Reversing Mesophication Effects on Understory Woody Vegetation in Mid-Southern Oak Forests

Mesophication has reduced fuel-bed flammability in the Mid-Southern US, limiting the effectiveness of fire alone in promoting disturbance-adapted woody species. We applied combinations of thinning (none, 7, and 14 m(2) ha(-1) residual basal area) and seasonal fire (none, October, and March) at three sites and monitored understory woody response from 2008 to 2016. In combination, thinning and burning had strong negative effects on some mesophytic species (Pious strobus, Ostrya virginiana, and Fagus grandifolia) and positively affected many shade-intolerant and fire-tolerant species formerly suppressed under closed canopies. Such compositional shifts were greatest at our most xeric site, and were related to treatment effects on overstory and midstory density. Seedling density of Quercus spp. nearly doubled (+2,256 stems ha-1()) from pre- to postmanagement. Sapling response was less dramatic; however, indicator and ordination analyses often associated mesophytic and disturbance-dependent saplings with unmanaged and managed treatments, respectively. Fire-season effects were subtle, but more species and greater understory densities were associated with March relative to October burning. Although some mesophytic species (Ater rubrum and Liriodendron tulipifera) responded positively to thinning and resprouted aggressively after fire, our results demonstrate how thinning and burning can initiate the reversal of mesophication's effects on understory woody vegetation.