Artificial Regeneration of Hardwoods
Randy Rousseau, Forestry Specialist
Amy: I know that in the past we have discussed artificial regeneration of pines, however we have not thoroughly covered artificial regeneration of hardwoods. Is there really that much difference between pine and hardwoods?
Randy: The difference between the two can be as much as daylight and dark because of a number of reasons. First, let’s discuss the number of species between hardwoods and pines. Southern pines are basically comprised of five different species, which includes longleaf, slash, loblolly, shortleaf and spruce pine. The primary commercial species that is grown in plantations throughout Mississippi is loblolly pine. The reasons for this is that this species is very adaptable to a variety of sites and is capable of growing in those areas that the other four pines grow on. This ability of this species to grow not only on sites throughout Mississippi but other sites throughout the southeast has been one reason why loblolly pine has been selected by most industrial programs.
But, when we talk about hardwoods we have to include a variety of commercial species because hardwoods are very site specific. In other words, hardwood grow best where the soils meet their specific needs and where they can effectively compete for moisture and nutrients. Today, there are more than 20 commercial hardwood species. Therefore, when we talk about hardwoods and specifically regeneration of hardwood species we typically focus on natural regeneration rather than artificial regeneration. The primary reason for using artificial regeneration is when the hardwood seed source is lacking. Today, this has been the case for the conservation reserve program and the wetlands reserve program where land clearing for agriculture production eliminated the hardwood seed source, this is especially true for heavy seeded species such as oaks.
Amy: What are other key points that a landowner needs to know if he wants to plant some type of hardwoods say in an old pasture or even an agricultural field into hardwoods?
Randy: Any time there is a question of what species you should use, it is best to talk to one of the forestry extension agents for that area. They would help you understand the general variability of the soil types and those species that commonly do well on them. But, if you want to understand this for yourself the best way is to use the Baker/Broadfoot site evaluation for commercially important southern hardwoods. This manual can be downloaded through the USDA Forest Service web site and listed as the General Technical Report SO-26. This will provide you with a 50-year site index score for 13 southern hardwoods including cherrybark oak, Shumard oak, Nuttall oak, water oak, willow oak, swamp chestnut oak, sweet pecan, sycamore, green ash, sweetgum, hackberry, sugarberry, and yellow poplar. There is also a 30-year site index for cottonwood. The guide provides easily questions concerning four factors including soil physical condition, moisture availability during the growing season, nutrient availability, and soil aeration. The answer to each question is placed into best, medium, and poor categories which are assigned a number. The total of all questions per species results in a site quality score or site index. If the number falls below the minimum site index score for that species the site is then determined to be unsuitable. For example if the site quality score is determined to be less than 70 than that site is unsuitable for seven species including sycamore, pecan, yellow-poplar, cherrybark oak, Shumard oak as well as water and willow oak. Once you have selected the species to plant you need to obtain a quality seedling from a respected nursery. You need to remember that the faster growing species such as cottonwood, sycamore, and yellow poplar should be planted at a wider spacing whereas oaks should be planted much closer together and typically inter-planted with a compatible species such as sweetgum to provide an overall better quality stem as the tree ages. When planting agricultural fields, site preparation will include disking and sub-soiling to alleviate any type of plow pan and ease planting. Pasture land maybe a little different in that if a heavy sod is left and should be eliminated prior to disking. Once the grass is dead the ground should be disked and then sub-soiled passing through any traffic pans. These tips should get make your hardwood plantation a success during not only the first year but many more to come.