Lacking shade-tolerant plant species in urban parks caused degradation of ecosystem services under woody canopies

Abstract

Herbaceous layer vegetation in urban parks provides ecosystem services such as a place to sit on the ground, keeping the ground from becoming muddy, preventing dust and soil erosion, and preventing flooding by infiltrating rain. Green spaces in urban areas have different species compositions due to their historical backgrounds. In newly developed parks on reclaimed land, shade-tolerant native species that grow on the forest floor in satoyama, remnants of early modern vegetation, may be missing from the species pool, and there is concern that ecosystem services on the forest floor may be degraded. In this study, the ecological traits of the species pool (shade tolerance and trampling tolerance in species pool level) were measured in various parks, and their effects on the ground-surface leaf area index were analyzed. The effect of trampling was taken into account using soil penetration resistance value, because vegetation in parks is also affected by trampling. The lack of shade-tolerant species in the species pool led to a lower leaf area index at the forest floor. The shade-tolerant species detected in this study were native species such as Houttuynia cordata, Ophiopogon japonicus, Oplismenus undulatifolius, Paederia foetida, Pleioblastus chino, and sedges. Species pools in parks with 'satoyama' tended to have these species. Species pools containing shade-tolerant native species are important for improving ecosystem services under the canopy, and it is recommended to conserve the historical 'satoyama' in parks to prevent the loss of native shade-tolerant flora when renovating or creating parks.