Can snowshoe hares control treeline expansions?

Area of Science:

• Ecology
• Climate Change Biology
• Arctic and Boreal Ecology

Background:

• Treelines in Alaska are advancing due to climate warming, expanding habitats for boreal species like snowshoe hares (Lepus americanus).
• Snowshoe hares are significant browsers of white spruce (Picea glauca), the dominant tree species at Alaskan treelines.
• Hares inhabit shrub communities beyond treeline, influencing white spruce establishment.

Purpose of the Study:

• To investigate the "snowshoe hare filter" mechanism affecting white spruce establishment near treeline in Denali National Park, Alaska.
• To model the impact of snowshoe hare abundance on white spruce establishment patterns from 1970 to 2009.

Main Methods:

• Modeled white spruce (Picea glauca) establishment patterns over a 40-year period (1970-2009).
• Analyzed the influence of snowshoe hare abundance, snow depth, and surrounding vegetation characteristics on spruce browsing.
• Identified factors controlling the "snowshoe hare filter" near treeline.

Main Results:

• Fewer white spruce (Picea glauca) established during periods of high snowshoe hare abundance.
• Snowshoe hare abundance, snow depth, and surrounding vegetation characteristics interact to influence spruce browsing.
• Hares can exclude spruce from optimal establishment sites, especially in floodplain locations with dense shrub canopies.

Conclusions:

• The snowshoe hare filter significantly modifies white spruce establishment near treeline.
• Climate warming-induced treeline expansion of white spruce will be strongly influenced by snowshoe hare population dynamics.
• Understanding the snowshoe hare filter is crucial for predicting future treeline dynamics in Alaska.