Fire, mowing, and hand-removal of woody species in restoring a native wetland prairie in the Willamette Valley of Oregon

Dl. Clark et Mv. Wilson, Fire, mowing, and hand-removal of woody species in restoring a native wetland prairie in the Willamette Valley of Oregon, WETLANDS, 21(1), 2001, pp. 135-144
Citations number
Categorie Soggetti
Journal title
ISSN journal
0277-5212 → ACNP
Year of publication
135 - 144
SICI code
The invasion of prairies by woody species is a worldwide conservation conce rn. Fire is frequently used to inhibit this invasion. However, there is lit tle documentation of the effect of fire in wetland prairies, which are also threatened with encroachment of woody species. The present study investiga ted wetland species responses to experimental burning, hand-removal of wood y species, and mowing with removal of cut material. The possible ecological mechanisms responsible for individualistic responses of species, including direct mortality, ability to resprout, and release from competition are co nsidered. We also evaluated these treatments as tools for meeting restorati on objectives of reducing the abundance of woody species, reducing or preve nting spread of non-native pest species, and increasing or at least maintai ning native species' abundance. After two years of treatments (1994 and 199 6) three patterns emerged. 1) Woody species: Burning and hand-removal caused the greatest reductions i n cover of woody species. Mowing with removal of cut material, however, did not reduce the cover of woody species compared to controls. As woody plant cover decreased, plant mortality increased, indicating that treatments inf luenced woody plant cover at least partially through mortality. 2) Native herbaceous species: Burning significantly decreased inflorescence production of Deschampsia cespitosa, the dominant wetland prairie grass. I n contrast, burning, along with mowing, significantly increased flowering o f Juncus tenuis. Flowering and cover of all native graminoids combined, how ever, showed no significant responses to treatments. Burning and hand-remov al significantly promoted the cover of native forbs as a group, with Lotus purshiana and Veronica scutellata showing the greatest increases. 3) Non-na tive herbaceous species: Burning and hand-removal significantly reduced the cover of non-native forbs as a group and particularly reduced the cover of Hypericum perforatum. The number of inflorescences of nonnative grasses (H olcus lanatus and Anthoxanthum odoratum) increased with hand-removal and mo wing. Overall, no treatment was clearly superior in fulfilling the restorat ion objectives. Burning was effective in reducing woody cover and did not p romote abundance of non-native herbaceous species. Burning, however, reduce d the flowering of the key native grass, Deschampsia cespitosa. Hand-remova l of woody species was also effective at reducing woody cover and promoted the abundance of some native species, but it sometimes increased the cover of non-native herbaceous species. Because mowing with removal of cut materi al was ineffective in reducing woody cover and tended to promote non-native herbaceous species, this treatment is not recommended as a management tool .