THE RELATIONSHIP OF SOIL TEMPERATURES AND PLANT POPULATION DYNAMICS AROUND THE PUHIMAU THERMAL AREA, HAWAII

This study was carried out as part of a field studies program that utilized field enquiry, scientific methodology, critical thinking and interdisciplinary approaches in learning introductory geology and biology courses. The purpose of this study was to look at soil temperature variation and its effect on plant distribution and diversity at the Puhimau Thermal area located in the upper east rift zone of the Kilauea Volcano. This thermal area has increased in size since its discovery in 1938, its growth being marked by the dying off of vegetation. This study indicated variations in soil temperature throughout the thermal area. Preliminary measurements also indicate a correlation between the soil temperatures and the plant density and diversity of the area. Regions that had higher ground and soil temperature indicated a decrease in the plant population density along with an increase in the number of the Portulaca sclerocarpa.

Field measurements were collected at the site over the course of half a day. Soil temperatures were taken along transects with the aid of infrared and soil thermometers. Plant life was logged within a one yard radius from temperature recordings. The recorded soil temperatures along the transects ranged from 33°C to 79°C for surface temperatures and 30.3°C to 83.7 °C for below surface temperatures. We infer that soils with the highest temperatures may be recording associated shallow intrusions below. Along the transects, in soils associated with high temperatures, plant diversity was low with pioneer and heat preferring plants such as Portulaca sclerocarpa appearing to be most dominant. In soils where temperatures were lowest, the diversity of plant life increased with more grasses, mosses and ferns. Further systematic and controlled measurements may aid in building thermal maps that may give a better insight of the area as well as its effects on the plant population Further research in this area will be important for increasing the understanding of the thermal area as well as understanding Kilauea’s internal volcanic plumbing.