Date of Award

8-1984

Degree Type

Thesis

Degree Name

Master of Science

Major

Botany

Major Professor

H. R. DeSelm

Committee Members

David K. Smith, B. E. Wofford

Abstract

Vegetation and environmental data from nine debris slides on Mt. Le Conte were analyzed in this study. Ages of the debris slides ranged from 1.5 to about 50 years at the time of sampling in the summer of 1980. Vegetation was sampled using 50 cm x 50 cm plots along horizontal transects across each slide. Data collected in each plot included the percent cover of each vascular plant species as well as depth to impenetrable obstruction, bare rock cover, bryophyte cover and lichen cover.

Debris slides were divided into vertical zones as horizontal zones based upon slide shape, slope angle and profile in cross-section. The first of the three vertical zones studied was the head zone at the top of the slide; the next lowest zone was the erosion-transportation zone; the lowest zone studied was the next one, the transportation-gully zone. A terminal zone, the deposition zone, was located below the transportation-gully zone but was not studied. Two horizontal zones, a center and margin at each lateral edge, were recognized.

The effects of time on debris slide recovery and revegetation were noted. With increasing age, soil depth increased, bare rock cover decreased, and cover vascular plants, bryophytes, and lichens increased on most parts of each debris slide.

Different trends in vegetation composition were noted among plots of the horizontal and vertical zones and among slides of different ages. Some species, such as Carex misera, were more frequent in the head zone rather than in the other two zones, while others, such as Saxifraga michauxii, occurred throughout. Individuals of certain species, for example, Carex misera, appeared with greater frequencies in young slides; other taxa, for example, Calamagrostis cainii, were found established only in older slides. Forbs and graminoids were the life forms occurring most frequently. Trees and shrubs were present less frequently in younger slides; numbers of individuals and cover increased from younger to older slides.

Analysis of variance indicated significant differences among vertical zones and horizontal zones as well as among slide age classes. Data used were mean values of depth to rooting obstruction, bare rock cover, bryophyte cover and lichen cover.

Seven community types were separated at the 45 percent dispersion level using cluster analysis. Three of these types, the Saxifraga michauxii type, the mixed herb type, and the Carex misera types were found in young slides and highly disturbed areas of somewhat older slides. Four community types, the Solidago glomerata type, the Diervilla sessilifolia type, the Rubis canadensis type, and the Calamagrostis cainii type, were found only in recovering, older slides.

Debris slides are dynamic areas but subject to ongoing natural disturbance. Successful colonizers appear to be stress-tolerant species able to withstand recurrent disturbance. Several rare vascular plant species, such as Gentiana linearis, Krigia montana, and Calamagrostis cainii, which require non-forest sites at high elevations were found in these debris slides.

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