We resurveyed the sites used by Coulter et al. (2010). Sites were on south facing slopes in the Applegate Valley near Ruch, Oregon, USA: China Gulch (42° 15′ N, 122° 3′ W) and Hukill Hollow (42° 11′ N, 122° 59′ W). The climate is a Mediterranean type with cool, wet winters and hot, dry summers: mean temperature 4 °C in January and 21 °C in July. For the years 2005 to 2012, annual rainfall ranged from 343 mm to 734 mm, with only 10 % of total precipitation in the summer months, June through September (www.wrcc.dri.edu/cgi-bin/cli-MONtpre.pl?or7391, accessed 20 Oct 2014). Summer rainfall varied from 0.5 cm to 7 cm during the interval between surveys (Figure 1).
Prior to mastication, the sites were dominated by buckbrush (Ceanothus cuneatus [Hook.] Nutt.), sticky whiteleaf manzanita (Arctostaphylos viscida Parry), Pacific poison oak (Toxicodendron diversilobum [Torr. & A. Gray] Greene), and California yerba santa (Eriodictyon californicum [Hook. & Arn.] Torr.). Mastication was employed to reduce the threat of high-severity wildfire by lowering fuels from standing vegetation to ground level (Kane et al. 2009, Southworth et al. 2011, Duren et al. 2012). Five years after mastication, the sites were treated with prescribed fire to reduce woody fuels on the ground.
At each of two sites, China Gulch (CG) masticated in 2001 and Hukill Hollow (HH) masticated in 2002, 30 1 m2 plots were installed randomly and the vegetation surveyed (Coulter et al. 2010). All plots (60 total) were treated with a prescribed burn in October 2005, year 0. Two weeks after the burn, 15 plots at each site (30 total) were seeded with four native bunchgrasses: Lemmon’s needlegrass (Achnatherum lemmonii [Vasey] Barkworth, syn. Stipa lemmonii [Vasey] Scribn.), California brome (Bromus carinatus Hook. & Arn.), blue wildrye (Elymus glaucus Buckley), and Roemer’s fescue (Festuca roemeri [Pavlick] S. Aiken var. klamathensis B.L. Wilson, syn. F. idahoensis Elmer sp. roemeri [Pavlick] S. Aiken). An equal number of paired control plots (30 total) were unseeded. Cover of all species was assessed in the first growing season, year 1 (2006), and in year 2 (2007). In June 2012, year 7, we resurveyed the seeded (n = 30) and unseeded (n = 30) plots. We estimated percent cover of plant species using midpoint values of FIREMON classes (0 % to 1 %, >1 % to 5 %, >5 % to 15 %, >15 % to 25 %, >25 % to 35 %, >35 % to 45 %, >45 % to 55 %, >55 % to 65 %, >65 % to 7 %, >75 % to 85 %, >85 % to 95 %, and >95 % to 100 %) (http://frames.nbii.gov/projects/firemon/FIREMON_SamplingMethods.pdf).
We used a two sample t-test in MINITAB v. 15 (Minitab Inc., State College, Pennsylvania, USA) with a significance threshold of α = 0.05 to compare bunchgrass cover in seeded and unseeded plots at replicate sites and to evaluate the change in species richness and percent cover from year 2 to year 7. We analyzed changes in percent cover of species within the same plot using paired t-tests, and changes in the frequency of plots with bunchgrasses in different years using χ
2. We performed a linear regression to compare the relationship between bunchgrass and introduced species cover.
To determine differences between the plant communities of seeded and unseeded plots, we compared seeded and unseeded groups by multi-response permutation procedures (MRPP) in PC-ORD v. 6 using Sørensen (Bray-Curtis) distance measures (McCune and Grace 2002, Peck 2010). We calculated A, the chance-corrected within-group agreement, and the P-value. We analyzed the two sites separately because they differed in total number of species.