Old Trees Trap More Carbon and Fight Climate Change

This article is reprinted with permission from SutroForest.org, a website fighting to save the century-old forest on Mount Sutro in San Francisco, CA.

The older a tree grows, the more carbon dioxide it grabs out of the air and sequesters, thus fighting climate change. Cutting down these large old trees releases this carbon back into the atmosphere.


An article published in the Nature Journal summarizes the results of a huge research project by the US Geological Survey. This directly disproves the myth that young trees sequester carbon rapidly, but large old trees do not.

“The trees that are adding the most mass are the biggest ones, and that holds pretty much everywhere on Earth that we looked,” says Nathan Stephenson, an ecologist at the US Geological Survey in Three Rivers, California, and the first author of the study, which appears today [i.e. 15th January 2014]  in Nature.

“Trees have the equivalent of an adolescent growth spurt, but it just keeps going.”

The study, which looked at over 673 thousand trees of more than 400 species, found it was universally true.  This confirmed the results of a 2010 study that had focused on redwoods and on a eucalyptus species.

Former trees in a pile of woodchips sm

All the huge old trees that are cut down in San Francisco were fighting climate change – but now, whether as mulch or as rotting logs, they are contributing to it.


Here is the abstract of the study, from the NIH website [formatting and emphasis ours]:


Rate of tree carbon accumulation increases continuously with tree size.
Stephenson, Das, Condit, Russo, Baker, Beckman, Coomes, Lines, Morris, Rüger, Alvarez, Blundo, Bunyavejchewin, Chuyong, Davies, Duque, Ewango, Flores, Franklin, Grau, Hao, Harmon, Hubbell, Kenfack, Lin, Makana, Malizia, Malizia, Pabst, Pongpattananurak, Su, Sun, Tan, Thomas, van Mantgem, Wang, Wiser, Zavala.

Forests are major components of the global carbon cycle, providing substantial feedback to atmospheric greenhouse gas concentrations. Our ability to understand and predict changes in the forest carbon cycle–particularly net primary productivity and carbon storage–increasingly relies on models that represent biological processes across several scales of biological organization, from tree leaves to forest stands. Yet, despite advances in our understanding of productivity at the scales of leaves and stands, no consensus exists about the nature of productivity at the scale of the individual tree, in part because we lack a broad empirical assessment of whether rates of absolute tree mass growth (and thus carbon accumulation) decrease, remain constant, or increase as trees increase in size and age.

Here we present a global analysis of 403 tropical and temperate tree species, showing that for most species mass growth rate increases continuously with tree size. Thus, large, old trees do not act simply as senescent carbon reservoirs but actively fix large amounts of carbon compared to smaller trees; at the extreme, a single big tree can add the same amount of carbon to the forest within a year as is contained in an entire mid-sized tree.

The apparent paradoxes of individual tree growth increasing with tree size despite declining leaf-level and stand-level productivity can be explained, respectively, by increases in a tree’s total leaf area that outpace declines in productivity per unit of leaf area and, among other factors, age-related reductions in population density. Our results resolve conflicting assumptions about the nature of tree growth, inform efforts to undertand and model forest carbon dynamics, and have additional implications for theories of resource allocation and plant senescence.


And here is a link to the study itself in Nature: Rate of tree carbon accumulation increases continuously with tree size.






“It is essentially certain that glyphosate causes cancer”

glen canyon glyphosate June 2016 - Shrubs encroaching on grassland video

Applying Glyphosate in Glen Canyon

Marion Copley was a scientist at the Environmental Protection Agency. She died of cancer in January 2014. Before she died, she sent the letter below to her former boss Jess Rowland, saying “It is essentially certain that glyphosate causes cancer.”

Now,  a lawsuit by people with cancer or who lost loved ones to cancer, asks to depose Mr. Rowland. They allege that Monsanto has influenced the EPA through its ties to people there. (The Huffington Post report on that is HERE: Questions about EPA-Monsanto collusion raised in cancer lawsuits )


Herbicides in San Francisco’s ‘Natural Areas’: 2016 Report

We finally received all the 2016 pesticide use reports from San Francisco Recreation and Parks Department (SFRPD), including of course the Natural Resources Department (formerly the Natural Areas Program). Coincidentally, it’s oxalis season, and by the logic of the NRD – it’s Garlon time. Of which more below.

