In what condition is wood most susceptible to decay?

Wood is most susceptible to decay at high humidity levels because moisture is a key factor in the decay process. Fungi, which are responsible for the decay of wood, thrive in environments where humidity is high, as they require moisture to grow and reproduce. This moisture can come from various sources, including rain, high humidity in the air, or damp soil.

In contrast, when wood is completely dry, conditions are unfavorable for fungal growth, as the lack of moisture inhibits the ability of decay organisms to thrive. Sunlight, while it can dry out wood and reduce humidity, does not directly cause decay, but rather can help in maintaining drier conditions. Low temperatures also tend to slow down the metabolic processes of decay organisms, making wood less susceptible to decay, as many fungi and pests are less active or dormant in cooler climates.

Thus, high humidity levels create an optimal environment for wood-destroying fungi, making it the condition under which wood is most vulnerable to decay.