SILVICULTURAL ASPECTS INTERMEDIATE CUTTINGS

by KENNETEd L. CARVELL, Professor of Silviculture, West Vir- ginia University, Morgantom, W. Va.

ABSTRACT. Correct timing of the first thinning in mixed oak stands depends largely on the composition and condition of the stands and on available markets for small wood products. Delaying first thinnings in high-quality seedling-origin stands until a long, straight, clear bole has developed is of primary importance in assuring high quality of the final crop trees. However, many of our present stands, particu- larly those of sprout origin, need improvement work; and improve- ment cuttings or thinnings should be started as soon as a commercial operation is possible. Growth response in diameter after thinning is usually a gradual process. Older oaks seldom show spectacular changes in diameter growth rate after release.

THINNING break-even point or at a profit. In these early 0 THIN OR NOT to thin? This is the commercial thinnings, cull trees left from T uestion. There appear to be two con- the previous rotation are removed, and the !icting views about the place for thin- stand is generally put in good order-or at nings in the management of even-aged, pole- least as good shape as the stand permits! stage oak stands. One view, expounded by Why this apparent conflict between Euro- European foresters, is that oak stands should pean recommendations and our actual field be kept tightly closed, except for early light practice in the eastern United States? Is it cleanings, until after full height growth is because we ignore European experience, attained. This would place the first com- when we know that they have raised excel- mercial cutting in the young-timber stage, lent stands of oak for centuries? Actually, if thus precluding the use of thinnings in pole- we examine the situations influencing each size oak stands. According to European silvi- philosophy, we find that our thinking is not culturists, stands should be kept in this dense in conflict. There is a place for both philoso- condition until age 40 or 60, to allow long, phies, each under the proper stand condi- straight, clear boles to develop. tions. The other view, adopted, or at least prac- Most European oak stands are far different ticed, by many American foresters, is that in composition, character, and condition our stands should be entered as early as pos- than our eastern American oak stands. Their sible to make needed intermediate cuttings. stands are of seedling or seedling-sprout ori- Often these cuttings are made just as soon as gin, well-stocked, and either pure or mixed enough merchantable material can be re- with a few desirable associates. When seed- moved to carry out these operations at a ling stands do not develop in this way, EWQ- pean foresters, with their more abundant and C sorting over of individual stems early in the cheaper supply of labor, use a light cleaning rotation. Superficially it would seem that all or a series of light cleanings to make certain stands would benefit from cleaning, but cer- that the stand reaches pole-stage in rela- tain recent evidence indicates that in many tively fine condition. oak stands desirable changes in composition Occasionally we encounter similar high- and stocking take place naturally without quality stands in American forests, which the help of expensive cleaning operations. have developed through some fortuitous cir- GROWTH RESPONSE I cumstance. Where such stands occur, most American foresters are reluctant to open AFTER INTERMEDIATE CUTTINGS these stands up until full height growth has Growth response is often given as the been attained. These occasional superior oak prime motive in thinning pole-size stands. stands will yield high quantities of quality Recent measurements in oak stands that sawlogs- and veneer bolts. have received previous partial cuttings cause However, most of our oak stands are not us to question whether the magnitude of re- of this high quality and give little hope of sponse for oaks, and for many other hard- quality development without aid through woods, is as great or dramatic as we learned silvicultural treatment. Many of our stands in our silvicultural textbooks. Perhaps much are of sprout origin, often 100 percent that has been written about growth response sprout. Here early removal of those stems has been based on experience with southern that show the greatest tendency to develop pines and other extremely responsive species. heartwood rots from the old stump seems An unpublished study of white oak re- extremely important. In addition, our oak sponse, conducted 8 years after a 40- ear-old stands are often diverse mixtures of both de- stand was thinned, showed no signif? cant in- sirable and less desirable oaks, heavily inter- crease in diameter growth, regardless of the spersed with low-value hardwoods that tree's vigor prior to thinning. threaten to suppress and crowd out the few In another study where northern red oaks desirable stems. Other problems confound- had been heavily released by selection and

< ing the management of these stands are past shelterwood cuttings, the diameter growth ground fires, disease, uneven stocking, and rate of trees on lower- and middle-third vines. slopes showed no change during the 7 years Thus we feel that most of our oak stands after release. Released red oaks on upper- should be molded as soon as merchantable third slope positions had a small but signifi- cuttings can be made, to improve composi- cant increase in annual diameter growth. tion, eliminate the undesirable sprouts, adjust However, unreleased controls on the same spacing, and improve bole form. Available site showed a small but significant decrease markets in each area determine just how in diameter growth during this same period early this first thinning can be made; but the (attributed to the same amount of wood earlier it is carried out, the better the final fiber being distributed over an increasingly stand will be. Here in West Virginia we larger girth). Thus it was concluded that often enter oak stands at age 25 and remove there had been a small increase in wood Dro- as much as one-third of the basal area per duction for oaks since the partial euAngs acre for pulpwood. (fig. 1). I If we assume that response to release, in terms of diameter growth, depends initially on the tree increasing its photosynthetic sur- Forest managers often wish that they had face and establishing a more extensive root a larger budget that would allow them to system (a slow process for most oaks), then carry out cleanings in their seedling-and- oak response in diameter growth would be a sapling-stage hardwood stands. Actually the gradual process, better demonstrated by need for cleaning is often diacult to assess, long-term studies. and no general statement can be made that We have just completed a 15-year sum- every young oak stand will benefit from a mary of 40 one-acre research plots at the West Virginia University Forest. Twenty- On the drier oak sites, northern red, black, four of these plots were established on oak white, and chestnut oaks competed success- sites. Half of these experimental areas re- fully with the less desirable species. How- ceived a cleaning during the sapling stage, at ever, where scarlet oak was abundant in IS years of age. This cleaning adjusted spac- young stands, its exceedingly rapid growth ing, favored the better species, and removed allowed it to crowd out more desirable oaks. poorly formed sterns. Other plots had no Thus we felt that the cleanings on the drier cutting until 10 years later, age 25, when a oak sites were justified where scarlet oak commercial thinning was made. Analysis of made up a considerable percentage of the plot data indicated that the cleaned plots had mixture, if other desirable oaks were present only a slight improvement in composition that could be favored. Northern red oak ap- over the plots where the cutting, performed peared well able to compete with all other as a commercial operation, was delayed. species except scarlet oak, and automatically On the better oak sites, whether cleanings dominated many sites where it was origi- were used or not, yellow-poplar and north- nally a major component. em red oak outgrew the other species and Cleanings may also be necessary, if the dominated the stand. Our conclusions for management policy favors white oak over these good sites were that if the cleaning the red oaks. In certain areas, particularly could be made at a profit for firewood, it was where the soils are derived from limestone, justified; however, if the cleaning had to be white oak of exceptional quality develops; made at a direct cost, as an investment, then and white oak brings a premium price. In the slight improvement gained through this mixed oak stands-such as the white oak-red operation was not justified. At present, it is oak-hickory type-white oak, because of its difficult to tell which plots had the cleanings slower height growth, often falls into the and which had this work done later through lower crown classes early in the life of the thinnings. stand. During the sapling stage, cleanings

