Redwood trees, with their impressive stature and distinctive coloration, are a notable feature in many landscapes. The unique reddish-brown hue of these trees and their timber often prompts questions when the color appears to change. Understanding the natural processes and environmental factors that influence redwood coloration helps clarify why these changes occur.
The Natural Color of Redwood
The characteristic reddish-brown color of redwood, particularly the heartwood, is attributed to natural organic compounds like tannins and other extractives. These compounds are present in the wood’s cells and contribute to a spectrum of shades, from lighter reddish-browns to deeper, darker tones. The specific hue can vary depending on the redwood species and the part of the tree. Tannins, which are typically brown, can range in color from light yellow to deep amber or nearly black, depending on their concentration and the plant source. Oxidation can also cause tannins to darken over time when exposed to air.
Color Changes in Redwood Lumber
Harvested redwood lumber naturally changes color when exposed to sunlight and rain. Over time, the vibrant reddish-brown of new redwood fades to a silvery-gray patina. This transformation is a natural weathering process, not decay, and is often a desired aesthetic for outdoor applications. UV radiation breaks down lignin, a wood component contributing to its original color; as it degrades, it washes away with rainfall, leaving behind gray or silver cellulose fibers. Moisture also causes water-soluble extractives, including tannins, to leach out of the wood, further altering its original hue.
Unhealthy Browning in Living Redwood Trees
Browning in living redwood trees can signal underlying health issues.
Inadequate Water
Inadequate water, leading to drought stress, is a common cause; needles may brown, often starting from the bottom and progressing upwards.
Pest Infestations
Pest infestations also contribute to browning foliage. Insects like cypress tip miners and bark beetles attack branches, while sucking pests like scales feed on tissue fluid, causing wilting and browning.
Fungal Diseases
Fungal diseases can manifest as browning. Root diseases (e.g., Armillaria, Phytophthora) cause branches to brown and die, often due to poor soil drainage. Canker diseases (e.g., redwood canker, Botryosphaeria canker) create dying plant tissue on bark, leading to widespread browning.
Nutrient Deficiencies
Nutrient deficiencies, such as iron deficiency in high pH soils, may also result in browning.
Distinguishing Healthy vs. Unhealthy Browning
Differentiating between healthy and unhealthy browning in redwoods involves observing the pattern and extent of the color change.
For living trees, a natural exchange of older needles occurs in late summer, where interior foliage turns orange-brown and drops. This shedding is normal, especially if the tree has new, green growth at the branch tips. However, widespread, rapid browning across the entire canopy or starting from the top, especially with no new growth, suggests severe drought stress or disease.
For redwood lumber, the natural transition to a silvery-gray is uniform across surfaces exposed to sunlight and rain. This differs from signs of decay, which include localized dark spots, a fuzzy or soft texture, or fungal growth. Discoloration like black stains near metal fasteners or overall dark patches can indicate iron stains or extractive bleeding.