What moisture content in wood is known to support fungi growth?

Wood moisture content is a crucial factor in determining the susceptibility of the material to fungal growth. The threshold known to support significant fungal activity is above 20 percent moisture content. At this level, the environment is conducive for various types of fungi that can cause decay and degradation of the wood.

When the moisture content exceeds 20 percent, it provides the necessary water for spores to germinate and for fungi to proliferate, making the wood more vulnerable to rot and structural damage. This perspective is supported by the understanding of wood's fiber saturation point, which typically occurs around 30 percent moisture content. However, fungi can begin to grow at moisture levels slightly lower than this but will require the environment to remain consistently above 20 percent for healthy growth and decay processes to occur.

Moisture content below 20 percent is generally regarded as safe for wood against fungal attacks, as it limits the water availability that fungi require for growth. Therefore, understanding that levels above 20 percent are directly linked to increased risk of fungal infestation provides clarity on why this is the correct answer.