Vegetation Succession on Fallow Land

Abstract

Wetland ecosystems inherently provide diverse ecosystem services and have been overwhelmingly reclaimed for agricultural land use around the world during the twentieth century. However, the rate of abandonment of agricultural lands began to increase exponentially in the 1950s. Local people are interested to know whether abandoned farmland naturally returns to historical wetland vegetation which is the basis of biodiversity and various ecosystem services. In this chapter, we focus on the succession of vegetation on fallow land in floodplain areas. The principal factors affecting wetland restoration on fallow lands are the supply of propagule of the historical vegetation and the suitable physiochemical conditions for their initial growth. The main propagule supporting the restoration of fallow lands includes soil seed bank and the seeds dispersed from neighbors. The effectiveness of the seed banks formed before agricultural development is largely dependent on the extent of divergence from the original site environment, especially the water environment. When the seed banks have declined, the amount of historical vegetation remaining in the surrounding area and the effectiveness of the natural flood regime are important. Water level and fertility are the most important factors influencing germination and initial growth of dispersed seeds on fallow land. In addition to these factors, the availability of vacant land for new recruitment is crucial. The plant community dominated by Phragmites australis, which is essential for the habitat of the red-crowned crane, has naturally regenerated in fallow lands in eastern Hokkaido. Thus, an increase of abandoned and fallow lands may provide additional suitable habitat for cranes and thereby contribute to increase their population size in the future.