Microclimate in the Fields with Cycas Hedges in Amami Oshima, Japan

Abstract

In the Amami Islands, an original culture has been created and is still maintained. This study focused on the fields with Cycas hedges called “Sotetsu-Bate”, which means “fields with Cycas hedges”, in the Amami Islands. Sotetsu-Bate had established as a locality and specific cultural landscape, in order to protect farm products from wind and seawater. The objective of the present study is to clarify the effects of Cycas hedges on the thermal environment in the fields. Field observations of air temperature, humidity, wind direction, wind velocity, and solar and long-wave radiation were carried out in and around the fields with Cycas hedges in the Kasari area, Amami City, Amami-Oshima.

In summer and winter, the wind reducing effect of Cycas hedges appeared in the field with Cycas hedges, and it is an effective countermeasure against damage of strong wind and seawater. The wind reducing effect of Cycas hedges against seasonal wind is particularly significant. It is cleared that wind velocity in the field with Cycas hedges was decreased with about 20% of that at the sandy shore, on average. The wind reducing effect of Cycas hedges did not appear clearly at observation points on the north-south main road, compared with the results of observation points in the field with Cycas hedges. This north-south main road was narrower in the old days. It is considered that the wind reducing effect in the fields with Cycas hedges was decreased by road extension.

In winter and in the early morning of summer, the difference in air temperature, vapor pressure, and relative humidity in the observation site was small. In the daytime of summer, air temperature at observation points in the fields with Cycas hedges was higher than that at the sandy shore in many cases. It is considered that the outdoor sensible temperature formed in the fields with Cycas hedges is very hot and dangerous for human health in the daytime of summer because the air temperature is high and wind velocity is calm or very light. It is advisable to eschew a work in the fields with Cycas hedges in the daytime of summer.