Results 2 years after initial treatment
There was good initial establishment of red oak regeneration, with no significant differences between site preparation treatments
Tables 3 and 4 (at links below) show that after two growing seasons, the ratio of seedling height growth to seedling diameter growth was highest on the control treatments and lowest on the chemical site preparation treatments. The ratio of height growth to diameter growth was highest for the premium seedlings, followed by the nursery run seedlings, and the planted acorns. Tree shelters improved height growth for both the seedlings and planted acorns. Seedling survival rates varied from 93 to 96 percent while the survival rates for the planted acorns varied from 16 to 22 percent. There were no differences in survival rates between site preparation treatments. (Duplissis, 1994).
Table 3. Mean percent survival of oak planting stock types in 1992 and 1993
Table 4. Mean height and growth of planted northern red oak seedlings and acorns by research block after 1 and 2 growing seasons
NOTE: 1993 height measurements may not be equal to 1992 height plus annual growth due to seedling mortality and rounding errors.
Results 29 years after initial treatment
We were unable to re-establish locations of the different 1991 research treatment plots, so we can’t draw any new conclusions about how the various treatments may have impacted oak survival after 29 years. We do know from the Duplissis thesis that after 2 years, there was good initial establishment of red oak on all plots, with no significant differences between treatments.
Overstory and Mid-story
Measurements in 2020 indicate a diverse hardwood stand. As shown in Table 5 below, red oak, black cherry, hackberry, paper birch, basswood, and elm have the greatest basal area and frequency. A variety of other species are also scattered throughout the stand in smaller amounts, including black walnut, boxelder, butternut, white oak and several others.
While the oak species present in the current stand are a combination of reserve trees left during harvest and trees that regenerated post-harvest, most of their abundance and volume is from trees that were reserved at harvest time, not trees that regenerated post-harvest.
Table 5.Tree species density by DBH class, and frequency on plots in 2020
We did not get as much oak regeneration as we had hoped for
In 2020, there are some oaks that regenerated post-harvest, but not nearly as many as we would have liked. This is in spite of good numbers of seedlings for at least the first two years on the research plots (see Table 3).
Frequency data shows that less than 20% of the site contains oak regenerated post-harvest. Total stem counts in the 3-5 inch DBH class are well below minimum stocking standards (Sanders, 1977). Figures 2 and 3 (see links below) show that all oak species regeneration abundance is underrepresented.
Figure 2. 3 to 5 inch DBH Regeneration by Species and Abundance
Figure 3. 5 to 9.9 Inch DBH Trees by Species and Basal Area
Explanatory note on use of DBH data to distinguish harvest residuals from trees regenerated post-harvest: We gathered tree data by diameter class as a practical way to help identify which oak trees were those reserved from harvest in 1991, and which were regenerated after harvest. We estimate that:
• All trees from 3 to 5” DBH, and the majority of those from 5 to 10” DBH (Table 5) regenerated post-harvest.
• Virtually all trees over 10” DBH (Table 5) are harvest residuals.
While not a perfect way for making the harvest residual vs. post-harvest regeneration distinction (since the 5-10” DBH class is mixed), it is the most helpful and practical methodology we could think of and provides very useful information.
Intermediate stand treatments to release oak would have been necessary for more oak to survive!
We know from data taken the first 2 years after treatment that there was good initial establishment of red oak seedlings on the research plots. The relatively low oak component in 2020 indicates that either vegetative competition, animal predation or more likely a combination of these two factors killed oak seedlings before they became “free-to-grow”. It clear that additional crop tree release and protection work in years 2-10 post-harvest would have been necessary to increase oak survival.
There is a modest amount of healthy, well-formed mature oak from harvest residuals
Red oak comprises 19.6 square feet/acre of basal area for diameter size classes greater than 9.9-inches DBH. Red oaks in these size classes are all reserve trees left during harvest rather than natural or artificially regenerated seedings/saplings/small trees post-harvest. While modest in number, they are well distributed throughout the stand. They have excellent form, healthy crowns, and have exhibited outstanding growth over the last 29 years.
The stand has an excellent component of healthy, well-formed black cherry
One of the positive outcomes of the treatments is the presence and abundance of healthy, well-formed black cherry in the stand. Time will tell whether the black cherry on this site (and several others observed during case study field work) will reach maturity in a healthy and merchantable condition, but it looks very promising after 29 years. There is some black knot disease and stem cankering, but it appears to be present on less than 30 percent of the stems. Of note for forest managers, the Native Plant Community (NPC) guidance for Southern Dry-Mesic Oak Forest (MHs37) indicates that black cherry may need some intermediate release to reach heights much above 10 meters. Our crop tree release treatment in 2014 was timely and likely had a very beneficial impact on black cherry health and vigor.
The stand has a notable component of butternut
There is a notable presence of butternut in part of the stand that established after the 1991 treatments. While there is individual tree mortality, and variable amounts of cankering, some of the live stems appear to be fairly healthy. It will be interesting to see if any butternuts survive over the next 20 years, or if they all die and are replaced by other species.
Over 30 percent of the competing elm and hickory stems girdled and chemically treated in the 2014 crop tree release survived
It is not clear from our observations why these stems survived, but we have seen the same phenomenon on several other case study sites. Follow-up discussions with Forestry staff will take place to determine if changes to crop tree release treatment specifications might be needed. These stems continue to compete with oak, cherry and other crop trees.
Because their impact on the future management of the stand is likely to be negligible, we did not collect understory regeneration data for sizes below 1” DBH. We did collect data for regeneration from 1 to 3” DBH and include it here because it may be of some interest to managers moving forward.
One notable takeaway from Table 6 (see link below) that may have the greatest impact on future stand management is the complete absence of sugar maple, and the low amount and distribution of ironwood. We conclude that future competition with crop trees will be negligible. While there is abundant hackberry and elm sapling regeneration, the impact on future crop tree management will be minimal due to crown position below the overstory crop trees, and intermediate shade tolerance.
Table 6. Stems/acre of 1 to 3 inch DBH regeneration by species and plot frequency in 2020
We did not take herbaceous plant sample plots in this case study. Our general observations during field visits confirms ground and shrub layer cover plants common to the Southern Dry-Mesic Oak Forest (MHs37) NPC.
The only invasive species we found was buckthorn, which is present at low to medium densities over the entire site. Buckthorn is a plant to be aware of and consider when planning future stand treatments and regeneration.