Structure and natural regeneration trend in uneven aged fir – beech stands: A case study in Belevine forest, Croatia

Current problems with selection forest management in Croatia are manifested by adverse stand structure (surplus of large trees, absence of stand vertical structure, and deficient natural stand regeneration). The aim of this paper is to investigate the influence of management (prescribed and realized selection cutting intensity) on structure development and stand regeneration trends in an uneven-aged fir-beech forest. Research on one part refers to the forest level (silver fir and beech management class) where analysis of management and stand structure development was made for a 60 year period, based on sample plot data from standbased forest inventory. The second part refers to a selection stand in which detailed stand structure, diameter increment and natural regeneration measurements were made in 1999 before an intensive selection cut (in the year 2000), and afterwards in the years 2005 and 2009. Calculating felling quantity based on the difference of growing stock before and after cutting under conditions of adverse stand structure and low percentage volume increment is also considered in this paper. The tree species volume ratio has been gradually changing: the share of beech increased from 3% in 1951 to 28% in 2009. It has been determined that using an average cutting intensity of 17%, mature growing stock has gradually accumulated in the forest over a fifty year period. Low cutting intensities based on low volume increment that were applied until the year 2000 have shown to be inadequate for sufficient natural regeneration and the formation of wellbalanced selection stand structure. Ten years following higher intensity cutting (24 % of stand volume), advantageous changes of stand structure and natural regeneration in the researched stand have manifested in a remarkably higher number of seedlings and recruitment with a greater share of broadleaved species, which increased indices of biodiversity. Due to these results, suggested cutting intensity was raised to 29% for the next ten year management period.