Case Study Objectives
- Our main objective was to assess the impacts of post-thinning basal area on epicormic branching in oak species and determine target post-thinning basal area to be incorporated into future thinning practices.
- An additional objective was to try to assess impacts of tree health and condition, and native plant community (NPC) on epicormic branching. Again, this information would be useful in designing future thinning practices.
- A final objective was, if possible, to develop post-thinning stand ingrowth information for use in updating oak stand growth models to better inform forest planning efforts. This would help us establish more realistic re-entry periods for thinning practices.
In the Sandstone DNR-Forestry administrative area, a considerable amount of thinning in oak stands was done between the years 2000 to 2010. Three of the major factors driving this work were:
- Professional interest of Forest Technician Bill Foss in hardwood management.
- Large acreage of oak and hardwood forest types reaching age and condition to make them good candidates for thinning.
- Existence of improved markets for hardwood timber in the area.
Forestry staff noticed greater-than-desired levels of post-thinning epicormic branching on oaks in some of these thinned stands; also, post-thin ingrowth was below expectations under existing modeling.
We selected six previously thinned sites where we had observed varying levels of epicormic branching during field examinations. Data was collected on basal area, tree diameter, age, crown canopy class, and number of epicormic branches in the lower 32 feet, in the summer of 2019.
Since we did not have data for basal area immediately after thinning, an estimate was calculated using tree-ring core measurements of tree diameter growth since harvest.
Further details of data collection methods and calculations are outlined in Figure 6.
What is epicormic branching and why is it important?
Excerpted from the document “Epicormic Branching In Red Oak Crop Trees Five Years After Thinning And Fertilizer Application In A Bottomland Hardwood Stand”; Lockhart, Michalek, and Lowe:
Epicormic branches are shoots arising from dormant buds on stems or branches of woody plants, often following stress and exposure to increased light levels after thinning, storm damage or fire (Helms 1998).
Epicormic branches are considered defects on tree boles because they result in undesirable knots on trees, reducing the monetary value of logs and lumber (Stubbs 1986). U.S. Department of Agriculture Forest Service factory log grade guidelines indicate that the size of the epicormic branch, in addition to the number and location of epicormic branches on the log, is important in determining log grades (Rast and others 1973). If an epicormic branch is > 3/8 inch in diameter at the point of origin on the log surface, then it is counted as a full defect; an epicormic branch ≤ 3/8 inch in diameter is only counted as a one-half defect on logs ≥ 14 inches in scaling diameter (Rast and others 1973). Theoretically, even a single, large epicormic branch ideally positioned on a small log can reduce the grade of the log. Meadows and Burkhardt (2001), in a case study using willow oak (Quercus phellos L.) logs, showed that as few as five epicormic branches on a 16-foot log reduced the log grade of trees with an average diameter at breast height (d.b.h.) of 19.1 inches. They also showed that epicormic branches developing on willow oak boles after partial cutting reduced willow oak log grades by 50 percent. The value of the lumber from these logs was reduced 13 percent due to surface knot defects caused by the epicormic branches.
A primer on timber quality and market value
Since we do most forest management through commercial timber harvest, improving timber value and marketability of a stand can improve forest management opportunities. Hardwoods are mostly used in products such as furniture, where appearance is the driving factor in determining value. Two major factors drive hardwood timber value:
- Appearance: Larger, straighter trees with few limbs on the lower bole and little or no rot produce boards with few appearance defects such as knots and are therefore worth more money.
- Species: Species is also a huge factor driving market value and red oak is consistently one of the highest demand species in the hardwood marketplace.