updated November 13, 2018

Why California burns — its forests have too many trees

By Thomas M. Bonnicksen, San Francisco Chronicle, November 13, 2018

Standing dead trees, called snags, in an area burned in the Rim Fire in California, July 7, 2016. A scientific debate is intensifying over whether too much money and too many lives are lost fighting forest fires, which biologists say are beneficial to hundreds of plants and animals.

The reason wildfires are burning California with unprecedented ferocity this year is because our public forests are so thick. It is our fault. We don’t manage our forests, we just let them grow. That is the simple truth. However, it is easier to deny the truth and blame a warming climate instead of admitting our guilt and taking action to prevent wildfires.

Hot, dry weather doesn’t cause catastrophic wildfires. It only makes them worse. In order for any fire to burn, it must have fuel. To spread wildly, it must have abundant fuel. Efforts in the 20th century to prevent fire and preserve forests have been too successful — they have disrupted the ecological balance and allowed more and more trees to grow.

Some California forests have more than 1,000 trees per acre when 40 to 60 trees per acre would be ideal. These overcrowded forests are filled with dead trees, piles of logs, and thickets of small trees. The perfect conditions for severe wildfires. No wonder wildfires are getting bigger and more destructive each year, and the cost to fight them is increasing as well.

In addition, greenhouse gas emissions from one acre of burned forest are about the same as the exhaust from 13 cars for one year, according to the study I did for the Forest Foundation in 2008. These gases stay in the atmosphere warming the climate for centuries. Only carbon dioxide can be recovered, and then only if a new forest is replanted. Unfortunately, California is losing forests on federally owned land at the rate of about 26,000 acres per year because of a lack of replanting after catastrophic forest fires.

Wildfires are predictable and preventable. Just look for the thickest forest or the oldest chaparral and that is where a catastrophic fire will burn. Reduce the fuel and you reduce the threat.

So, why don’t we stop the destruction and human suffering? Mainly because politicians and government officials find it easier to justify spending money to fight wildfires than to reduce the fuel that causes them.

Unfortunately, the annual ritual of death and destruction from wildfires will continue to plague Californians in the decades ahead. We know it is unnecessary. We know that thinning our dangerously overcrowded forests will prevent it. We just lack the will to do it.

Thomas M. Bonnicksen is professor emeritus of forest science at Texas A&M University and author of “America’s Ancient Forests” (John Wiley & Sons, 2000). He is a graduate of UC Berkeley.


updated May 8, 2018

Unfortunately, Measure C is promulgating failed 20th century forestry policies in our 21st century world.  Measure C tells us that after the 795-acre limit for converting Oak woodlands to another use is reached, the remaining Oak woodlands will be left intact, along with new stringent regulations limiting the number of oak trees which can be cut.  These new regulations limiting cutting oak trees will promote forests that then will become overcrowded with more deadfall and brush, leading to unhealthy forests.   This overcrowding will set the forest up to become more susceptible to disease, insects, drought and hot fires.   Forests are like any plant: the more there are of them the more water they will use, which will ultimately result in less water being released into our streams and creeks, which is exactly the opposite of the Measure C goals.

Below are a small selection of  articles that will help all of us to better understand how our forests of today should be managed.

While the science-based articles here are mostly based on the Sierra Nevada mountains, I believe they are applicable to our own mountains.   In reading the “Forest Fires in Sierra Nevada Driven by Past Land Use,” consider hillside vineyards as a modern positive land use modification to our forests. Hillside vineyards will check the path and intensity of fires and thus are powerful tools in reducing soil erosion, air pollution and helping preserve property and lives.


When trees became the enemy: Why North American cities must thin overgrown forests to improve water supplies

By Helen Poulos, January 5, 2018

……it’s worth asking: does our universal mindset linking afforestation with basin health and water quantity actually, well, hold water?

