l ~ -' ~~ '-. " .';,: :~< " 1" • ',t, . 1.0 . 1._-:: ~i~ ~II~ E~~ I~ I~ '.;' ." I~ ....::: ~ 1.1 .......I.. ~ 111111.8 i 111111.25 111111.4 111111.6 "i , ~p .~. ; . ~ " " Thinning Practices in Forest Service Southern Pines-With Technical Bulletin 1703 Pest Management Recommendations Acknowledgments Contents We are indebted to the following for their work in Introduction. .. 3 literature searches, reference checking, reviews, and cri­ Growth of Trees and Stands. .. 4 tiques fo~: this paper and the related study: C. A. Height and diameter growth. .. 4 Blanche, J. J. Schmitt, C. R. Honea, J. P. Barnett, R. C. Stand development ........................... 4 Thatcher, and G. N. Mason. The following contributed Stocking.... ... .. .... ........ .... .... .. 5 to field discussions: V. D. Ammon, T. Matney, T. Terry, Thinning Practices in the Southern Pines . .. 6 T. Ebner, P... Blackwelder, J. Hughes, ari.:~ 3. Watson. Initial spacing and the need for thinnings . .. 7 We also appreciate the cooperation of the following com­ Timing of the first thinning .................... 8 panies: Weyerhaeuser, Champion, Masonite, Interna­ Intensity. .. 10 tional Paper, American Can, and Crown Zellerbach. Frequency ................................... 10 Photographs for figures :5, 7, and 11 were kindly pro­ Methods .................................... 10 vided by Dr. Ronald F. Billings, Texas Forest Service. Thinning systems . .. 13 With special tribute to the late D. M. Moehring, who Beneficial Effects of Thinning . .. 17 brought us together and envisioned the ideal of improved increased growth . .. 17 forestry practices through better interdisciplinary under­ Increased utilization .......................... 18 standing. Reduced susceptibility to diseases and insects ..... 18 Genetic improvement . .. 19 Other benefits ............................... 19 Adverse Effects (Ilf Thinning ..................... 19 Felling-related damage to residual trees .......... 19 Skidding-related damage to site and residual stems. .. 19 Indirect thinning damage . .. 21 Impacts of Thinning on Nontimber Values ......... 24 Discussion .................................... 24 Growth factors. .. 24 Damage factors . .. 24 Management Recommendations to Reduce Losses . .. 25 Minimizing damaging agents . .. 25 Minimizing felling injuries. .. 28 Minimizing skidding inj uries . .. 30 Summary ..................................... 31 Literature Cited . .. 31 The use of trade, firm, or corporation names in this publication is fnr the information and convenience of the reader. Such use does not constitute an official endorse­ ment or approval by the U.S. Department of Agriculture of any product or service to the exclusion of others that may be suitable. December 1985 2 Thinning Practices in Southern Introduction Pines - With Pest Management Recommendations T. Evan Nebeker, John D. Hodges, The management of pine forests in the southern Bob K. Karr, and David M. Moehring! United States has intensified on some ownerships as timber resource value has increased and the need for sus­ tained production has become evident. Recent increased demands for wood products, widening price differentials between pulpwood and sawlogs, and greater utilization of both small material and a larger number of tree species have increased the attractiveness of forestry investments. The practice of thinning to improve growth rates has received increased attention as forest management has ac­ celerated during the past 30 years. This has led, in turn, to a significant accumulation of literature on thinning of the major southern pine species. This treatise presents the concept of thinning, reviews and summarizes thinning research, and surveys current field practices. The positive and negative aspects of these practices on current or potential problems are discussed based on recent 'Respectively, professor, Department of Entomology; professor, research. Management approaches are suggested that will assistant professor, and professor (deceased), Department of Forestry, help minimize losses caused by damaging organisms and Mississippi State University, Mississippi State, MS. logging injuries. Intensively managed forest on Vernon Ranger District, Kisatchie National Forest. 