In April 2016, SF Department of the Environment rolled out its new guidelines for pesticide use. Since then, the other parks sections nearly eliminated pesticides – but not NRD. They reduced their use of Roundup quite drastically (thankfully, since it’s a probable carcinogen). But they increased their usage of Garlon and Imazapyr.


San Francisco Recreation and Parks Department (ex Harding Golf Course, which is under a management contract with the PGA Tour) has all but stopped using herbicides – except for the so-called Natural Resources Department.


nrd-vs-sfrpd-herbicide-application-2016-smLooking at the whole of 2016, SFRPD used pesticides 159 times. Of those, 143 applications were by the NRD.

NRD used more of nearly all Tier I and Tier II herbicides. It used 48% of the total Roundup SFRPD applied; 100% of the Garlon; 100% of the Imazapyr (Stalker, Polaris); and 99% of the Milestone VM.

Excluding for Greenmatch, a herbicide that is considered organic (but still classified as Tier II), NRD used more Tier I and Tier II herbicides than the rest of SFRPD put together. (As usual, we exclude Harding Golf Course, which is under a management contract to the PGA Tour and uses pesticides to maintain tournament readiness.)

The good news is that NRD has succeeded in reducing herbicide use, mainly by cutting back sharply on Roundup. Even if not as much as other SFRPD departments, it’s progress. It is still not down to 2009  or even 2008 levels, but has reduced substantially from 2013, which was peak pesticide for NRD (then NAP).



This year, NRD also started managing – i.e. spraying with herbicides – certain parks belonging to SF PUC:

  • Lake Merced,
  • Laguna Honda, and
  • part of Twin Peaks.

Since they are following the same regimen and using NRD staff, we include the PUC data along with NRD information.


We thought we’d take a look at which parks they treated most often with herbicides in 2016. Bayview Hill was the clear “winner” with 34 applications. McLaren Park was hit 27 times, and Twin Peaks 25 times. Glen Canyon had 10 applications of herbicides, and Mt Davidson was herbicided 8 times.


To return to Garlon, the most toxic herbicide SF Environment allows for use in SFRPD. It’s classified as Tier I (Most Hazardous) and the notation on the list says: Subject to “Limitations on most restricted
herbicides”. Use only for targeted treatments of high profile or highly invasive exotics via dabbing or injection. May use for targeted spraying only when dabbing or injection are not feasible.

It’s been “High Priority to Find Alternative” in all the years we’ve been studying this issue. Here’s the solution: Stop obsessing over oxalis.

The only current use for Garlon in SFRPD is battling oxalis in “Natural Areas.” It’s been used 23 times in 2016 by NRD – and zero times by all the other departments.

The obsession with oxalis makes no logical sense. Our article Five Reasons it’s Okay to Love Oxalis and Stop Poisoning it points out that:

Honeybee in oxalis flower

Honeybee in oxalis flower

1) It’s already part of the ecological food web in our city, providing nectar to honey-bees, bumblebees, butterflies and other pollinators. Ironically, the pollination doesn’t benefit the oxalis, which doesn’t set seed in San Francisco.

2) It’s good for wildlife, providing food for gophers, a foundation species that in turn feed predators from hawks and owls and herons to coyotes and foxes.

3) The myth is that oxalis leaves the ground bare after it dies down in summer. Actually, it enriches the soil with phosphorus, which benefits the grasslands in which it grows.

4) Oxalis has little impact on native plants. NRD argues that oxalis takes over grasslands and destroys them, particularly the native grasses. However, grasslands in most of California including San Francisco are dominated non-native grasses. The change occurred over 100 years ago, when these grasses were planted for pasture. So the grassland that NAP is defending with herbicides are primarily non-native anyway.

