Let’s face it, pine seedlings can be pretty tough. Just because your seedlings are alive doesn’t mean that they are growing at their best. Survival is not enough to guarantee a good stand of timber at final harvest. Pine seedlings require sufficient sunlight and nutrients to become firmly established. Any other vegetation near that seedling will compete for site resources until the seedling reaches 4 to 5 feet in height. So, why bother doing an herbaceous or woody release treatment? The simple answer is that a little bit of extra care in those first few years can result in more value at the end of rotation. A release treatment allows the seedling room to grow by controlling the competing vegetation. Not only does free growing space increase survival chances for the seedling, but it also increases the growing potential of the seedling, allowing it the potential for greater quality growth over time (Cunningham et al., 2019). Controlling weeds in the early years of a tree’s development leads to larger stem diameters (Miller et al., 2003) and will have more growth flushes and longer shoot elongation at each flush, effectively increasing height growth (Hansen and Bilan, 1989). Release can be accomplished using mechanical or chemical methods, or by a combination of the two.
Mechanical release treatments include mowing, brush cutting or physical removal by pulling or chopping. When landowners establish a plantation in an old agricultural field or pasture, the layout of the plantation can be designed to allow mowing for grass and herbaceous control by spacing rows 2 to 3 feet wider than the width of the equipment being used. The first year of plantation establishment will have more frequent need of mowing than later years. As the trees get taller, mowing can be limited to once per season around midsummer until the trees have successfully out-competed the surrounding vegetation. Hand-release treatments may be needed in cases where invasive species and difficult-to-control species must be physically removed from around seedlings. In these cases, once the competing vegetation has been removed from the seedling, a follow-up spot application of herbicide may be needed to prevent resprouting.
Landowners who reestablish plantations on cutover forestland may find they have both herbaceous and woody competition issues in the first few years of stand growth and development. These landowners can use brush cutting or hand chopping effectively where hardwood sprouts are competition. Combining chopping with prescribed herbicides can result in greater effectiveness, especially for hard-to-control species. Cost can become a factor in hand-release treatments so it is important to only control as much as needed to allow the seedlings room to be “free to grow.”
Chemical release treatments involve the application of herbicides. This treatment strategy is very effective at controlling unwanted competing vegetation in planted pines. However, there is generally a higher cost per acre for the use of herbicides, and special licenses must be obtained by the applicator. Use of herbicides for pine release normally occurs when pine seedlings are between 1 and 3 years old and depends on the amount of competing vegetation present on the site. In order to prevent damaging the young pine trees, use of herbicide as a release treatment is normally applied during the summer and early fall. These chemicals are targeted to species other than pine. The timing of the application coincides with the time of year with peak leaf area on the competing vegetation, allowing maximum absorption of the chemical herbicides. There are many methods available to apply a chemical release treatment from either ground-based equipment or aircraft. Methods of applying herbicides for release include:
Spot spraying: The herbicide is applied using a backpack sprayer to an area around each individual seedling.
Strip spraying: The application of a path of herbicide about 2 feet wide along the line of planted seedlings. This can be accomplished using a backpack sprayer or a ground-based spraying apparatus attached to a vehicle (tractor, skidder, 4-wheeler, etc.).
Broadcast spraying: The application of herbicide to the entire planted area by ground or aerial equipment using state-of-the-art technical support equipment to prevent off-target application of herbicides and overapplication of chemicals.
After the trees are greater than 5 feet in height, allowing woody competition to overtop (become taller than) the pine saplings can be detrimental. If hardwood competition remains untreated, it will restrict pine growth over time, causing a loss of profits. Landowners might believe that once the pines outgrow the smaller hardwoods that the competition impacts will go away. Unfortunately, research has shown this is not the case (Harrington and Edwards, 1999; Moorhead, 2001). Even though the hardwoods are smaller than the pines, they are competing with them for the resources of growing space, water and nutrients. For each unit of hardwood basal area, a corresponding potential pine basal area of 1.5 to 2.5 square feet is displaced. This means, for example, that if a landowner allows their hardwoods to reach 6 inches in diameter and there were around 102 hardwood trees per acre in the pine plantation (20 square feet of basal area), those trees would displace between 30 and 50 square feet of potential pine basal area. So, because a 14-inch diameter pine tree has about 1 square foot of basal area, the landowner has effectively removed between 20 and 50 saw-timber class pine trees per acre by allowing the pulpwood-sized hardwood to remain. That is at least a truckload of wood lost!
So, are your seedlings free to grow, or are you asking, “Where did they go?” Do your pine trees need a release treatment?
Cunningham, K; Taylor, E.; Barber, B.; Holley, G.; and M. Blazier. 2019. Forestry Herbicide Prescriptions: Western Gulf Region. https://www.uaex.edu/publications/pdf/MP553.pdf.
Hansen, R.S. and M.V. Bilan. 1989. Height. Growth of Loblolly and Slash Pine Plantations in the Northern Post-Oak Belt of Texas. So. J. Appl. For. 13: 5-8.
Harrington, T.B.; and M.B. Edwards. 1999. Understory vegetation, resource availability, and litterfall responses to pine thinning and woody vegetation control in longleaf pine plantations. Can. J. For. Res. 29(7):1055-1064.
Miller, J.H.; Zutter, B.R.; Zedaker, S.M.; Edwards, M.B.; and R.A. Newbold. 2003. Growth and Yield Relative to Competition for Loblolly Pine Plantations to Midrotation- A Southeastern United States Regional Study. South. J. Appl. For. https://www.srs.fs.usda.gov/pubs/ja/ja_miller073.pdf.
Moorhead, D. 2001. Forest Herbicides. Warnell School of Forest Resources online publication.
Virginia Department of Forestry. Managing Your Pine Forest. http://www.dof.virginia.gov/manage/pine/how-to.htm.
Texas A&M Forest Service. Herbaceous Weed Control After Planting. https://tfsweb.tamu.edu/uploadedFiles/TFSMain/Manage_Forest_and_Land/Landowner_Assistance/Stewardship(1)/Herbaceous_Weed_Control_After_Planting.pdf.