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Klinger, L.F., 1988

Successional change in vegetation and soils of southeast Alaska

Bibliographic Reference

Klinger, L.F., 1988, Successional change in vegetation and soils of southeast Alaska: University of Colorado, Boulder, Ph.D. dissertation, 234 p., illust., maps.


A general hypothesis is presented which states that paludification is a successional process whereby, in the absence of large-scale disturbance, mature forests develop into bogs via the invasion and spread of bryophytes (especially Sphagnum mosses), which stress and kill surrounding trees by altering physical and chemical conditions of the soil, groundwater, and atmosphere. This hypothesis is tested in undisturbed forests in a remote area of southeast Alaska. Gradient analysis and environmental monitoring techniques are used to compare observed vs. predicted trends in community composition, age structure, bryophyte cover, soil chemistry and morphology, and other environmental factors along the following hypothesized late successional sequence: spruce/hemlock forest, hemlock/spruce forest, hemlock/cypress forest, cypress/hemlock forest, cypress/hemlock pygmy forest, pine pygmy forest, pine bog, sedge bog. Tree age and size structure analyses suggest that forests are progressing to bogs according to the above sequence at a slow, but undetermined rate. Multiple regression analyses indicate that Sphagnum cover explains the most variation in descriptors of community physiognomy, community composition, tree health, and tree growth. Data also indicate that root mortality (and resultant tree mortality) may be due to conditions of heavy metal toxicity and/or anaerobicity created in the rooting zone by Sphagnum mosses. Evidence suggests that acidification and chelation in soils by Sphagnum compounds accelerate podzolization and iron hardpan formation, leading to impeded drainage. Strongly acidic rain detected in the study area is thought to be mainly biogenic. Stratigraphic analyses indicate that forest to bog transitions occurred in the early and mid-Holocene. Other studies in the region provide circumstantial evidence for past and present paludification of old-growth forests. These results suggest that models of succession may have to more carefully consider the process of paludification as a progression, rather than a retrogression of succession. Old-growth forests in southeast Alaska, and perhaps elsewhere, may actually be early to mid-successional with respect to bogs. Future work on paludification should be directed at obtaining better data on community attributes and mechanisms of vegetation change that can be used to evaluate and test models of succession.

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