Because of the inherent value of the species, there has been considerable interest in the planting of black walnut in Indiana. Plantations are established for a variety of reasons, including long-term investments, establishment of legacies for children or grandchildren, or the enjoyment of planting and tending trees with the recognition of future economic returns. Properly planned and managed, a black walnut plantation can be a sound economic investment while also providing aesthetic and environmental benefits.
Before proceeding with plans for a black walnut plantation, there are several important factors you should consider. Is your land suitable for black walnut? What type of planting stock should you use? What management techniques will be employed? How long will it take the plantation to mature? These are factors that will help you decide if establishing a walnut plantation is appropriate for meeting your objectives. This bulletin introduces some basic information concerning black walnut, and points out where additional information and assistance can be found.
Black walnut grows best on moist, well- drained soils that are deep and fertile. Ideally. soils should be at least 36 inches deep and high in organic matter. Loams or sandy loams provide the best combination of moisture holding capacity and drainage. Black walnut does not tolerate flooded or saturated soil conditions well, nor does it perform well on dry south or southwest facing slopes, or on ridgetops where soils are commonly thin. Black walnut often performs best on moist bottomland sites where drain- age is adequate to prevent soil saturation.
The superior strains of walnut have been selected primarily for stem straightness and rapid height and diameter growth. On good sites, with proper cultural treatments, these trees will perform better, on average, than common black walnut trees. Tests have shown that over the first 15-20 years, average stem straightness was improved by over 20 percent, average height growth was increased 25-35 percent, and average diameter growth was 15-30 percent greater. It is still too soon to tell whether these improvements will hold up over the entire life of the stand. These tests were all performed in Indiana, and care should be taken in extending the results of these tests to other states where conditions may be quite different. Also, actual growth performance will depend on site quality, plantation care, and intensity of management.
The primary benefit of the superior grafts is that, with proper management, they will typically produce a given sized tree in a shorter length of time. These trees also will likely have better stem form and, therefore, be more valuable, particularly for lumber. There are still some questions yet to be answered concerning the impact that faster growth rates will have on the veneer qualities of these trees.
The primary drawback of the superior planting stock is currently the high cost per tree. In 1995, the cost is approximately $25 per tree, although this will likely change over time as availability and demand changes. The high cost per tree is partially offset by planting fewer trees per acre; however, initial plantation establishment costs using superior grafts are substantially higher than they are when using nursery produced seedlings.
Black walnut nursery stock is very capable of producing high-value crop trees; though, on average, its growth will be somewhat slower and form somewhat poorer than that of genetically superior stock. With time, proper care, and selective thinning, however, these seedlings can produce quality black walnut trees. Planting more trees than needed, and then selecting the better trees to remain during a series of plantation "thinnings" can result in a successful plantation containing fast growing trees with excellent stem characteristics.
The main benefit of nursery stock is the low cost per seedling which, even at higher planting rates, will result in lower plantation establishment costs than planting with improved grafted stock. This benefit will be partially offset by the need for more intensive plantation management, especially pruning and thinning.
While wide spacing allows for rapid tree growth, it also allows room for weeds and other competing vegetation. When uncontrolled, this can reduce tree growth in the same way as if they were competing with other trees in the
Planting Stock Type Trees per Acre Average Tree Spacing (ft) -------------------------------------------------------------------------- Superior Grafted Stock 140 17-18 (plant 15'x20') Superior Seedling Stock 200-300 12-15 Nursery Stock 400-500 9-10 --------------------------------------------------------------------------
plantation. Wide spacing also promotes the development of larger lateral branches, and does not help correct poor stem form the way closer spacing does. Finally, wide initial spacing in the plantation means you will have fewer trees to select from when thinning the plantation to favor the best trees.
The decision of how many trees to plant represents a trade-off. Wide initial spacing promotes rapid tree growth, but may increase costs associated with cultural treatments such as pruning. Closer spacing can lower these costs, but does so at the expense of individual tree growth rates and leads to longer rotation lengths.
The correct planting density will depend, in part, on your management objectives, the stock type planted, and the management practices you employ. Another important consideration is the type of equipment you will be using in your plantation. The spacing between rows should allow adequate room for you to move within the rows while mowing, pruning, or performing weed control.
In most cases where an investment is made in a black walnut plantation, one primary objective is to produce large, high-valued trees. This usually includes the production of veneer grade logs, but may also include production of both sawtimber and nuts. Under this objective, the goal is to get the trees to the minimum merchantable sawtimber size, and then to the larger veneer grade sizes, as quickly as possible. This is best done by maintaining rapid individual tree growth, which is best accomplished by keeping the tree density below the point where trees are strongly competing with one another.
Given the objective of rapid production of high value trees, recommendations can be made for appropriate planting densities for different stock types. Realize, however, that these are only recommended target tree densities which may vary. For example, if nut production is also an objective, tree spacing might be increased slightly (i.e. lower density) to allow for the development of larger crowns. If an intercropping system is being considered, tree density may be even lower. If you're interested in minimizing the costs of certain cultural treatments, then density might be higher.
