Can coppicing planted saplings improve the growing position of mid-tolerant northern hardwood tree species in harvest gaps?

Abstract

Group harvesting is often used to regenerate mid-tolerant tree species. However, in managed northern hardwood forests of the Great Lakes region, regeneration failures are common among mid-tolerant species regardless of gap size. Coppicing advance regeneration has the potential to alter recruitment patterns within harvest gaps, as some mid-tolerant species have large dormant season carbohydrate reserves in the root system. However, the comparative sprouting abilities of northern hardwood saplings are not well quantified. Furthermore, variation in light availability and chronic browsing from white-tailed deer may modify comparative sprouting abilities. In this study, we tracked the effects of dormant season coppicing and deer exclusion on the initial sprouting response and five-year survival, height growth, and final height of seven-year-old volunteer white ash saplings and planted yellow birch, paper birch, northern red oak, sugar maple, red maple, and American beech saplings across a gradient of harvest gap sizes (10–35 m diameter, <0.5–1.25 tree height) in a mature even-aged northern hardwood stand in northern Lower Michigan, USA. In addition, saplings were given a growing position ranking, which integrated sapling final height and survival status relative to competitors to evaluate the effects of coppicing and deer exclusion on sapling development. Overall, coppicing produced a strong initial sprouting response with nearly all red maple and northern red oak stems initially sprouting. In the absence of deer, appreciable differences in sprout survival and height growth occurred among mid-tolerant and intolerant species and contributed to changes in growing position. Northern red oak sprouts significantly gained growing position over all species through a combination of high survival and modest height growth across all gap sizes. In contrast, coppiced yellow birch and paper birch sprout survival was significantly lower than uncoppiced stems, which contributed to declines in growing position for both species across all gap sizes. Coppicing in the absence of deer had less effect on the growing position of mid-tolerant red maple and white ash and shade tolerant sugar maple and American beech. Without deer exclusion, browsing limited the effectiveness of coppicing by reducing height growth and final height of all mid-tolerant species. Collectively, our results indicate that coppicing does not benefit mid-tolerant species equally and is unlikely to benefit browsing-preferred species in areas with high deer density. Nevertheless, in areas of lower deer density or in situations where sprouts can be protected, coppicing may improve the competitiveness of northern red oak saplings within harvest gaps.