The structuring of canopy arthropod communities was reviewed and investigated
in relation to tree species diversity and its component factors, interspersion of different
species and density of each tree species. Fifteen treatments of Douglas-fir (Pseudotsuga
menziesii) and red alder (Alnus rubra) (various densities and proportions of each) were
randomly assigned to 0.073 ha plots, replicated three-fold at each of two locations in
Western Oregon: the Cascade Head Experimental Forest and the H.J. Andrews
Experimental Forest. The six treatments used in this study were two densities of
Douglas-fir and red alder monoculture (1000 trees/ha and 500 trees/ha), and mixtures of
Douglas-fir and red alder (500 trees/ha of each) planted simultaneously or red alder
planted 6 years after the Douglas-fir. Trees were initially planted in 1985-1986. The
arthropod communities were sampled in the summer of 1998 by bagging and pruning
branches from the mid-canopy of both tree species.
Multivariate analyses distinguished the arthropod communities found on each tree
species and geographical location, but not among the different diversity and density
treatments. Many arthropod taxa and functional groups residing on a single tree species
had significantly different abundances between locations. The most commonly
encountered taxon, Adelges cooleyi Gillette (Homoptera: Adelgidae), was most abundant
on Douglas-firs in the 500 trees/ha monoculture and the mixture with younger red alder,
and least abundant in the mixture with both species planted simultaneously (the 1000
trees/ha Douglas-fir monoculture was intermediate). Adelgids showed no significant
response to location, but did respond to combinations of location x treatment. The
functional group of sap-feeders was dominated by adelgids, and showed similar treatment
differences on Douglas-fir. Defoliators on red alder responded in abundance to location,
treatment (most abundant in the 500 trees/ha monoculture and even-aged mixture, least
abundant in the 1000 trees/ha monoculture), and location x treatment.
This study demonstrated that tree species and geographical location are the
primary determinants of forest arthropod community composition at this spatial scale.
However, tree species diversity and density can affect the abundance of certain arthropod
taxa, apparently through some combination of resource quality and plant apparency. / Graduation date: 2000
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/33189 |
| Date | 17 March 2000 |
| Creators | Schaerer, Brett L. |
| Contributors | Schowalter, Timothy D. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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