Abstract
<jats:p>This study assesses the influence of group (biogroup) versus solitary growth modes on the stability of English oak (Quercus robur L.) trees in an urban oak forest. The research was conducted in a Luzulo pilosae-Herbal oak forest at the N.V. Tsitsin Main Botanical Garden of the RAS (Moscow) on 60 trees aged 110–140 years. The sample was divided into two equal groups: solitary trees and trees in natural biogroups with interlocking crowns. The resistography method (Resistograph R650-EA) was applied to evaluate wood structural integrity and detect hidden defects. It was established that trees within biogroups are characterized by significantly higher growth stability. While mean diameters were similar for both groups, the coefficient of variation and variance of diameter were substantially higher for solitary specimens. Biogroup trees were on average 1 m taller with lower height variability. Analysis of resistograph data revealed significantly higher homogeneity of healthy sapwood in biogroups. Phytosanitary assessment demonstrated a significantly higher proportion of sound wood and a lower number of hidden defects (zones of reduced drilling resistance) in biogroup specimens compared to solitary ones. The results substantiate the effectiveness of utilizing the group planting approach as a silvicultural technique for enhancing the stability, longevity, and phytosanitary condition of oak stands in urban and recreationally stressed areas.</jats:p>