Ecology of Lake Clark: Tundra, Forest, Glaciers, Lakes and Salt Marshes

In the boreal forest of Lake Clark National Park and Preserve, black spruce seeds need fire to sprout. That is one of many links between plants, animals and place in this Alaska park, described in a National Park Service student handout written at a 5th grade reading level.

The roadless wilderness of Lake Clark National Park and Preserve is habitat for species from migratory birds to brown bears and caribou. Photo: NPS/K. Miller.

The park holds boreal forest, tundra, freshwater lakes and rivers, snow- and glacier-covered mountains, and coastal beaches and salt marshes. An ecosystem is a community of organisms, such as plants and animals, that interact in their environment. Some species, like bears and blueberries, live in several ecosystems; others, like sedges (grass-like plants of wet ground), need a specific one.

Tundra: a land of extremes

Alpine tundra grows at high elevations, where temperatures are cold, winters long and snow covers the ground most of the year. It is a low mat of lichens, mosses and small plants such as cranberries or blueberries. With a short, harsh growing season and dry, howling winds, plants stay close to the ground in dense mats to hold heat and moisture and grow tiny leaves and flowers, a world in miniature. Caribou, ground squirrels and ptarmigan live here.

Open tundra looking up into the Neacola mountain range. Photo: NPS/E. Wilcox.

Boreal forest

Boreal forests have short, cool summers and long, cold winters. At Lake Clark the trees include black spruce, white spruce, cottonwood, birch, aspen, willow and alder, over a thick mat of mosses, lichens, sedges, grasses and berries. Wildfire is common. It can be dangerous to people but is natural in the boreal forest, where it opens patches for new plants to grow. Lynx, red fox and moose must survive the long winters and short dry summers.

Fire is a natural disturbance that helps shape the boreal forest. Photo: NPS/Y. Matsui.

Freshwater: glaciers, lakes and rivers

A glacier is a massive river of ice that flows slowly downhill. It forms high in the mountains from snow that does not melt in summer, building up in layers that compress into solid ice over hundreds of years. Like bulldozers, glaciers carve the rugged terrain into wide U-shaped valleys. Their summer meltwater sends clean, cold water downhill to the headwaters of rivers and lakes where sockeye salmon hatch. As the climate warms, the park's glaciers are melting and shrinking.

Glaciers are always moving and shape the park's landscape. Photo: NPS/K. Lewandowski.

Creeks, rivers and lakes cover the landscape. Lake Clark, the park's largest lake, is 41 miles long, 1 to 4 miles wide and 870 feet deep, a long, narrow, deep glacier-carved lake ringed by mountains. Water flowing from the mountains supports what the handout calls the world's most productive sockeye salmon fishery. Salmon return each year to the waters where they were born, and the clean, cold water that supports them supports people too: the Dena'ina people have lived at Lake Clark for thousands of years.

Coastal salt marshes

Along the coast, tides bring nutrients and saltwater onto the land, and salt-tolerant sedges and grasses grow in the mix of fresh and salt water. Fish, migratory birds and mammals live in this rare habitat. The handout compares a salt marsh to a biological supermarket: it takes nutrients from the ocean water and feeds other animals, as dead plants break down and feed insects and small fish, which feed larger fish, birds and mammals.

Brown bears depend on it. Hungry after the winter den, they use the coast to fill up, and the marsh sedges are high in protein, which sustains bears and their cubs while they wait for the salmon.

Brown bears feed on vegetation in the Chinitna Bay meadow on the coast. Photo: NPS/J. Pfeiffenberger.

Salt marshes also improve water quality, holding nutrients that feed plants and animals; take carbon dioxide from the air and store it in plants and soil; and limit coastal erosion by slowing waves and trapping sediment, which protects shorelines from wind, water and ice.

Sources

• National Park Service, “Ecology of Lake Clark” (https://www.nps.gov/articles/000/ecology-of-lake-clark.htm), a student research handout for Lake Clark National Park and Preserve; photos credited to the National Park Service; rewritten in hubnx's own words.