Questions: Grassland degradation due to agriculture, changing fire regimes, and invasive species negatively affects forb communities. Conserving forbs and the services they provide requires a better understanding of their responses to interacting disturbances. Although fire and livestock grazing are important disturbances, their effect on forb communities in the Pacific Northwest Bunchgrass Prairies is not fully understood. Our objectives were to: 1) determine how prescribed fire and livestock grazing influence forb community composition, cover, species richness, and diversity over a 10-year span; 2) identify indicator species for each treatment; and 3) quantify forb responses to increasing cover of the invasive grass Ventenata dubia.

Location: Pacific Northwest Bunchgrass Prairie, Oregon, USA.

Methods: We monitored plant responses in a manipulative study established in 2004 with four treatments (prescribed fire, livestock grazing, both fire and grazing, and a control with no fire or grazing). Fall burns occurred in 2006 and 2016.

Results: Forb communities changed significantly over ten years and were influenced more by fire than cattle grazing. Treatments involving fire were more associated with annual forbs and fewer perennial species than treatments not burned. Although forb cover was lower in grazed compared to ungrazed treatments, richness and diversity did not differ among treatments. Several fire-adapted forb species were associated with burned treatments. V. dubia cover was negatively correlated with forb cover and richness in 2016 and 2018 when cover of this invasive species reached 20-37%.

Conclusions: We found fall prescribed burns at a ten-year return interval affected forb community composition and cover but not richness or diversity. Fire may promote annual and fire-tolerant perennial forbs, but this relationship may be compromised by V. dubia invasions. This study provides insights into management strategies aimed at conserving forb communities and emphasizes the need for continued monitoring of the invasion of V. dubia in this unique prairie.

Data were collected at 16 grassland plots on The Nature Conservancy's Zumwalt Prairie Preserve, Wallowa County, Oregon in 2008, 2010, 2016, and 2018

See Watson et al. (2021) for description of study site and experimental design.

Methods

Plots were rectangular in shape with a short side of 100 m and a long side of 300 m. All four corners were documented with GPS coordinates, and one corner (the "origin") was marked with fiberglass stakes for re-location.

In 2008, all cover data were collected on six, 100 m transects spaced 50 m apart, parallel to the short side of the plots and distributed evenly across the plot. Foliar cover for all forb species was recorded using line-point intercept methods with a reading every 3 m using a tripod-mounted laser pointer.

In 2010, the transect configuration was altered to nine, 50 m transects, spaced 30 m apart, parallel to the short side of the plots. This re-design was done to intensify the sampling and to incorporate a buffer around the inner edges of the plots to exclude fenceline effects. Foliar cover was recorded using line-point intercept methods with a reading every meter along each transect, using a tripod-mounted laser pointer.

In 2016 and 2018, the monitoring protocol from 2010 was used to resample foliar cover of all 16 plots.

In all years, sampling for foliar cover on grazed plots was collected prior to any livestock grazing.

Since foliar cover includes all species in contact with the laser from canopy to soil surface, cover can be recorded as over 100%.

Metadata files:

Data from: Forb Community Response to Prescribed Fire, Livestock Grazing, and an Invasive Annual Grass in the Pacific Northwest Bunchgrass Prairie

Applied Vegetation Science

Created by: B.L. Watson, S.B. Lukas, L.R. Morris, S.J. DeBano, H.J. Schmalz, and A.J. Leffler

See Watson et al. (2021) for description of study site and experimental design.

GENERAL DESCRIPTIONS OF WORKSHEETS IN WORKBOOK

Cover_Diversity_Richness: Worksheet of Ventenata dubia cover, forb cover, Shannon diversity of forbs, and species richness of forbs at each of the 16 sites in 2008, 2010, 2016, and 2018

FG_Cover_Data_All Years: Worksheet of cover of all forbs, by species, for each plot in 2008, 2010, 2016, and 2018

INDIVIDUAL WORKSHEET DESCRIPTIONS

Cover_Diversity_Richness Worksheet

Column A: PlotID = PlotID is a concatenation of the block, treatment, and year.

Column B: Year = Indicates the year the data were collected.

Column C: Block = Identifies one of four blocks (1, 2, 3, or 4).

Column D: Treatment = Indicates one of four treatments applied to each plot."BOTH" indicates sites that were burned and grazed by cattle, "BURN" indicates sites that were burned but not grazed, "GRAZ" indicates sites that have been grazed by cattle but not burned , and "CNTL" indicates sites that have not been grazed by cattle or burned within the course of the study.

Column E: VEDU Cover = Percentage of all "hits" that were Ventanata dubia (VEDU).

Column F: FORB Cover = Percentage of all "hits" that were forbs.

Column G: ShannonDiversity = The Shannon diversity index of forbs for each plot during in each year.

Column H: Richness = The total number of forb species in each plot in each year.

FG_Cover_Data_All Years Worksheet

Column A: PlotID=PlotID is a concatenation of the block, treatment, and year.

Column B: Year=Indicates the year the data were collected.

Column C: Treatment = Indicates one of four treatments applied to each plot."BOTH" indicates sites that were burned and grazed by cattle, "BURN" indicates sites that were burned but not grazed, "GRAZ" indicates sites that have been grazed by cattle but not burned , and "CNTL" indicates sites that have not been grazed by cattle or burned within the course of the study.

Column D-FG: Varies = Percentage of "hits" on indivdiual forb species for each plot in each year. Forb species are abbreviated using USDA PLANTS dabatase plant symbols: https://plants.usda.gov/home.

Column H: Grand Total = Sum of all individual forb species cover for each plot in each year.

Literature Cited

Watson, B.L., Lukas, S.B., Morris, L.R., DeBano, S.J., Schmalz, H.J., and A.J. Leffler.2021 Forb community response to prescribed fire, livestock grazing, and an invasive annual grass in the Pacific Northwest Bunchgrass Prairie. Applied Vegetation Science.