Site and size but not species mixture drive wood properties of second-growth western redcedar

Wood is far more than a simple building block; it is a living material whose internal architecture determines whether it will hold up a roof, float a boat, or simply snap under pressure. For foresters and timber growers, the quality of wood is not just about how tall or thick a tree gets, but about the microscopic details inside its fibers: how dense the material is, how the tiny cellulose strands are oriented, and how thick the cell walls are. These traits dictate strength, stiffness, and how well the wood resists shrinking or swelling with changes in humidity. As the world shifts toward using wood as a renewable alternative to steel and concrete to fight climate change, understanding what shapes these qualities in managed forests has become urgent. The forests of the Pacific Northwest are increasingly dominated by second-growth stands—trees that have grown back after logging or fire—rather than ancient, untouched old-growth. In these younger forests, managers often mix different tree species together to create resilient ecosystems, but a lingering question remains: does planting a tree alongside its neighbors change the quality of the wood it produces?

To answer this, researchers traveled to two distinct forest sites in British Columbia, Canada, nestled within the Coastal Western Hemlock zone. They focused on the western redcedar, a tree prized for its straight grain, natural resistance to rot, and use in everything from siding to decking. Unlike many commercial trees that are often grown in single-species rows, redcedar naturally thrives in mixed stands, yet little was known about how its wood properties respond to the specific mix of neighbors, the local environment, or the size of the tree itself. The team selected 72 redcedar trees across two locations, Hushamu and Malcolm Knapp, which shared similar productivity levels but differed in elevation and rainfall. They carefully categorized the trees by size—small, medium, and large—and measured the proportion of redcedar trees surrounding each sample to quantify how "mixed" the stand was. Using a specialized tool called SilviScan, which combines high-resolution X-rays and optical microscopy, the scientists extracted thin strips from the tree cores to analyze the basic density, the angle of the cellulose fibers, the thickness of the cell walls, and the width of the cells.

The study began by testing a common assumption: that the company a tree keeps matters. Foresters often worry that mixing species might force trees to compete for light and nutrients in ways that alter their wood structure, perhaps making it weaker or less stable. However, the data told a different story. The researchers found no significant link between the proportion of redcedar neighbors and any of the wood properties they measured. Whether a redcedar stood in a stand that was half redcedar or nearly all redcedar, its wood density, fiber orientation, and cell structure remained consistent. This suggests that for western redcedar, the specific mix of neighboring conifer species does not dictate the quality of the wood it produces. The only slight exception was a minor trend in cell wall thickness at one site, but even that did not hold up as a general rule across the board. In short, the presence of other tree species did not seem to rewrite the internal blueprint of the redcedar.

Instead, the study revealed that the environment and the tree's own growth rate were the true architects of wood quality. The two sites, though similar in overall productivity, produced distinctly different wood. Trees at the Malcolm Knapp site, which sits at a higher elevation with less rainfall, started with higher density and a different fiber angle compared to those at the lower, wetter Hushamu site. Over time, however, the patterns shifted. As the trees matured, the wood at the higher site became less dense and had thinner cell walls, while the trees at the lower site maintained a different structural profile. This highlights that local conditions—such as elevation, temperature, and soil moisture—leave a lasting imprint on the tree's anatomy, creating a "signature" of wood quality that varies from place to place.

Perhaps the most striking finding concerned the size of the trees, which served as a proxy for their growth speed. The researchers discovered that smaller, slower-growing trees produced wood with higher basic density, thicker cell walls, and a lower angle of cellulose fibers. In the world of wood mechanics, these are the hallmarks of a stiffer, stronger, and more dimensionally stable material. Conversely, the larger, faster-growing trees tended to have lower density and thinner cell walls, traits often associated with more flexible but less rigid wood. It is as if the slower pace of growth allowed the tree to build a denser, more reinforced structure, while the rapid expansion of the larger trees prioritized size over structural density. This relationship held true regardless of the site or the mix of neighbors, suggesting that managing for slower growth rates could be a key strategy for producing higher-quality timber.

The implications of these findings are clear for the future of forest management in the Pacific Northwest. Since mixing species does not appear to harm the wood quality of western redcedar, foresters can confidently plant these trees in diverse, mixed-species stands to boost ecosystem resilience against pests, disease, and climate shifts without sacrificing the value of the timber. The study suggests that the focus should shift away from worrying about species composition and toward understanding how site conditions and growth rates shape the final product. By recognizing that smaller, slower-growing trees naturally produce stiffer and stronger wood, managers can better predict the quality of their harvests and tailor their strategies to balance the need for rapid growth with the demand for high-performance wood. Ultimately, the research confirms that while the forest around a tree may change, the tree's own size and the ground it stands on are the primary forces writing the story of its wood.