Responses of ground flora to a gradient of harvest intensity in the Missouri Ozarks

The relationship between the intensity of timber harvest and the composition and diversity of ground vegetation was investigated in upland mixed oak forests in the Missouri Ozarks. Pre- and post-harvest data were collected from 420 permanent vegetation plots to determine if changes in the composition and diversity of ground flora depended upon the intensity of the harvest treatment and, if so, how this varied among life forms of ground flora. The five harvest treatments (no-harvest control, single-tree selection, group selection, thinning, and clearcut) imposed a gradient of overstory canopy cover with reductions ranging from 12.8% in the controls to 83.6% in clearcuts. Both total cover and species richness of the ground flora increased proportionally to harvest intensity. Harvest intensity also caused a proportional impact on the collective relative cover of seven identified life forms of ground flora: annuals/biennials, forbs, graminoids, legumes, woody vines, shrubs, and tree seedlings. The direction of this change was nearly identical for all harvest treatments, reflecting the consistent and proportional decrease in the relative cover of legumes, and increase in the relative cover of annuals/biennials, forbs, graminoids, and woody vines, following all harvest treatments. Closer inspection revealed that changes in relative cover, compared to levels in uncut stands, were observed at different levels (thresholds) of harvest intensity for different life forms, although almost all life forms showed significant differences between uncut and clearcut conditions. Managers may be able to use these differential thresholds of response to harvest intensity to develop silvicultural prescriptions specifically intended to increase or decrease the short-term abundance of certain life forms.