Sapwood is the newer, outermost layer of wood found beneath the bark of a tree. It plays a crucial role in the tree’s life by acting like a pipeline, transporting water and dissolved nutrients from the roots up through the trunk to the leaves, where photosynthesis takes place. Sapwood is essential for a tree’s growth, as it also serves as a storage area for vital nutrients that the tree uses for development and sustenance.

When a tree is felled, the nutrient reserves stored in the sapwood remain within the timber even after it is sawn into components. However, this nutrient-rich wood becomes a prime target for various species of fungi and insects, making sapwood susceptible to biological attacks. The risk of such infestations increases significantly if the wood’s moisture content rises above 20%. A condition that can arise from factors such as poor installation practices or inadequate maintenance.

Pressure treatment protects the timber against wood rot and insect attack. But these treatments do not provide all round protection against weathering. The elements and UV rays will slowly degrade the effectiveness of the pressure treatment. Improper treatment can lead to elevated moisture levels in sapwood, which creates an environment conducive to fungal growth and insect infestation as the effects of the pressure treatment degrade over time. This not only compromises the structural integrity and longevity of the timber but also diminishes its aesthetic and functional value. Therefore, it is essential to ensure proper handling, installation and maintenance of sapwood-containing timber to mitigate these risks and preserve the wood’s quality and durability.

Heartwood is the dense, strong inner core of a tree, composed of dead or “retired” sapwood that no longer plays a role in the tree’s nutrient transport system. Unlike sapwood, heartwood is highly resistant to decay due to its reduced moisture content and the presence of natural compounds that make it less appealing to fungi and insects. As long as the tree’s outer layers—such as the bark and sapwood—remain intact, the heartwood continues to retain its strength and durability. In some tree species, heartwood contains naturally occurring chemicals, like tannins or oils, that enhance its durability, providing a natural resistance to decay and insect attack. However, the degree of this natural durability varies significantly between species; for example, cedar and teak have heartwood that is more resistant to decay, while other species may have less durable heartwood.

Modern Forestry

In modern forestry and timber production, the timber used for building often contains higher proportions of sapwood, which is less durable than heartwood. This shift is largely due to forestry management practices aimed at maximizing production yields and harvesting younger trees, which have not yet developed a substantial amount of heartwood. As a result, contemporary construction wood is more susceptible to decay and pest infestation, particularly when it includes high proportions of sapwood.

To address this issue, preservation treatments are commonly applied to enhance the durability of less durable sapwoods. A frequently used method is tanalising, which involves a pressure treatment process in which preservatives are forced deep into the wood fibers. This treatment significantly enhances the wood’s resistance to rot, fungi, mold and insect damage, making it more suitable for outdoor use and increasing its lifespan even in harsh environmental conditions. Tanalised wood can withstand extreme weather conditions better than untreated wood, offering improved performance and longevity for construction projects.

However, it’s important to note that while pressure treatment improves resistance to biological threats, it does not completely prevent wood from reacting to environmental factors over time, particularly changes in heat and humidity. Wood, even when treated, can expand, contract, warp, or crack in response to fluctuating weather conditions.

Wood treatment

It is for this reason that we recommend that our planed timber gates are treated with a modern UV Oil for planed timber such as Osmo . Click here for more information. The oil contains an active UV filter that preserves the colour of the wood. Any outdoor wood that is sealed with oil at least once every year will repel water. Oil also stops wood drying out unevenly, which can lead to warping. Gates will last longer and look better than wood that is simply left to the elements.

Pressure treated softwood that has deterioated in the weather over a period of time due to natural weathering

Pressure treated oiled softwood