Forest Regeneration – Methods and Models

Regeneration, the replacement of existing trees with new ones, is the key to sustainability of both managed and unmanaged forests. In managed forests, an understanding of how different tree species regenerate is fundamentally important to the development and design of regeneration methods that remove existing stands and create new stands to satisfy management objectives. And this understanding of how tree species regenerate can be used to develop regeneration models that can be applied to existing stands to predict regeneration outcomes and guide managers in their choice of methods to apply.

Our research shows:

• Most tree species in our upland hardwood forests have a “persistence” regeneration strategy. In other words, the presence of these species (including oaks, hickories, and many others) in new stands created by the application of a regeneration method, depends on their prior presence as advance reproduction that persists through disturbance and (or) mature trees that can sprout after the disturbance.
• Larger advance reproduction of these species has a higher probability of competing successfully in the new stand than small advance reproduction.
• Moderate disturbance is required to develop larger advance reproduction of many species on intermediate to high-quality sites.
• Relatively few tree species can become established as new seedlings and compete successfully after disturbance. Some, however, can do so prolifically, e.g. yellow-poplar.
• Models to predict species composition of regeneration can be constructed using a combination of information from experts and empirical relationships.
• Oak regeneration is easier to accomplish on lower quality, drier sites.
• On higher quality, moist sites, successful regeneration of oak requires special treatments to develop large advance reproduction before substantial overstory removal.

Modeling Stand Development

Understanding the compositional and structural development, and treatment response of existing stands is necessary to address the provision of many benefits from forests. Historically, modeling growth and yield of stands of trees has been an important part of research that provided information on the production of wood products. More recently, we have sought to develop models that can provide information about changes in forest composition and structure over time, and that can be related to wildlife habitat. Our unit has a long history of research in this type of modeling. We established and maintain a large set of plots that provide high-quality, long-term databases for developing individual tree and stand level models. In addition, we established and maintained a substantial number of case studies of stand development following regeneration, some dating to the 1920s and 1930s.

Working with several partners, our research shows:

• Provided both individual-tree and stand-level models that allow projection of important stand and tree characteristics into the future.
• Provided estimates of response to thinning at the tree and stand level.
• Shown that production of plant material available to herbivores can be increased by thinning.
• Utilized permanent inventory plots in stands on moist and dry sites for comparison of the response of species to competition.
• Monitored the response of arborescent species to natural disturbance in an old-growth hardwood stand.
• Obtained data on the development of natural hardwood stands that replaced predominantly pine stands killed by the southern pine beetle.
• Demonstrated that the growth response of young trees growing in small (half-acre) openings in the forest canopy, is similar to the response of trees in large, stand-size openings.

 

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