Green California suffers from lack of urban trees – lowest per capita in US  


Despite city tree benefits, California urban canopy cover per capita lowest in US

Trees in California communities are working overtime. From removing carbon dioxide and pollutants from the air, intercepting rainfall and increasing property values, California’s 173.2 million city trees provide ecosystem services valued at $8.3 billion a year. However, according to a recent study, more benefits could be realized if the Golden State’s urban forests didn’t have the lowest canopy cover per capita in the nation.

Percent tree canopy cover within California urban areas. CREDIT University of California, Davis

“The structure, function and value of urban forests in California communities,” recently published online in Urban Forestry and Urban Greening, reports that California’s 109 square yards of city tree canopy per person lags behind other urban canopy-poor states, such as Nevada (110), Wyoming (146) and Montana (148). And there’s no comparison with well-treed states, such as New Hampshire (1,514), Connecticut (1,214) or Alabama (1,182).

“There’s no question that Californians are deriving significant benefits from their urban forests,” said Greg McPherson, lead author of the study and a research forester with the U.S. Forest Service’s Pacific Southwest Research Station. “However, the fact remains that more can be done and will need to be done in light of the recent tree mortality epidemics plaguing some of our urban forests.”

In southern California, for example, the invasive shot hole borer has killed thousands of city trees and poses a threat to 33 percent of the urban tree population in the region. More than 50 tree species there are reproductive hosts for the insect, making them vulnerable to the lethal fungus it transmits.

City tree population and species composition figures were generated through an analysis of 1,385 study plots located across the state. Costs and benefits of ecosystem services were derived through numerical models that factored in the tree’s species, size and location across six climate zones within the state. Canopy cover estimates and state comparisons were calculated by analyzing aerial imagery from the 2012 National Agricultural Imagery Program.

“One of the factors driving the low per capita rating for California city trees could be the fact that 20 of the nation’s 100 most densely populated cities are in California, meaning there’s a higher volume of people in a confined space for trees,” said Natalie van Doorn, study co-author and research urban ecologist with the Pacific Southwest Research Station. “California’s arid summer climate also can suppress tree establishment and growth, which also could be a contributing factor for the results we observed.”

Still, with about 236 million vacant tree sites within cities, van Doorn noted that Californians have ample room for new tree plantings.

“In fact, our study results are already being used by municipal and state agencies to identify priority areas for planting and tree conservation, as well as examining potential disparities in disadvantaged communities,” she said.


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December 5, 2017 8:11 am

Yes, but…

Most of the highly urbanized parts of california are DESERTS. I see no reason why the cities should sport MORE trees per km² than what might naturally have covered the area. In fact, if you compare all well-wooded cities to the surrounding rural areas, I dare say that their boreal coverage (loosely defined) is only a small fraction of the native cover.

So, let’s go with that.
If city leafy cover is only 33% of an open rangeland in the same area (or whatever kind of cover naturally would be there), then that should be the standard for ALL climes.


Tom in Florida
Reply to  GoatGuy
December 5, 2017 8:17 am

Plus they are using “per capita” as the defining metric.

Bryan A
Reply to  Tom in Florida
December 5, 2017 9:35 am

A few more reasons for lower tree count…
OH power line density in heavily populated metropolitan areas negate planting larger leafy trees
California was/is a desert state
California is also a bread basket state with vast crop lands requiring open space

Michael Jankowski
Reply to  Tom in Florida
December 5, 2017 9:40 am

“Per capita” would seem to give a better score for “deserts” than one based on land-area.

Reply to  Tom in Florida
December 5, 2017 2:13 pm

Maybe the problem is with the “per capita” numbers. Fewer “capita’s”. better rate.

george e. smith
Reply to  Tom in Florida
December 7, 2017 5:31 pm

Trees do not pay taxes.

Capita’s pay taxes. So why would Jerry Brown’s California want more trees. He needs capitas to fund his never ending vote buying schemes.