3 Growth of Trees and Stands The principles of forest management are not greatly Stann Development different from those affecting other agricultural crops. Trees, like other crops, require light, water, nutrients, Growth of stands is influenced by site quality, age, space, and protection from insects and diseases. The species, stocking level, and forestry practices. fundamental growth processes are quite similar. The ma­ A tree's environmental standing can be expressed jor difference is the length of time required to reach through the concept of site quality. The site index is an maturity. Given this difference, the economics of inten­ integration of several environmental factors, but em­ sive management of a system as extensive as a forest has phasizes the quality and quantity of soil nutrients and not always seemed favorable. water. The rate of stand development increases with in­ The growth potential of a tree is determined creased site index. Thus, the carrying capacity of a given genetically, but actual growth is determined largely by the unit of land for tree production increases with increasing environment. Numerous environmental factors affect site quality. growth; of these, water, nutrients, and light intensity are most easily manipulated. 19 18 17 Saw timber-only UJ 16 Ql heavy thinning .s::. 15 Height and Diameter Growth u c 14 13 Height growth in the four major pines of the ::C a:i 12 Southeast is indeterminate. Additional flushes c::i 11 c (multinodal growth), particularly during midseason, Ctl 10 Ql reflect current soil moisture conditions. However, the ini­ ~ 9 tial terminal bud is formed in the year before extension, 8 and the height growth from the extension of that bud is 7 closely related to availability of soil water during the late 0 1 I I I I I I I 15 18 21 24 27 30 33 summer of bud formation. If height increment is plotted against age, growt. begins slowly at first, climbs more Age of stand (years) steeply, then flattens out (Prodan 1968). It is in these Growth response as a result of thinning (from steeply climbing intermediate years, the grand period of Burton 1982). growth between ages 10 and 30, that foresters try to regulate growth through thinning. Diameter growth is also closely related to availability In an even-aged pure stand, the stages of develop­ of soil water. Cambial cells begin dividing in early spring ment are similar througho.ut the stand at a given age, when soil water is not limited and stop in late summer although more advanced Hages are reached earlier on when conditions are reversed. Across this ring of annual better quality sites than on low-quality sites. For similar growth, early wood cells are abruptly followed by late stockings, a stand on a high-quality site will require thin­ wood cells whose greater density increases the specific ning earlier than one on a low-quality site. gravity. Although the transition from early to late wood Part of the popularity of even-aged silvicultural is not a well-understood process, a decrease in soil water management is the simplicity of stand structure. By availability usually precedes the formation of late wood definition, most trees are of similar age, reaching sapling cells and a continued moisture deficit stops cell division. status-and to a lesser extent, pole and sawlog status-at However, cell division may begin again in midsummer to roughly the same time or stage in stand development. late summer with increases in soil moisture, as evidenced However, taller trees with larger diameters and crowns by false annual rings. In addition, late wood cells con­ suppress the growth of neighboring trees, which may tinue to form until late summer or early fall if soil water become overtopped and eventually die. (Four standard is available (Moehring and Ralston 1967). It is partly crown classes are recognized in forestry: dominant, through these biological principles that growth in­ codominant, intermediate, and overtopped or sup­ crements of individual trees can be regulated through pressed.) As a stand matures, the natural process of com­ thinning practices or stand density control. petition concentrates the growth potential of the stand in the dominant and codominant trees. 4 Uneven·aged southern pine stand, showing size classes. Stocking spacing and thinning to achieve management objectives. The preceding discussion establishes t.he following What are the implications of stocking and stand premises: development? Proper stocking is a term commonly used but as difficult to apply as to define. First of all, proper • Stand differentiation, or stages of development, oc­ stocking is tife number of trees per acre that fully utilizes curs at earlier ages on high-quality than on low­ the site's potential to grow trees. It follows that a high­ quality sites. quality site has a higher carrying capacity and, if properly • Competition directs growth potential of the stand stocked, would carry more trees per acre than a low­ toward dominant and codominant trees. quality site. Second, a given site may be properly stocked, • Competition promotes l:rown differentiation in the once the carrying capacity is reached, with an initial stand. spacing as low as 450 trees/acre or as high as 1,000 or • Realized growth potential is a function of site, stand, more trees/acre. Third, the