Date of Award
Master of Science
David K. Smith
Ken McFarland, Sally P. Horn
The Southern Appalachian spruce-fir forest is experiencing the chaotic conditions of ecosystem destruction resulting from the balsam woolly adelgid (Adelges piceae (Ratz)) infestation. In the present study, I have examined the community structure of bryophytes on fir logs in the high elevation spruce-fir forest of the Great Smoky Mountains National Park (GSMNP) to learn about the responses of bryophytes to the sudden change in forest structure.
This study has four primary objectives: 1) to provide an updated list of the epixylic bryophytes on fir logs in the spruce-fir forest of the GS MNP; 2) to compare results with previous epixylic bryophyte studies performed in the Great Smoky Mountains National Park; 3) to describe bryophyte communities on logs and describe the environmental factors that control community structure; 4) to create a quantitative method for sampling bryophyte species cover on logs.
Epixylic bryophytes on 79 Fraser fir (Abies fraseri (Pursh) Poir.) logs were sampled. Relative frequency values for the species were scored within the upper surface of a 60 degree arc on the log, in cm x 100 cm quadrats . Environmental variables such as general location, longitude and latitude, slope. slope aspect. elevation. dominant tree and shrub species, and canopy cover were recorded for each plot.
Three different multivariate techniques were used in this study, TWINSPAN, Detrended Correspondence Analysis (DCA), and Direct Gradient Analysis (DGA). TWINSPAN separated all the sites sampled into three different bryophyte communities. Nowellia curvifolia, Brotherella recurvans, and Brotherella recurvans/Hypnum imponens. These communities were separated into nine unions that describe different combinations of species and environmental conditions. TWINSPAN also separated all the species that perform similarly into six different clusters. These clusters are directly related to environmental conditions such as available light and decay stage. DCA provided a two-dimensional scatterplot of each species's overall average response within sampled sites. Finally, DGA provided insight into the environmental factors that significantly influence species distribution.
The results of this study suggest that each bryophyte species responds uniquely to environmental factors and that species replacement occurs in a unidirectional pattern. There seem to be five factors that most significantly influence the presence of a species on a log: species life strategy, species ability to colonize optimal substrate, the amount of bryophyte cover on the log, the decay class of a log, and the canopy conditions.
The epixylic bryophyte communities on Fraser fir logs in the GSMNP have drastically changed since the health of the spruce-fir forests have declined. A total of 19 species that were present on Fraser fir logs in the past are now missing completely, and many other species that were once abundant are declining. Three main union types have been lost: unions found on very wet logs, unions of corticolous species found on recently fallen fir trees. and unions of soil species found on completely decayed logs. Furthermore, there seems to have been a shift from species rich communities that used to be found on moist logs in a healthy spruce-fir forest. to less species rich communities that are currently found on dryer logs in the decimated forest.
Choberka, Erica, "A Study of Epixylic Bryophyte Ecology on Fraser Fir Logs in the Great Smoky Mountains National Park. " Master's Thesis, University of Tennessee, 1998.