Valley. Tubbs. Nun. Atlas. Kincade. Glass. The onslaught of wine-country infernos in recent years makes it clear: frequent and intense fire is now a fact of life in California wine country.
Growers can take specific steps to prepare for and mitigate the effects of fire, and many are. But with dry conditions across the west, another protracted fire season is looking almost inevitable. The more important question might be: how can vineyards recover?
Well-managed vineyards—surrounded by cleared or grazed defensible space, free of brush or tall grass to pull fire into the blocks, with closely mowed or tilled floors—seldom burn down. But fire can damage vines and vineyard infrastructure without ever entering the blocks.
Much discussion of these indirect effects has focused on smoke taint, but experts say there's much more to consider than that.
Assessing damage from heat
“Grapevines don’t withstand heat from fire very well,” says Glenn McGourty, retired viticulture and plant science advisor with University of California Cooperative Extension. The strong winds that often accompany fire cause more than smoke damage, he says: the scorching air blowing into vineyards can injure vines to the point of no return.
“The hot air causes water in the vascular tissue to heat and expand. Boiling sap triggers cells to burst, killing the living tissue within the vine.”
Photo courtesy Cliff Walters
Small vineyards surrounded by wildlands are more susceptible to heat damage, as heat from surrounding fire can penetrate further inside the block. Large vineyards tend to sustain damage only in the outer rows closest to the fire. McGourty notes that regrowth on fire-damaged vines doesn’t necessarily indicate the vine will thrive again: even with regrowth, the vascular tissue can be sufficiently compromised to inhibit nutrient movement and impact production.
Cutting across the wood in multiple places will reveal the extent of fire damage. “If all leaves are brown, the ground is blackened, and drip irrigation systems are melted, vines typically have sustained significant damage and need replaced. Heavy pruning, down to healthy tissue, may rejuvenate vines, but if the wood is grey or brown and dry, the vine is dead.”
"Fires often follow creeks and other riparian areas into the vineyard and damage adjacent vines," McGourty says, "but the most pervasive fire damage is often felt outside the vineyard blocks."
While sustainable practices such as no-till, use of cover crops, and mulching help limit erosion on hillsides, fires will increase soil erosion potential. That's in part because soils heated by intense fire become temporarily hydrophobic, resisting water infiltration, which increases runoff. "Growers can anticipate a high sediment flow through creeks and culverts after fires,” McGourty says.
Conditions after the fire may determine how or if growers choose to mitigate erosion concerns. “Much depends on storm intensity," notes Bill Birmingham, Conservation Project Manager at Napa County Resource Conservation District (NCRCD). "Light rains will help settle the ash and germinate the existing seed bank within the soil. The impact of individual raindrops can dislodge exposed soil. Heavy rains have the potential to affect hillsides stability."
Photo courtesy Bill Birmingham
While debris slides are always a concern, Birmingham believes the rain intensity and degree of slope play a larger part in slides than does fire. Chip Bouril, a USDA NRCS soil conservationist, agrees.
“We recommend concentrating efforts within the vineyards," he says. That means evaluating infrastructure such as drainage systems: when plastic culverts catch fire, the roads above them can collapse into the void left by disintegrated pipes. Growers should watch for ponding of water on roads that may indicate damage to culverts, and clear any blockages from fire debris.
Managing wildland fuels
“It is difficult to see the burned hillsides and forests," Bouril acknowledges, "but the wildlands are resilient. Native plants are adapted to fire cycles—seeds survive for generations just waiting to germinate until fire clears the land.”
In the immediate aftermath of a fire, disturbing the ground may exacerbate erosion and expose landowners to risk from ash and treefall. But in the big picture, Lucas Patzek, Ph.D., executive director at NCRCD, does see opportunities for growers to help address tree mortality and reduce fuel buildup.
Wildflowers bloom over trees burned in the 2020 Glass Fire.
“These large wildfires have taken care of overgrown forest understories, which provides us with an opportunity to manage for healthier forests and watersheds, reduce invasive weed populations, and achieve other goals to benefit agriculture, community safety, and native habitats,” Patzek says.
NCRCD, USDA NRCS, CAL FIRE and other partners are working to assist wine country landowners in developing forest management plans—and to develop a broader vision for a fire-resistant landscape. “The forest management plans outline specific projects on a private property to reduce fuel loads, properly construct firebreaks, and other actions to reduce fire risk and improve forest health," Patzek explains. Similar efforts are happening throughout California and across the American West.
More than ever, growers whose properties include forested land face the challenge of actively managing non-arable areas in addition to their vineyard or farm. It's no small task, but help is available: reach out to your local Fire Safe Council or resource conservation district for more information on technical and financial support available near you.