Contrasting weathering and climate regimes in forested and cleared sandstone temples of the Angkor region

Abstract

Comparative assessment of stone weathering intensities and bioclimatic conditions was conducted at four temples located in cleared and forested sites of the Angkor Park, based on similar protocols. Four thousand sculpted lotus petals carved in the same grey sandstone were categorized by using two customized scales of weathering intensity, and climate monitoring was conducted from December 2008 to November 2009. Whereas 70% of the sandstone lotus petals are almost completely destroyed by mechanical weathering in cleared areas, 74% of petals located in forested environments appear to be totally free of mechanical weathering and are only affected by superficial biochemical weathering. Ambient conditions are also contrasting, with the magnitude of the diurnal surface temperature and relative humidity ranges being three times higher at cleared sites than in wooded areas. As wetting–drying cycles are the driving force of sandstone decay at Angkor, causal links are suggested between weathering and climate regimes. In wooded areas, the microclimate is buffered by the forest and the associated lithobionts, which maintain constant humidity levels, reduce thermal stresses at the stone surface and induce a slow biochemical weathering regime. In cleared areas, direct exposure to sunshine and monsoon rains induces pronounced wetting–drying cycles conducive to swelling–shrinking movements and other potential processes, provoking the rapid mechanical decay of the sandstone. Even if local damage can be caused by tree roots, the forest cover and the associated lithobionts obviously play an overall protective role. Additionally, microtopographical factors related to architectural designs and post‐building events probably explain intra‐site and between site minor differences in the amount of sandstone decay, by influencing key factors such as the water residence time at the stone surface. Last, the contrasting weathering regimes in forested and cleared sites are but a trend, for besides overwhelming mechanical weathering, chemical weathering is also operative at cleared sites, as indicated by salt efflorescences and ferric oxidation. Copyright © 2012 John Wiley & Sons, Ltd.

Exploring ecological relationships in the biodeterioration patterns of Angkor temples (Cambodia) along a forest canopy gradient

“…It has already been stressed that the forest canopy has a strong influence on stone conservation [24], and how it can influence biological colonisation, according to their varying abilities to tolerate desiccation. Such effects caused by temperature can explain green algae's lower tolerance of overheating and desiccation with respect to cyanobacteria, and therefore their absence in non-forested areas; it also explains certain changes in lichen communities, particularly those with Endocarpon, which was only found in sunny conditions.…”

“…These papers highlight as the biodeterioration effects concern to physicchemical alteration due to the penetration of the adhesion structure (rhizoids, roots and hypha) resulting in disaggregation and loss of stone materials. With regard to the conservation of the Khmer temples, some authors [21][22][23][24], however underlines the positive effects of forest cover and of the biological colonization in stabilizing the microclimate, preventing the negative effects of overheating and ventilation, and regulating moisture on the sandstone. The importance of a better knowledge of the relations among forest canopy and biodeterioration pattern was emphasized in a previous contribution [25].…”

Influence of microclimate on the directional dependence of sandstone pillar weathering in Angkor Wat temple, Cambodia

“…These weathering processes are thought to be restricted by direction dependent (Waragai 2005b;Waragai et al 2006;André et al 2012;Hiki 2012;Hiki and Waragai 2014;Waragai 2016), especially for the temples at Angkor. Regarding cultural stone weathering, previous studies have shown the importance of direction or aspect related to heating-cooling repetitions and moisture changes (Meierding 1993;Paradise 1995Paradise , 2002Williams and Robinson 2000;Waragai 2017).…”

Biological colonization patterns on the ruins of Angkor temples (Cambodia) in the biodeterioration vs bioprotection debate

“…This lythotype shows low compressive strength, high porosity and constituent minerals susceptible to alteration (Delvert, 1963;Uchida et al, 1999). The greenish greywacke used for the Ta Keo temple has a similar chemical composition to "grey to yellowish brown sandstone", although, it is slightly rich in CaO (Andr e et al, 2008(Andr e et al, , 2011. However the fundamental difference between these two types of sandstone is in their porosity: this is 10e20% for the sandstone of the Ta Nei temple, while for Ta Keo's sandstone it is less than 5% (Uchida et al, 1999).…”

“…Now it also displays lower levels of biological colonization, often limited to wide black patinas of cyanobacteria and lichen communities. On the basis of a comparison of the observed rate of weathering of this temple and that of the temples covered in vegetation, some authors (Andr e et al, 2008(Andr e et al, , 2011 have concluded that most biological colonizations, and especially lichens, have a bioprotective action.…”