VIRGIN FORESTS AND FOREST RESERVES IN ... - Natura 2000

COST Action E4: Forest Reserves Research Network 103
a very small area. This is the reason why cyclic development is less distinct and less
obvious in a virgin forest than in a managed forest (OTTO 1994; BONČINA 1997).
The main criterion for determining an individual patch (stands) is developmental phase.
Therefore we used developmental phases to denote a stand type. In studies on virgin
forests different methods are suggested for a patch pattern analysis. A virgin forest is
classified into stand types, life phases, developmental phases or developmental stages.
Different concepts are used but the aim is similar, if not the same, that is, to describe at
one’s best, under given natural conditions, diversity of forest stands and, above all, to
show their development. The mapping of developmental phases of a virgin forest is easier
if stands of optimal stage prevail, whereas stages of decay and juvenile stages are more
demanding, since stand structure changes more rapidly. Spatial structure of a forest does
not depend only on forest stand structure, but also on spatial scale employed for the
analysis of a virgin forest and criteria used, which in turn depend on the intent of a study.
Thus, maps of developmental phases are only an approximate description of different
stands and mainly an aid for understanding the structure of stands and their
developmental dynamics.
An analysis of the patch pattern of a virgin forest is based on methodology developed by
LEIBUNDGUT (1959, 1982), MLINŠEK (1980), and KORPEL (1993, 1995). We divided the
developmental cycle of a virgin forest stand into three stages - juvenile, optimal and
decaying. Stands (or patches) at different developmental phases were classified in
individual stages. The optimal stage is distinguished by a high growing stock, high crown
density, and, in most cases, a uniform stand structure. The decaying stage is characterised
by intensive die-back of trees in the upper layer, hence crown closure is full of gaps. The
growing stock of such stands is decreasing, the quantity of dead trees is high, and stand
structure is often uneven or it consists of different layers. The juvenile stage is
distinguished by an increase in volume increment of a new generation of trees, whose
ingrowth is intensive, and by a decrease in the number of trees of previous generations.
Stands of juvenile and decaying stages are often interlinked. If the growing stock of the
new generation trees is higher than that of the previous generation, the stand is classed as
juvenile stage. Different stages were assessed in the field but they could have been
determined objectively only with measurements and a study of the development of stands
during a certain period.
Table 3: A list and the proportion of developmental stages and developmental phases in
the virgin forest Rajhenavski Rog in 1995 (BONČINA 1997)
Developmental stage Developmental phases
Juvenile stage (12%): Stand initiation phase, two-layered stands, selection phase
Optimal stage(52%): Optimal phase, late optimal phase
Terminal stage (36%):
Stand re-initiation phase, selection phase, two-layered stands,
gaps
In the first mapping of horizontal structure of virgin forest stands, stands were classified
according to developmental phases (MLINŠEK et al. 1980, HARTMAN 1987). Results of