Innovative forestry practices that use natural disturbance and stand developmental processes as models to increase forest complexity are now being considered as a way to conserve biodiversity while managing for a range of objectives. We evaluated the influence of harvest-created gap size (6, 10, 20, 30, and 46. m diameter gaps and uncut references) over 12 growing seasons on planted tree seedling growth and survival for four tree species that tend to experience poor recruitment in both managed and unmanaged northern hardwood forests in eastern North America. We expected, based on silvics, that the three mid-tolerant species (yellow birch [. Betula alleghaniensis], red oak [. Quercus rubra], and white pine [. Pinus strobus]) would perform best in intermediate-sized gaps, and the one shade tolerant species (hemlock [Tsuga canadensis]) would perform best in small gaps. However, all four of the species grew taller with increasing gap size, while survival was highest in intermediate gap sizes. Although gap size had statistically significant effects on growth and survival, the magnitude of the effects were modest. With the exception of a small portion of white pine individuals (35% of survivors were >150. cm tall), trees were short (<1. m) and few survived (<30%) 12. years after planting. Evidence from deer exclosures and individual gaps with high shrub (Rubus idaeus) densities suggest that browsing and shrub competition resulted in poor tree growth and survival, and may have constrained the magnitude of many potential tree seedling responses to gap size. Our study highlights the management challenges of using gap size as a tool to influence future forest composition in forests with overly abundant deer and pervasive shrub layers and underscores the importance of silvicultural prescriptions that include measures for reducing these impacts.
Bibliographical noteFunding Information:
This study was supported by the U.S. Forest Service: the Northern Research Station (and former North Central Research Station) funded research staff to design, collect and analyze data, the Chequamegon-Nicolet National Forest (and former Nicolet National Forest) provided logistical support of the timber harvest to implement study design, and the Washington Office Research & Development program, the Scientist Recruitment Initiative, supported scientist training at the University of Minnesota for Kern. The research could not have been completed without the additional mentoring and leadership of Brian Palik, Anthony D’Amato, and John Zasada. We greatly appreciated the technical assistance from the Reich and Montgomery Labs, Adam Weise, Kris Gray, Emma Schultz, and Ben Gosack, among many other field technicians. Terry Strong designed the study and led data collection in growing seasons 1-4. Christel Kern led data collection in growing season 12, analyzed the data, and wrote the initial and most of the subsequent drafts of the paper. Rebecca Montgomery and Peter Reich contributed equally to the manuscript providing guidance and ideas in data analyses and interpretation and contributed to the writing.
- Gap partitioning
- Ground-layer plant competition
- Harvest-created gaps
- Northern hardwood forest