Figure 1.
Fire and soil scarification effects in hemlock-hardwood forest.
(a) Undisturbed hemlock forest was used as a reference site. (b) Soil was scarified by a bulldozer used for fire control. (c) Portion of hemlock forest was burned by a natural-origin fire in late May 2006.
Figure 2.
Effect of fire and scarification on the understory environment.
Environmental variables (mean ±1 standard deviation; n = 10) that were potentially impacted by disturbance: (a) direct under-canopy radiation, (b) diffuse under-canopy radiation, (c) basal area, (d) exposed mineral soil, (e) low decay coarse woody debris (decay classes 1–3), (f) high decay coarse woody debris (decay classes 4 and 5), and (g) sapling density. Environmental variables that can affect plant communities: (h) slope and (i) aspect. Lowercase letters denote results of Mann-Whitney pairwise comparisons by disturbance type, with different letters indicating significant differences at α = 0.05. All environmental variables were measured in July 2007, approximately one year after disturbance.
Figure 3.
Annual changes in seedling densities by disturbance type.
Mean seedling density of the five most abundant woody species by time since disturbance (2007: one year; 2008: two years; 2009: three years) and disturbance type: (a) fire, (b) scarification, and (c) undisturbed. Error bars represent one standard deviation (n = 10). Asterisks indicate error bars that exceed the figure scale.
Table 1.
Significant indicator species by disturbance type in 2007; one year after disturbance.
Table 2.
Significant indicator species by disturbance type in 2008; two years after disturbance.
Table 3.
Significant indicator species by disturbance type in 2009; three years after disturbance.
Figure 4.
Annual herbaceous-layer community change by disturbance type.
Non-metric multidimensional scaling (NMDS) ordination scores depicting relative changes in species composition by disturbance type and years since disturbance. Each vector represents the magnitude and direction of change for each plot from one to two years (a; 2007–2008) and two to three years (b; 2008–2009) after disturbance. The NMDS ordination was three-dimensional with a final stress 14.2 and instability <0.001 in 380 iterations. Only the two dominant axes are displayed (Axis 3: r2 = 0.32; Axis 1: r2 = 0.30) whereas the third axis (Axis 2: r2 = 0.20) is excluded.
Figure 5.
Drought conditions occurred in northern Wisconsin during 2007 and 2009.
Growing-season (May-September) Palmer Drought Severity Index (PDSI) for Wisconsin Climate Division 1 is plotted by year (National Climatic Data Center, 2012). PDSI values during the sampling period are indicated by dark circles, and the 115-year mean is plotted as a straight line.