Báo cáo khoa học: "An overview of oak silviculture in the United States: the past, present, and future"

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Original article An overview of oak silviculture in the United States: the past, present, and future DL Loftis Rogers PS Johnson R 1 1 University of Wisconsin, Stevens Point, WI 54481; 2USDA Forest Service, North Central Forest Experiment Station, 65211 Columbia, MO; 3 USDA Forest Service, Southeastern Forest Experiment Station, Asheville, NC, 28802 USA (Received 6 January 1993; accepted 2 June 1993) Summary — Oaks (Quercus) are important components of forest systems throughout the United States. This overview describes past, present, and future silvicultural practices within the oak- hickory ecosystem of the United States. Past land-use activities favored oak development, but wild- fire and livestock grazing controls have caused severe oak regeneration problems that were not recognized until recently.Prescriptions for weedings, cleanings and the use of stocking charts to con- trol intermediate thinnings were early silvicultural developments. More recently, growth and yield models for managed stands were developed to predict current and future timber volumes. Currently, silviculturists are developing solutions to natural and artificial regeneration problems. Research re- sults indicate that, other factors being equal, regeneration success is favored by simultaneously re- ducing over and understory densities and that oak seedling survival and development is enhanced in large seedlings that have high root to shoot ratios. Future silvicultural practices will have an ecosys- tems focus. oak I silviculture I regeneration / thinning I model Résumé — Un aperçu global de la sylviculture des chênes aux États-Unis : passé, présent, futur. Aux États-Unis, les chênes (Quercus) constituent partout des composants importants des sys- tèmes forestiers. Ce travail a pour but de décrire les pratiques anciennes, actuelles et futures à l’in- térieur de l’écosystème chêne-hickory des États-Unis. Autrefois, les activités réalisées dans l’utilisa- tion des terres favorisaient le développement des chênes. Toutefois, la lutte contre les incendies de forêt spontanés et le pâturage du bétail a entraîné des problèmes sévères pour la régénération des chênes, problèmes non reconnus juqu’à ces derniers temps. Les prescriptions pour le désherbage, le défrichement et l’emploi des tableaux de stockage pour contrôler l’éclaircissement intermédiaire de sylviculture étaient des anciens développements en sylviculture. Plus récemment, on a dévelop- pé des modèles de croissance et de rendement pour les peuplements aménagés afin de prévoir les volumes de bois actuels et futurs. Actuellement, les sylviculteurs sont en train de formuler des solu- tions aux problèmes de régénération naturelle et artificielle. Les résultats des chercheurs indiquent, que, toutes choses égales d’ailleurs, le succès en régénération est favorisé par la réduction sponta- née de la densité des voûtes inférieure et supérieure et que la survie et le développement des plants de chêne sont augmentés chez les grands semis qui ont un rapport racine-pousse élevé. À l’avenir, les pratiques de sylviculture seront centrées sur les écosystèmes. sylviculture/ régénération/ éclaircissementt / modèles chêne /
Early forestry programs in the United INTRODUCTION States focused primarily on protectionist activities such as wildfire prevention and The International Union of Forestry Re- suppression. These activities extended to search Organizations (IUFRO) held its all tree species and ecosystems including 100th anniversary meeting during the peri- those containing oaks (Quercus). od 31 August to 4 September, 1992 at the Oaks have been and currently are ex- IUFRO birthplace in Eberswalde, Ger- tremely important components of forest many. The theme of this meeting revolved systems throughout the United States. around where we have been, where we They extend from the northeastern hard- are, and where we are going in forestry re- wood forests bordering the Atlantic Ocean search. The paper presented here is to the western hardwood rangelands of based on a talk delivered at this special California, Oregon, and Washington and meeting. from the northern mixed conifer forests of Time and space limitations necessarily the Great Lakes and Canada southward to forced us to define more narrowly the the bottomland hardwood and southern scope of the topic of oak silviculture in the yellow pine woodlands that adjoin the Gulf United States. Hence, the material here of Mexico. should not be viewed as a comprehensive