Forest dieback proceeds rapidly around the coastal lake Sugari-oike in Owase City, Japan

ABSTRACT

Recently, forest dieback around the coastal lake Sugari-oike, National Natural Monument of Japan, has rapidly increased. To clarify the factors affecting the forest dieback, we examined species composition, stand structure, and mortality at the lake-edge and landward areas for 3 years. We also examined water quality, and measured how much the water level varied within a year. Forest dieback did not affect specific species, and there was no bias in the diameter at breast height of dead individuals. Mortality in the lake-edge area was more than 10% per year, which was considerably greater than that reported for other temperate broad-leaved evergreen forests. Mortality for the landward area was 2.8% per year, significantly lower than that in the lake-edge area. The basal area of the landward plots increased slightly during the census period, while that of the lake-edge plots decreased, reflecting the high mortality. Water level fluctuated greatly within a year, rising by 40 cm at its peak. The water has been eutrophic for 20 years, suggesting that eutrophication did not cause the recent dieback. We consider that the period during which trees on the lake edge are flooded is increasing. To confirm this, future studies should investigate water-level fluctuations over multiple years, and also soil conditions. This would help to delineate the long-term dynamics of the forest and would further our understanding of the causes of dieback in this area.

KEYWORDS:

• Coastal lake
• flood
• forest dieback
• forest dynamics
• mortality

Acknowledgments

We thank Dr. Satoshi Nanami and Dr. Akira Itoh for providing support during this study. We are also grateful to Board of Education, Owase City for the permission to conduct research in Sugari-oike.

Disclosure statement

No potential conflict of interest was reported by the authors.