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Better insights into spatio-temporal climate signals are needed to understand more clearly the applicability to palaeoclimatic analysis and dendrochronological dating of the long tree-ring oak chronologies currently being compiled in Eastern Europe. This study investigates the climate sensitivity of two recent oak tree-ring width (TRW) chronologies from Transcarpathian and Ciscarpathian Ukraine and their coherence with 35 oak chronologies from Ukraine, Poland, Slovakia, Romania, and Hungary. The new Transcarpathian chronology consists of 247 TRW series of living trees from 13 sites covering the period 1836–2020, while the new Ciscarpathian chronology consists of 215 TRW series from 13 sites and spans the period 1775–2020. Despite the strong similarity between these two chronologies, their responses to climate differ significantly. Growing-season precipitation and particularly drought (three-month SPEI index) were found to be the primary drivers of oak growth on the border between the Carpathians and the northeastern Pannonian Basin. Spatial correlations of the Transcarpathian chronology show particularly high explained variability in the April-August SPEI index, roughly between 18.5–28.5°E and 45–52°N. In the Ciscarpathian, June precipitation primarily influenced oak radial growth but the spatial correlation was quite low. While the Transcarpathian TRW chronology was strongly correlated with eastern Slovakian and northwestern Romanian chronologies, the Ciscarpathian chronology revealed very low correlations with surrounding chronologies. This study indicates the great dendroarchaeological and palaeoclimatic potential of the Transcarpathian chronology and points to the need to analyse additional living trees from the Ciscarpathian region to understand the spatial variability of oak growth and its climate signal better. • Climate sensitivity of oak TRW chronologies divided by the Carpathian Arc differs. • Transcarpathian chronology strongly reflects summer hydroclimate conditions. • Transcarpathian chronology correlates well with Slovakian and Romanian chronologies. • Ciscarpathian chronology shows very low correlations and needs further research. [ABSTRACT FROM AUTHOR]

• We examined the impact of trampling on pine root growth using dendrochronological tools. • The highest root-stem radial growth coherency (RGC) was found for exposed roots. • Only exposed lateral roots subjected to trampling had no missing rings. • The majority of scars and PRDs were found in exposed trampled roots. • Two different sets of factors explained root-stem RGC in trampling and buried roots. The impact of hiking in forested areas is one of the main factors affecting the condition of tree growth along hiking trails. Trampling causes common exposure of roots and quantification of the human impact on root radial growth and wood anatomy requires careful assessment. To accurately identify the radial growth changes in Pinus sylvestris roots, we conducted a stepwise cross-dating using trampled roots from a hiking trail and reference roots. Such approach was previously not applied in a lowland area. In addition, we investigated the factors that influence the root-stem radial growth coherency, including soil properties, root and trail morphology. Changes in radial growth and wood anatomy were examined in three parts of the root system: buried, transition and trampling zone. The radial growth for each root zone was compared with corresponding stem and reference root and stem chronology. In total, we investigated 204 roots and 97 tree stems for the common period 1970–2015. Missing rings were found to be a common phenomenon in all root zones, except in the exposed lateral roots in the trampling zone. The highest number of wedging and missing rings was observed in the trampling and transition zones, respectively. The total number of wedging rings increased with an increasing distance from the stem. The events of root exposure in the trampling zone were highly coupled with the formation of scars (r = 0.51, p < 0.001) and pronounced resin ducts (PRDs) (r = 0.52, p < 0.001). The majority of the wood anatomical changes (i.e., 84% of scars and 85% of PRDs) were identified in the trampling zone. The highest degree of correlation between raw stem chronology and raw root chronology was found for the exposed trampled roots (r = 0.69, p < 0.001). In the trampling zone, the root-stem radial growth coherency was determined primarily by root type (77.3%) and root age (17.4%), whereas in the buried zone, by the soil organic matter content (55.4%) and soil compaction (39.7%). It has been proved that the record of radial growth and wood anatomy changes in Scots pine roots serve as a valuable ecological archive of trampling impact with high temporal resolution. [ABSTRACT FROM AUTHOR]

Physiological and ecological mechanisms that define treelines are still debated. It has been suggested that the absence of trees above the treeline is caused by low temperatures that limit growth. Thus, we hypothesized that there is a critical minimum temperature (CT min ) preventing xylogenesis at treeline. We tested this hypothesis by examining weekly xylogenesis across three and four growing seasons in two natural Smith fir (Abies georgei var. smithii) treeline sites on the southeastern Tibetan Plateau. Despite differences in the timing of cell differentiation among years, minimum air temperature was the dominant climatic variable associated with xylem growth; the critical minimum temperature (CT min ) for the onset and end of xylogenesis occurred at 0.7±0.4°C. A process-based modelling chronology of tree-ring formation using this CT min was consistent with actual tree-ring data. This extremely low CT min permits Smith fir growing at treeline to complete annual xylem production and maturation and provides both support and a mechanism for treeline formation., (Copyright © 2017 Science China Press. Published by Elsevier B.V. All rights reserved.)