Revista pădurilor

Rezumat

Articolul prezintă rezultatele unui exercițiu de teren privind aplicarea răriturilor în făgete tinere. Suprafață demonstrativă (SD) utilizată, cu mărimea de 2.000 m²(50 x 40 m) şi aparținând Domeniului Mikes de la Zăbala (Covasna), face parte din fosta u.a. 15B, U.P. V. Bixad şi este în prezent administrată de O.S. Covasna din cadrul Regiei Naționale a Pădurilor-ROMSILVA. Arboretul (fag dominant – 80% -, alături de mesteacăn, salcie căprească şi ulm de munte, în pondere cumulată de 20%) are vârsta de 40 ani şi este de clasa a II-a de producție, cu un volum de 128 m³/ha şi o creştere curentă de 7,9 m³/an/ha (conform amenajamentului intrat în vigoare în anul 2005).

În 1996, arboretul a fost parcurs cu lucrări de curățiri, ulterior fiind pus în valoare pentru rărituri în cursul anului 2010. Prin măsurarea diametrului de bază al tuturor celor 270 de arbori din SD, precum şi a înălțimii la 85 de arbori (inițiali sau marcați pentru rărituri), au rezultat câteva caracteristici importante referitoare la arborii inițiali, arborii puşi în valoare sau arborii rămaşi după aplicarea răriturii, respectiv:

• desimea arboretului inițial: 1.350 arbori/ha
• desimea arboretului rămas după răritură: 965 arbori/ha
• densitatea arboretului inițial: 31,98 m²/ha
• desimea arboretului rămas după răritură: 24,9 m²/ha
• diametrul mediu al arborilor de fag inițiali: 15,7 cm (variație 8-32 cm)
• diametrul mediu al arborilor de fag rămaşi după răritură: 16,6 cm (variație 8-32 cm)
• înălțimea medie a arborilor de fag inițiali: 17,7 m (variație 11,5-22 m)
• înălțimea medie a arborilor de fag rămaşi după răritură: 19,2 m(variație 15-22 m)

Datele medii referitoare la diametrele şi înălțimile medii ale arborilor de fag inițiali şi rămaşi după răritură indică aplicarea unei intervenții combinate, cu accent de jos, prin care se vor extrage cu precădere exemplarele din plafonul inferior, cu diametre şi înălțimi mai mici decât valorile medii ale acestor parametri înainte de răritură.

În condițiile în care volumul real al arboretului pe picior atinge cca 298 m³/ha, masa lemnoasă pusă în valoare de personalul unității silvice din Covasna se cifrează la peste 62 m³/ha (21% din volum, față de 22% din suprafața de bază şi 29% din numărul de arbori), o cantitate care depăşeşte consistent volumul recoltat în mod obişnuit prin rărituri în România.

În pregătirea exercițiului de teren realizat în suprafața demonstrativă instalată, s-a procedat la alegerea şi însemnarea a 23 arbori de viitor (14 “adevărați” şi 9 “pentru eventuala înlocuire, în caz de nevoie, a celor “adevărați”), pe baza criteriilor vigoare, calitateşi spațiere. S-a continuat cu prezentarea principalelor probleme ale gospodăririi făgetelor din România, care ar trebui conduse printr-o silvicultură dinamicăşi de arbori individuali, pentru a produce indivizi cu diametre mari (50-60 cm) în maximum 100 de ani. Celor 15 participanți la exercițiu, personal al unor unități silvice de stat şi private, li s-a cerut ca, pe baza celor prezentate, să realizeze o punere în valoare specifică răriturii de susşi care să includă (a) selecționarea arborilor de viitor şi (b) alegerea arborilor de extras prin prima răritură. Principalele rezultate ale acestui exercițiu constau din:

• în SD au fost aleşi, în medie, 25 arbori de viitor (125 exemplare/ha), cu o variație de la 12 la 66;
• numărul de arbori de extras la nivel de SD a oscilat între 28 şi 170 (140-850 ex/ha);
• volumul de extras la ha a variat între 46,8 şi 174,3 m³;
• intensitatea răriturii a atins 10-63% (pe N), 17-58% (pe G) şi 16-59% (pe V), valori care depăşesc simțitor cele recomandate prin normele tehnice în vigoare;
• deşi s-a cerut aplicarea unei rărituri de sus, în realitate răriturile propuse de diverşi participanți au variat de la de jos până la de sus, trecând prin cea combinată.

