鹿过度放牧降低了饲草的生物量，但并未根除驯鹿偏好采食的地衣类群。