Individual study: Short-term response of montane wetland plant communities to a controlled burn within Big Coyote Pasture, Sycan Marsh Preserve, Oregon, USA
Elseroad A.C., Aldous A. & Neugarten R. (2008) Effects of fire on wetland plant communities at Sycan Marsh Preserve: one year following burning. The Nature Conservancy, USA
Historically, fire regularly affected the ponderosa pine Pinus ponderosa/lodgepole P.contorta pine forests of southern Oregon (northwest USA) before fire-suppression policies were enacted, and the wetlands adjoining these forests likely burned periodically as well. To date, little is known about the effects of fire on plant community composition in these mid-elevation (~1,500 m) wetlands.
Study area: Sycan Marsh Preserve spans over 14,000 hectares in the headwaters of the Klamath River Basin of southern Oregon. The study described here focuses on plant communities within the Big Coyote Pasture in the northwest corner of the preserve.
Treatment and monitoring: Three community types were identified in the Big Coyote Pasture: 1) dominated by smooth meadow-grass Poa pratensis; 2) dominated by tufted hair-grass Deschampsia caespitosa and Baltic rush Juncus balticus; and 3) Dominated by J.balticus and Sierra rush J.nevadensis var. nevadensis. Poa-dominated communities tolerate longer dry periods than do Deschampsia-dominated communities, which in turn, tolerate longer dry periods than do Juncus-dominated communities. Two vegetation monitoring plots were established within the prescribed burn area in each community, plus two plots outside the burn boundary in the Deschampsia community, to serve as a control. Each plot consisted of 64, 1 mÂ² nested-frequency quadrats. Preliminary plant community composition (before treatment) was assessed in the summer of 2005.
A prescribed burn was conducted in late October of 2006 which consumed between 85% and 90% of above-ground plant biomass. Post-treatment community composition was assessed in the summer of 2007. Pre- and post- species and/or guild frequencies were compared using paired t-tests, as were pre- and post- species richness. Deschampsia community response was compared to the control (unburned Deschampsia communities) using analyses of variance. Within-plot changes in species and/or guild frequencies were analyzed with a ΧÂ² test.
Average plant species frequencies, guild frequencies, and species richness (number of species/m²) for burn and control Big Coyote Pasture Deschampsia caespitosa-Juncus balticus plots in 2005 (pre-burn) and 2007 (post-burn) are summarized in Table 1 (attached).
In all communities, native annual forbs, native perennials, and straightleaf rush Juncus orthophyllus frequencies decreased significantly between 2005 and 2007. Species richness also decreased. Deschampsia frequencies across all communities increased in the same time frame. Frequencies of native perennial forbs, sedges, and rushes did not change significantly between 2005 and 2007. Comparisons between burned Deschampsia plots and control Deschampsia plots suggest that only the increase in relative Deschampsia abundance can be directly attributed to fire; all other changes in community composition between 2005 and 2007 may be due to differences in weather between years, hydrology (2007 was a drier year than 2005), or some interaction of these with the prescribed burn. Within Deschampsia communities, data also indicate that fire is associated with increases in Microseris spp. and decreases in Juncus spp.
These results suggest that a single autumn burn does not substantially affect plant community composition or species richness in these wetlands. However, fire response is known to vary according to post-burn water availability during regrowth and seedling establishment; the response seen here in the dry conditions of 2007 may not be indicative of responses in wetter years.
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