Exercițiul de teren realizat reprezintă un bun exemplu pentru utilizarea practică a suprafețelor demonstrative în pregătirea personalului silvic de teren, reprezentând şi o excelentă ocazie pentru diverşii “actori” din sector de a schimba idei, impresii, neînțelegeri şi de a gândi împreună la viitorul Silviculturii.

Thinning of young European beech stands: the outputs of a demonstration field exercise (Mikes Estate, Zăbala-Covasna)

1. Introduction

As shown in both Romania (Nicolescu, 2005) and abroad (Belgium – Baar and Snoeck, 2004; Baar et al., 2005), demonstration plots can be a valuable tool for the “training” of field foresters on different issues related to forest management.

Taking into account this conclusion a demonstration plot of 2,000 sq.m (50 x 40 m) was established on September 13, 2010 in a forest stand (formerly sub-compartment 15B, Forest Management Unit V Bixad) part of the Mikes Estate (Zăbala-Covasna) and managed by the Forest District of Covasna. The demonstration plot was established by Prof. Valeriu-Norocel Nicolescu (University “Transilvania” of Braşov) together with a group of French students in forestry from AgroParisTech-ENGREF, Centre de Nancy as well as some local foresters. This plot is part of a large (24.6 ha) 40-year old stand (European beech mixed with hornbeam, goat willow, silver birch, and mountain elm), highly productive (second yield class). According to the last forest management plan released in 2005, the standing volume per hectare is 128 cu.m and the current annual increment is 7.9 cu.m/ha.

The only silvicultural intervention performed in this stand since its regeneration is a cleaning-respacing in 1996. In addition the stand was marked for thinning by the field foresters of Covasna Forest District earlier this year. Silvicultural racks to provide easiest access within the stand and limit logging damages have not been opened yet.

2. Main characteristics of European beech stand before, during and after thinning

After establishing the demonstration plot all existing trees (270 individuals) within it have had their dbh measured. In addition 85 individual trees (both initial and marked for thinning) had their total heights measured as well. The main data of initial trees, trees marked for thinning and trees remained after the thinning to be performed later on are shown in table 1.

As shown above the species composition of stand is 80% European beech, 15.6% hornbeam and 4.4% other broadleaved species (silver birch, goat willow, and mountain elm). Silver birch and goat willow are two pioneer species without value in this stand. Because of their large diameters (mean diameter: 31.1 cm) and heights (mean height: 19.4 m), they should be removed progressively to avoid opening the canopy too strongly and create large gaps.

The initial stand density is 1,350 trees per hectare, which is quite high for this age. Furthermore many beech trees are strongly affected by cankers or are forked at low heights (Photo 1) and the stand canopy is fully closed.

Photo 1. A European beech tree forked at low height and strongly affected by canker.

The mean diameter as well as median diameter of basal area of initial, marked and remaining trees found in the demonstration plot are shown in table 2.

In case of all species the median diameter of basal area is higher than the mean diameter, the highest difference between the two values (4.9 cm) being found for European beech.

According to these figures a mixed thinning(but mostly from below) was marked so the values of mean and median diameters of dominant species (European beech) after thinning have increased insignificantly by removing especially trees from the lowest part of diameter range (very wide in case of both European beech – 8-32 cm - and other broadleaves – 18-42 cm). The wide range of diameters is a certain proof for the lack of interventions in the last decade combined with the from belowcharacter of cleaning-respacing performed back in 1996.

In terms of heights, their amplitude is lower than the one of diameters. This is due to the fact that the stand is almost even-aged so has no obvious layers (dominant and suppressed) (table 3).

The character of mixed thinning(but mostly from below) is obvious also in the case of mean heights that have increased insignificantly for remaining trees (e.g., from 19.1 m up to 19.3 m of h_gof European beech trees).

The stand volume is much higher than the one from the management plan + increment/5 years (168 cu.m/ha) and reaches about 298 cu.m/ha. The standing volume of initial trees is composed of 75% European beech, 9% hornbeam and 16% other broadleaves(table 4).

As the quality of pioneer species (silver birch and goat willow) is low, they can be used only for firewood so their gradual elimination by thinning to improve the stand quality and approach the target species composition (90% European beech 10% other tree species) is strongly advised.