According to a study: “Oxalis is a poor competitor. This is consistent with the preferential distribution of Oxalis in disturbed areas such as ruderal habitats, and might explain its low influence on the cover of native species in invaded sites.
The California Invasive Plant Council rates its invasiveness as “moderate,” considering it as somewhat invasive in sand dunes and less so in coastal bluff areas.
oxalis and california poppies sm
In San Francisco, every place where oxalis grows is already a disturbed environment, a mix of non-native grasses and plants with native plants (some of which have been artificially planted).  Here,  oxalis appears to grow happily with other plants – including, for instance, the native California poppy in the picture above.

5) Kids love it, and it’s edible. Parents know that children will often nibble on “sourgrass” – indeed, so do parents sometimes! Adding toxic herbicides is a poor idea, especially since it is usually applied during the flowering season.

Photo credit: Badjonni (Creative Commons - Flickr)

Photo credit: Badjonni (Creative Commons – Flickr)

So, to summarize:

“There’s no sign that oxalis has a negative impact on wildlife, and plenty of evidence it’s already part of the ecological food web of our city.  The evidence also suggests it’s not having a negative effect on other plants in San Francisco either. Lots of people find this flower attractive; one writer described it as the city smiling with Bermuda buttercups.

In any case, even Doug Johnson of the California Invasive Plant Council doesn’t think it’s worth attacking at a landscape level: the payoff isn’t worth the expense. Removing it from the hundreds of acres in Natural Areas isn’t as simple as eradicating it from a small yard where it’s clashing with the garden design. It requires a lot of work, a lot of powerful herbicides, a multi-year effort – and for what?

The justification for using strong pesticides like Garlon to control it is weak. We call on NAP to stop using Tier I and Tier II herbicides altogether.”


NRD has been trying to reduce the amount of Garlon in each application used by changing to a new surfactant for Garlon: CMR Silicone Surfactant. (A surfactant is a chemical used with a pesticide to make it spread better.)

This is also a dubious chemical.A 2016 NIH paper, Toxicological Risks of Agrochemical Spray Adjuvants: Organosilicone Surfactants May Not Be Safe, suggests that these surfactants have a deleterious effect on bees (which we know visit oxalis), and point out that they are under-regulated:

“Agrochemical risk assessment that takes into account only pesticide active ingredients without the spray adjuvants commonly used in their application will miss important toxicity outcomes detrimental to non-target species, including humans.”

(You can download the whole paper as a PDF here: fpubh-04-00092

Mullin CA, Fine JD, Reynolds RD and Frazier MT (2016)

Toxicological Risks of Agrochemical Spray Adjuvants: Organosilicone Surfactants May Not Be Safe.
Front. Public Health 4:92.
doi: 10.3389/fpubh.2016.00092

Rally for Trees & Against Pesticides in Our Parks!  Feb 28, 2017


Rally for Trees & Against Pesticides in Our Parks!

Join Our City and San Francisco Forest Alliance to demand that the San Francisco Board of Supervisors vote to reject the Environmental Impact Report (EIR) that allows the Recreation and Park Department to cut down over 18,000 trees and spray toxic herbicides to ‘manage’ our public parks.

After the rally we will assemble in the City Hall Board of Supervisors chamber, room 250, to speak in favor of the appeal to block Rec & Park’s plan.

WHEN:       1:00 pm Tuesday February 28th
WHERE:     SF Civic Center Plaza (across from City Hall, Polk St. steps

WHEN:       3:00 pm Tuesday February 28th
WHERE:     Board of Supervisors Chamber, SF City Hall, Room 250
(come early to get a seat)

Map – http://tinyurl.com/SFCityHall-Plaza-BART
Directions – http://sfgov.org/cityhall/directions-city-hall

More information: https://sfforest.org and https://sfforest.org/blog-updates/

See you at City Hall!

San Francisco Forest Alliance

Public opinion does make a difference!

Thank you for your support

The San Francisco Forest Alliance is a non-profit 501(c)4 environmental organization working to protect urban forests, reduce pesticide use, and preserve access to our parks.


Mt Davidson: Toxic Garlon, Felled Trees

On a recent trip to Mount Davidson, a visitor saw that Garlon had been sprayed on oxalis.

The Natural Resources Department (NRD, formerly Natural Areas Program) is the most frequent user of pesticides in San Francisco Recreation and Parks Department (SFRPD).  It applied herbicides on Mt Davidson 8 times in 2016. Other SFRPD units have all but stopped using herbicides.

