Computer models predict the future? Garbage in, garbage out

Computer modeling is an increasingly popular tool used in ecological studies.  The rapidly changing climate is putting pressure on scientists to predict the trajectory of the change and the impacts those changes will have on the environment.  However, a computer model is only as predictive as the assumptions used to build it.  In other words, “garbage in, garbage out.”

That sets the stage for a study published in 2018 that predicted that “grassland may be a more reliable carbon sink than forests in California.”(1) The study was quickly adopted by native plant advocates as a weapon in their battle to destroy non-native trees in favor of grassland they prefer. (2) They prefer grassland because it was the pre-settlement coastal landscape.  They don’t acknowledge that burning by Native Americans and grazing by native ungulates were the primary reasons why grassland did not succeed to shrubs and forests prior to settlement. Pre-settlement grassland was as much a human creation as any modern landscape.

Source: US EPA, 2018

Most carbon storage is below ground, in roots and soil.  That is true of both grassland and forests. If the forest burns, the carbon it has stored in soil remains, just as the below ground carbon sink of grassland remains. 

The study (1) that claims grassland may be a more reliable carbon sink than forests reaches its erroneous conclusion by comparing below ground carbon storage in grassland with above ground carbon storage in forests. It’s a classic case of inappropriately comparing apples with oranges to the disadvantage of forests.  It seemed such an unlikely comparison that I asked the study’s authors to confirm they had compared below ground carbon storage in grassland with above ground carbon storage in forests.  They confirmed that they did, indeed, make that inappropriate comparison.

The study also bolsters its mistaken conclusions by erroneously claiming that forests are more likely to burn than grasses:

“The fire resistance for grasses is 0.5 while that of trees range from 0.1−0.3, making grasses more resistant to wildfires than trees, which is roughly consistent with field-observations since in the event of a wildfire, when compared to trees, a smaller fraction of the biomass of grass is damaged.” (1)

However, the study cited as the source of this statement (3) says exactly the opposite:

“The fraction of individuals killed depends upon the prescribed PFT fire resistance, which represents the PFT survivorship during a fire (see Table 1). In the fire model, grasses and litter are fully consumed.” (3)

Table 1 PFT parameter values for fire resistance
PFTFire Resistance (%)
Tropical broad-leaved evergreen12.0
Tropical broad-leaved raingreen50.0
Temperate needle-leaved evergreen12.0
Temperate broad-leaved evergreen50.0
Temperate broad-leaved summergreen12.0
Boreal needle-leaved evergreen12.0
Boreal summergreen12.0
C3 grass100.0
C4 grass100.0

Table 1 is consistent with this statement in the abstract of the cited study:  “Estimated litter moisture is the main driver of day‐to‐day fire probability.”  (3) Forests retain more moisture in the soil and leaf litter because of the shade provided by the tree canopy.  I wrote to the study author again, asking “where is the source of your statement that grasses are more fire resistant than trees?”  He did not reply.

If a study doesn’t seem to make sense, or it contradicts other sources of information, it is worthwhile to look under the hood.  What is driving the model?  Is it fueled by hot air?  Is it serving an activist agenda? Are cited studies accurately quoted? 

Some truth emerges from the model’s black box

Despite the erroneous assumptions of the computer model used by this study, there is some truth in the conclusions it reaches.  Vegetation type conversions are occurring now and they will continue as the climate continues to change because when the climate changes, the vegetation changes. We are presently witnessing the transition of native conifers at high altitudes to lower altitude hardwood trees. Although these changes will occur gradually and there will be many intermediary transitions, the fact is that grassland is more likely to survive than forests in a warmer, drier climate in the long run. 

The Guardian has published a comprehensive report about the loss of forests all over the world.  In the Rocky Mountains, one-third of places where trees burned 20 years ago are now occupied by shrubs and flowers.  About 15% of forests in the Rocky Mountains are not expected to grow back if killed by fire because the climate is no longer suitable for them.  About half of existing forests in Alberta, Canada are expected to vanish by 2100.  The “megadrought” in south-western US is expected to convert 30% of forests to shrubland or another type of ecosystem.

In the short run, the loss of forests can be mitigated by reforestation with tree species that are better adapted to a warmer, drier climate.  The study (1) acknowledges the potential for mitigation to preserve forest ecosystems:  Factors such as species traits, biodiversity, rapid evolution, and human management intervention could alter our model-based findings from the projections provided here. Consequently, our results indicate the potential direction of change as opposed to predictions that consider the full ensemble of ecological, physiological and management factors that can alter pathways and responses of ecosystems to climate change.”

From the standpoint of carbon storage, it is not good news that grassland is likely to inherit hot, dry lands previously occupied by forests.  Forests and wetlands store more carbon than grasslands, as the above chart in a USDA publication about carbon storage shows.  Sustaining below ground carbon sinks will depend on carbon sequestration by above-ground plants and trees.  Because above-ground carbon sequestration is primarily dependent upon the biomass, forests will always do a better job than grassland in the long run.  In the short-run, grassland will grow back more quickly than forests, but it will never achieve comparable biomass. 

