Uporedna analiza usmerenog i spontanog razvoja mešovitih šuma jele, smrče i bukve na Tari

Abstract

Podaci periodičnih potpunih premera stalnih oglednih površina i odeljenja u kojima se one nalaze, u periodu 1955/60-2005/2010, predstaljali su osnov za ova istraživanja. Dva seta podataka iz vremenskog opsega od 50 godina omogućila su komparativnu analizu niza strukturnih i numeričkih elemenata redovno gazdovanih prebirnih šuma jele, smrče i bukve sa šumama koje su se manje-više spontano razvijale na oglednim površinama. Broj stabala u tanjim kategorijama se smanjuje, ali je u odeljenjima u kojima se redovno gazduje on delimično kompenzovan podmlađivanjem i urastanjem, koje iznosi 7,9 stabala godišnje, sa dominacijom jele. U šumama spontanog razvoja urastanje ili izostaje ili je minimalno i iznosi 2,7 stabala godišnje. S aspekta očuvanja prirodne kompozicije ovih šuma, a time i njihove biološke stabilnosti, zabrinjavajući je značajan pad broja bukovih stabala, pre svega u najtanjim debljinskim kategorijama. Nagomilavanje stabala jakih dimenzija izraženije je na oglednim poljima u odnosu na odeljenja u kojima se redovno gazduje. Ovakav trend je rezultirao visokim iznosima temeljnice (max. je u 131. odeljenju i na kraju analiziranog perioda iznosi 37,8 m2·ha-1, a na OP-2 55,7 m2·ha- 1) i zapremine (max. od 605,4 m3·ha-1 ostvarene u 66. odeljenju, sa učešćem jele 79%, odnosno 898 m3·ha-1 na OP-2 u kojoj jela učestvuje 71%). Povećanje zapremine u debljinskim kategorijama iznad 50 cm u odeljenjima u proseku iznosi 120%, a sastojinama spontanog razvoja čak 230%. Tekući zapreminski prirast je visok i u odeljenjima na kraju perioda prosečno iznosi 12,9 m3·ha-1, a na oglednim površinama 14,9 m3·ha-1. U obe vrednosti jela učestvuje sa 80%. Međutim, procenat prirasta, kao pouzdaniji izraz vitalnosti i dobrih stanišnih i sastojinskih uslova opada, sa 2,54% na 2,32% u posmatranim odeljenjima i sa 2,31% na 1,91% na oglednim površinama, u uslovima spontanog razvoja. Na osnovu prethodno iznetog, mogu se konstatovati izvesni poremećaji i negativni trendovi, kako u redovno gazdovanim šumama, tako i u sastojinama spontanog razvoja, pri čemu su oni znatno izraženiji u drugom slučaju. Ovo se ogleda u nepovoljnim prostornim odnosima i svetlosnom režimu, posledično u otežanom podmlađivanju, uraštanju (posebno bukve) i usporenoj dinamici ovih šuma i u konačnoj instanci u poremećaju njihove strukturne izgrađenosti i funkcionalne vrednosti. U redovno gazdovanim šumama uzrok leži u krutom shvatanju prečnika sečive zrelosti i slabijeg zahvata sečama u jači deo inventara, koji je usporio dinamiku i otežao podmlađivanje i uraštanje. Jačim zahvatima u ovaj deo inventara ostvario bi se bolji prostorni raspored stabala (horizontalno i vertikalno), bolji svetlosni režim i ubrzao bi se razvoj ovih šuma. U prilog ovome je i činjenica da bez prebirnih seča, prepuštena samoregulacijskim procesima (spontanom razvoju), prebirna šuma postepeno osiromašuje stablima donjeg i srednjeg sprata i pretvara se u jednoslojnu strukturu sa horizontalnim sklopom što se dešava na istraživanim oglednim površinama.

The data of periodic complete measurements of permanent sample plots and compartments in which they were located in the period 1955/60-2005/2010 served as the basis for this research. Two sets of data from a 50-year time span enabled a comparative analysis of a number of structural and numerical elements of regularly managed selection forests of fir, spruce and beech that more or less spontaneously developed in the sample plots. The number of trees in low-diameter categories decreased in the regularly managed compartments, but it was partly compensated by regeneration and ingrowth, which amounted to 7.9 trees per year. In forests with spontaneous development, the ingrowth is either missing or minimal, and it amounts to 2.7 trees per year. From the aspect of preserving the natural composition of these forests and thus their biological stability, a significant decline in the number of beech trees is worrying, above all in the lowest-diameter categories. The accumulation of large-dimension trees is more pronounced in the sample plots in relation on the compartments with regular management. This trend resulted in high basal area values (max. was observed in compartment 131 and at the end of the analyzed period, it amounted to 37.8 m2·ha-1, and in SP-2 to 55.7 m2·ha-1) and volume (max. 605.4 m3·ha-1 was achieved in compartment 66, with a 79% share of fir, i.e. 898 m3·ha-1 in SP-2 in which the share of fir is 71%). Increase of volume in diameter categories above 50 cm amounts to on average 120% in compartments, and in stands with spontaneous development to as much as 230%. Current volume increment is high and at the end of the period it amounted to on average 12.9 m3·ha-1 in the compartments, and 14.9 m3·ha-1 in the sample plots. In both these values the share of fir is 80%. However, increment percentage, as a more reliable indicator of vitality and good living and stand conditions decreased from 2.54% to 2.32% in the observed compartments and from 2.31% to 1.91% in the sample plots, under the conditions of spontaneous development. On the basis of the above, certain disturbances and negative trends can be identified, both in regularly managed forests and stands with spontaneous development, while they are significantly more pronounced in the latter case. This is reflected in the unfavorable spatial relationships and light regime, and consequently difficult regeneration and ingrowth (especially of beech) as well as the slowing dynamics of these forests, which finally disrupts their structure and functional value. In regularly managed forests, the reason for that is the rigid understanding of the felling ripeness diamater and lower intensity cutting of large-dimension inventory, which slowed down the dynamics and made regeneration and ingrowth difficult. More intensive operations in this part of the inventory would provide a better spatial distribution of trees (horizontal and vertical) and a better light regime, while the development of these forests would be accelerated. This is confirmed by the fact that forests with self-regulation processes (spontaneous development) become gradually depleted in low and medium storey trees and turn into a one-layer structure with a horizontal canopy which was observed in the investigated sample plots.