Throughout the world's temperate zone, trees experience sap's rise and fall. In the spring, sap starts flowing. Come the cold of winter, it recedes.
Sometimes, loggers harvesting particular species, such as Ponderosa pine and holly, prefer to fell timber in the winter when the sap is down. Their logs then have little chance to develop a sap-born fungus called blue stain, which discolors the wood and lowers its value.
In tropical Mexico and Nicaragua, loggers intent on harvesting the valuable primavera tree must pay close attention to its sap flow, too. If they cut when the sap runs high, it seeps out the ends of the log and quickly attracts a horde of insects that damage the wood before it gets to the mill. But how, in continually mild weather, can they tell when the sap is low? It's simple enough to them: They watch the moon.
Like ocean tides, the sap of the primavera tree follows the phases of the moon. When the moon is on the increase, the sap rises. In the dark phases of the moon, it falls. So that's when the harvest of this unusual tree begins.
Primavera wood, without the defect of tiny pinholes caused by insects, becomes beautiful furniture. Its yellowish-red color, streaked by brown, orange, and red, frequently displays a fiddle-back figure. If moonstruck, however, the wood has little value.
Illustration: Jim Stevenson