Regarding the hornbeam, it represents only 9% of standing volume and is located especially in the lower canopy. As its trees protect the lower bole of European beech against the occurrence of epicormic branches or sun-scorches after the sudden exposure of boles to sunlight following heavy thinning, they should be removed only if competing with the dominant species in the upper canopy or rubbing the boles of final crop trees.

Considering the thinning marked by the field foresters of Covasna Forest District, three issues are to be considered:

a. The intensity of interventions varies between 21% (by volume), 22% (by basal area) and 29% (by number of trees). It is a heavy thinning(intensity higher than 16% in all cases) but mostly from below, removing especially trees from the small diameter classes (mostly less than 16 cm dbh – figure 1) and heights.

Figure 1. Distribution of initial trees and trees remaining after thinning in demonstration plot.

2. The total volume of marked trees has reached over 62 cu.m/ha, a quite high amount compared to the average situation in Romania (on average between 20 and 40 cu.m/ha) but possible owing to the high standing volume per ha (about 298 cu.m). However, the intensity of thinning by volume is higher than the one recommended by the Romanian technical norms in use (14%) (xxx, 2000).

3. No potential final crop trees were considered (choice and painting) when marking the thinning. Unfortunately (but as everywhere in Romania) this operation is not usually performed at the sub-compartment level regardless the species composition of stand.

Taking into account this fact, after the establishment of demonstration plot, the participants have selected and painted two categories of final crop trees of European beech:

• “genuine” = 14 individuals (70 trees/ha), “equipped” with a red dot;
• “for potential replacement of “genuine” final crop trees” = 9 individuals (45 trees/ha), with a red dot and a question mark ?.

The main characteristics of the two kinds of trees are shown in table 5.

3. Field exercise in demonstration plot

3.1. Background

A week after the establishment of demonstration plot, a short presentation about the main characteristics of European beech influencing its silviculture was given by Prof. Nicolescu in front of a group of participants (e.g., forest engineers, forest technicians, forest rangers, forest students, managers of state and private forest districts, etc.) to the field exercise (photo 2).

Photo 2. Presentation of field exercise.

The presentation dealt with the main defects affecting European beech stands (high frequency of forking at low heights, occurrence of red heart, and evidences that encourage thinning from above: low potential to epicormic branching after interventions strongly opening the canopy; strong and quick reaction to thinning up to the age of 80 years, etc.). This background data served to emphasize the need for a more dynamic tree silviculturein European beech stands, including thinning from abovefocusing on final crop trees, selected based on three criteria (vigour, quality and spacing) and aiming to produce large-diameter trees (50-60 cm dbh) as soon as possible (maximum 100 years). Such practice is rather new and often poorly understood by the Romanian foresters constrained by obsolete technical norms in place since mid1980’s.

This presentation was followed by a visit of several sub-compartments, some of which have been thinned recently according to Romanian norms and others which are old enough to undergo the first thinning. In one of this latter stands, a practical demonstration of a thinning from abovewas performed.

After this activity, by using a specially designated form all participants were asked to carry out (within the demonstration plot established earlier) a thinning from aboveas explained previously. This activity had included two separate operations to perform:

1. Selection of final crop trees (“les plus beaux des plus gros”) based on three main criteria: vigor, quality and spacing;
2. Selection of trees to be removed (thinned) during the first intervention to follow in order to improve the growth of those individuals chosen as final crop trees.

Subsequently, the results have been gathered and the data analysis was performed.

3.2. Main results of field exercise

The 15 participants had spent an hour to check all trees within the plot and select both final crop trees and trees to thin. The results of this work are shown in the table no. 6, 7, and 8.

On average, 25 final crop trees/plot (range 12-66) meaning 125 trees/ha (range 60-330 trees/ha) were chosen by participants. It represents only 9% (range 4-24%) of initial trees of the stand. It seems that this mean density of final crop trees (N/ha) is quite low but it is enough taking into account the vigour and especially the quality of these trees. In addition, this density is much higher than the one recommended in other central European countries with a longer tradition in European beech silviculture as follows: maximum 70 trees/ha in France (Bock et al., 2005), 60-80 trees/ha in Germany (von Teuffel and Hein, 2004), 80 trees/ha in Belgium (Baar et al., 2004). Most of these individuals are European beech trees but some participants have also selected a few hornbeams or other broadleaved species. Such solution should have been avoided as both hornbeam and other broadleaves have a shorter life span and rotation age so can not contribute to the stand when reaching the rotation age of European beech.

