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Home Research Naturally durable woods



Naturally durable woods


Certain wood species are naturally resistant to termite attack and offer an alternative to preservative-treated wood. It is important to note, however, that it is only the heartwood (and sometimes the bark) that exhibits termite resistant properties. Thus, in the brief descriptions below, it is only the heartwood that is being considered.


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redwood

Redwood (Sequoia sempervirens)
This wood species has been known to possess some natural resistance to decay and termite feeding. Our research with redwood indicates a fairly high durability in short-term exposures to high termite activity. Findings also suggest that extractives from this wood are quite toxic to Formosan subterranean termites.



Alaska cedar; Pacific Coast yellow cedar (Chamaecyparis nootkatensis)
Termite bioassays with Alaska cedar have shown this wood to be slightly more durable than redwood. Short-term exposure to high termite activity also resulted in slightly higher termite mortality than redwood. The same study also revealed that given a choice, subterranean termites actually preferred Alaska cedar less than redwood. Alaska cedar can be considered to be a reasonable construction material substitute for redwood in terms of its resistance to subterranean termites.



Laotian teak (Tectona grandis)
Teak shows considerable resistance to subterranean termite attack. Its resilience in field tests have resulted in it being compared to lumber treated with ACZA and CCA. Perhaps the greatest drawback in teak is its relatively high cost, which is likely to limit its use in construction. It is currently unknown how resistant teak is to drywood termites.



sugi Sugi (Cryptomeria japonica)
Commonly used for construction in Japan, this wood has a high resistance to subterranean termite attack. Along with tallowwood and milo, sugi holds much potential as a Hawaii-grown wood species for cultivation and utilization in termite-resistant wood products.


kou Kou (Cordia subcordata)
Along with kamani, kou possesses substantial natural resistance to feeding by subterranean termites. In the past, Hawaiians commonly used it to make tableware. This species is now somewhat rare, however, making future use of this species for construction doubtful.


kamani Kamani (Calophyllum inophyllum)
Kamani is a wood species with considerable natural resistance to termite attack. Although it is occasionally used for construction in some parts of the world, it suffers from substantial shrinkage during drying and can be difficult to work with. 


milo Milo (Thespesia populnea)
Milo is a fairly dense wood with a relatively high resistance to shrinking, lending itself to cabinet and boat construction in some parts of the world. In Hawaii, it is commonly used for fashioning crafts and bowls. This wood may have some potential as a Hawaii-grown termite-resistant species.


Tallowwood (Eucalyptus microcorys)
This wood is used extensively for construction in Australia, and exhibits fairly significant resistance to subterranean termite feeding. One of the slower growing species of the Eucalyptus genus, E. microcorys shows potential for use as a plantation species here in Hawaii.


casuarina pine Casuarina pine (Casuarina equisetifolia)
The casuarina pine is one of several termite-resistant trees of interest to the Hawaiian forestry industry. It is found both in Hawaii and Malaysia and has been shown to be very resistant to subterranean termite feeding. Findings from laboratory studies indicate that extractives in this wood may be somewhat toxic to termites.


kempas Kempas (Koompassia malaccensis)
The Malaysian kempas tree showed considerable termite resistance and high termite toxicity in a recent laboratory study. However, these results contrast somewhat from field studies conducted in Malaysia, where Koompassia spp. suffered significantly greater degrees of termite damage.


tualang Tualang (Koompassia excelsa)
Another Malaysian tree, tualang has been shown in a recent laboratory study to be somewhat toxic to Formosan subterranean termites. The same study also showed this wood species to be quite resistant to termite feeding.


sentang Sentang (Azadirachta excelsa)
Sentang (the Malaysian name for this tree), a relative to the neem tree, is not necessarily the most resistant wood to termite attack. However, a recent laboratory study has shown it to be quite toxic to Formosan subterranean termites. Although it may not have the same construction potential of some of the other naturally resistant woods, it does hold potential for use as a plantation wood. 




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