But also, California has more than its share of non tax paying capitas, wh help keep the state permanently in liberal democrat hands.


Michael Jankowski
Reply to  GoatGuy
December 5, 2017 8:33 am

Seems like that would go for a number of other states, all that are going a better job per-capita.

Reply to  GoatGuy
December 5, 2017 8:38 am

Contrary to popular belief most urbanized parts of CA are not in a Desert. Most are in a Mediterranean Climate.

Tom O
Reply to  Kevin
December 5, 2017 11:22 am

They may be in a “Mediterranean climate,” but they DO have a desert water supply. Trees, unfortunately, require water. When the state is suffering from drought over half of the time, it doesn’t make really lots of sense to me to expect them to be growing more trees. It just sounds like “let’s have a nutter butter peanut butter science study,” heavy on the nutter. I live in Phoenix, which was a prairie sort of climate in the 1880s, and it takes more water to keep my one grapefruit tree happy than I use for everything else.

Reply to  Tom O
December 5, 2017 11:34 am

California has really variable climates and natural vegetation. Where I grew up, San Jose, the natural vegetation on the valley floor was open oak woodland. The Santa Cruz mountains on the west varied between redwoods to madrone to scrub oak and pine. The east hills were mostly grass and scrub.
Those were the range of climates within a one or so hour drive, and the state is much more variable than that.

Reply to  Kevin
December 5, 2017 12:43 pm

True, except for analyzing what you’re promoting in the Los Angeles basin, along with Sacramento, San Francisco, the Central Valley, San Diego, the greater Bay Area and oh, maybe Bakersfield. Before Europeans came blasting thru, there was open oak woodland in much of this space. California’s oak forests, quite unlike the East Coast’s or the Appalachians, or the Berkshires, or even the Smokey Mountains of Kentucky, are not dense forests. Never were. Quite open. Just like the open-oak hills remain in present not-populated parts of the coastal regime of the state

The point is, that if the nominal open woodland canopy cover is perhaps 25%, then why should we really be alarmed when the same space, “citified” is less than half that? I’d say “its OK”. Good enough.


Count to 10
Reply to  Kevin
December 5, 2017 3:07 pm

Davis, for instance, stands out from the grasslands it is surrounded by as a clearly man made forest.

Reply to  Kevin
December 6, 2017 3:59 am

O December 5, 2017 at 11:22 am

“Trees, unfortunately, require water”.
trees do NOT destroy water. Well, they do turn a very small part of it into wood, released when they are eaten/burned, but most of it, like 99%, is just returned is the air to fall back into rain not so far away, so the water circuit is pretty closed.
Actually, evidence are that forests induce more rain (cooling, producing nucleus for water drops,…). And they also increase the water reserve of the soil.

So you don’t have to fear water shortage because of trees, quite the opposite, you fight water shortage with forests.
Of course you don’t want to plant willows, rather some kind of Mediterranean climate tree.

Reply to  Kevin
December 6, 2017 1:45 pm

@ paqyfelyc December 6, 2017 at 3:59 am

He didnt say they destroyed water , you did. He said they require water, which is true. Your nice little closed loop water model works nicely in environments with with good rainfall, but dont work in arid situations. If everything was so awesome we wouldnt have deserts at all.

Reply to  GoatGuy
December 5, 2017 9:05 am

One wonders if the authors of such reports are even familiar with southern California? The urban areas, while not deserts are (or were) chaparral, a mix of sage, grasses, shrubs, cacti, and the occasional Live Oak tree. Palm trees are right out, as are those nasty eucalyptus. The area was never a forest except in the local mountains that separate the high Mojave desert from the lower coastal basin.
In many areas nonnative tree species have been imported and grown in suburban areas and provide much appreciated shade. But, such invasive forests do not come without a cost. Droughts which are regular place a lot of stress on the local water table and landscaping swallows a big gulp.
BTW the shot-hole borer was affecting drought stress damaged trees in the local mountains. Large pines growing at about 8000 ft altitude. Not too many of these trees growing in the LA basin…no snow.