Although oaks are widespread, they treatment of the subject, but rather as a predominate in central and eastern United document that highlights certain events States forest and form the upland and bot- that we believe are important. tomland oak ecosystems. Together, these 114 million ecosystems encompass≈ and provide a habitat for > 75 tree acres DISCUSSION species, 230 species of birds and mam- mals, plus numerous other plants and ani- mals. This covers an area which is 30% = Forestry in the United States had its begin- larger than all of Germany. nings about the time that IUFRO was Generalizing about oak silviculture over founded in 1892. Although the American time and space is difficult because there Forestry Association was founded in 1875 are many oaks that grow under a wide in order to educate people about the need range of conditions. Nevertheless, by fo- for forest conservation measures, the con- cusing attention on the upland regions of servation movement in the United States eastern oak ecosystems, we can make became a reality when our national forest several universal statements about early system was started in 1891, just a year be- silvicultural practices and how those prac- fore IUFRO came into being. However, tices have evolved to address current silvi- scientific forestry in the United States was cultural problems, and how they may be not introduced until after the turn of the modified and used in the future. century when the US Forest Service was established in 1905 and IUFRO was al- Usually forest resource managers adopt ready 13 yr old. We owe our forestry ori- modify silvicultural practices after con- or gins to Europe because it was European sidering both natural and social forces that methodology that was transplanted to the act upon the forest. Our current oak forest US by early American foresters like Gifford shaped by presettlement and early were Pinchot, the first chief forester of the US settlement activities. These activities fa- Forest Service. vored oak development by disrupting sec-
succession. Fires Silviculturists at that time realized that ondary during presettle- ment, and land clearing combined with fre- merchantable yield could be influenced by quent fires and grazing by cattle during manipulating stand density. However, they settlement times gradually eliminated com- needed to determine which density levels deterred their develop- produced the greatest yield and further peting species or ment (Lorimer, 1989; Abrams, 1992). how stand density levels affected tree quality. Because of the need for this kind Oaks became important just prior more of information, the US Forest Service ini- to and during the 1930s as a consequence tiated studies in the late 1940s to deter- of the demise of the American chestnut mine the extent to which density effected (Castenea dentata) due to chestnut blight growth and yield of oak in the upland oak (Endothia parasitica). During this time, region. 85% of the eastern upland oak forest con- tained oak. These forests were mostly sec- In this regard, tree stand density is typi- ond-growth stands of sprout origin. Despite cally expressed by units such as basal the high percentage of oak in these per unit area or numbers of trees per area stands, most were understocked, un- unit While these units provide objec- area. healthy, and in a run-down condition as a measures of stand density silvicultur- tive result of indiscriminate cutting, grazing, ists soon realized they were poor meas- fire, disease, and insects (Schnur, 1937). ures or indicators of the extent to which trees within the stand were using space Understandably, early silvicultural prac- available to them. tices were geared toward modifying stand density and protecting oak stands from de- Lexan (1939) and Chisman and Schu- structive agents such as wildfires and graz- macher (1940) worked on this problem and ing. Paradoxically, early protectionist silvi- developed a method called tree area ratio cultural practices unwittingly created a for relating a tree’s growing space require- regeneration problem that was not recog- ment to its stem diameter. But it remained nized until much later. These past land-use for Samuel Gingrich (1967) to adapt the activities and accompanying silvicultural findings of these researchers by integrat- prescriptions resulted in ecologically unsta- ing density measures and stand size de- ble even-aged stands dominated by oak. scriptors with tree area ratio. Gingrich used the previously mentioned oak growth and Schnur foresters like Luther Early yield studies initiated in the 1940s by the (1937) conducted studies to develop yield, US Forest Service to determine the grow- stand, and volume tables for these even- ing space requirements of the upland aged upland oak forests. He found that ful- oaks. One of the most useful results of ly stocked oak stands of average site quali- Gingrich’s work was the development of a ty (18 m tall at 50 yr) grow at an annual rate of 3.36 m per ha if they are not thinned. 