The Angkor complex is the remains of the capital city of the Angkor dynasty (circa 9th to 15th century). A large collection of sites such as Angkor Wat are concentrated here. Located to the northwest of Angkor Thom, the Ta Nei site is a temple ruins built during the reign of King Jayavarman VII from the end of the 12th to the beginning of the 13th centuries similar to the Bayon temple. While the grounds of most ruins are actively used such as to cut trees or relay stone blocks, the Ta Nei site remains virtually untouched.

Similar to other sites within the complex, the Ta Nei site is mainly constructed of sandstone and laterite stone, but the surface of the stone is overgrown with living organisms such as lichen and mosses, and due to lack of maintenance this has become conspicuous. While such organisms are often removed as part of standard maintenance of the ruins due to a recognition that they cause the deterioration of the ruins, a radical solution is difficult without knowing the full effect of these organisms.

This project attempts to verify the attributes of the organisms growing on the surface of the ruins and the exact effect the organisms are having (or not having) on the ruins. The aim of this is to identify what kind of state the organisms should be maintained in the future to keep the ruins in good condition and what concrete measures should be taken to ensure that state.

To understand the site's environment, a weather station has been installed at the site since 2000, automatically measuring items such as temperature, humidity, wind speed and direction, and insolation. This data collection is carried out by Cambodian researchers who underwent training in Japan. Aside from where the weather station is installed, a fisheye lens has been used to shoot hemispherical photography at places where typical organism species can be seen. This enables a survey to be made of how sunlight hits different parts of the site.

Together with the National Museum of Nature and Science, Tokyo, we surveyed and identified organism types growing on each section of the ruins. 34 genera and 41 species of lichen; 8 families 8 genera and 9 species of bryophytes with 2 families, 2 genera and 3 species of marchantiophyta were identified and algae was also observed at the Ta Nei site. Generally, lichens thrive in sunny, dry places while mosses thrive in places with little sun and moist places such as water channels.

We verified what kind of differences could be found between the stone under points where each type of organism is growing and stone where they are not. Rebound hardness test with an Equotip tester and magnetic susceptibility measurements were carried out on the places where the stone surface was exposed after removing mosses; places where lichen is flourishing; and places where fresh stone is exposed by fracture surface or peeling plaster were subject to the same conditions, making other conditions same. We also took bounding stones home to Japan for analysis.

It was revealed that the hardness and magnetic susceptibility of the stone directly under the mosses is lower than the fresh stone and the stone covered with lichen. While the hardness of the stone covered with lichen has a slightly low value, large differences were not discovered in the magnetic susceptibility and a significant reduction in physical properties could not be detected. A microscopic observation found that the surface layer of the stone covered with mosses has a large number of pores, and it was confirmed that the stone under mosses is deteriorating.

The direct cause and effect relationship between lichen and stone disintegration could not be identified at this point. It was confirmed that the stone under the mosses is disintegrating, but decisions on how to deal with existing mosses will depend on whether the mosses accelerated the stone disintegration or the mosses started to grow after the stone disintegrated. Therefore, stone was placed at the site after its initial physical properties had been measured, and mosses are being grown on the stone surface to verify how physical property changes come about.

We insist that replicating the environment of places with mosses in places without mosses, or more specifically, attempting to improve sunlight and moisture conditions, would help to prevent further stone disintegration. On the other hand, testing is ongoing to verify the results and the effect on the stone when the existing organisms are cleaned off. Methods to remove organisms with absolute certainty and not cause a change to the stone's physical properties in the process are being examined.