Topsoil and Tree Changes in an Oak Ecosystem Within a Period of 37 Years

Abstract

The aim of this study is to analyze tree, as well as forest floor and topsoil (0–10 cm) changes, within a period of 37 years and related impact on forest growth in an oak ecosystem in northern Greece. The study was carried out in the area of the Taxiarhis University forest, which is located in central Halkidiki. In the experimental plot, the tree age was 70–72 years, the forest stand was healthy, and the site quality was medium. The parent material of the study area is schist and the topsoil is characterized by high organic matter content and a sandy clay loam texture. For the purpose of this research project, forest floor (O₁ + O₂) and soil (0–5 and 5–10 cm) samples were collected from 30 sampling points. To study the mycorrhizal colonization (%), 15 root samples were taken. The average tree height in 1981 was 14.2 m and in 2018, it was 19.3 m. The diameter increased by 4.05 and 5.40 cm within 17 (2001–2018) and 37 years (1981–2018), respectively, and the trees grew 5.1 m taller. Higher radial increment (4.2 cm/20 years) was observed only in the predominant trees. In 2018, the forest floor increased its weight by 18.273 kg/ha, compared with 37 years ago. Nutrient amounts increased and there was a balance between the quantity of organic matter on the forest floor and the topsoil. Most of the nutrient amounts in the forest floor and topsoil were higher in 2018 compared with 1981 and the acidity of the soil decreased. Moreover, most of the nutrient amounts were found much higher in the upper part of the topsoil (0–5 cm) than in the forest floor, except for phosphorus, iron, copper, and zinc. No significant statistical differences were found for the C/N ratio between 2001 and 2018. The study results highlight the importance of letting oak ecosystems grow and mature rather than cutting them down within the short period of 30–70 years. Also, the importance of coexistence, of ecosystems interconnections, the trees’ resilience to stressors such as drought, and the role of mycorrhizal colonization are addressed. Concluding comments address the significance of soil properties in relation to sustainability, especially in the context of the ongoing climate change.