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ŠUMARSKI LIST 7-8/2009 str. 43     <-- 43 -->        PDF

T. Dubravac, S. Dekanić: STRUKTURAI DINAMIKA SJEČE SUHIH I ODUMIRUĆIH STABALA HRASTA... Šumarski list br. 7–8, CXXXIII (2009), 391-405

on the growth, vigor, and decline of red oaks in fakultet Sveučilišta u Zagrebu, str. 310, Zagreb.
Ozarks. Forest Science 54(1): 8–20.

Wargo, P. M., 1996:Consequences of environmental

Vukelić, J., Đ. Rauš,1998: Šumarska fitocenolo-stress on oak: predisposition to pathogens.Ann.
gija i šumske zajednice u Hrvatskoj. Šumarski Sci. For. 53:359–368.

SUMMARY: From the literature sources and observations from the field forestry
experts, two major assumptions regarding the relationship between the pedunculate
oak dieback and the stand´s age and phytocoenological community emerge: (1) middle-
aged, older and old stands are most susceptible to oak dieback and decline, and

(2)highest intensity of oak dieback and decline occurs in the stands of pedunculate
oak in microtopographically lowest positions – microdepressions. In the current contribution,
we investigate two afforementioned statements in the pedunculate oak
stands from first to sixth age class in the Spačva forest complex. As an indicator of the
susceptibility of the stands to oak dieback and decline we used dynamics and structure
of the harvest of the dead and declining oaks in the period of 11 years (1996–
2006). Analysis is based on the available data regularily gathered during the forest
management in the “Hrvatske šume” Ltd., and archived in the database HS Fond.
From the acquired data, total of 962 subcompartments with total area of 20 671 ha
were selected according to the set of criteria for the further analysis, and divided into
three groups according to phytocoenolgical association (Table 2 and Table 3).

In the selected subcompartments during the monitoring period in total 850 835
m3of pedunculate oak was harvested, out of which 58 % (492 583 m3) were dead
and declining trees (Figure 9 and Figure 10). In more than 69 % of the subcompartments,
harvest events were recorded three and more times, and in the 20 % almost
every second year (five harvesting events) (Figure 8).

With regard to stand age, intensity of the harvest of the dead and declining oaks
increases steeply after the stand age of 80 years (Figure 11). However, further analysis
showed great variability of the intensity within the same age class (Figure 12).
Thus, it is impossible to arrive at the general conlcusion about the role of the stand
age in the proces of oak decline, because stand age most likely only amplifies negative
factors already present in the stand.

There were no statisticaly significant differences in the total intensity of the harvest
of dead and declining oaks (m3/ha) during the monitoring period between the
stands of the different phytocoenological communities (Figure 14; Kruskal-Wallis
test, n=891; H=3,825; p>0,05). Difference is more prouounced with regard to dynamics
of harvesting intensity. In that sense it is confirmed that stands in the microdepresions
are more unstable compared to the stands of the other two forest
communities with highest (7,1 % in 1998) but also the lowest (1.8 % in 2000) recorded
average yearly intensity of oak growing stock harvested trough dead and declining
trees (Figure 13). Moreover, the consequences of the harvest of the dead and
declining trees are more severe given the lack of the understory in the stands in the
lowest microtopographical positions. Further research is needed to properly quantify
those differences.

Spatial database of the pedunculate oak stands in the Spačva forest that emerged
as one of the results in this research will be continuously updated in the following
years. Interconnection of this database with other spatialy explicit databases, e.g.
measurements of groundwater levels, will enable more complex and in-depth spatiotemporal
analysis of oak decline and dieback. Conclusions based on the results of this
research relate to the pedunculate oak stands in the Spačva forest, and require verification
for other larger oak complexes in Croatia with further application of the methodology
outlined in this contribution.

Key words:pedunculate oak, dieback, Spačva forest, stand age, phytocoenological