3 stocking chart (fig 1). Gingrich’s stocking chart for upland During the 1930s, silvicultural activites oaks is a graph that relates the amount of were geared mainly toward providing ade- growing space in a given stand to a refer- quate growing space for featured species, stand that is at average maximum such as oaks, and to ensuring their perpet- ence or 100% stocked. The vertical axis uation in future stands. Notable treatments density shows basal area per acre and the hori- included weedings and cleanings, and in- zontal axis shows the number of trees per termediate thinnings. Stands were regen- acre. Quadratic mean stand diameter, a erated by conventional clearcutting, seed- tree and shelterwood methods. measure of stand size, and stocking ex-
rotation the site (Gingrich, a on same 1971 ). This study and others provided the ba- sis for constructing computer models dur- ing and following the 1970’s that simulated growth and yield in upland oak stands with and without cultural treatment. Some ex- GROAK, SILVA, TIMPIS, amples are COPPICE, G-HAT, OAKSIM and TWIGS (Dale, 1972; Rogers and Johnson, 1984; Hilt, 1985; Marquis, 1986; Perkey, 1986; Shifley, 1987). With some exceptions, most oak cultu- ral work has focused on intermediate treat- ments which alter stand density and com- position by thinning. Less attention was given to the regeneration phase of oak management. Traditional regeneration techniques were relied upon to regenerate oak stands following stand removal. How- ever, it was not until the 1970’s that forest- ers began to realize the seriousness of the regeneration failures that were occurring thoughout the oak region. The scope of the problem was not ap- until methods were available to preciated evaluate the adequacy of oak advance re- pressed as percent relative density are production (Sander et al, 1984). overlayed on the graph. This chart depicts the relation between stocking and density Subsequently, silviculturists learned that and allowed us, for the first time, to com- for many oak ecosystems, regeneration pare the adequacy of site utilization in related to the size and num- success was stands of different ages and site qualities. bers of advance regeneration (Sander, This is possible because a constant stock- 1971; Sander et al, 1984). Past and cur- ing percent allocated tree area on the ba- rent regeneration surveys showed a lack of sis of tree size. Stocking charts are rou- adequate size and numbers of oak regen- tinely used to evaluate stand denstity in eration with the result that some oak fo- oak stands to determine the need for thin- rests were being displaced by more toler- ning. ant species (Nowacki et al, 1990). The cumulative effect of this and other factors In addition to the developing stocking like the spread of oak wilt, gypsy moth, chart, Gingrich also discovered that the and urban development has resulted in a greatest volume returns resulted from thin- substantial decline in the areal importance ning stands regularly at 10- to 15-yr inter- of oak. vals beginning at age 10 yr. He found that such a stand would at least double the Substantial research is currently under- merchantable volume produced by a simi- way to better understand natural regenera- lar but unthinned stand over the course of tion processes in oak ecosystems. Such
research is called Nuttall oak. However, bottomland oak regeneration ecology. However, generalizing about the problem forests are often displaced by other spe- of oak cies because of prolonged periods with lit- regeneration across species and ecosystems is difficult because of differ- tle or no oak advance reproduction due to ences in regeneration strategy among the low seedling survival rates and infrequent oaks. Seeding, various modes of sprout- acorn crops (Johnson, 1975; Johnson and ing, and vegetative multiplication represent Krinard, 1983; Aust et al, 1985). different tactics that oaks employ in their We are learning more about the popula- regeneration strategy. Although all North tion dynamics of oak advance reproduc- American oaks rely to some extent on both tion. Several recent studies provide evi- seeding and sprouting, the extent to which dence that the occurrence of new they rely on one tactic over the other dif- seedlings is