Condition, protection and maintenance of age-old pedunculate oak trees in Feofania forest

Large old trees are significant elements of forests, arboretums, botanical gardens and parks and perform a number of unique functions contributing to ecosystem integrity and biodiversity. At the same time human activities such as compaction of topsoil layers, deterioration of soil permeability and soil aeration drive the decline of large old trees. The human impact is also exacerbated by plants inevitable physiological age-specific changes. The presence of such old trees in urban environments brings great scientific promises enhancing a social, cultural and historical forest value, although these benefits increase responsibility for trees maintaining. Regarding old-growth trees historical, cultural, and environmental significance and their overall vulnerability, the individual-by-individual tree protection measures are required. Pedunculate oak (Quercus robur L.) is among the most widespread long-lived species in Europe, in particular in Ukraine. In Feofania (or Theophania) forest, that is an oak-hornbeam forest located in southern part in Kyiv, the age of the oldest oak trees reaches about 300 years. In this article, we aim to estimate vitality, overall condition, and recreational digression stages of pedunculate oak trees and to develop the recommendations to maintain and extend trees longevity in Feofania forest. We estimate the stages of recreational digression and vitality using an approach of Hensiruk et al. (1987) and Sanitary Regulations in forests of Ukraine (1995) respectively. The dendrochronological analysis is performed on core samples from sixteen age-old pedunculate oaks in order to determine their exact cambial age and to evaluate their growth rates. We use at least two cores per tree extracted at a height from 0.5 m to 1.3 m above ground level with an increment borer. The tree-ring widths are measured using AxioVision (Carl Zeiss) software to the nearest 0.01 mm. To identify false rings we employ stereomicroscope MBS-1. The individual tree-ring series are cross-dated, standardized and checked using the COFECHA program. Then we determine exact cambial age of oak trees as number of tree-rings in individual series. To estimate the age of trees with cores without pith we use a graphical method. The analyze is performed on 42 increment cores containing 7335 annual rings formed in the period from 1746 to 2016. Measured diameter of the age-old oaks ranges from 57.6 cm to 165.2 cm. The longest chronological series contains 271 years. The age of studied trees varies from 202 to 275 years averaging 175 years and radial growth ranges from 1.07±0.400 mm to 2.85±1.487 mm averaging 1.95±0.792 mm. In recent years the reduction of radial growth isn’t observed, although in a long time interval in five studied trees the rings width not exceeds the individual series average value. However, the growth rate reducing could not be regarded as critical for trees vitality because it is above 10 % of the average value yet. The evaluated mean increment coefficient is 5.13±1.482 years in cm that allows to estimate the age of dominant and codominant oaks in the association of Galeobdoloni luteae-Carpinetum in other forests. The estimated vitality is mostly of 6–7 points. Five oaks are in «satisfactory condition», nine oaks are «weakened», one oak is «very weakened» and one tree is «dying». «Weakened» trees are with mechanically damaged stem and are often suffered from leaves defoliation caused by Acrocercops brongniardella and Microsphaera alphitoides. Regarding wood samples maintenance, the «dying» oak stem is found rotted in its center. The recreational digression is at the stage 1–4. For eight oaks it is at the first stage, for four oaks at the second stage, for two oaks at the third stage and for two oaks at the fourth stage with 60 % destruction of the understorey. The number of age-old Q. robur trees is limited, thus measures to care could consider individual tree-specific features. Given trees vitality and stages of recreational digression, we develop the guidelines to preserve and extend trees longevity. We also propose to include four old-growth oaks in the list of monumental plants.