Semi-natural grasslands maintained through burning, grazing, and mowing, were once widespread across Japan and harbored high and unique biodiversity. Since the 20th century, mainly due to the energy and green revolutions, grassland plant materials are no longer utilized as fodder for livestock, green manure, or roofing materials. Consequently, most semi-natural grasslands have undergone land-use changes, including abandonment, afforestation, and conversion to agricultural fields, resulting in a reduction to less than one-tenth of their original area over the past century. This drastic loss has put many grassland-dependent species at risk of extinction. Recent studies have revealed that while biodiversity in semi-natural grasslands is rapidly lost after land-use changes, it does not recover to its original level even when grassland environments were restored and have been maintained over several decades.
Traditionally in ecology, grasslands in regions outside climatically determined grassland biomes (such as cold or arid regions) have been regarded as transient vegetation that appears during early stages of primary or secondary succession before transitioning to forest. However, recent research has increasingly demonstrated that old-growth grasslands can develop in areas subject to regular natural or anthropogenic disturbances, and that their diversity and species composition differ markedly from those of early-successional grasslands.
In this presentation, we introduce the concept of old-growth semi-natural grasslands to the audience, and report on how plant and herbivore (including pollinator) communities change with the duration of grassland persistence using old-growth and young semi-natural grasslands on ski slopes and irrigation pond levees as examples. We also discuss how the unique diversity and composition of old-growth semi-natural grasslands are formed, and demonstrate that these ecosystems are irreplaceable for maintaining Japan's biodiversity.