predictable only probabilisti- fers greatly among species. cally, while seedling survival is more pre- Oak reproduction consists of seedlings, dictable deterministically because it can be seedling sprouts, and stump sprouts. related to stand and site characteristics When present before a silvicultural event such as over and understory density, light, such as clearcutting or shelterwood remov- moisture, frost and predation by animals al, all 3 growth forms are collectively termed (Beck 1970; Loftis, 1988, 1990a; Crow, advance reproduction. All living oaks from 1992). seedlings to mature trees thus can contrib- Successional replacement of oaks by ute to the regeneration potential of a stand. oaks is heavily dependent upon conditions Oak regeneration in the drought- that favor the long-term accumulation of affected oak forests of the Missouri Ozarks oak reproduction with a high root to shoot is largely dependent on sprouting, and with ratio combined with a large root mass few exceptions these forests are seldom (Johnson, 1979; Dickson, 1991).Lacking successionally displaced by other species those characteristics, oaks are usually at a (Sander et al, 1984). competitive disadvantage. High root to shoot ratios are obtained in oaks by recur- Oaks of the arid Southwest may regen- rent shoot dieback. The accumulation of erate almost exclusively by sprouting from oak reproduction under a parent stand is below-ground root-like structures: ligno- one of the most important aspects of the tubers, rhizomes, and true roots (Tiede- regeneration ecology of oaks. et al, 1987). mann Recurrent fire promotes the accumula- Northern red oak, a mesic species, is tion of oak reproduction. When fires are flexible in its regeneration strategy because frequent and intense, oak savannas may it can regenerate from seedlings estab- result (Curtis, 1959; Haney and Apfel- lished after a harvest as well as from baum, 1990). But not all oak-dominated sprouts from large parent trees of advanced ecosystems require fire or disturbance for age. However, unlike the xeric oak forests their sustainment. Many dry oak forests of the Missouri Ozarks and elsewhere, like those in Missouri appear to be relative- northern red oak forests are frequently dis- ly stable communities and can accumulate placed successionally by other species oak reproduction for 50 or more yr (Sand- (Johnson, 1976; Lorimer, 1983; Crow, 1988; Loftis, 1990a; Nowacki et al, 1990). er, 1979). Such forests are called auto- accumulators. Seedlings combined with sprouting is an Despite the complexity of the oak regen- important regeneration tactic of some bot- tomland oak species like water oak and problem, most oak researchers eration
agree that there is a general relation be- bution of numbers of advance red oak re- tween site quality and regeneration suc- production under equilibrium conditions (fig 2). Seedling survival and seedling input cess: the better the site, the more difficult rates are assumed to be intrinsic to a par- it is to regenerate oaks (Arend and Scholz, ticular oak ecosystem. The value of the 1969; Trimble, 1973; Lorimer, 1989, Loftis, model is not that it will accurately predict 1990b). the numbers of advance regeneration on Although there are no universal pre- the ground in a given year, but rather that scriptions for the regeneration problem, we it gives us good information about the like- have learned that modified shelterwood lihood of observing such a number in a giv- systems increase both seedling survival en year. In certain respects, likelihoods and dominance probabilities in some oak provide a better basis for making forest forests. Such systems use a series of par- management decisions than exact values. tial cuts to reduce both canopy and sub- Such models will be ecosystem specific canopy densities prior to overstory re- and will be related to ecological classifica- moval. Decreasing the density of both can- tion systems currently being developed for opy layers allows more light to reach the many of our ecosystems. Forest managers forest floor thereby increasing both seed- will be able to evaluate alternative silvicul- ling survival and dominance probabilities tural prescriptions suggested by using of oak advance reproduction and/or under- these models to simulate stand dynamics planted oak seedlings (Beck, 1970; Loftis, in specific oak ecosystems. Oak silvicul- 1988, 1990a; Crow, 1992). ture of the future will rely on maintaining We have brief view of the presented a links between observable responses, com- past and current state of oak silviculture in puter simulation models, ecological classi- the United States. But, what