A comparative analysis of directed and spontaneous development of mixed forests of fir, spruce and beech on Mt. Tara
Authors: Obradovic Snezana , Pantic Damjan , Medarevic Milan , Sljukic Biljana 
Published: January 2018

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 catagories 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 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.