Taking into account all participants, the final crop trees had a mean diameter of 19.4 cm and a mean height of 19.4 m. At individual level, the mean diameter of final crop trees varies from 16.9 cm and 23.2 cm (range = 6.3 cm) whereas the range of mean heights is much lower (1.0 m, from 19.0 m up to 20.0 m) (table 7).

As for the trees marked for thinning, their number within the plot varies from 28 to 170 (140-850 trees/ha) or between 10% and 63% of trees found in the demonstration plot. Concerning the species to be thinned, on average more than 77% (range 66-94%) of number of trees belong to European beech, 16% (range 6-25%) to hornbeam and 7% (range 0-17%) to other broadleaves.

A similar high variety of situations is found when taking into account the volume to thin per hectare which ranges between 46.8 cu.m and 174.3 cu.m. However, in case of only 6 participants out of 15 this volume is lower than 100 cu.m/ha.

As for the intensity of thinning it ranges between 17 and 58% (by basal area) and between 16 and 59% (by volume). Obviously these figures are much higher than the one recommended by the Romanian technical norms in use (xxx, 2000).

A summary of all data related to the trees marked for thinning is shown in table 8.

Comparing the three intensities of thinning (by N, G, and V) one may say that the approaches to thinning used by various participants range from thinning from below(participants no. 2, 9) to mixed thinning(participants no. 4, 8, 10) or even thinning from above(no. 1, 5, 7, 12, 15). Such result is very surprising as all participants were asked since the beginning to use a combination of selection of final crop treesand thinning from abovethat is considered as the best approach that should be used in case of European beech silviculture in Romania as in other parts of our continent.

4. Conclusions

The above field exercise seems to be a good example of the practical use of demonstration plots when training professional foresters. It shows that the interest and understanding of different people can be very variable and, combined with the lack of experience in a brand new field it can lead to very variable results such as extremely high volume of thinning/ha. It seems to be a quite long way up to the large scale application of single-tree silviculture in European beech forests of Romania, even though such approach is performed since at least 20 years ago in the central part of Europe.

In addition, such exercise is an excellent opportunity for professional foresters to exchange views, impressions, misunderstandings and think together about the future of Silviculture (Photo 3). Such exercises should be repeated because they stimulate reflection and openness.

Photo 3. After-exercise discussion of participants

References

• Baar, F., Snoeck, B., 2004: Exercices interactifs et présentation de la sylviculture d’arbres « objectif » en feuillus. Forêt Wallonne, no. 68, janvier-février, pp. 9-14.
• Baar, F., Snoeck, B., Balleux, P., Claessens, H., 2004: La sylviculture d’arbres « objectif » ou d’arbres de place. Forêt Wallonne, no. 68, janvier-février, pp. 2-8.
• Baar, F., Balleux, P., Claessens, H., Ponette, Q., Snoeck, B., 2005: Sylviculture d’arbres-objectif en hêtre et chêne: mise en place d’un dispositif de parcelles de démonstration et d’expérimentation. Forêt Wallonne, no. 78, septembre/octobre, pp. 34-46.
• Bock, J., Boisteaux, R., Fabbri, B., Kiefer, E., Seynave, I., Vautier, F., Vinkler, I., 2005: Le hêtre en Lorraine. Guide des sylvicultures. Office National des Forêts, Direction Territoriale de Lorraine, Nancy, 88 p.
• Nicolescu, N.V., 2005: Suprafețele demonstrative, un instrument util în pregătirea studenților pentru aplicarea lucrărilor de îngrijire şi conducere a arboretelor. Revista pădurilor, nr. 2, pp. 29-34.
• Teuffel, von, K. Hein, S., 2004: Sylviculture du hêtre proche de la nature en Bade-Wurtemberg (Allemagne). Revue Forestière Française, LVI(6), pp. 519-528.
• xxx, 2000: Norme tehnice pentru îngrijirea şi conducerea arboretelor. Ministerul Apelor, Pădurilor şi Protecției Mediului, Bucureşti, 164 p.

Authors

Stud. FIF Ludovic LEJOUR

Stud. FIF Elise PARES

AgroParisTech-ENGREF, Centre dde Nancy

14 rue Girardet, 54042 Nancy Cedex-FRANCE

E-mail: lejour.ludovic@hotmail.fr