No abstract

Research on old-growth forests is essential for understanding forest ecosystem functioning and for the development of forest management strategies. Their structural dynamics depends on disturbance patterns (White and Pickett, 1985). In recent decades, much research in old-growth forests has focused on natural disturbances. However, over several centuries, the natural disturbance regime has been severely altered by forest fragmentation, changes in fire regime, fauna extinctions, the introduction of forest management into the forest matrix surrounding old-growth, forest road infrastructure, and, in the last few decades, by overbrowsing, air pollution and climate change (Nowacki and Abrams, 1994;Uotila et al., 2002;Oulehle et al., 2010). Present-day old-growth forest structures are often a result of complex interactions between natural and anthropogenic disturbances (McLachlan et al., 2000). In Europe, old-growth forests have been significantly influenced by millennia of civilization. Thus, studies of

Floodplain forests are the most rapidly disappearing ecosystem in the world, especially in temperate regions of Europe where anthropogenic influence has been pronounced throughout history. Research on primeval forests is crucial to further our understanding of their natural dynamics and interaction with climate but is limited by the lack of such preserved forests. The aim of this study was to investigate how a primeval floodplain forest in Southeastern Europe has responded to climate variability during the last 250 years through comparison of tree growth and climate, canopy disturbance and recruitment dynamic of two dominant tree species with different tolerances to flooding/drought. Our analysis revealed induced stress caused by several consecutive severe drought events in the 1940s, which led to a significant increase in sensitivity to increasing temperatures and decreasing river water levels. This trend is particularly pronounced in pedunculate oak. Age structure analysis revealed one larger episode of oak regeneration culminating after periods of intense growth release. Such period co-occurs with summer drought, which is part of a complex system of natural disturbances and a significant natural driver of the cyclical regeneration of primeval oak ecosystems.

Motivated by the evidence that odontogenic keratocysts are associated with genetic alterations, we examined the possibility that development of other odontogenic cysts can be attributed to gene malfunctioning, in particular to the PTCH gene. Cyst epithelium was examined for polymorphism on chromosome 9q22.3, the region that contains the PTCH gene. Loss of heterozygosity (LOH) for the D9S287 marker and/or D9S180 marker was observed in about 50% of dentigerous cysts, whereas radicular cysts gave no indication of lesions in the PTCH region. As a more direct argument for PTCH involvement in cystic growth, we report evidence of PTCH expression in dentigerous cyst lining, which indicates malfunctioning of the relevant signaling pathway. While we found no reason to believe that PTCH should be associated with radicular cysts, other genes may be implicated in their development. We performed immunohistochemical comparisons of keratocysts, dentigerous and radicular cysts for the nonmetastatic marker Nm23. A graded response placed radicular cysts in between the other two types, suggesting a similar neoplastic character for their epithelial proliferation.