Reply to  GoatGuy
December 5, 2017 9:07 am

If the issue is that LA and San Francisco are deserts (arguable) then how could Nevada be doing better at this metric? I mean seriously, your argument is that San Francisco is too arid to be compared to Las Vegas?

Reply to  chadb
December 5, 2017 12:46 pm

Nope, I’m saying, “picking these particular examples to go all ooooh-aaaah about is pointless”. The cities of Pittsburgh PA, of Atlanta GA, of New York NY … are only “barely covered” with trees compared to the native land once that they were. That’s all. I see nothing wrong at all with the “sand dunes of San Francisco” now being rather MORE covered with trees than they were when dunes. And still only 15% tree-covered. Its OK.

That’s all.

Tom Gelsthorpe
Reply to  GoatGuy
December 5, 2017 9:09 am

Natural tree cover in Southern California is next to nothing, except in moist ravines, owing to the semi-arid climate. Same for much of the San Joaquin Valley. That’s a big reason why drought-tolerant palms became so popular, although many are exotics, and few cast significant shade.

Plenty of urban trees will survive if they’re irrigated, either directly or from adjacent lawns. Sacramento, with only about 15″ of annual rainfall, mostly in three winter months, does well in that regard.

Central California has a lot of eucalyptus, both in urban and rustic settings. They’re fast-growing, picturesque exotics from Australia, not entirely suitable for street trees because they’re “trashy” and drop a lot of bark, seeds and twigs. Eucalyptus forests are fire-prone. One of California’s worst urban fires started in eucalyptus forests in Oakland in 1991, not far from where I lived in 1970.

All these landscaping decisions are trade-offs. I lived in California for a few years and made a decision I’ve never regretted — not to live again in an area with less than 30″ annual rainfall, and no more dry summers. The eastern third of the U.S. qualifies easily.

December 5, 2017 8:26 am

….and put up a parking lot

Reply to  Latitude
December 5, 2017 5:25 pm

Consider what has been done in what is now the state of Israel. It is very green (in the photosynthesis sense) compared to the surrounding areas and compared to what it was 100 years ago. It is also now much better supplied with water than it was and is anywhere else around it.

Some of the objections voiced here about what is ‘natural’ for California and what can be reasonably done with existing water supplies may simply be lack of vision. The question exists of whether more trees would be a benefit, as claimed in the article – if they were possible, If the answer is yes, perhaps consideration should be given as to whether those benefits are obtainable by observation of what has already been demonstrated as possible. Cost vs benefit analysis should apply.

December 5, 2017 8:30 am

Oh they say the arid climate might have something to do with it. How long did it take them to come up with that? Maybe they invoked the spirit of Einstein to help them come to that mind shattering conclusion.

I wonder, do they factor in irrigation demand when figuring up the “ecosystem services”. Maybe there is a good reason Californians aren’t trying to grow sugar maples.

December 5, 2017 8:53 am

For this one I had to snicker. As I understand it one of the problems during the recent wine country fires was the choice of trees used as wind breaks around the vineyards. Apparently they were exotic trees that not only burned readily but helped spread the first.

Erik Magnuson
Reply to  Edwin
December 5, 2017 9:02 am

Pretty much my thoughts as well. Heard many horror stories of fires spreading by igniting trees. On the other hand, some trees are much less of a fire hazard than others.

Comment also timely with respect to the fire in Ventura County.

Reply to  Erik Magnuson
December 6, 2017 1:42 pm

exploding gum trees can spot fires kilometres downwind, once these things get going ideas like tree windbreaks are pretty academic/useless

December 5, 2017 8:54 am

On the subject of LA, haven’t heard a squeak from DiCaprio lately. That’s gotta be a good thing. Whenever he flies out to educate the world, the average IQ of LA increases.
When I move to LA to become an actor I will bring my three pot plants, that should improve the balance.

