Izvorni znanstveni članak
Dynamics of Establishing the Selection Structure in Beech-Fir Stands on Papuk
Mario Božić
; Šumarski fakultet Sveučilišta u Zagrebu, Zavod za izmjeru i uređivanje šuma, Svetošimunska 25 HR-10 000 Zagreb, HRVATSKA
Juro Čavlović
; Šumarski fakultet Sveučilišta u Zagrebu, Zavod za izmjeru i uređivanje šuma, Svetošimunska 25 HR-10 000 Zagreb, HRVATSKA
Ernest Goršić
; Šumarski fakultet Sveučilišta u Zagrebu, Zavod za izmjeru i uređivanje šuma, Svetošimunska 25 HR-10 000 Zagreb, HRVATSKA
Krunoslav Teslak
; Šumarski fakultet Sveučilišta u Zagrebu, Zavod za izmjeru i uređivanje šuma, Svetošimunska 25 HR-10 000 Zagreb, HRVATSKA
Sažetak
Diameter class distribution data, as well as diameter increment and increased number of trees, provide a basis for the simulation of stand development. With advances in computer technology, modelling and stand development research has shown increasing importance.
The objective of this paper is to explore the establishment dynamics of a selection stand structure in mixed beech-fir forest on Papuk. In the past, these forests were managed as even-aged forests.
The research was carried out in the Management Unit »Zapadni Papuk Zvečevački«, Kamenska Forest Office. Using the data from forest management plans (plans of 2006, 1996 and 1986), ten stands were selected for which dynamics simulation of conversion into uneven-age stands was performed. The stands were selected on the basis of age, tree diameter distribution, density and mixture. After simulation, sub-compartments 34b, 42b and 56a were selected for display. The data for these stands are shown in Table 1.
Theoretical growing stock models for mixed fir and beech stands were designed according to Klepac (1961). Felling dimensions for both species were 60 cm, while the growing stock mixture consisted of 60% fir and 40% beech (as set down in the management plan). The theoretical model was designed for both site class combinations: fir II/III – beech II, and fir III – beech II/III, using the original theoretical models by Klepac. To calculate the growing stock, we used local one-entry volume tables by species and site classes from the management plan. Table 2 and 3 show the designed theoretical models.
Simulations were carried out with Excel files generated for this purpose. Input data for the simulation consisted of diameter distribution of trees taken from the management plan. Consequently, diameter distribution of trees for all coniferous was displayed as fir and all deciduous trees as beech. Simulation was carried out according to three scenarios, which define the felling volume as follows:
Scenario 1: Felling volume is calculated according to Klepac’s formula.
Scenario 2: Volume of the first three felling is calculated on the basis of maximally allowed felling intensity of 30% of the growing stock. After this, Scenario 1 is applied.
Scenario 3: Felling volume is calculated as the difference between the actual growing stock before felling and the theoretical growing stock after felling.
The simulations were carried out for the time interval of 100 years.
The results presented in Fig. 2 show long-lasting establishment of an uneven stand structure in the stands with initially too large growing stock and lack of small diameter trees. In all the three scenarios, the beech approaches the theoretical model more rapidly than the fir, particularly in smaller tree diameter classes. Assumed achievement of mixture ratio to the theoretical one led to the faster decrease of the large firs.
According to all the tree scenarios, the growing stock is reduced below the theoretical one (Fig. 3), but after this it begins to increase. In Scenario 1, this decrease is smaller, but longer-lasting than in the other two scenarios, which is the consequence of lower felling intensities in the first 50 years. Scenario 2 assumes the largest reduction in the growing stock, when a total of 30% of initial growing stock is felled in the first three selection felling cycles. The actual growing stock just before the fourth felling amounts to 87% of the theoretical one. In our opinion, the growing stock can be reduced so as not to fall below 70% of the theoretical growing stock. According to Scenario 3, extreme felling intensity in the year 2013 is the consequence of too large growing stock. The mixture ratio approaches more or less linearly the theoretical one.
