Báo cáo khoa học: " Improvement and silviculture of oaks"

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Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp quốc tế đề tài: Improvement and silviculture of oaks...

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article Original Improvement and silviculture of oaks in Hungary R Solymos Forest Research Institute Budapest, Romaisanc U, 17, H-2000, Szentendre, Hungary January 1993; accepted 2 June 1993) 6 (Received The most indigenous oak secies (Quercus Summary — in the important species Hungary tree are sessiliflora, Q robur, Q cerris). They form mixed stands, most frequently with hornbeam (Carpinus betulus) and beech(Fagus sylvatica). They occupy nearly 35% of the Hungarian forests. For oak timber, the allowable cut exceeds demand; it is therefore possible to export the more valuable mix- tures. Producing valuable oak timber is of great importance for Hungarian forestry. Veneer logs of good quality can be harvested from mixed 2-storied oak stands (Carpineto quercetum, Querceto fa- getum). The majority of these stands should be regenerated naturally. The success of regeneration depends on the acorn yield, the opening of crown closure, as well as the game population. The r.um- ber of seedlings per ha varies between 50 and 100 thousand, which should be decreased to 150- 450 stems per ha by the rotation age of 100-130 yr, depending on site quality. The results of re- search on natural regeneration and thinning are employed in forestry practice. The yield tables and tending models for unmixed and mixed oak stands have become basic references for valuable oak timber production. The importance of oaks in Hungarian forestry will remain decisive. The recent oak decline has caused considerable damage and is only improving slowly. This does not, however, re- duce the importance of oaks which are not only a source of valuable timber, but also an indigenous structural part of stable forest ecosystems. valuable oak I stand model I mixed and unmixed forest Résumé — Amélioration et sylviculture des chênes en Hongrie. En Hongrie, les plus impor- tantes essences forestières sont les chênes indigènes (Quercus sessiliflora, Quercus robur, Quer- cus cerris). Les chênes constituent le plus souvent des peuplements mélangés avec le charme et le hêtre. Ils occupent près de 35% de la surface forestière. La possibilité de l’exploitation du chêne dé- passe les besoins du pays et l’on peut exporter les assortiments ayant la plus grande valeur. L’im- portance de la production de chêne de qualité est décisive pour la sylviculture hongroise. On peut produire des grumes de bonne qualité pour l’industrie de placage, en premier lieu dans les chênaies mélangées à double étage (Carpineto Quercetum, Querceto Fagetum). On doit les régénérer dans la majorité des cas par voie naturelle. Le résultat dépend, outre l’importance de la glandée, de l’ou- verture du peuplement et de l’importance du gibier. En général, la densité de semis, qui au départ varie de 50 000 à 100 000 tiges/ha, est progressivement réduite et atteint au moment de la coupe définitive (100 à 130 ans) 150 à 450 tiges/ha (en relation avec le type de station). Dans la pratique, pour la régénération naturelle et les coupes d’amélioration, on utilise couramment les résultats de la recherche. Les tables de production créées pour les chênaies pures et mélangées et les modèles de
sylviculture sont devenus des aides Dans essentielles pour la production du chêne de grande valeur. l’avenir, les chênes continueront à avoir une importance décisive pour la sylviculture hongroise, tant par la production de bois de grande valeur, que comme composante essentielle de la stabilité des écosystèmes forestiers. Le dépérissement du chêne, qui a causé au cours des dernières années des dégâts considérables, diminue maintenant. chêne / forêt mélangée et pure / modèle de sylviculture THE ROLE OF OAKS Oaks in Hungary form pure and mainly mixed stands. The oak-hornbeam (Quer- cus-Carpinus) and oak-hornbeam-beech Hungary is the home of broad-leaved fo- (Quercus-Carpinus-Fagus) as well as rests, predominantly oaks. The country’s oak-Turkey oak mixed stands are the ecological conditions are mainly favoura- most characteristic. The existence of oaks ble for sessile oak (Q sessiliflora) pedun- at a relatively high production rate can be culate oak (Q robur) and Turkey oak attributed to their good sprouting capacity. (Q cerris). All 3 species are autochthonous An unfavourable factor is that the ratio of in Hungary and together cover 34.2% of sessile: Turkey oak stands of coppice ori- the forested area in the country. The grow- gin is high, ie 51% coppice to 39% seed ing stock of oak stands amounts to 40% of origin and the value of pedunculate oak the total of all forests. The percentages of stands is ≈ 8%. The coppice system has the 3 oak species, in numerical order, are spread in connection with fuelwood pro- as follows: sessile oak 12%, Turkey oak duction, although valuable oak timber can 11.3%, pedunculate oak 9.2%. The re- be produced in coppice forests in a smaller maining 1.7% is composed of pubescent quantity. However, growing high-value tim- oak (Q pubescens) and red oak. Accord- ber is most expedient in oak stands of ing to estimations, 9 different oak species seed origin, mixed with hornbeam, beech are found in the country. and lime (Tilia parvifolia).