Notice of Garlon 4 Ultra on Oxalis on Mt Davidson, San Francisco CA

Garlon 4 Ultra on Oxalis on Mt Davidson, San Francisco CA

The Natural Resource Department (NRD, formerly Natural Areas Program or NAP), observed the SF Department of the Environment guideline to use blue dye with its herbicides (so people can see and avoid those areas).

Blue dye indicates Garlon 4 Ultra on Mt Davidson Jan 2017

Blue dye indicates Garlon 4 Ultra on Mt Davidson Jan 2017

Unfortunately, they flouted the SF Environment guideline that says there should be no herbicides used within 15 feet of a trail. “Blue dye is right next to and on the trails…” said the visitor.

Here’s a picture of blue dye on the trail.

Blue dye shows Garlon on the path on Mt Davidson, Jan 2017

Blue dye shows Garlon on the path on Mt Davidson, Jan 2017

Garlon by the trail on Mt Davidson, San Francisco, Jan 2017

Garlon by the trail on Mt Davidson, San Francisco, Jan 2017


The SF Department of the Environment (SF Environment), which is responsible for the Integrated Pest Management guidelines, lists Garlon 4 Ultra as a Tier I chemical, Most Hazardous. Ever since we started following this issue, it’s been on the list with a bold, capitalized statement: HIGH PRIORITY TO FIND AN ALTERNATIVE.

Garlon is also supposed to be twenty times as toxic to women as to men. (See page 28 of this California Native Plant Society Presentation which discusses best management practices in herbicide use: Law_Johnson 2014 presentation toxicity )

An article on SaveSutro.com, based on a detailed study by the Marin Municipal Water Department, describes some of the issues with Garlon:

  • Garlon “causes severe birth defects in rats at relatively low levels of exposure.” Baby rats were born with brains outside their skulls, or no eyelids. Exposed adult females rats also had more failed pregnancies.
  •   Rat and dog studies showed damage to the kidneys, the liver, and the blood.
  •   About 1-2% of Garlon falling on human skin is absorbed within a day. For rodents, its absorbed twelve times as fast. It’s unclear what happens to predators such as hawks that eat the affected rodents.
  • Dogs  may be particularly vulnerable; their kidneys may not be able to handle Garlon as well as rats or humans.  Dow Chemical objected when the Environmental Protection agency noted decreased red-dye excretion as an adverse effect, so now it’s just listed as an “effect.”
  •  It very probably alters soil biology. “Garlon 4 can inhibit growth in the mycorrhizal fungi…” ( soil funguses that help plant nutrition.)
  •  It’s particularly dangerous to aquatic creatures: fish (particularly salmon); invertebrates; and aquatic plants.
  •  Garlon can persist in dead vegetation for up to two years.

parent and child with oxalisThis highly toxic chemical is used by NRD against oxalis during its flowering season – in winter and spring. On Mount Davidson, they used it in February  and December 2016 as well.

It doesn’t make logical sense. Here’s our article on Five reasons it’s okay to love oxalis and stop poisoning it.


Meanwhile, another visitor sent us a series of pictures showing trees being felled at the southwest end of the forest.

tree-noticed-to-be-removed-mt-davidson-jan-2017 tree-x-ed-out-jan-mt-davidson-2017 former-trees-mt-davidson-jan-2017.





San Francisco Forest Alliance Appeals to Board of Supervisors

Our supporters are aware that we intended to file an appeal when the Planning Commission certified the deeply-flawed Environmental Impact Report on the “Significant Natural Resource Areas Management Plan.”

Here’s our letter:

sffa-appeal-letter-pg-1 sffa-appeal-letter-p-2(Then it continues into details of the failings of the EIR and the mitigations required.)

The complete letter is here: appeal-letter_final_1_5_17







Season’s Greetings, and Best Wishes for 2017

We’d like to wish all our readers and supporters Greetings of the Season…

Great horned owlets in eucalyptus. San Francisco. Janet Kessler

Brown creeper forages on eucalyptus

The eucalyptus-tree nest hole of the red-shafted flicker - San Francisco. Janet Kessler

and Best wishes for 2017!