Glacier Bay National Park
Scientists and other observers came to Glacier Bay to see the great glaciers and found here the ideal natural laboratory for the study of the infant theory of plant succession. How do plants recover a raw landscape? What happens when nature wipes the slate clean and starts over from scratch? Glacier and plant studies go hand in hand. Rapid revegetation change following the glaciers' speedy retreat has enabled us to map and photograph the course of plant succession.
When naturalist John Muir came to Glacier Bay in 1879 he was seeking corroboration of the continental glaciation theories of Louis Agassiz, whose controversial Etudes sur les Glaciers was published in 1840. Here, in the aftermath of retreating glaciers, Muir found a landscape not yet formed. At Glacier Bay you watch a vegetative wilderness being createdand also see its culmination in coastal forest. A trip up the bay mimics glacial retreat and rolls back plant succession, from the mature forest at Bartlett Cove to the naked Earth structure at the fjords' farthest reaches. Biological succession produces profound change here in a mere decade.
Earnest, long-range studies of plant succession began in Glacier Bay in 1916, with the work of Professor William S. Cooper. His plant studies were continued in 1941 by Professor Donald Lawrence and others. Plant recovery may begin here with no more than "black crust," a mostly algal, feltlike nap that stabilizes the silt and retains water. Moss will begin to add more conspicuous tufts. Next come horsetail and fireweed, dryas, alder, willows, then spruce, and finally hemlock forest. (On the park's outer coast the final or climax stage of plant succession may be muskeg, because soil packing causes poor drainage.)
Where plants' seeds happen to land, of course, can be critical. The chaotic rock-and-rubble aftermath of a glacial romp is deficient in nitrogen. Alder and dryas are important pioneers because they improve the soil by adding to it nitrogen from the air. Much of northern Europe and America were pioneered by dryas when the last Ice Age ended. Sitka alder begins to form dense entanglements that are the bane of hikers.
Spruce takes hold and eventually shades out the alder. A forest community is begun. Each successive plant community creates new conditions that lead to its replacement by plants more competitive under those new conditions. The theory holds that plant competition modifies the environmentlight and moisture availability, and soil nutrientsso that plant populations also change. Over time, successive plant communities will occupy the environment, hence plant succession. The time from naked rock to revegetation is not necessarily long.
The patterns by which animals reinhabit the land after glaciers retreat are not as neat as with plant succession. There are no true pioneer species paving the way for succeeding species. Land mammals must either walk or swim. They cannot, as plant seeds and spores do, hitch rides on wind and waves or with birds. Extensive water, ice, or mountains loom as impassable barriers. Low mountain passes are often the conduits through which land mammals begin to repopulate the park. Usually they will live off this young terrain at first only part of the year. Then resident populations may gradually build. The process of colonization at Glacier Bay and throughout Southeast Alaska is somewhat hindered by the fact that mammals in general have not had enough time since the Wisconsin Ice Age wound down to recolonize the land.
Tlingit Indians were the original inhabitants of Glacier Bay and still consider it their ancestral home. Hunters and gatherers of salmon, seals, berries and roots, they were driven from the bay by advancing glaciers during the Little Ice Age. Naturalist and adventurer John Muir is credited with discovering the bay in 1879, and tourism to this land of ice and snow began soon after. Pioneering homesteaders began farming in Gustavus around 1923, when fish canneries and salteries dotted the region. Though a few hardy men and women have chosen to live in Glacier Bay and on the outer coast in times past, the area remains largely isolated and undeveloped.
Details mentioned in this article were accurate at the time of publication
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