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Restoration treatment effects on the understory of ponderosa pine/Douglas-fir forests in western Montana, USA

Author(s): Kerry L. Metlen, Carl E. Fiedler
Year Published: 2006

Fire exclusion and high-grade logging have altered the structure and function of ponderosa pine (Pinus ponderosa) forests across the American West. Restoration treatments are increasingly being used in these forests to move stand density, structure, and species composition toward more historically sustainable conditions. Yet little research has focused on how restoration treatments influence the associated understory plant communities, particularly in the northern Rocky Mountains of the USA. To this end, we implemented a replicated (N = 3), randomized block experiment in a second-growth western Montana ponderosa pine/Douglas-fir (Pseudotsuga menziesii) forest that initiated after harvest in the early 1900s and has not burned since. We evaluated the effects of no action (control), silvicultural cutting (thin-only), spring burning (burn-only), and silvicultural cutting followed by spring burning (thin-burn) on the understory community. Treatments were implemented at an operational scale (9 ha). Data were collected before treatment and in three subsequent years, at two spatial scales: plot (1000 m2) and quadrat (1 m2). Richness, Simpson's evenness index, and cover were calculated for the total vascular plant community. Species origin and lifeform were used to further investigate richness and cover responses to treatment. Treatments differentially impacted the understory community, with the most dramatic changes in the thin-burn. The burn-only treatment initially reduced richness and cover of the understory, but by year three all active treatments increased plot-scale understory richness relative to pre-treatment and the control. Simpson's evenness increased the first growing season after burning, but was not influenced by treatment in subsequent years. Forbs, both native and exotic, were the most responsive lifeform and increased in richness and cover after thinning, with the greatest response in the thin-burn. Increased native richness was not detected at the quadrat-scale in any treatment, but was significant at the plot-scale in numerous combinations of treatments and years. A short-term reduction in shrub richness and abundance after burning was detected at the quadrat-scale. Sapling density was reduced in all active treatments. Although active treatments create more open overstories and increase understory diversity at the stand level, a mix of treated and untreated areas will likely maximize heterogeneity and diversity at the landscape scale.

Citation: Metlen, Kerry L.; Fiedler, Carl E. 2006. Restoration treatments effects on the understory of ponderosa pine/Douglas-fir forests in western Montana, USA. Forest Ecology and Management. 222(1-3): 355-369.
Topic(s): Fire Ecology, Fire Effects, Ecological - Second Order, Vegetation, Fuels, Fuel Treatments & Effects, Mechanical treatments
Ecosystem(s): Ponderosa pine woodland/savanna
Document Type: Book or Chapter or Journal Article
NRFSN number: 7900
FRAMES RCS number: 265
Record updated: Jul 2, 2018