does the fu- fication systems, geographic information ture hold for us? We will limit our specula- systems, and global positioning tech- tions to the next decade. We believe great nology. effort will be expended in continuing the For the most part, past oak silviculture research in oak regeneration ecology. Pre- in the United States has focused on single dictive regeneration models for oak eco- species and single values. Future silvicul- systems will be developed just as various ture will deal with oaks as part of an eco- oak growth and yield models have been developed over recent years. Such predic- tive models have been particularly useful tools for the silviculturist. However, these new regeneration mod- els will differ from growth and yield models whose usefulness depends upons the cer- tainty of their predictions. Rather, the new regeneration models will capture the chaotic regeneration process by modelling the probability of regeneration events. For example, SIMSEED, developed by Rogers and Johnson (1993) is a probabilistic simu- lation model of advance reproduction den- sity of northern red oak. Any given run of the model shows the pattern of the distri-
Dale ME (1972) Growth and yield predictions for logical unit capable of having multiple val- upland oak stands 10 years after initial thin- ues. Our improved understanding of eco- ning. US For Serv Res Pap NE 241 physiological processes together with the Dickson RE (1991) Episodic growth and carbon new emerging technologies mentioned physiology in northern red oak. In: Proc Oak previously will help us develop cultural sys- Res Upper Midwest (SB Laursen, JF Deboe, tems for managing communities of oak fo- eds) Minn Ext Serv Publi NR-BU 5663-S, rests to achieve general goals like biodi- 117-124 versity and old growth as well as for SF (1967) Measuring and evaluating Gingrich prepetuating specialized communities like and stand density in upland hard- stocking oak savannas. wood forest in the central states. For Sci 13, 38-52 Gingrich SF (1971) Management of young and ACKNOWLEGMENTS intermediate stands of upland hardwoods. US For Serv Res Pap NE 195 Haney A, Apfelbaum SI (1990) Structure and dy- This paper was presented at the Centennial namics of midwest oak In: Proc Meeting of the International Union of Forestry savanna. Manage Dyn Ecosystems (JM Sweeney ed) Organizations in Eberswalde/Berlin, Germany, N Central Sect Wildl in September 1992. Soc, 19-30 (1985) OAKSIM: an individual-tree Hilt DE growth and yield simulator for managed, even-aged, upland oak stands. US For Serv REFERENCES Res Pap NE 562 Johnson PS (1975) Growth and structural devel- Abrams MD (1992) Fire and the development of opment of red oak sprout clumps. For Sci 21, oak forests. Bio Sci 42, 346-353 413-418 Arend JL, Scholz HF (1969) Oak forests of the Johnson PS (1976) Modal development of re- Lake States and their management. US For generation in clearcut red oak stands in the Ser Res Pap NC 31 Driftless Area. In: Central Hardwood For Aust WM, Hodges JD, Johnson RL (1985) The Conf/Proc (JS Fralish, GT Weaver, RC origin, growth and development of natural, Schlesinger, eds) S ILI Univ, 455-475 pure, even-aged stands of bottomland oak. Johnson PS (1979) Shoot elongation of black In: 3rd Biennial Southern Silvic Res Conf oak and white oak sprouts. Can J For Res 9, Proceedings (E Shoulders, ed) US For Serv 489-494 Gen Tech Rep SO 54, 163-170 Johnson PS, Rogers R (1984) Predicting 25th- Beck DE (1970) Effect of competition on survival year diameters of thinned stump sprouts of and height growth of red oak seedlings. US northern red oak. J For 82, 616-619 For Serv Res Pap SE 56 Chisman HH, Schumacher FX (1940) On the Johnson RL, Krinard RM (1983) Regeneration in tree-area ratio and certain of its small and large sawtimber sweetgum-red oak applications. J For 38, 311-317 stands following selection and seed tree har- vest: 23-year results. Sout J Appl For 7, 176- Crow TR (1988) Reproduction mode and mech- 184 anisms for self-replacement of northern red oak (Quercus rubra)— a review. For Sci 34, Lexen B (1939) Space requirements of pondero- 19-40 sa pine by tree diameter. US For Serv Res Note PSW 63 Crow TR (1992) Population dynamics and growth patterns for a cohort of northern red Loftis DL (1988) Regenerating oaks on high- oak (Quercus rubra) seedlings. Oecol Plant quality sites, and update. In: Proc Guidelines 91, 192-200 Regen Appalachain Hardwood Stands (HC Smith, AW Arlyn, WE Kidd Jr, eds) Soc Am Curtis JT (1959) The Vegetation of Wisconsin. Univ Wisconsin Press, Madison, WI For Publi 88-03, 199-209
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