Professor Tsutomu Hiura of the Graduate School of Agricultural and Life Sciences at the University of Tokyo and Professor Masahiro Nakamura of the Field Science Center for Northern Biosphere at Hokkaido University and their colleagues clarified the interactions between above-ground and below-ground parts of forest succession through a large-scale outdoor experiment spanning 14 years.
In urban and suburban forest green spaces, soil compaction caused by heavy machinery and humans is one of the main causes of soil degradation. In order to clarify the mechanisms of forest development under such conditions, a forest succession experiment has been ongoing since 2007 at the Tomakomai Research Forest of the Field Science Center for Northern Biosphere, Hokkaido University, to observe the effects of manipulating soil conditions.
In this study, we clarified that soil compaction reduced the number of aboveground tree species and tree biomass (expressed as the total cross-sectional area per space at a height of 130 cm from the base of trees growing in a given space) by approximately 1.2 to 2.4 times the number of species and approximately 2.3 to 5.3 times the biomass compared to the control area.
In addition, a positive interaction exists between the number of tree species above ground and the decomposition activity of soil microorganisms, and soil compaction reduces soil health (multifunctionality of soil microbial communities) not only above ground but also below ground. Furthermore, soil compaction was found to inhibit the establishment of trees, particularly those whose seeds are dispersed by birds.
These results suggest that aboveground tree diversity and underground soil health are mutually dependent. The findings of this study provide important insights for the natural regeneration of abandoned land and the creation of urban forests. For example, when thinning out overcrowded trees during forest development, specific operational methods such as selective cutting of species with large populations without reducing the number of tree species may be effective. The experiments in this study were conducted in a cool-temperate deciduous broadleaf forest on immature volcanic soil (pumice), but future verification in other soils and forest types is expected.
Paper information:【Urban Forestry and Urban Greening】Effects of soil compaction on above- and belowground interactions during the early stage of forest development