December 5, 2017 9:09 am

Comparisons are difficult. There certainly should be a rain-fall and available shallow aquifer factor in such statistical summary statistics and comparisons.

Cincinnati has a huge urban forest/park or two (recalling news report of a child being lost in one for over a week). One ancestor’s farm there included a small forested river island that they said was still in the family in the 1980s. OTOH, histories I’ve run across said carriage-makers and early auto manufacturers cleared white oaks and maples from large swaths of Ohio for making dash-boards.

Chicago’s “forests” are a sad thin joke by comparison (other relatives were/are park system employees).

Kansas City is at the edge of what was once called the Great American Desert (see also bread-basket) but has a large moderately well-forested central city park only smaller that NY’s Central Park. I was always very aware of the sere edge of tree growth just west of town while living there (and that was around a stream and reservoir).

Red SoCal is much more of a desert environment. They have to artificially irrigate even the planted xeriscape succulents, using recovered “brown” water. Lots of trees in Sili Valley, but many orchards and other wooded areas outside crony socialist set-asides seem to be shrinking, displaced by human hive structures and offices. Relatives told me that they saw orchards cleared for housing and offices back in the late 1960s.

December 5, 2017 9:30 am

Part of the problem in California was unfortunate tree choices, like American Elms that were not replaced after blight, or trees planted by developers that were equally bad choices.

December 5, 2017 9:40 am

Sure, just empty Lake Tahoe for the water. Nevada won’t mind.

December 5, 2017 9:54 am

Well, they just get in the way of high speed rail lines and green energy projects. As Bill would say, it depends on your definition of green.

Peta of Newark
December 5, 2017 10:39 am

It ain’t gonna happen.
Nope. No possible. Nada chance. Zilcho hope-oh. Do Not Bet Your Paycheck

Maybe, 1, 2, 5 or 10 mill years ago yes.
Not now, tomorrow or any time soon. We *are* talking ‘Geological’ soon as well
No matter how much CO2 Greening, how many Sputniks say so, what NASA think – that ‘greening’ is nothing to do with CO2
Any trees you put there now will be weak, slow growing, prone to disease, burn easily and generally die. Period

And they will continue to die UNTIL Old Ma Nature runs a bulldozer over the place and clears away all the old, tired out, nutrient free, barren and infertile dirt there is there.
That nobody seems to be in any way shape or form even slightly aware of that is A Genuine Cause For Concern

A nice sheet of ice, slow moving, at least a mile thick and lasting maybe 50,000 years will do. Like we get here in Northern Europe by example. Clears out the old sdirt and grind up some new rock

There is hope in the shape of all the tectonic faults under there but Ma Nature is obviously not in any sort of hurry.
Work-in-progress *will* be rather messy so all you folks had better be thinking about ‘temporary accommodation’ for if & when she finally gets her finger out.

You’re wasting yer time planting trees until then.

Reply to  Peta of Newark
December 5, 2017 3:03 pm

Sources please?
I grew up in the tropics, in places where giant forest grow on geologically recent limestone rock. The Forest makes it’s own soil. That area shows no evidence of ice sheet scraping, so by your definition, it should be a dead zone.
I live on the top of a hill, where all soil was bulldozed off to make a house pad. Instead of soil, my back yard is rock and clay. There is a mini rain forest, including fruit and nut trees growing in the rock, it makes it’s own soil.
Soil fertility is a function of land use and species selection. Planting trees has always been part of the solution. They grind there own rocks up.

December 5, 2017 10:50 am

City-owned trees are expensive to operate in California.

December 5, 2017 11:56 am

More urban trees = more fallen leaves in autumn = more work for low-skill illegal immigrants = more leaf blower sales = economic growth. What’s not to like?

