Final answer:
Warmer temperatures are causing the deciduous forest to move north and causing tamarack mortality due to reduced growing seasons and increased pest infestations.
Step-by-step explanation:
Warmer than normal winter and summer temperatures are causing the deciduous forest to move further north and also causing high amounts of tamarack mortality. The warmer temperatures reduce the growing season of plants, which increases the risk of low productivity. Additionally, shorter and milder winters fail to kill pests, leading to damaging infestations in subsequent seasons.