Morphological and dendrochronological analysis of damaged pedunculate oak trees (Quercus robur L.) in old stands of the Spačva forest
Creators: name: Dekanic, Stjepan
Publisher: name: figshare
Year: 2021
Subjects: subject: 70504 Forestry Management and Environment
subject: FOS: Agriculture, forestry and fisheries
subject: FOS: Agriculture, forestry and fisheries

description: PhD Thesis defended in 2014 on Zagreb University, Faculty of Forestry, Department for Ecology and Silviculture under the auspices of mentor Academician Igor Anić, PhD. Thesis is in Croatian language with Summary in English and here is presented together with supporting data that were derived during the research process. ABSTRACT: Single-tree mortality is currently predominant type of the pedunculate oak decline in Croatia with serious negative consequences and problems with regard to the management of these forests. Main characteristics of the process are: (i) dieback of old trees; (ii) final tree death is preceded by the progressive decline of vitality and the reduction of the increment, followed by the progressive decline of foliage in the crow and appearance of the symptoms of insects and fungi; (iii) multiple biotic and abiotic factors are involved in the process of decline with varying intensity and duration. Main goal of this research was to establish the role of the morphological features of pedunculate oak trees in the whole decline process, by means of morphological and dendrochronological comparison of damaged and healthy trees within the same site conditions.Research was done in parts of 10 old forest stands in the forest basin Spačva, with total area of 100 ha. 106 circular plots with total area of 7,5 ha were established and measured, morphological features were recorded for 547 pedunculate oak trees, and 343 increment cores were processed in the dendrochronological part of the investigation. Damaged trees are clearly separated from the healthy trees by those morphological features which indicate the size of the growing space that tree has occupied in the stand, with the most important parameters being the crown diameter and the crown projected area. Regression analysis showed that damaged trees have smaller crown diameters and less growing space for the same tree diameter compared with healty trees. Damaged trees had less volume of living cells (i.e. sapwood) compared to healthy trees, but still managed to have a significantly higher ratio of the sapwood volume per growing space unit area. This result indicates the imbalance of the morphology of damaged trees, i.e. greater demand on carbon than the tree with the space available and limited resources was able to supply. Almost all of the dead trees and the major part of the declining trees had the crown projection area smaller than the critical values established for the self-thinning conditions. Dendrochronological analysis revealed that damaged trees in all investigated stands lagged with radial increment behind the healthy trees for long periods of time. Radial increment of the damaged trees in the period 1945-2007 was 20.1% to 39.8% lower compared to the healthy trees. Large variability and fluctuations of the radial increment, indicative of the growing in unfavorable conditions, was also established in damaged trees. Four negative indicator years were discovered in the increment cores of all investigated stands, suggesting that 1957, 1971, 1979 and 1998 were the years with difficult growth conditions in the whole of the research area. In the process of single-tree pedunculate oak decline, the morphological features have a very prominent role as a predisposing factor. Failure to acquire the necessary share of the potential growing space for the species is the first step in the gradual decline of tree's vitality and its increment. Tree becomes more vulnerable to the negative impacts of inciting factors such as drought, water-logging or defoliation by insects. Impact of the inciting factors, as established in the four negative pointer years, contributes to the further decline in tree's vitality, followed by the attacks of pathogens which in the end eventually kill the tree.