What adverse effect can high moisture levels in wood cause?

High moisture levels in wood can create an environment conducive to fungal growth. Fungi thrive in damp conditions, and when wood absorbs excessive moisture, it can lead to rot and decay. This not only compromises the structural integrity of the wood but also poses significant challenges in aviation applications where strength and durability are critical.

The other options do not align with the impact of high moisture in wood. Color fading is typically associated with exposure to light rather than moisture alone. Increased flexural strength is not a result of moisture; in fact, excessive moisture can weaken the wood. Inhibition of insect pests is also unlikely because many pests are attracted to moist wood, which can lead to infestations rather than prevention. Thus, the correct answer is that high moisture levels in wood support fungal growth, highlighting an essential consideration in materials management in aviation.