Editor’s Note: Several months ago, the Growers/Vintners for Responsible Agriculture approached the Register about contributing a regular column, each written by different members, sharing information about about conservation and our valley.

The group provided the following statement to describe its work:

“Protecting our valley, the place that we all share and call home, is crucial if we are to sustain our agricultural, natural, residential and business resources. Napa Valley is a national treasure and we are committed to preserving its integrity and beauty by recognizing the importance of a healthy watershed, intact forests and shrub lands. The health of our environment is a shared resource and we must protect it to retain Napa Valley’s unique biodiversity and rural character. In this column, we share the science, values and experiences that guide our efforts to protect Napa Valley. Thank you for joining us on this journey.”

Napa County Growers/Vintners

for Responsible Agriculture

The first column is by Tiffany Yap, a biologist with the Center for Biological Diversity.

Napa County supervisors deserve big credit for starting work on a new ordinance to protect streams, forests and hillsides as the wine industry continues to expand rapidly.

But what exactly should be in this ordinance?

As a scientist, I was pleased to hear so many people at a recent public forum urging county supervisors to base the new conservation measure on science.

Indeed, to truly safeguard Napa County’s environment, we have to understand the key facts. And then, of course, we have to accept those facts and take action, rather than engaging in further debate and delay.

I’d suggest starting with four major points grounded in solid science.

1. Excessive planting

on slopes crumbles Napa’s hillsides.

Science supports the board banning development on hillsides with more than 30 percent slope. Removing trees from steep slopes is both dangerous and environmentally harmful.

Forest cover plays a critical role in soil stabilization, regulating water flow, maintaining water quality, promoting groundwater recharge, and maintaining overall watershed health.

Reduced forest cover has been shown to result in increased runoff, erosion, and sedimentation. A study from the U.S. Forest Service found that in western U.S. watersheds, tree removal led to increased runoff and erosion and ultimately degraded watersheds.

But Napa County residents don’t need to look to this study. They can see this in the Napa River’s muddy waters, the loss of native fish, and the road closures due to erosion from hillside vineyards.

Based on county vegetation cover data from UC Davis researchers, tens of thousands of acres of forest — especially oak woodlands — remain vulnerable to development in Napa County. To avoid further erosion and degradation of these watersheds, the county must retain as much tree canopy as possible and restrict development on slopes.

2. Setbacks from streams ensure clean water for everyone.

Science supports the need for large setbacks from streams and wetlands to protect drinking water and groundwater recharge. Napa County’s rivers and streams are lifelines for its residents and agriculture. The county needs clean drinking water and enough groundwater storage to survive drought years.

A scientific review from the University of Illinois at Urbana-Champaign found that robust stream and wetland conservation buffers would protect water resources by stabilizing stream banks, minimizing erosion, and facilitating groundwater recharge.

In addition, wider setbacks would provide much-needed habitat for sensitive species, such as California newts, western pond turtles, and migratory birds — all of which help maintain these ecosystem services by keeping watersheds healthy.

3. Protecting tree canopy fights climate change.

A strong, international scientific consensus has established that human-caused climate change is causing widespread harms to human society and natural systems.

A 2018 report from the Intergovernmental Panel on Climate Change, the leading international scientific body for the assessment of climate change, established that aggressive reductions in emissions within the next decade are essential to avoid the most devastating climate harms.

In Napa County, climate change will result in higher temperatures and reduced precipitation levels and water availability. The county needs to take rapid action to combat climate change and enhance the resilience of its communities and ecosystems.

That’s where trees come in. According to studies conducted by the U.S. Department of Agriculture, UC Berkeley and UC San Diego, mature forests, shrublands, and native grasslands efficiently sequester carbon within their woody vegetation and soils. Replacing trees and chaparral with vineyards and disturbing the soil will release carbon stores, releasing it to ramp up climate change.

4. Even small new vineyards can have out-sized impacts.

Science tells us that long-term sustainability of ecosystems and the services they provide requires the conservation of diverse habitats and species.

Napa County supervisors are considering that five-acre parcels be exempt from the new ordinance. But the cumulative impacts of land use can have a major impact on watershed health. A study by UC Berkeley researchers found that increased coverage of vineyards in Sonoma and Napa counties led to decreased biodiversity in streams.

In complex landscapes, such as those in Napa County, maintaining high-diversity habitats and safeguarding imperiled wildlife is essential to protecting biodiversity and environmental systems that benefit everyone who lives in the county.

Napa’s special ecosystems are the backbone of its idyllic scenery. They provide important ecosystem services vital to the county’s prosperity and way of life, including water-quality protection and erosion control.

But development and agricultural expansion into important habitats are threatening these biological communities. Without a strong new conservation ordinance, Napa County could lose these special ecosystems and the valuable benefits they provide.

The science is here — and it’s clear. Napa County needs bold new environmental protections to safeguard its communities and way of life. The next step is up to the Board of Supervisors.

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Tiffany Yap is a biologist with the Center for Biological Diversity.