Thinning and burning result in low-level invasion by nonnative plants but neutral effects of natives

• Published in: Ecological applications 2008-04, Vol.18 (3), p.762-770
• Main Authors: Nelson, C.R, Halpern, C.B, Agee, J.K
• Format: Article
• Language: English
• Subjects: alien plants; botanical composition; Coniferous forests; Conservation biology; Conservation of Natural Resources; ecological invasion; Ecosystem; ecosystem management; exotic plants; Fire ecology; Fires; Forest ecology; forest ecosystems; Forest management; Forest restoration; Forest stands; forest thinning; forests; fuel-hazard reduction; introduced plants; invasive species; native plants; nonnative plants; Pinus ponderosa; Plant Development; plant ecology; Plants; Plants - classification; prescribed burning; prescribed fire; thinning; Time Factors; underburning; Understory; understory plant composition; Vegetation; Washington
• ISSN: 1051-0761; 1939-5582
• DOI: 10.1890/07-0474.1

Many historically fire-adapted forests are now highly susceptible to damage from insects, pathogens, and stand-replacing fires. As a result, managers are employing treatments to reduce fuel loadings and to restore the structure, species, and processes that characterized these forests prior to widespread fire suppression, logging, and grazing. However, the consequences of these activities for understory plant communities are not well understood. We examined the effects of thinning and prescribed fire on plant composition and diversity in Pinus ponderosa forests of eastern Washington (USA). Data on abundance and richness of native and nonnative plants were collected in 70 stands in the Colville, Okanogan, and Wenatchee National Forests. Stands represented one of four treatments: thinning, burning, thinning followed by burning, or control; treatments had been conducted 3-19 years before sampling. Multi-response permutation procedures revealed no significant effect of thinning or burning on understory plant composition. Similarly, there were no significant differences among treatments in cover or richness of native plants. In contrast, nonnative plants showed small, but highly significant, increases in cover and richness in response to both thinning and burning. In the combined treatment, cover of nonnative plants averaged 2% (5% of total plant cover) but did not exceed 7% (16% of total cover) at any site. Cover and richness of nonnative herbs showed small increases with intensity of disturbance and time since treatment. Nonnative plants were significantly less abundant in treated stands than on adjacent roadsides or skid trails, and cover within these potential source areas explained little of the variation in abundance within treated stands. Although thinning and burning may promote invasion of nonnative plants in these forests, our data suggest that their abundance is limited and relatively stable on most sites.