Which of the following is NOT a common threat to forests?

Snow is generally considered a natural occurrence and not a common threat to forests. While heavy snowfall can occasionally cause damage, such as breaking tree branches or leading to structural damage in vulnerable areas, it is not typically classified as a primary threat to forest ecosystems. In contrast, humans, insects, and fire are significant threats to forests. Human activities can lead to deforestation, habitat fragmentation, and pollution, while insects can cause widespread damage to trees through infestations. Fires can be natural but often pose a significant risk to forest health, particularly when they are exacerbated by climate conditions or human practices. Therefore, in this context, snow does not represent a common threat to forests compared to the other listed factors.