Báo cáo khoa học: "Silviculture of high-quality oaks: questions and future research needs"

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Original article Silviculture of high-quality oaks: questions and future research needs GT Weaver H Spiecker 1 Department of Forestry, Wildlife and Fisheries, The University of Tennessee, PO Box 1071, Knoxville, TN 37901-1071 USA; 2 Institut für Waldwachstum Bertoldstr 17, DW-7800 Freiburg, Germany (Received 6 January 1993; accepted 2 June 1993) Summary — Oak forestsare economically and ecologically important in Central Europe and eastern United States of America. In the former oak forests are being returned by artificial regeneration to many sites where oaks had been replaced by other species. Artificial and natural regeneration meth- ods are being sought. Coppice forests are being replaced by forests of seed origin on many sites throughout Central Europe. Methods using wider spacing and shorter rotations which produce high- quality timber adapted to site quality are being considered. In the USA reliable regeneration remains a key silvicultural problem. Effective means of both artificial and natural regeneration are being sought. Oak forest are and will be managed for a broader range of objectives in Central Europe and the USA. Future research needs include ecophysiology, growth and development, regeneration, sil- vicultural systems and oak decline. Quercus spp / silviculture I ecology I coppice I high forest / Central Europe I USA Résumé — Sylviculture des chênes de haute qualité. Questions et besoins en recherches fu- tures. Les forêts de chênes sont économiquement et écologiquement importantes en Europe et dans l’est des États-Unis d’Amérique. Dans le premier cas, les chênaies sont revenues grâce à la ré- génération artificielle sur de nombreux sites où elles avaient été remplacées par d’autres espèces. Des méthodes pour la régénération naturelle et artificielle sont recherchées. Les taillis sont rempla- cés par des futaies dans beaucoup d’endroits en Europe. Les méthodes utilisant de larges espace- ments et des rotations courtes qui produisent des bois de haute qualité adaptés aux stations sont maintenant prises en considération. Aux États-Unis, une régénération efficace reste une des clés de la sylviculture. Des moyens performants de mise en &oelig;uvre de la régénération artificielle et de la ré- génération naturelle sont recherchés. Les chênaies sont et seront aménagées pour un très large éventail d’objectifs en Europe et aux États-Unis. Les besoins futurs en recherche incluent l’écophy- siologie, la croissance et le développement, la régénération, les traitements sylvicoles et le dépéris- sement du chêne. Quercus spp / sylviculture / écologie / taillis / forêt / Europe centrale / États-Unis
and effective pre- preparing appropriate INTRODUCTION scriptions. The history of present stands affects The Technical Session of P1 06 "Improve- their current status, responses to treatment ment and Silviculture of Oaks", held during and potential for producing goods and ser- the IUFRO Centennial Meeting at Eber- vices. These factors have to be considered swalde/Berlin in 1992, has 2 principal when preparing silvicultural prescriptions. goals: 1) to determine the status of oak sil- Coppice forests continue to predominate in viculture in Central Europe and the United many regions. These forests often produce States; and 2) to identify research that stems of inferior quality and are generally supports future management of oaks and regarded as less desirable than those from oak forests. seeds or planted seedlings. A problem for Conditions, problems and trends identi- silviculturalists is to determine how best to by authors for various countries and fied convert these stands to high forests (those major research needs have been summar- originating from seed). Often, several age ized in this paper. On behalf of the partici- classes are unevenly distributed within pants at the sessions and those who will management units, which complicates re- benefit from the published papers, our generation and management for sustained gratitude and appreciation are expressed yield. to the authors for sharing their expertise regeneration by planting and di- Artificial and insights with us. seeding with a tendency towards wid- rect er spacing prevails in Central Europe. Nat- ural regeneration with various levels of PAST AND PRESENT weeding and tending have been success- ful in some regions. In the uplands of the United States, natural regeneration of oak The papers in this series stress the eco- forests is much more common but is in- nomic and ecological importance of oaks completely understood and is unreliable in the past and present in Central Europe under many conditions. Regeneration of and the United States. Their present eco- oaks on high-quality sites is especially diffi- nomic importance is closely related to the cult and is a primary constraint to intensive percentage of valued wood produced. oak silviculture. Techniques for overcom- Ecological importance is due to the wide ing this problem are being studied in sever- range of climatic provinces and sites pres- al countries. ently or formerly occupied by oaks, and their importance as components of the Ecophysiological factors, including wildlife habitat, and in the protection of soil drought resistance, light requirement and and water resources. However, many other environmental parameters have present oak forests are not naturally been studied for some important species. established and do not occupy the full Individual tree parameters (crown dimen- range of sites to which they are adapted. sion, stem diameter) and stand structure Conversely, many stands have been es- (density, age and species composition) tablished and treated by silvicultural pre- have been studied for several European scriptions with little consideration for suita- species. The relationship between growth bility taking into consideration differences and these parameters are known for some in site quality. The historical origins and species, but effective practices for estab- lishment, tending and thinning stands are past treatment of these stands are often inadequately known for most species. uncertain and increase the uncertainty of