The evidence points in the opposite direction. Indeed, the comfortable notion that more trees invariably result in more water, stability, livelihoods, clean air, or biodiversity has begun to look misguided at best and, at worse, catastrophic. Rather than replenish downstream runoff, aquifers, wetlands and streams, aggressive afforestation tends to dry them out and clog them up. …

Complete article:

Seeing the Forest for the Trees: Report Says Thinning Forests Key to Saving Redwoods

by Mina Kim, KQED, April 19, 2018

Fewer Trees, More Water: Study Finds Runoff Boost From Forest Thinning

by Matt Weiser, May 7, 2018,

State of Redwoods Conservation Report, April 2018

One of the keys to conserving California’s redwood forests might be to cut trees down, according to a new report by Save the Redwoods League. Scientists say restoring the big and complicated ecosystems is key for new growth but so is thinning out some of the young, densely packed trees.

Guests: Emily Burns, director of science, Save the Redwoods League

DROUGHT WATCH: Why More Trees in the Sierra Mean Less Water for California

By Lauren Sommer, September 15, 2014

Managing Overgrown Forests

“I think the water piece is really huge,” says Scott Stephens, professor of fire science at UC Berkeley. “I think it’s under-appreciated but it’s massive.”

Stephens has found similar results in the Illilouette Creek basin in Yosemite National Park. About 40 fires have been allowed to burn there over several decades, reducing the number of trees per acre.

“It looks like there’s 20 percent more surface water leaving the streams in that area since the fire program began in the mid-1970s,” he says. ……

Complete article:

Billions of gallons of water saved by thinning forests

Too many trees in Sierra Nevada forests stress water supplies, scientists say

April 24, 2018, National Science Foundation

Summary: There are too many trees in Sierra Nevada forests, say scientists. That may come as a surprise to those who see dense, verdant forests as signs of a healthy environment. After all, green is good, right? Not necessarily. When it comes to the number of trees in California forests, bigger isn’t always better.

Complete article:

How much water do forests use?

By Forestry Commission, UK, undated

….. The amount of water that a forest uses remains an important subject of debate around the world. Trees and forests have the ability to use more water than shorter types of vegetation. This has led to concerns that major afforestation schemes could reduce water supplies, leading to water shortages and increased costs….

Complete article:

Forest Fires in Sierra Nevada Driven by Past Land Use

by Mari N. Jensen, University of Arizona College of Science, November 14, 2016

Changes in human uses of the land have had a large impact on fire activity in California’s Sierra Nevada since 1600, according to research by a UA researcher and her colleagues.

Complete article:

UC Merced Expert: Forest Thinning Could Free Up Water, Reduce Fire Risk

by Joe Moore, May 12, 2015, University of Arizona News

….UC Merced scientists say thinning overgrown Sierra forests to the density of around 100 years ago could free up as much as 1 million additional acre feet of water a year…..

Complete article:

Freshwater runoff from the Sierra Nevada may decrease by as much as one-quarter by 2100 due to climate warming on the high slopes, according to scientists at UC Irvine and UC Merced

September 2, 2014, University of California Irvine

Irvine, Calif., Sept. 2, 2014 — The study findings appear this week in the early online edition of Proceedings of the National Academy of Sciences.

…..According to the data, freshwater mountain runoff is highly sensitive to expanded vegetation growth.

The authors found that greater vegetation density at higher elevations in the Kings basin with the 4.1 degrees Celsius warming projected by climate models for 2100 could boost basin evapotranspiration by as much as 28 percent, with a corresponding 26 percent decrease in river flow.

Complete article:

Can cutting down trees protect New Mexico’s water?

A new collaboration seeks to ease wildfire’s impacts by thinning overgrown forests.

by Leah Todd, May 26, 2016, Solutions Journalism Network, High Country News, Colorado

….Gary Harris stood on a dirt road that cut across a forested hillside outside Tierra Amarilla, New Mexico. To his left stood a crowded forest: tall Ponderosa pine grew just a few feet apart, further crowded by shorter trees and shrubs. Dry logs littered the ground, some the scattered remains of past logging operations.

“It gets tough to walk through some of this,” said Harris, a forestry consultant based in Chama, New Mexico.

But on the other side of the road stretched a new kind of forest – a patch the size of a football field that looked more like an orchard than a dry jungle. Ponderosa pine still stood tall, but the ground was carpeted by only a thin bed of pine needles, free of small trees and shrubs. A truck could easily drive between most of the trees.

Complete article:

Environmentalists plan logging to restore California’s redwood forest

by Paul Rodgers, Bay Area News Group, April 17, 2018