Abstract:

Objective: Ancient wooden-structure building is a valuable material for the study of Chinese ancient history,culture,art,science and technology and economy. This study aimed to investigate the selection principle of wood species and the relationships between the principle and biological diseases of wooden components in ancient wooden-structure buildings in severe wood biological diseases area,to understand the wood species allocation pattern and biological disease regulation. It was expected to provide scientific basis for the repair and protection of ancient wooden-structure buildings and for the study of ancient architectural history. Method: A total of 30 old wooden components replaced when 12 ancient wooden-structure buildings were repaired,were used as objects to detect the types,locations and degrees of biological diseases. Wood samples were taken from wooden components and embedded in carbon wax. 15-20 μm thick microsections were prepared from embedded wood samples by sliding section microtome. The microstructure and biological diseases characteristics were observed by optical microscope. Wood identification and the grade of biological diseases were determined,according to the identification characteristics list of IAWA softwood and hardwood and the relevant national standards. Result: The species in wooden components of 12 ancient buildings involved 14 genera and 12 families. The proportion of softwood and hardwood was 43.3% and 56.7%,respectively. Cunninghamia sp., Betula sp., Populus sp. and Pinus sp. were commonly used species. Zhejiang Province was the most abundant in wood species used,Henan and Guizhou provinces were mainly hardwood,whereas Hunan Province was dominated by softwood. Among the 10 kinds of wooden components,the wood species of load-bearing and large volume wooden components were mainly composed of Cunninghamia sp., Larix sp., Ginkgo sp., Pinus sp. Betula sp., Castanopsis sp., Phoebe sp., Quercus sp., Ulmus sp., Populus sp., Pometia sp. and Temstriemia sp.,but the wood species of non-essential load-bearing structure,small volume or decorative wooden components were mainly composed of Cunninghamia sp., Betula sp., Populus sp., Tilia sp., Ulmus sp. and Ailanthus altissima. Among the wood physical and mechanical strength of 14 wooden components, Quercus sp. had the largest air-dry density and bending strength,while Cunninghamia sp. was the smallest. There were 9 kinds of wood with strong resistance to decay and 4 kinds of wood easy to crack. Wooden components were damaged by various degrees of decaying fungi,carpenter bees,beetles and termites. The wood species vulnerable to carpenter bees were Cunninghamia sp., Betula sp. and Pinus sp.. Pinus sp., Betula sp. and Populus sp. were the most vulnerably attacked by beetles,while Cunninghamia sp., Ulums sp., Quercus sp. and Castanopsis sp. were susceptibly attacked by termites. All wood species were vulnerable to the damage of decaying fungi,of which Cunninghamia sp., Betula sp. and Populus sp. accounted for a large proportion. Conclusion: In terms of wood utilization,there are obvious differences among areas with severe wood biological diseases. There are also differences in wood utilization among different types of wooden components,as well as the same type of wooden components. The selection principle of wood species is as follows: 1) Considering the safety performance of buildings,the physical and mechanical properties of wood are the primary factors in the selection of wood species. 2) Considering the economic convenience of material sawing and transportation,local common native wood species should be selected. 3) "Local species" is an important principle of wood utilization,which leads to great differences in different regions. 4) To some extent,the selection principle of wood species is affected by the use of wooden components. 5) To some extent,the selection principle of wood species is affected by the location and function of ancient buildings. Wood biological diseases are closely related to wooden components selection: 1) Although the natural decay resistance of wood species is different,fungal decay is still the primary biological disease factor of wood quality deterioration of 12 ancient buildings. It shows that the decay is more closely related to the climate and environment where ancient buildings were located. 2) Carpenter bees and beetles are the main insects of wooden components. The selection of wood species for nest building is related to the species of carpenter bees,the kinds of wooden components and building region.

Key words: ancient wooden-structure building, wood identification, hazards of bacteria and insects, decay, carpenter bee, beetles