Race across the tundra: White spruce vs. snowshoe hare

The tale of the tortoise and the hare is being retold. In Alaska's far north, it's become the race of the white spruce tree and the snowshoe hare.

As some tree species shift northward, it's the tale of the spruce vs. the hare in northern Alaska. Image credit: NPS

With Alaska's warming climate, forests are moving upward to higher elevations and northward to higher latitudes. Scientists at the National Science Foundation (NSF) Bonanza Creek Long-Term Ecological Research (LTER) site in Alaska are working to understand interactions between changing tree lines and plant-eating animals such as the snowshoe hare.

They found that fewer young spruce trees had taken root during periods when snowshoe hares were abundant.

Spruce twigs are an important winter food for snowshoe hares; when the hares can get at them, these herbivores may nibble every branch in sight.

The habitats and ranges of snowshoe hares and white spruces overlap. Hares and spruces are common residents of forested floodplains, but hares, being mobile, are often faster than spruce seedlings in reaching the best habitat.

Snowshoe hares have now made their way north to Alaska's shrubby environment beyond the state's forest tree line. As spruce trees follow behind, they must pass through a "snowshoe hare filter."

The filter was especially evident after the last hare population peak in 2009. With greater numbers of hares feeding on spruce trees, fewer spruce seedlings were able to grow to adulthood.

Spruces became well-established on more open floodplain sites due to the lower hare population there, but those sites placed the trees at greater risk of drying out during the hot summer months. The hares are effectively pushing spruce trees into unfavorable habitats.

As far-northern tundra gives way to low-growing shrubs and then to forests, the distribution of snowshoe hares is a factor in where spruce trees can successfully grow. Forest scientists and resource managers should therefore keep in mind the ecosystem role of small herbivores like snowshoe hares. (National Science Foundation)

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