December 5, 2017 1:37 pm

These comments are from a retired urban forester friend, and former City Forester:

I don’t know Van Dorn, but I do know MacPherson. I have to believe this study is somewhat skewed….there are lots of people living in true desert locations in CA where urban trees simply cannot survive without artificial water supplies … and this skews the study. How can Nevada (for instance have more canopy coverage per capita than CA? Easy. NV’s population is sparse in the desert/rural areas and very heavy in places like Reno/CC/Tahoe/Vegas where their urban trees are located.

Sacramento has (or at least had) the largest urban forest in the US….even larger than places in the east like NYC and Chicago.

CA and many other States do have serious problems with introduced pests, not only in the agric sense, but in their urban forests and in their native forests; not just insects, but also fungi. It would be interesting (to me at least) to see some study that shows the number of introduced tree species that are being used in the urban landscapes in CA compared to the same in other States. When one begins to consider the odd-ball species used in CA, it becomes mind-boggling (Carob, Eucalyptus, Palms, Fig, Araucaria, … the list goes on and on).

A bit more trivia: Chico, CA’s Bidwell Park is the largest city park in the U.S. and was the filming location for much of the movie Robin Hood.

Also, in Chico, are a handful of the very rare native U.S. Chestnut trees – Chico is inland and isolated from the fungus that wiped out chestnut from virtually all of its native range in the eastern U.S. In fact, I had never even seen a real (mature) American chestnut tree until I saw the ones in Chico. My mother told me about them from the days in the ’20’s when she was a child in Indiana.

Reply to  brians356
December 5, 2017 1:45 pm

PS The film referred to is “The Adventures Of Robin Hood” (1938) starring Errol Flynn and Olivia de Havilland.

December 5, 2017 2:47 pm

I live in Australia. I travel between relatively wet Mediterranean climates, and deserts, climates similar to California. I think most comments here are dismissive of an important article. My comments refer mainly to inner cities and freeways.
– There are the arguments on the significance of the Urban Heat Island Effect. Green electorates in Australia typically are hotter than the surrounding suburbs because they are in city centers. Planting trees can partially counter the urban heat island effect.
– Green electorates, by extension being inner city traffic hubs, have higher pollution levels. Planting trees can reduce air pollution in addition to cooling the temperatures, in particular car exhaust particulates.
– I note that some trees are not suitable. For example, Australian eucalypts can be explosive. There are consultants who advise local councils on what trees to plant for whatever reason to avoid whatever pest and so on. It’s a science in it’s own right. If California was to implement a tree planting program, then I am sure California has similar consultants.
– I have read elsewhere of the effect of planting forests, or cutting them down on precipitation. California is dry. Planting forests in your cities could, if enough trees were planted, may affect Californian rainfall.
– Cities have one big problem. Waste. For example, modern civilization generates huge amounts of grey water. Black water can be very simply processed. Both can be recycled. In Australia, local councils pipe the recycled water and irrigate parks, streets and sports grounds. I am 60, I have watched with interest as our dry dusty towns grew trees. Californian cities may want to recycle their waste water and, like Australian desert towns, use it to irrigate trees, it may liven up the dead inner city “Greenie” enclaves.
– I refer to the recent article, that Greens live in inner city enclaves in Australia, and possibly many other places. When I have visited those enclaves, I have been struck at how desolate those “Green” electorates are, with the concrete jungle, lack of vegetation, exhaust fumes and heat. Planting trees might go some way to countering people’s political views in Green electorates. No idea if it would work, I have never seen anything on this, but what is the harm?

I think this study, for whatever its flaws, makes an important point. Planting trees will use waste water to cut pollution, reduce the urban heat island effect, possibly increase local precipitation and create an attractive environment. It may change voting patterns. It’s something even nutty Californian politicians could embrace.

Patrick MJD
Reply to  Peter
December 6, 2017 5:26 am

“Peter December 5, 2017 at 2:47 pm

In Australia, local councils pipe the recycled water and irrigate parks, streets and sports grounds. ”

Recycled grey and black water, really? Don’t see it happening in Sydney. Maybe your council says it does, but does it?