Another option to consider is to plant a lower density of walnuts and interplant other species. A common approach is to interplant with a "nurse" tree, such as European black alder or white pine, to help promote better stem form on the walnuts. Professional foresters commonly recommend planting a mixture of species in a plantation. Matching black walnut with another species of similar growth rate can provide better utilization of site resources and provide greater diversity which may lend itself better to multiple objectives.
The final target number of trees per acre to manage for can vary, and will depend on the owners preferences. If your goal is to continue to maximize individual tree growth and shorten the rotation as much as possible, then a reasonable target would be to manage for 25-35 trees per acre when the average tree diameter has reached 18-20 inches (35-40 foot average spacing). A more conservative approach would be to manage for 50 to 75 trees per acre when average diameter is 18-20 inches (25-30 foot spacing). The higher density will result in a longer rotation as the trees take longer to reach the target size. but total stand volume will be greater and the slower tree growth may result in a higher quality veneer.
Because of the higher variability in common nursery stock, an even greater number of seedlings must be planted to provide adequate assurance that enough trees of suitable quality will be included in the plantation. Common recommendations call for planting at least 400-450 TPA (about a 10 foot spacing) (Table 1.). Again, this will provide for greater selectivity when thinning, and the tighter spacing may enhance tree form. The same thinning targets apply, but additional early thinnings will definitely be needed to reduce tree competition.
The easiest way to control weeds in a plantation is with herbicides. Safe and effective herbicides, labeled for use in forest situations, are available for many plantation weed control needs. Other methods, such as using organic or plastic mulches also exist. While often more time consuming and labor intensive, they offer a choice for those not wishing to use chemical herbicides. Mowing is often used in conjunction with herbicides or mulches but is mostly cosmetic and should not be considered a weed control method.
A common misconception in hardwood plantation management is that control of broad- leaved weeds is adequate to ensure good tree growth. Numerous studies have indicated, however, that control of sod forming grasses may be more critical than controlling broad-leaved weeds.
All plantations should receive early weed control. Higher density plantations reduce weed control problems somewhat, but do so at cost of tree growth. In low density plantations, where complete crown coverage is not maintained, weed control, and particularly sod control, will likely provide benefits throughout the life of the stand. Whether the increased tree growth out- weighs the costs of weed control over the life of the plantation is difficult to say. It will likely depend on the management practices used and the weed problems inherent to the site.
Corrective pruning is the removal of multiple leaders or forks in the stem so that the tree maintains a single, straight stem. This is often necessary because black walnut is prone to producing multiple stems following injury to the terminal bud. Genetically superior stock has been selected for stem straightness, and therefore, requires less corrective pruning. Corrective pruning is done relatively early in the life of the tree; generally up to a tree height of about 17 feet.
Lateral pruning is the removal of branches along the main stem which allows the tree to produce wood without knots. This "clear" wood is more valuable and, in the case of veneer, is required. Lateral pruning should be started when trees reach 6-8 feet tall. A series of prunings gradually increases the length of clear stem on the tree. Each pruning should try and leave 40 to 50 percent of the tree height with a clear bole, but no more than 25 percent of the total length of the crown should be removed in any one pruning. Ideally, you want to prune up as high as practical. At a minimum, you should prune the lower 17-18 feet of the stem and, if possible, the lower 24-25 feet should be pruned. Before pruning, you should make sure you are familiar with proper pruning techniques. Improper pruning can sharply reduce the value of your trees.
With high-quality planting stock, grown on very good sites and managed for rapid individual tree growth, you can expect average tree diameter (at 4½ feet above the ground) to approach 14-15 inches in 30-40 years. Reaching the 18-20 inch diameter class, where higher veneer values are attained, will take longer, perhaps 45-55 years. Use of common nursery stock planted at 400-500 TPA and thinned regularly to select the highest quality trees will result in somewhat longer rotation lengths than attained using superior grafted stock. If you are planting on less desirable sites, or if you do not provide the recommended intensive management practices, then the time needed to produce large diameter trees can be increased significantly.
Rotation length can be an extremely important financial consideration. For example, if we assume a $1,000 per-acre investment in the plantation, with a 50-year rotation you would need to generate $19,936 per acre to realize a 6 percent return on your investment. To realize the same 6 percent return over a 60-year rotation would require $36,271 in per acre revenue-an increase of nearly 82 percent! Extending rotation length can be desirable if it results in bigger trees and thus greater per acre value. However, extending the rotation length just to produce the same economic returns that could be produced in a shorter period under a different management approach will result in a decreased return on your investment.
The Indiana Division of Forestry has district foresters located throughout the state which provide free advice to landowners on forestry matters. In addition, private consulting foresters provide a full range of services including tree planting, weed control, and eventually marketing of your trees. A list of certified consulting foresters is available from Purdue University, state district foresters, or the Indiana Forestry and Woodland Owners Association.
Additional information concerning black walnut management and marketing may be obtained from the Walnut Council, Inc. located at 260 South First Street, Suite 2, Zionsville, IN 46077-1602. Their phone number is (317) 873-8780. There is also a Walnut Council Hotline to answer specific questions. Their phone number is (618) 453-2318.