The role of oak stands will not decrease late oak is the tree of the lowlands. In view in Hungarian forestry practice in the future. of the lowland character of Hungary, pe- dunculate oak would be the country’s most Their area is increasing slightly. Production important species, if the stands that cov- of valuable oak timber will remain the prin- ered much of the good-quality areas for cipal goal even in times to come wherever this tree had not been removed in former site and stand conditions are suitable. centuries to make way for valuable agricul- tural land. A proportion of its most favoura- ble sites has been occupied by fast- SITE CONDITIONS AND OAK SPECIES growing hybrid poplars during the last dec- ades. At the same time, Turkey oak covers Considering the country’s site conditions, larger areas; this oak species, owing to its sessile oak is of the greatest importance. Mixed with hornbeam and beech, it forms abundant acorn crop and excellent sprout- the most favourable stable ecosystems in ing capacity, is to be found on many sites and not only on dry, shallow soils. In many mountainous and hilly regions. Peduncu-
instances, it has displaced pedunculate ing valuable oak timber. Proof of this is in- oak and sessile oak stands even from dicated by the fact that the one-time Euro- sites of better quality. The site require- pean shipbuilders preferred the good- ments of all oak species have been deter- quality oak timber produced in Hungary. mined by research work. On the basis of This demand also contributed to the de- the results achieved, in the future it will be crease in the area of the earlier oak possible to choose the oak species to be stands. Both centuries-old experience and planted according to site quality. the large proportion of oak stands promot- ed the development of oak-growing in Hun- gary. TRADITIONS OF OAK GROWING Organized forestry research started in AND THE RESEARCH IN FORESTRY Hungary 95 years ago. Oak growing was a high-priority theme in the initial period of It also follows from the above-mentioned research. In recent decades, research on brief statements that growing oak stands oak has further increased. The national for production of high-value timber is of pri- network of long-term forest tending and mary importance. The economic benefit of yield experimental plots has been devel- producing large-sized timber of excellent oped in the last 30 yr. A short review will quality and high value is indisputable. For now be given of research results and prac- this purpose suitable ecological conditions tical experience relating to growing oak have to be taken into account. This fact stands of high value on the basis of the re- has been previously recognized by forest- peated inventory of experimental plots. ry in Hungary though, in the course of the Several researchers have been and still earlier centuries, oak stands were utilized are engaged in this research work: they in- mainly for masting (pig-breeding) and pro- clude Z Fekete, G Róth, R Kiss, A Szappa- ducing fuelwood. However, in the last cen- nos and A Béky. For the time being, this tury, the sawmill and panel industries (ve- research is directed by A Béky. neer production) developed rapidly, and Forestry research provides tables which the demand for the products of these in- given information on the results attainable dustries increased the importance of grow- by growing oak species all over the coun- try, and on the preconditions for producing high-value oak timber on suitable sites. Oak species to be chosen for the various site-types and growing target are deter- mined the basis of these tables in man- on agement plans which remain valid for 10 yr. objectives are: 1) production of Possible oak timber; 2) production of high-value lower value assortments in larger quanti- ties; 3) production of assortments of varied quality. The future directives on oak growing have been compiled by researchers ac- cording to ecological conditions. Among them the following are the most important:
In addition, some methods aimed at the in- the role of oaks in Hungary will be of de- - of acorn crops have been devel- terminative importance and their area will crease oped for the most excellent stands. Collec- increase to a slight degree; tion and storage of acorns produced by production of high-value oak timber is to - controlled methods, however, present be a target of primary importance, where problems. There are well-proven and suc- site conditions are suitable for this pur- cessful techniques for seedling production. pose; In general, traditional methods have been better quality oak coppice forests are to - implemented, although vegetative propa- be converted into stands of seed-origin as gation is also practiced to a small degree possible; soon as with promising results. sessile oak and pedunculate oak stands - have to reforest those sites which are suit- able for them and were lost as a result of SOME PROBLEMS exaggerated poplar and conifer planta- OF REFORESTATION tions, or due to incorrect silvicultural prac- AND AFFORESTATION WITH OAKS tice; to be restricted to its suita- Turkey oak is The natural regeneration ability of oak is - ble sites. excellent, both as regards regeneration from seeds and from sprouts. In spite of this, the quality of oak regeneration