Inter-tree variability of autumn leaf phenology of European beech (Fagus sylvatica) on a site in Ljubljana, Slovenia

Temporal variability of leaf senescence (autumn phenology) was observed in 2020 in 11 European beech (Fagus sylvatica) trees in Tivoli, Rožnik and Šišenski hrib Landscape Park in Ljubljana, Slovenia, and also observed for spring phenology in the same year. General leaf colouring, BBCH94, occurred between 19 and 24 October 2020, with lower inter-individual variability than that of leaf unfolding, BBCH11. The trees had active leaves (time between leaf unfolding and leaf colouring) between 177 and 199 days. In only three trees total leaf fall, BBCH97, occurred before 19 November 2020. Leaf colouring of the tree included in the long-term monitoring program of the Slovenian Environment Agency ARSO occurred on 24 October 2020. This is 7 days later than the 65-year average of the same tree/location and is ascribed to weather conditions. Investigation of tree tissues showed that the width of the last formed tree-ring in the wood varied between 0.39 and 9.61 mm and in the phloem between 0.09 and 0.26 mm, and that the tissues reflect the health condition of the trees.

Impact of Temperature and Wetness of Summer Months on Autumn Vegetative Phenological Phases of Selected Species in Fageto‑Quercetum in the Years 2011–2015

The work presents the result of the drought impact on the onset and the development of autumn phenological phases of tree species (Quercus robur L., Carpinus betulus L., Prunus avium L.) in the central part of Slovakia. The selected autumn phenological phases of tree species were observed in the years from 2011 to 2015. From meteorological parameters we examined precipitation, number of tropical days, and their periods from June to August. We revealed distinct differences in air temperature and precipitation between the years, which affected the onset of individual phenological phases. Based on the calculations of the Thornthwaite moisture index and climatic water balance, the year 2014 was wet (except for June) with the shortest periods of tropical days. The extreme drought and the longest 13‑day period of tropical days in the year 2015 shifted leaf colouring of hornbeam and cherry tree by 16 and 22 days earlier and the leaf fall by 5 and 16 days earlier than the average of the period from 2011 to 2015. Oak was the least sensitive to the weather extremes, which was documented by a balanced course of the phenological phases with the lowest variation. The 5‑year‑long average onset of the autumn phenophases of oak and hornbeam was shifted by 1 – 4 days later and of cherry tree by 4 days earlier than the 25‑year‑long average.

Effect of biometeorological variables on the onset of phenophases derived from MODIS data and visual observations

In this study we analyzed the effect of selected biometeorological variables on the onset of phenophases in three beech stands in different climatic areas (warm, moderately warm and cold). We have focused on two phenophases - leaf unfolding and leaf colouring. Timing of both phenophases was identified visually and using series of MODIS satellite images. The data were collected during a 13-year period (2000-2012). For the spring period, we found a significant dependence between temperature and precipitation-based biometeorological variables and leaf unfolding in both datasets - those based on visual and remote sensing-based observations. The average air temperature in the period from February-April was the most significant factor which initiated the onset of beginning of leaf unfolding in all three investigated stands. The evapotranspiration-based biometeorological variables (climatic water balance, actual evapotranspiration, dryness index) had no effect on the onset of the beginning of leaf unfolding observed using both methods. The high precipitation totals in April caused the later onset of leaf unfolding in all stands. The relationship between the first autumn phenophase - leaf colouring and biometeorological variables was found significant in beech stand in the warm climatic area only.

Meteorologischer und phänologischer Jahresrückblick 2009 | Meteorological and phenological annual review for 2009

In 2009, average temperatures above the norm, and in particular the extremely warm months of April, May and August, significantly influenced the development of vegetation in Switzerland. In contrast, the drought that prevailed temporarily did not influence this development. The growing season began in normal time or slightly delayed with hazel flowering in March. Few weeks later, at the time of the last spring phenological phases, vegetation was early, in particular the beech leaf unfolding. A warm April and unusually high temperatures in May are responsible for this turnaround. The early arrival of phenological summer was truly exceptional, with some new record dates. Thus, in summer 2009, due to the heat in May and August, an advance of vegetation development of two to three weeks compared to the standard was temporarily observed. Unlike most previous years, the fall of 2009 showed a clear trend to the late occurrence of autumnal phenological phases that are leaf colouring and leaf fall.

Phenology of four broad-leaved forest trees in a submountain beech forest

The phenology of four deciduous forest tree species (<I>Carpinus betulus</I> L., <I>Fagus sylvatica</I> L., <I>Quercus dalechampii</I> Ten., <I>Tilia cordata</I> Mill.) was studied in a submountain beech forest stand in Central Slovakia. Two spring phenological phases – bud-burst and leaf unfolding as well as one autumn phase – autumn leaf colouring were monitored over the period of 13 years. The results documented interannual variability in the dating of phenological phases within the species, while the differences among the species were also revealed. Significant correlations (<I>P</I> < 0.05) were detected between the dating of leaf unfolding and air temperature; the coefficients of correlation (<I>r</I>) ranged from –0.86 (hornbeam and beech) to –0.92 (oak). Significant relationships were also revealed between cumulative precipitation amounts and timing of autumn leaf colouring phase (<I>r</I>-value ranged from –0.73 in oak to –0.81 in hornbeam). The trend analysis showed that the onset of phenological phases was slightly shifted to the earlier dates during the period of 13 years. However, the trends were not statistically significant.

Meteorologischer und phänologischer Jahresrückblick 2007 | Meteorological and phenological annual review for 2007

The year 2007 was stamped with the warmest winter (2006/07) and spring ever recorded since the beginning of measurements in 1864. The vegetation did strongly react to that situation. In the phenological year 2007, 21.3% of the dates of phenological observations were registered as new records, i.e. they were never recorded so early before at that location. This extremely early development of the vegetation could be observed above all in spring and even stronger in summer. The absolute record has been observed when the black elder flowered with 64.5% record-breaking dates. The phenological autumn was not so extreme. However, a strong tendency toward early leaf colouring and leaf fall could be registered. The phenological year 2007 is unique in the history of phenological observations made by Meteo Swiss, which started in 1951.