Principal investigator: Mike Saunders, professor, Forestry and Natural Resources, Purdue University (msaunder@purdue.edu)
Co-authors: Stacy Clark, research forester, USDA Forest Service, Southern Research Station; Don Carlson, forester, Forestry and Natural Resources, Purdue University; Mikaela Scherzinger, assistant forester, Forestry and Natural Resources, Purdue University; Brian Beheler, forest property manager, Purdue University; Clayton Emerson, assistant forest property manager, Forestry and Natural Resources, Purdue University; Robert McGriff, installation forester, Naval Support Activity (NSA) Crane.
Oak regeneration is problematic throughout eastern North America and researchers fear that the probability of a large-scale replacement of oak by more shade-tolerant tree species, such as sugar maple (Acer saccharum) and American beech (Fagus grandifolia), may be imminent.
Decades of research in the Ozarks and Appalachia show that successful regeneration of oak species on mesic habitats, or environments with moderate moisture, is possible but often requires the use of shelterwood regeneration systems in conjunction with repeated application of prescribed fire.
This approach has not been as reliable in xeric, or very dry, sites within eastern North America, however. In addition, many landowners do not have the capacity or desire to use fire, or to apply various management techniques in their woodlands enough to achieve success. The use of gap-based silvicultural systems, which involve creating gaps in the canopy to mimic natural disturbances, in combination with enrichment planting, or planting trees to increase the number of a desired species in a forest, may serve as a viable alternative for the regeneration of oak and other hardwood species.
By utilizing the existing enrichment planting study of white oak (Quercus alba) at Naval Support Activity Crane in southern Indiana and also establishing a network of plantings in recently harvested gaps on four Purdue Forestry and Natural Resources woodland properties across the state, researchers aim to better define proper management techniques (cultural regimes) for white oak and black walnut in underplanting and enrichment planting contexts. They also hope to provide a network of enrichment planting sites that can be used for physiological and genetic studies, which, in time, may be used for studies of precommercial crop tree release and other intermediate treatments.
In addition, researchers look to corroborate past research on white oak completed at Naval Support Activity Crane, where white oak seedlings were marginally competitive in a partial shade environment after three years. In that case, white oak seedlings could not compete in full sun environments even with two years of competition control. With that project now in its fourth growth season after planting, researchers will compare the midterm effects (i.e., years 5-6) of light levels and competition control on planted white oak in the context of both enrichment planting and underplanting.
Initial hypotheses are that growth and survival of the planted white oak will be inversely related to overstory light availability, increase with a longer period of competition control and vary by seed source, with local sources having the best growth and survival rates.
The second objective of the project will build on the Crane study by utilizing a wider variety of seed sources as well as multiple species, which will be planted across a much wider array of site conditions. This work will begin on three Purdue properties: Miller Woodlands, Southeast Purdue Agricultural Center (SEPAC) and Okocha.
It is anticipated that delayed planting of black walnut and/or butternut will allow the persistence of white oak; competition control will result in an increase in growth and survival on productive sites as opposed to less productive sites; and growth and survival of white oak will be greatest on the feathered edge, with black walnut (Juglans nigra) and butternut (Juglans cinerea) doing best in the gap interior. Survival and growth responses will be assessed by species and site conditions over the next four years, covering each of three growing seasons.
This part of the project began with the removal of the entire overstory and midstory in small areas (2-3 acres) and thinned the overstory and midstory to reach a 50% overstory canopy cover in a zone around each area. In May 2024, researchers underplanted 2-0 white oak throughout the harvested areas and into the adjoining unharvested areas. Trees were either tubed or placed inside fenced research plots.
Researchers anticipate that white oak will need release from competitors for a longer period than walnut, likely 2-3 years or more. It is also expected that white oak will survive and be more successful in areas with partial shade from overstory. Walnut, on the other hand, is predicted to be more successful in areas without overstory shade.
In 2025, the team will gather year 1 growth measurements on the white oak, plant black walnut seedlings into the fenced research plots on the existing sites and add three more planting sites to the study (i.e., SEPAC 2, Miller 2, and Martell).
“We expect these studies to provide guidance to professionals and landowners on cultural practices for enrichment planting in forested gaps and under existing canopy,” principal investigator Mike Saunders said. “Furthermore, the Crane study, in particular, can provide strong guidance on future crop tree release treatments with the goals of achieving white oak dominance.”
Goal:
Researchers aim to better define proper management techniques (cultural regimes) for white oak and black walnut in underplanting and enrichment planting contexts. They also hope to provide a network of enrichment planting sites that can be used for physiological and genetic studies.
Methods:
The study is planned for six stands across four FNR properties through the state, which vary in site quality and overstory composition. In each stand, three 0.4 – 0.7 hectare openings, or gaps, have been or will be harvested. All overstory is removed within each gap. Edges around the gaps are being feathered to reduce overstory canopy cover to 50%. The midstory is being removed in these feathered areas as well.
Black walnut and/or butternut hybrids will be added to the plantings one growing season after the 2-0 white oak. In sum, each site will have 650-700 white oak and 100-200 black walnut or butternut planted across gap edges. In all cases, ground vegetation and woody competitors will be controlled for the first two growing seasons after white oak planting.
Analysis of two-year growth and survival trends will primarily test for early differences among species and gap positions (North, East and West).
Collaborators:
Stacy Clark of the SRS of the USDA Forest Service
Matt Salima, master’s degree student, Purdue.
Mikaela Scherzinger, assistant forester, Purdue Forestry and Natural Resources, who was key to installing the study on the first three sites.
Brian Beheler, senior farm operations administrator; Don Carlson, forester; and Clayton Emerson, assistant property manager, Purdue FNR, also helped immensely with the work.