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Date Permissions Signed
Date of Award
Master of Science (MS)
Peterson, Merrill A., 1965-
Hooper, David U., 1961-
Matthews, Robin A., 1952-
Timber management, especially clear-cut logging, dramatically alters forest ecosystems. In temperate conifer forests of the Pacific Northwest, succession following deforestation is a slow process, lasting several decades for early and mid-successional stages and several hundred years for late maturity and old growth stages. Despite the history of logging in the region and the importance of these forests to wildlife, it is not well understood how animal communities respond to forest disturbance, particularly over successional gradients. In this study, I examined the response of macromoth communities to habitat change in western Washington State by sampling moths along a chronosequence of previously-logged sites and by making comparisons to moth communities in old growth areas. Based on previous research on moths in a variety of forest ecosystems, I expected to find that abundance, species richness, and diversity would all be lowest in recently-logged sites but would increase with stand age. I also predicted that the proportion of rare and unique species (species occurring at only one site) would increase with stand age, as would the number of specialist feeders, but I expected the relative abundance of pests and non-natives to decrease with increasing stand age. I found that moth abundance increased with stand age among previously-logged sites, while average species richness and diversity (measured by the alpha index) were greater in old growth areas for both observed and sample size-corrected values. Based on rarefaction curves, it was evident that sample sizes were not large enough to attain a firm measure of total species richness at each site, but a modest increase in sampling effort may be sufficient to achieve this in some sites. Shifts in community structure were detected by analyzing proportions of species and individuals within functional groups. For example, the relative abundance of generalist feeders and pest species decreased with increasing stand age, while the proportion of oligophagous and conifer-feeding individuals increased with stand age. In old growth sites, the average proportion of specialist feeding species was greater than in previously-logged sites. The effects of deforestation were most pronounced in stands less than 10 years old. Moth communities at these sites had distinct community structure and species assemblages. Despite the large differences among very young sites, moth communities in previously-logged stands increasingly resembled those in old growth forests as stand age increased for many of the community variables examined, and this similarity was generally most pronounced for the oldest previously-logged sites. The community-wide responses following deforestation suggest that moths are potentially useful indicators of habitat disturbance and quality. The geometrid subfamily Larentiinae and noctuid subfamily Xyleninae closely represented overall patterns in moth community dynamics and would likely serve well as indicators of macromoth species richness and diversity in forest stands of different ages within this region and elevation range. Specifically identifying which factors associated with stand history were responsible for the observed shifts in moth community structure was not an objective of this study. Given the important relationship between moths and their larval host plants, it is nonetheless likely that changes in plant community structure and canopy complexity during secondary succession influence macromoth communities. Further studies should address if changes to forestry practices, such as shifting from clear-cut to selective harvesting, might improve moth biodiversity by retaining aspects of plant diversity and forest structure. Based on my results, simply increasing the length of harvest rotations in these forests could result in important changes to moth biodiversity, which may have important ecological consequences for the numerous species utilizing moths as a food source. However, it appears that even after 85 - 95 years, moth communities in previously-logged sites do not fully resemble communities in old growth sites.
Western Washington University
Washington (State), Western
Copying of this thesis in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this thesis for commercial purposes, or for financial gain, shall not be allowed without the author's written permission.
Fisher, Matthew R., "Changes in macromoth community structure following deforestation in Western Washington State" (2011). WWU Graduate School Collection. 102.