How a dry moss patch can restart
Mosses have no roots that draw water from deep soil and no plumbing system to move it through the plant. Much of their water comes directly from rain, dew, or damp air, so their tissues can dry out when the weather turns harsh. In many mosses, drying slows metabolism—the chemical activity that keeps cells functioning—to a near standstill.
That pause is not the same as death. Some mosses tolerate losing most of the water in their tissues while protecting their cells from damage. Their cell membranes and other structures can survive the dry spell, though the degree of tolerance varies among species and conditions.
Water switches the work back on
When moisture returns, water enters the tissues and the cells regain their working conditions. Photosynthesis—the process that uses light to make sugars—can resume, and the moss may regain its green appearance as its pigments and tissues rehydrate. The change can happen quickly enough to make a brown, crisp-looking patch seem to wake up after rain.
The moss is not growing without water during the dry period; it is enduring it. Once wet, it can resume growth and reproduction, provided the conditions are suitable. This strategy lets mosses persist on exposed surfaces such as rocks and tree bark, where moisture comes and goes rather than staying available in the soil.