Figure 1-A comparison of the diameter growth rate of the controls and the released red oaks during the period 1957-63. Although the middle- and lower-third slope oaks did not show an increase in annual diameter growth, they did not decline during this period, suggesting an annual increase in wood fiber production. I i

YEAR can effectively discourage the faster-grow- ing; and when thinning, where a choice of ing oaks and increase the proportion of species is possible, often those known to white oak permanently. produce the most epicormic branches are re- Another situation under which cleaning is moved. Light thinnings and low thinnings often needed, and where the need is evident have been favored, because there seems to be early in the rotation, is where mature oak a direct correlation between thinning in- stands, which had an understory of oak seed- tensity, crown disturbance, and epicormic lings, were clearcut to allow this understory branching. to form the nucleus of the new stand. If the Recently, genetic differences have been crown canopy of the mature stand was kept identified as a major factor in determining tightly closed during the latter part of its the number of epiconnic branches produced rotation, the oak understory seedlings are of after thinning. Evidently within a species low vigor, and their recovery rate after ex- some individuals have a proclivity for posure is slow. Low-vigor oaks are easily ducing epicormic branches, while otye ers identified by their lack of a vigorous leader, produce few or none. Most trees that feather and by their flat or umbrella-shaped tops. out heavily after thinning give some indica- When low-vigor oaks make up the majwity tion of this tendency in the number of epi- of the oung stand, response to release is cormic branches present on the bole before slow, oJ ten requiring 3 to 5 years. the stand is opened up. Our studies, however, showed that most During the past few years I have used the low-vigor oaks will recover a good growth number of epicormic branches on the bole as rate. During this recovery period, red maple, a guide in marking in pole-size oak stands, to sassafras, blackgum, black locust, and various determine which trees to leave and which to shrubs and small trees may grow rapidly cut. Observations after cutting seem to sup- and resuppress these oaks before they have port this method of restricting epicomic regained a competitive growth rate. Many production. Trees with no epicormic of our stands of poor species, occupying branches before cutting generally have few former oak areas, have gained control of the after cutting, and these few shoots are re- site in this manner. A well-timed cleaning stricted to the area immediately below the can often mold the composition on such sites crown. Those oaks that have many epi- and assure that oak will dominate the next corrnic branches before cutting feather out crop. very heavily after exposure, and these branches are distributed over a great length EPlCORMlC BRANCHING of the bole. Most hardwood foresters are concerned Epicormic branching evidently cannot be about epicormic branching. This condition eliminated entirely, but whether to withhold appears to be stimulated after opening the intermediate cuttings for this reason seems stand through intermediate cuttings, par- to be clearly a question of choosing the ticularly after thinning. Often e icormic lesser of two evils. If the thinning will gener- branching is given as the reason ?or with- ally improve the composition and form of holding thinnings. In extremely high-quality the remaining trees, and will yield sufficient stands, I agree that this is a valid reason for income to offset the degrading effect from delaying thinnings for many years-at least "controlled" epicormic branching, then until late in the rotation, when the defect thinning must be considered the lesser of two caused by these branches will occur only in evils. the superficial wood. Many recommendations have been made LIBERATION CUTTING about how to reduce epicormic branching after thinning. Hardwood thinning patterns One intermediate cutting that should play that leave only strong upper-crown-class a more prominent role in oak management- trees are favored. Certain species are known and one that costs relatively little yet can to be especially prone to epicormic branch- have a profound effect on the development of the new stand-is liberation cutting. Old cide is applied. Injected trees rarely break cull trees left from previous logging opera- off at the point of injection. Trees treated tions often tower above our young second- in this way remain standing after death and growth oak stands. With each passing year disintegrate gradually on the stump, causing these standards expand their crowns and do little or no damage to the young stand be- increasing dainage to the developing stand neath, as the twigs, limbs, and finally the beneath. With our presently available herbi- bole come down piecemeal. Of all the inter- cides, these cull trees can be removed easily mediate cutting, it appears that more good and inexpensively. can be done throughout a forest with The tree injector offers the most promise judicious investment of limited funds for for this work, because injecting does nor liberation cutting, than from any other im- weaken the tree at the point where the herbi- provement operation.