in Hun- GENETIC ASPECTS gary is questionable in many instances, the main reason being damage due to game. Growing of high-value oak timber In Hungary great importance is attached to and its stand-structural basis is disturbed population genetics in the production of by game species on many occasions. In high-quality oak timber. Our provenance some areas, the valuable young growth trials verify the genetic diversity of oak has been totally nibbled away, oak plants stands and the possibilities indicated via frequently become completely extinct and breeding for production of high-value their area is occupied by hornbeam or by large-sized oak timber. The oak genetic an even less valuable species. stock in Hungary also constitutes a consid- erable value at the international level. Our To grown high-value oak timber, the es- aim is to preserve this gene stock in its tablishment of new oak forests by natural natural variation. There are seed crop regeneration from seeds or artificially by stands in sufficient quantity to supply the acorn-sowing is necessary. whole country with good quality acorns The generative ability of oak species is produced by controlled methods. These promoted by the weight, high water con- stands and the surrounding reservations tent and protective seed-coat of acorns, by provide the basis for growing high-value vigorous cotyledons and vigorous rooting oak timber in the future. of seedlings. At the same time, in oaks the susceptibility of germinating plants to frost The oak tree periodic acorn production and dryness and the high oxygen demand remains a problem in Hungary. In the of acorns are unfavourable traits. Oak course of research on flowering biology acorns are a favourite source of food for and fruit setting, protection against patho- game, and this is also disadvantageous. It gens has been developed. As a result, this is considered favourable, on the other periodicity has been somewhat moderated.
hand, that abundant leaf fall after acorn fall When crop is abundant, sons. an acorn promotes the development of water con- sowing in rows is widely practiced, gener- tent and the well-oxygenated environment ally by using 600 to 800 kg acorn per hec- necessary for the germination of acorns. tare. Stand establishment via planting Forest-floor litter remains moist, because seedlings is usually successful. For the the condensation during nighttime cooling time being, 6 to 10 thousand seedlings per ensures a high vapour content and favour- ha have been planted. This number of able conditions for germination. seedlings is enough, mainly if hornbeam, beech and accessory species from natural The best seed bed is provided by dense regeneration fill in the vacant areas. pedunculate oak stands, because their soil surface is not overgrown with grass as in sessile oak stands. Maintenance of a SOME RECOMMENDED PRACTICES denser stand structure, required for grow- FOR GROWING OAK TIMBER ing high-value oak timber, also helps natu- OF HIGH VALUE ral regeneration. Following reforestation and afforestation in METHOD OF NATURAL oak stands tending tasks, are extremely REGENERATION complicated due to the very diverse struc- ture of stands. In addition to the general di- rectives, specific practices are to be deter- In Hungary the shelterwood regeneration mined by subcompartments. method, beginning with uniform opening of stands and lasting for 6 to 12 yr, is widely Frost sensitivity, the vitality of accessory applied due to the rarity of acorn crops. species, the formation of wild offshoots The first acorns appear, in general, when and the demand for increased light with the tree is aged 50 yr; then, every 6th to age all cause difficulties in regenerating 10th year the crop is more abundant. Tur- stands. At the same time, the good regen- key oak and red oak are exceptions. The erative ability, the considerable differentia- abundant acorn crops of these oak spe- tion between trees at young ages and the cies make up for the lack of sessile oak potential for longevity, all indicate favoura- and pedunculate oak acorn crops in the in- ble solutions. Research on tending, which has been conducted for 3 decades in long- tercurrent periods. According to research, the flowering of these latter species is also term experimental plots, has determined the following: abundant, but frosts and various patho- gens may decimate or spoil the crop. after successful reforestation or affores- - Therefore we prefer individuals and stands tation with oak species, sprouts of oaks of later budding, if they are of sufficient and undesirable subordinate species are quality. removed. However, to produce high-value oak timber, heavy opening of stands should always be avoided. The first clean- ARTIFICIAL REGENERATION ings, which have to be repeated every 4 to 6 yr, are generally characterized by group selection; we encourage natural regenera- Though tion, 75% of our oak stands have to be thinnings begin at age 30 to 40 yr when ≈ - artificially reforested owing to several fail- the choice of plus (superior) trees is possi- ures of natural regeneration and other rea- ble. The number of plus trees ranges be-
