A Dráva durvaszemcsés folyóvízi üledékéből előkerült szubfosszilis uszadékfák dendrokronológiai és faanatómiai vizsgálata

Abstract: This paper presents preliminary results of dendrochronological analyses of the first occurrence of subfossil tree trunks from Drava alluvial sediments. Driftwood logs were found at an outer bend of the Drava river near the village of Babócsa. The site is covered by >6 m fluvial sand and gravel. Trunks are arranged horizontally, roughly in the same bed, between massive gravel and sand layers.. Fourteen samples had been collected within a hundred metre long outcrop, arranged in three distinct sets.. Half of the samples are oak (Quercus robur L., n=7), fewer samples belonged to beech (Fagus sylvatica, n=2), wych elm (Ulmus scabra, n=1), european white elm (Ulmus laevis, n=2) and finally a there are one sample each of poplar (Populus spp.) and larch (Larix decidua). The samples were processed following the standard dendrochronological protocol. Ring width was measured to the nearest 0.01mm. Despite the most likely origin of the samples is the riverbank; the oak trunks had narrow tree-ring sequences. An oak trunk of a diameter not more 20 cm contains more than 240 rings and two other oak samples have about 200 rings. These three long series could be crossdated, forming a 249 year long chronology. The chronology built from the three synchronized records (sample codes BAB002, BAB003, BAB007) was tested with surrounding oak master chronologies, without success. The first subfossil wood remains from the Drava river and their loating chronology will be of help to understand changes in river dynamics and the former composition of the tree species on the floodplain

Coupled Hydro-Climatic Signals in the Radial Growth of Oaks Benefitting from Groundwater Availability

Lowland forests benefiting from groundwater availability are important ecosystems in Central Europe, both from ecological and economic perspectives. Besides a great reduction in their extent in the historical times and further shifts in the land use and water management regimes intensified during the industrial era, continuing changes in the groundwater and overall hydro-climatic conditions can pose significant challenges to them. Although tree-ring analyses serve as widely used tools to assess the climatic impact on tree growth and vitality, few studies have attempted to investigate the effects of subsurface hydrology on interannual fluctuations in xylem production. In this study, we compared the tree-ring width series of pedunculate oak (Quercus robur L.) from a forested area in southwestern Hungary with the time series of monthly groundwater depth and climatic variables over the period of 1920–2017 with a specific focus on 1961–2017. The radial growth of the studied trees showed the strongest relationship with late winter and early spring groundwater and drought conditions preceding the growing season, differing from the commonly reported climatic signals marked by early summer meteorological conditions of the vegetation season. The results suggest that the groundwater recharge during the dormant period preceding the vegetation season and the groundwater levels in early spring were among the key limiting factors on tree growth in the study area. In the growing years starting with a sufficiently high groundwater table, even scarce summer precipitation did not seem to limit radial growth drastically. However, unfavorable shifts in climatic conditions during the past few decades and the associated uncertainties in the future groundwater regime imply that additional active measures aimed at maintaining and restoring groundwater conditions may well be highly beneficial for sustaining groundwater-dependent forest ecosystems and their productivity