Effects of Midstory Removal Timing on Natural Oak Regeneration in the Southern Ozarks of Arkansas, USA

Abstract Oaks ( Quercus spp.) are ecologically and economically important but often experience regeneration failure largely from insufficient access to limiting resources such as light and space that are exploited by other co-occurring species (i.e., competition). Thus, determination and evaluation of effective management strategies that facilitate oak growth into the midstory and canopy are needed. Shelterwood regeneration methods promote natural oak reproduction by maintaining an overstory or ‘shelter’ of mature conspecifics while creating a relatively open canopy through an overstory establishment cut of select mature trees. The efficacy of this process can be enhanced through removal of midstory competitors; however there are few tests to determine the optimal timing of midstory removal implementation. We tested the hypotheses that midstory removal 1) influences oak reproduction, 2) effectiveness on oak reproduction development differs on north- and south-facing slopes, and 3) timing impacts oak reproduction. In 2017, initial abundance of oak reproduction was measured from 18 plots on five treatment blocks that included both north- and south-facing forests in Arkansas, USA. Treatments were midstory removal using chemical thinning methods in relation to an overstory establishment cut: 1) 2 yrs before, 2) 1 yr before, 3) year of, 4) 1 yr after, and 5) control (no midstory removal). Oak reproduction measured 2 years after the overstory establishment cut generally had the largest increases on north-facing slopes when midstory removal was implemented 1 year before the overstory establishment cut, whereas after 6 years, advance oak reproduction was greatest when midstory removal was implemented 2 years before the overstory establishment cut on south-facing slopes, and total oak reproduction was greatest on control plots. These results indicate midstory removal is only an effective silvicultural tool in a narrow set of conditions.