and thinning of stands in Central Tending regeneration of some oak species by plant- have traditionally maintained Europe ing may be successful using various shel- dense stands to produce wood with rela- terwood techniques in place of the more tively narrow growth rings. Slower growth traditionally used clearcutting method. Ad- was believed to be necessary for the de- ditional information on the ecophysiological sired wood quality. Oak decline is of major responses of many species to light levels, concern both in Central Europe and east- soil conditions and on growth relations of ern United States. Although specific caus- competing species will be needed to gen- es have not been identified, research indi- eralize prescriptions to other species and cates physiological stress due to interacting regions. The genetic diversity of many oak factors (site conditions, drought, insects, forests is unknown due to the uncertain ori- diseases, tree age, genetics). gins of stands, seed sources and, in the United States, to repeated high-grading of stands. Assessment of genetic status of FUTURE TRENDS stands and techniques for genetic improve- ment of stands being regenerated are needed. Interest in both the economic and the eco- Restoration of natural oak woodland logical value of oaks will continue and communities in Central Europe is of in- probably increase in the future in Central creasing interest. Species selection and Europe and the United States. When eco- silvicultural treatments should be adapted nomic return is the goal, emphasis will be to sites and include mixtures of non-oak on high forests managed for maximum pro- species. These forests will be managed in- ductivity - either through short rotation creasingly as sustainable ecosystems for a crops or on longer rotations for high valued wider range of products and services than timber. Past criteria for evaluating wood at the present. Where economic return is quality, especially the narrow width of important, systems to produce valuable growth rings, are being reevaluated. Trees crop trees will be needed. Integration of with larger diameters, clear boles and wid- management for multiple outputs will be er growth rings will be sought. In forests more important. Simultaneous considera- managed for high-quality wood products, tion of economic aims, benefits to wildlife, either natural regeneration or seeding or aesthetics, recreation and soil and water planting at wider spacing will be used to protection will increase. New silvicultural lower costs. Efficient management will be systems will be required as the uses of oak accomplished by several means, including forests diversify. However, oak silviculture selection of a relatively small number of remains very intensive and often expen- crop trees and regulation of early stand de- sive. velopment to concentrate site potential on these trees to produce large stems and de- sirable form. Also thinning and greater mix- FUTURE RESEARCH ACTIVITIES ture of species in stands may become more important, as will site-related man- agement decisions. The status of oak forests and trends in their management in Central Europe and The trend is toward development of more efficient methods for natural and arti- the United States as described in this se- ries of papers suggest 5 broad areas for ficial regeneration in Central Europe and the United States. There is evidence that additional research. These areas, with spe-
cific recommendations, follow. 1) Ecophy- low-cost systems for managing natural oak siology: determine the responses of sever- woodland communities for a variety of al important species to varying site and goods and services. This includes: i) sys- environmental conditions, including anthro- tems for a greater proportion of high- pogenic environmental changes and to valued wood on shorter rotations (< 100 treatments for establishing, tending and yr); ii) systems for natural stands of more thinning. 2) Growth and development: de- diverse species compositions for a greater termine the relationship between growth of combination of goods and services; iii) sys- trees of several species and crown struc- tems for integrated management where ture, stand structure (stocking and species multiple output is desired. 5) Oak decline: composition) and site quality. 3) Regener- determine the relation between oak decline ation: develop reliable natural regeneration and stand age and structure, species-site methods for stands of mixed composition interactions, and pollutants, insects and pathogens and their regulation by silvicul- for a range of sites and environmental con- ditions. 4) Silvicultural systems: develop tural treatment.