Graduate Thesis Or Dissertation

 

The effects of two fuel reduction treatments on chaparral communities in southwest Oregon Public Deposited

https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/5d86p429w

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  • Fuel reduction treatments are being applied to public lands, affecting significant acreage at considerable expense. This study compares the short term effects on a chaparral plant community of two different fuel reduction methods, brush mastication and "hand piling and burning" (HPB). Ceanothus cuneatus dominated the southwestern Oregon study sites where permanent paired plots were established on either side of treatment-control boundaries. Two years of sampling included a census of all vascular plant species within each plot and an abundance measure for each species. Species composition and abundance were analyzed using multivariate statistical techniques. Differences in species composition were detected for plots grouped by presence-absence of small Ceanothus, as well as plots grouped by abundance of mature Ceanothus. There were more Ceanothus seedlings in treatments than in controls. Abundance of all stages of Ceanothus was more reduced by the mastication treatment than the HPB treatment. The plot characteristic that had the most influence on species composition was the presence of a tree canopy which was positively correlated with abundance of perennial species. Both Ceanothus and oak canopy provided areas with higher abundance of natives and perennials compared to open areas that were dominated by exotic annual grasses. The effects of treatment were surprisingly small. Time passed since treatment, 1 yr or 2 yr, had a stronger effect on species composition than did the method of treatment. Species abundance and richness were greatest in the first year after treatment compared to the second year or to controls. In the mastication treatment, species abundance and richness were lower than in their controls in the second year after treatment. These measures were reduced in the second year HPB treatment plots compared to the first year, but were still higher than in controls. In general, fuel reduction treatments appeared to increase the abundance of annuals, forbs, exotics, introduced weeds, and special status plants (taxa monitored by the Bureau of Land Management) during the first two years after treatments. Special status plants did not appear to be negatively affected by treatment, but treatment areas excluded known sites of occurrence for these species so there was scant data. The HPB treatment had a greater effect on plant communities than the mastication treatment because of the inclusion of fire rings remaining after the burning of piles. In the second year after treatment, fire rings had a higher proportion of annuals, exotics, and introduced weeds than their surrounding HPB treatment plots. Ceanothus germination was stimulated in fire rings but also occurred in the majority of plots, whether treatment or control. Resprouting of cut Ceanothus stems was also common in both types of treated plots. Short term evidence suggests that the HPB treatment may lead to an increase in weedy and/or exotic species and the mastication treatment may reduce species diversity. The HPB treatment may increase species diversity by allowing fire-cued species to establish. When applied to limited areas, both treatments will increase the heterogeneity of the overall chaparral community in the absence of wildfire, which also increases heterogeneity.
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