This dissertation describes arthropod responses to and effects on decay processes in
ponderosa pine, a dominant forest canopy tree in northern California. We used both
descriptive and experimental field techniques to establish how arthropod assemblages
depend on and are important to the disintegration of woody structures in forests of this
type. The first study used pitfall traps placed within and on the outsides of fallen, large
old ponderosa pine trees to establish the effects of microenvironments created during
tree death. We studied the internal and external structures of fallen trees as well as the
forest floor in canopy gaps and in the surrounding undisturbed forest. Five trees were
surveyed, representing a decay sequence from newly dead and with distinct canopy gap,
to well-decayed with recovering canopy. Arthropod assemblages were distinct among
the different microenvironments, but were less so with increasing tree/gap age.
Differences between tree and soil faunae decreased with increasing decay, as did the
differences between gap and non-gap catches from the forest floor. The second study
used experimental exclusion techniques to examine how longitudinal (bark beetle) and
transverse (woodboring) insect colonists could influence rates of mass loss and carbon
respiration from young, dead ponderosa pine. We found that both groups enhanced the
prevalence of staining fungi in the sapwood, which in turn was negatively related to the
degree of structural failure in the sapwood, associated with decay fungi. Carbon
respiration was positively related to sapwood structural failure and we believe that the
two insect groups act in concert to suppress wood decomposition in this system. This is
contrary to prevailing wisdom among forest practitioners who have suspected that decay
and insect activity are positively correlated, but in agreement with laboratory studies
showing antagonism between stain and decay fungi. Lastly, we observed that neither
forest harvesting nor fire had strong effects on the development of exemplar taxa from
decay communities in ponderosa pine two years post-treatment. Though time since
treatment did affect all functional groups inside of logs, only undisturbed old-growth
treatments showed a reduced variability in composition, leading us to suspect effects to
emerge at longer time intervals. / Graduation date: 2004
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/30989 |
| Date | 25 June 2003 |
| Creators | Lemieux, Jeffrey P. (Jeffrey Phillips) |
| Contributors | Judd, Darlene D. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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