In such stands there should be several intensive fellings, as is the case in Scenario 2, provided that the interval of the actual mixture ratio approaching the theoretical one is longer. This would allow for earlier felling of mature fir trees, especially if the loss of their quality is a matter of concern. This would also intensify the appearance of young trees. According to Scenario 1, a specified volume of the first felling is 151 m3/ha, according to Scenario 2 it is 149 m3/ha and according to Scenario 3 it amounts to 193 m3/ha. For the same stand, Zelić (2003) points out that the felling volume could be 104 m3/ha and 107 m3/ha, respectively. The ten-year volume increment based on the management plan for this stand is 107 m3/ha and the felling quantity is only 73 m3/ha (68% increment), which is 17% based on the actual growing stock at the moment of measurement. Such low felling volume, if achieved, will cause further decline of the stand structure and slow down the process of its conversion into the selection stand structure.
According to the results shown in Fig. 4, the selection stand structure is established much earlier in stands that do not contain too large growing stock and that initially have trees in smaller diameter classes.
Considering that the initial growing stock is slightly lower than the theoretical one (Fig. 5), according to Scenario 1 and 3 it begins to rise in proportion with increased felling intensity. Similarly to the stand mentioned above, Scenario 2 leads to a significant reduction in the growing stock in comparison to the theoretical one. For this reason, felling intensity in the fourth felling treatment is significantly lower.
Such stands require 2 – 3 more intensive felling treatments in the beginning, as is the case with Scenario 2. This would intensify regeneration and transition of young trees into higher diameter classes.
According to the simulation results for sub-compartment 42b (Fig. 6), the procedure of converting young stands into the selection stand structure is relatively fast. The biggest problem with these stands relates to the low mean diameter of felled trees (about 20 cm for fir and 15 cm for beech).
As for the low initial growing stock, it rises in all the three scenarios (Fig. 7). The biggest initial growth is related to Scenario 3 as the consequence of the absence of felling in the year 2015, because the simulated felling volume was less than 0. Scenarios 1 and 3 are appropriate for such stands.
The percentage of annual volume increment given in the management plan based on management classes is 2.76%, whereas the prescribed ten year felling volume is 20.2%. Such low felling volumes will slow down the establishment of the selection stand structure.
The results of this research show that the establishment of the selection stand structure is a long process that depends on its initial stage. This is in accordance with earlier results of selection stand simulation in stands with disturbed structure (Čavlović et al. 2006a, Čavlović et al. 2006b, Čavlović and Božić 2007–08), or in stands which were converted from even-aged (spruce) into uneven-aged stands (Hanewinkel and Pretsch 2000). Relative to the stands on Papuk, Zelić (2003) writes: »a part of the stands intended for selective stand management are over 80 years old; consequently, management of these stands should aim at converting them into selection stand management in short time (30–50 years)«. The management plan states that it will take at least 30 years to establish theoretical selection stand structure. The results of this research show that the process will take even longer, which coincides with Šafar’s (1963) writing: »Often it takes more than half a century for a stand to form a new structure. Every conversion from one form into another that occurs too fast is harmful because attempts to rapidly create different structures are detrimental to those trees which provide good increment«.
The biggest problem of establishing the selection stand structure in stands that lack small diameter trees is the fact that it takes sometimes more than 40 years for the seedlings to emerge and reach the diameter of 10 cm (see the transition times in Fig. 1). Observing just the part of the stand above 10 cm in diameter with the theoretical model reveals additional degradation of the structure. Considering that the young growth does not occur over the whole area simultaneously, the time needed to achieve the theoretical recruitment is even longer. In order to accelerate the process of natural regeneration, group selection system is recommended wherever possible. Provided that intensive and timely tending treatments are applied in groups of trees below 10 cm diameter, the recruitment will be more intensive (Cestar 1960, Špalj 1962). The size of the tree group depends on site conditions and ecological requirements of particular tree species, especially in terms of their shade tolerance (Šafar 1963, Nyland 1998).
We are aware of the fact that, with the passing of time, the actual stand structure in the field will more or less diverge from the simulated and theoretical model, among other things because felling is not predicted for diameter classes with insufficient number of trees. In addition, the prediction of recruitment, particularly for longer periods, is never accurate.
Ključne riječi
Even-aged stand; simulation; felling intensity; stand structure development; theoretical selection stand structure
Hrčak ID:
68186
URI
Datum izdavanja:
8.4.2011.
Posjeta: 2.025 *