Cedar is a highly valued building material often chosen for its natural beauty, distinct aroma, and reputation for durability. This wood, particularly from species like Western Red Cedar and Eastern Redcedar, is frequently marketed as being naturally resistant to decay and insects. However, termites, which are tiny yet immensely destructive pests that feed on wood cellulose, pose a significant threat to wooden structures globally. This raises a fundamental question for homeowners and builders: Is cedar truly immune to termite attack, or is its resistance merely a deterrent? Understanding the specific biological and chemical properties of the wood provides the definitive answer to its ability to withstand these persistent pests.
The Direct Answer: Cedar’s Natural Defense
Cedar does possess a notable, natural resistance to termites, but it is not completely termite-proof. The protective quality lies almost entirely within the dense, inner wood known as heartwood. Heartwood is the older, darker, non-living core of the tree that accumulates protective compounds as the tree grows. In contrast, the sapwood, the lighter, outer layer, offers little to no resistance to termites. Sapwood is the living wood that transports water and nutrients and lacks the high concentration of defensive chemicals. Therefore, lumber with a high ratio of resistant heartwood is significantly more durable against pests.
The Chemical Mechanism of Repulsion
The defense mechanism of cedar heartwood is rooted in the presence of potent natural chemicals called extractives, including polyphenols and essential oils. These compounds are deposited in the heartwood during its formation. Among the most significant defensive chemicals are the tropolones, specifically Thujaplicins, which act as natural fungicides and insecticides. These chemicals, along with sesquiterpenoids like cedrene and cedrol, are toxic to termites. They function as antifeedants, making the wood unpalatable, or as contact toxins that disrupt the termite’s digestive symbionts, which is the primary reason the heartwood is considered resistant.
Factors Affecting Long-Term Resistance
The practical durability of cedar’s resistance is not permanent and depends heavily on environmental conditions and application.
Leaching and Weathering
Leaching and weathering are the primary factors that degrade the wood’s natural protection over time. When cedar is exposed to constant moisture, rain, or soil contact, water gradually washes the protective extractives, including the Thujaplicins, out of the wood. This loss of chemical concentration significantly reduces the wood’s inherent toxicity and can leave it vulnerable to attack, particularly in ground-contact applications. Additionally, ultraviolet (UV) light from the sun can initiate photochemical reactions on the wood surface, contributing to the breakdown of the protective lignin and extractives. The rate of resistance loss is accelerated in harsh outdoor environments where the elements rapidly deplete the chemical reserves.
Termite Species Variation
Resistance levels also vary depending on the specific termite species present in a region. The natural oils in cedar may deter common subterranean termites more effectively than they deter drywood termites. While one species may find the wood actively toxic, another may only find it unappealing, choosing to consume it if no other food source is available.
Physical Integrity
The physical integrity of the lumber also plays a role in its long-term defense. Any cuts, cracks, or damage to the heartwood can expose the non-resistant sapwood beneath the protective layer. This provides an easy entry point for termites, allowing them to bypass the concentrated chemical defenses in the heartwood’s core. Maintaining an intact heartwood surface is important for maximizing the wood’s natural defense against infestation.