In California’s forests, removing small trees leaves water for bigger ones and for dwindling reservoirs

IN THE early 1900s, an average forested acre in California supported fewer than 50 or so trees. After a century of efforts to fight wildfires, the average has risen to more than 300 (albeit mostly smaller) trees. Some might reckon such growth wonderful, but it is a problem far more serious than, say, the fact that horses can no longer trot through areas where they once could. The extra fuel turns today’s wildfires into infernos hot enough to devastate the landscape, torching even the big older trees that typically survived fires in the old days. Beyond this, the extra trees are worsening California’s driest ever drought.

“Like too many straws in a drink,” trees suck up groundwater before it can seep into streams that feed reservoirs, says David Edelson of The Nature Conservancy. The project director for the Sierra Nevada range, source of 60% of California’s consumed water, notes that as a warmer climate lengthens the growing season, trees’ thirst will only increase. This has led to a push for large numbers of trees to be cut or burned down. Overgrown forests catch more snow and rain on leaves and needles, where wind and sunlight increase the amount of moisture lost to evaporation.