| Understory herbaceous vegetation is a vital component of eastern deciduous forests, typically comprising the largest proportion of forest diversity. Understory composition is often correlated with microenvironmental and site conditions such as topography, light availability, and edaphic conditions and provides important indications of site quality, overstory regeneration patterns, and ecosystem health. To better understand understory dynamics and disturbance response, this study examined herbaceous vegetation in managed and mature mixed-mesophytic forests of southeastern Ohio. Specific objectives were to examine: (1) spatial and temporal variability of understory vegetation in an old-growth mixed-mesophytic forest; (2) herb layer dynamics relative to site quality in recently logged and mature oak forests; (3) the relationship of understory vegetation to seasonal soil nitrogen availability in logged and mature stands; (4) the role of the seed bank in post-harvest forest succession; and (5) effects of postharvest light and soil physical properties on understory forest herbs. Sampling season, topographic aspect, and spatial scale (micro- vs. meso-scale) strongly influenced old-growth understory composition and diversity. In recently clearcut and mature forests, age, sampling season, aspect, and fertility significantly influenced understory composition. Soil C:N ratio was a strong predictor of understory richness in mature forests but weakly related in clearcuts. Seed bank composition differed markedly from aboveground vegetation, but both showed strong topographic and disturbance responses. Experimental treatments simulating post-harvest light and soil compaction conditions caused reduced growth in most study species while patchy, intermediate light levels mimicking mature forest understories often enhanced growth. Results suggest that: (1) forest understories may be frequently undersampled, with sample size, area, and season critical considerations for diversity assessment; (2) understory disturbance response varies seasonally and with site quality, factors important to our understanding of forest management impacts; (3) given the strong relationship of soil nitrogen and forest understory diversity, changes in nitrogen availability may dramatically influence understory dynamics, diversity, and disturbance response; (4) a better understanding of environmental and sampling influences is needed to clarify the role of the seed bank in forest recovery; and (5) management approaches mimicking natural light, soil, and disturbance properties may be essential to the maintenance of eastern forest herbs. |