Patrick MJD
Reply to  Patrick MJD
December 6, 2017 5:28 am

“Patrick MJD December 6, 2017 at 5:26 am

Peter December 5, 2017 at 2:47 pm”

Grey water for irrigation of non-food plants is fine. DO NOT USE IT FOR FOOD PLANTS.

December 5, 2017 3:11 pm

Ecosystem services?
I own a lot of trees, where is my money?

December 5, 2017 3:30 pm

The sub-headline: Despite city tree benefits, California urban canopy cover per capita lowest in US

Key sentence: However, according to a recent study, more benefits could be realized if the Golden State’s urban forests didn’t have the lowest canopy cover per capita in the nation.

The map: Napa

The facts: Last October the “canopy cover” in Napa and Sonoma counties caught fire and burned over 160,000 acres, destroyed more than 7,000 structures, and killed at least 41 people.

Is irony the right word? Or is this gummit pseudo science so bad it’s deadly?

More contiguous biomass as measured from outer space is not so much a benefit to your city as it is a catastrophic holocaust waiting to explode. Californians and others, please grasp this and act upon it by reducing, not expanding, the volume and continuity of the vegetation and other flammables. Your life might well depend on it.

Reply to  Anton Arock
December 5, 2017 4:42 pm

and it’s burning again.

December 5, 2017 5:59 pm

Reads like a Daily Mail story.

Los Angeles is a desert; naturally. Planting a bunch of non-native trees ain’t gonna make things for decades to come.

John F. Hultquist
December 5, 2017 6:57 pm

Seems there are to be a few fewer trees in L. A.:
WUWT Oct 2

“LA’s palm trees are dying. And most won’t be replaced.”

wayne Job
December 6, 2017 2:10 am

California, LA especially needs more power plants wether coal or nukes does not matter and big desalt plants. Water and plants turn sand into soil[ plus a lot of Co2]

December 6, 2017 8:04 am

California also has what some call ‘fire season’. Between the comparatively low rainfall rates and the occasional Santa Ana winds, the fire danger is often high. Urban building codes even ban the use of ‘shake’ roofing – roofing made of wooden shingles. Desiccated trees in urban areas present a preventable fire hazard.

Harri Luuppala
December 6, 2017 2:13 pm

As a referenssejä, In Finland 5.5 million inhabitants) we plant 100+ million new trees every year. Last year alone 156 million saplings. During busy spring/summer time its 8,5 million saplings per week! Of course we cut also a lot, but planting is larger that cutting. We started this process over 100y ago.

December 7, 2017 1:28 am

The climate sceptic Rupert Murdoch found out to his cost recently that it does not pay to denigrate climate change, as reported in this article:

California’s fire season usually ends in November but the hottest summer on record and delayed rains have left the region tinder-dry into December. Some scientists have linked the conditions to climate change.

“This fire is big, fast, and furious. But the most striking thing about its vast size, bewildering speed, destructive power is that this fire blew up in December. Repeat: December,” said Char Miller, a Pomona college professor of environmental analysis and expert on wildfires. “This is a sign that the fire season is lengthening as the drought in southern California deepens. That the fire season is intensifying in response to climate change.”

Murdoch, 86, has ridiculed climate change as “alarmist nonsense”, a scepticism echoed in his media empire.

Reply to  ivankinsman
December 7, 2017 8:42 am

Ivan, I lived in California for over 40 years, and just when rainy season starts is quite variable. Claiming a “late start” is pure zealotry.

Reply to  Tom Halla
December 7, 2017 11:02 am

So why would a senior fire chief make this statement then? What would be his reason for telling a lie? He had an expert on fires whereas you are not. Why are you being so obtuse?

Reply to  ivankinsman
December 7, 2017 11:15 am

Ivan, fire chiefs, just like police chiefs, are direct appointees of the political leadership. Sucking up to the boss is a job requirement.

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