tween 150 and 450 per ha. The thinning regime of the soil and the growth of water cycle is 6 to 8 yr in young stands, and 10 these species. to 14 yr at later ages. It is an important rule The first task in these stands is to regu- that thinning operations cease 15-20 late the mixture of species of the following years before the final cutting age. Efforts 4 tilth depth categories: 41-60 cm, 61-80 have to be made to ensure that the stands cm, 81-100 cm, and > 100 cm. Up to 60 are composed of the highest quality trees cm the role of hornbeam is increased, from and that they are fully stocked by that age. 61-80 cm beech is increased in the mix- ture, over and above oaks, and between As result of the research carried out, a 81-100 cm the proportion of beech and tending regime tables at our disposal are oak should be nearly the same, because in for pure stands of all of our oak species this case beech trees are already in the and for mixed oak-hornbeam, oak- dominant (upper) crown story and not in hornbeam-beech and oak-beech stands. the lower one. These tables provide directives on the time (age) and intensity of cleanings and thin- Taking into account the growth of trees: nings, the recycling time, and provide nor- up to tilth depth of 60 cm on a dry site, the mative information on the following data of growth of pedunculate oak is the most vig- the remaining stand: number of stems (N/ orous oak species. In the course of thin- ha), total basal area (G m mean DBH /ha), 2 nings and cleanings, limitation of horn- (D mean height (H wood volume ( V beam and beech does not constitute a ), m ), m /ha) 3 m and spacing. In addition, tables problem. cutting and give the age of final the num- If the depth of tilth ranges between 61- ber of plus trees. All these data are shown cm and the water supply is favourable, 80 in tables by yield classes. owing to their higher vitality, hornbeam trees are able to grow better than the 2 other species. Their limitation therefore de- TENDING OF MIXED mands more labour. Pure hornbeam con- OAK-HORNBEAM-BEECH STANDS sociations have been developed in Hun- gary on these sites due to faulty tending operations. Considering the limited length of this On fresh and half-dry sites with tilth of paper, description of the methods on grow- 80-100 cm deep, beech trees grow vigor- ing high-value timber for all valuable oak ously. Hornbeam tree growth is restricted, stands in Hungary is not possible. On this but sufficient growing space is to be en- occasion, only the tending of mixed oak- sured for oak trees in due time. hornbeam-beech stands will be described they produce the most valuable oak tim- Soils with tilth of > 100 cm can be found as ber. in in valleys where all 3 Hungary mainly species grow well. Due to the frequent risk The site of requirements pedunculate of frost and late frosts, beech tree growth oak, beech and hornbeam are simular, is retarded and hornbeam trees become though some of their traits, eg light require- dominant. Individual stems of oaks grow ment, growing vigour, etc, are considerably excellently on these sites. different. First, the growth of tree in height and in diameter must be equalized. Both For oak stands mixed with beech and factors are very important for producing hornbeam the regime tables, different from those generally used, were prepared in the high-value oak timber. The common base course of the research. In these tables, is the depth of tilth which determines the
consider the extraordinarily wide diversity research amongst other areas. We there- of these stands, the time for cleaning, thin- fore propose to initiate research coopera- ning and final cutting, and the data of the tion in the theme of managing mixed natu- remaining (to be maintained) stand relat- ral forests, by drawing into this study all ing to the finishing point of time of these those interested in our continent. operations are given. In addition to the mixture proportions to be attained in stands depending on the age, the tables REFERENCES also show the above-mentioned data (N, G, D H V) for the 3 species - oak, ,, mm Solymos R (1962) Research on forest tending hornbeam and beech. and yield-science in ERTI. Az Erdõ 11 (12), Only the major problems of growing 560-565 high-value oak timber have been outlined. R (1965) Thinning investigations in the Solymos These problems will continue to be given sessile oak stands at Lajosforrás. Erdészeti Kutatások 61 (1-3), 29-38 priority in the country’s forestry research programme even in the future. In my opin- Solymos R (1969) New yield tables for the Hun- ion, as regards international research co- garian forests. Az Erdõ 18 (3), 125-129 ordinated within the frame work of IUFRO Solymos R (1978) Trends in thinning. Az Erdõ and the European Community, Hungary 27 (10), 472-476 could provide most scope in the establish- Solymos R (1980) Selection and treatment of ment, maintenance and development of seed-crop stands. Az Erdõ 29 (9), 400-401 mixed, stable broad-leaved forests, espe- Szappanos A (1969) Exposure to light of sessile cially in connection with growing high- oak stands and its effect on renewal growing. value oak timber. The political and eco- Erdészeti Faipari Egy Tud Közl 2, 89-104 nomical changes which took place in our Szappanos A (1983) Directive on growing ses- country in 1989-1990 have favourably pro- sile oak elite trees and plus trees. Erdészeti moted international cooperation in forestry Faipari Tud Közl 2, 85-100