All About the Oze Marshland
Peat forms when conditions such as cold temperatures and excessive humidity prevent dead vegetation from fully decomposing, leaving behind a greater amount of organic material. Oze has an average annual temperature of 4°C, about the same as the inside of a refrigerator, easily cold enough to inhibit the decaying process.
The partly decayed material builds up and condenses over many thousands of years, eventually turning into peat soil. The rate of peat growth in Oze is approximately 0.7 – 0.8 mm a year, although this can vary depending on the plants and the climate. If a hiker were to step off the boardwalk and make a 1-centimeter depression in the peat, it would take ten years for the marsh to recover. Researchers believe that it took 6,000 to 8,000 years for the moor’s peat surface to reach its present thickness of 5 meters.
The plants that cover the Ozegahara marsh vary depending on the makeup of the vegetation under the surface and how the habitat was formed. There are over 1,800 bog pools, ranging from 2 to over 100 meters in diameter, with depths from around 10 centimeters to over 3 meters.
Most of the marshes of Ozegahara are the result of repeated flooding. Each time the rivers retreated, they left wetlands on both sides, separated by high banks. (See illustration.) These wetlands are an ideal habitat for reeds, grass-like sedges, and plants such as bogbean (Menyanthes trifoliata). As these plants partially decompose, they form peat, filling in depressions and creating a flat surface.
The marshes near Lake Ozenuma developed differently, starting as bog pools that gradually filled with earth and sand as their banks eroded. This created a thriving environment for aquatic plants that also turned into peat as they decomposed. This type of marsh is called a “low moor,” as the surface is usually at the same level as the surrounding water table. The peat receives nourishment from the river water, which is vital to the fields of mizubasho (Asian skunk cabbage) that grow here.