Forests are presently absorbing about one-quarter of all human carbon emissions annually. Forests make a significant contribution to reducing carbon emissions, but planting trees is not a panacea as long we continue to burn fossil fuels to generate energy. The loss of carbon-sequestering capabilities of forests will exacerbate climate change in the long-run.  It’s one of many dreaded feedback loops that are reaching tipping points:  the impacts of climate change are destroying the mechanisms that mitigate climate change. 

The study (1) acknowledges that by the end of the 21st Century, under current climate conditions (warming limited to 0.3⁰ – 1.7⁰ Centigrade) forests will have removed 5 times more net carbon (carbon storage minus carbon loss) per hectare from the atmosphere than grassland in California.  See Table 1 in the study (1).  Thus, the study agrees that forests store more carbon than grassland.

From the standpoint of wildlife, it is not good news that grassland is likely to replace forests in a warmer climate. The insects, birds, and animals that live in the forest will lose their habitat. Forests are home to over 80% of terrestrial species.  We will lose our shade in a warming climate and our windbreak. 

Not an argument for destroying forests

This study (1) is unfortunately being used by the native plant movement to advocate for the preemptive destruction of healthy urban forests that are not more likely than native forests to burn in wildfires.  Virtually all wildfires in California occur in native vegetation. There is no advantage to destroying healthy forests that are expected to live for another 100-200 years.  We don’t amputate our limbs to avoid breaking them.  Nor should we destroy our forests before they die.

(1)“Grasslands may be more reliable carbon sinks than forests in California,” Pawlok Dass, Benjamin Z Houlton, Yingping Wang and David Warlind, 10 July 2018, Environmental Research Letters, Volume 13, Number 7 

(2) “Importance of Grasslands for Carbon Storage,” Yerba Buena Chapter of California Native Plant Council, Quarterly Newsletter, March 2021, page 6. 

(3) “The role of fire disturbance for global vegetation dynamics: coupling fire into a dynamic global vegetation model,” Thonicke K, Venevsky S, Sitch S and Cramer W 2001,  Glob. Ecol. Biogeogr.10 661–77

Adapting to more wildfire in western North American forests as the climate changes

The National Academy of Sciences (NAS) has published its recommendations for a new approach to managing forests in the American West to adapt to the increasing frequency and intensity of wildfires in the changing climate.  The authors of the NAS publication regarding adaptive forest management in the changing climate are 12 academic scientists from major public universities in 8 western states. (1)

Although the National Academy of Sciences was created by an Act of Congress in 1863, during the Lincoln administration, it is a non-governmental non-profit that receives no direct government funding.  Its charge is “providing independent, objective advice to the nation on matters related to science and technology. … to provide scientific advice to the government ‘whenever called upon’ by any government department.” Members of the Academy serve without salary as “advisers to the nation.” Election to the National Academies is one of the highest honors in the scientific field. The independence of NAS is ensured by lack of governmental funding and salaries to its members.  However, 85% of NAS funding is government grants and contracts. (2)

In other words, this publication is an important policy document, prepared by distinguished scientists and published by America’s most prestigious scientific institution.  It deserves our attention and respect.

Why is a new forest management approach needed?

In the past, forest management policies have focused primarily on preventing fire, reducing fuel loads, and restoring burned areas.  Given the increasing intensity and frequency of wildfires, there is a new understanding that these approaches are no longer adequate to address new conditions created by the changed and changing climate.  The new approach recognizes that fuels reduction cannot alter regional wildfire trends and therefore must adapt ecosystems and residential communities to more frequent fires, including “planning residential development to withstand inevitable wildfire.”  This represents a shift from restoring historical conditions, now considered unsustainable, to developing fire-adapted communities.

The authors of this publication tell us that managing forest fuels has been ineffective:  “Mechanical fuels treatments on the US federal lands over the last 15 years totaled almost 7 million hectares, but the annual area burned has continued to set records.  Regionally, the area treated has little relationship to trends in the area burned, which is influenced primarily by patterns of drought and warming.”  Where fuels treatment was done, wildfires subsequently occurred:  “10% of the total number of US Forest Service forest fuels treatments completed in the 2004-2013 period in the western United States subsequently burned in the 2005-2014 period.”  This suggests that “most treatments have little influence on wildfire.” In any case, only 40% of wildfires occurred in forests since 1984, with most fires burning grasslands and shrublands.  Clearly, these projects have been a waste of time, trees, and taxpayer money.

This area on the west side of Grizzly Peak Blvd is known as Frowning Ridge. It is one of the first areas that was clear-cut by UC Berkeley over 10 years ago. Destroying the trees did not prevent the grass and shrubs from igniting in the August 2017 fire. Pictures of that area before and after the trees were destroyed are available here:  The fire in August 2017 was stopped when it reached the forest on the opposite side of the road.

Nor do the authors consider “thinning” of forests a viable method of reducing fire hazards because “when thinning is combined with the expected warming, unintended consequences may ensue, whereby regeneration is compromised and forested areas convert to non-forest.”  When trees are thinned, the trees that remain are more vulnerable to wind and they lose the ability to share resources with the neighboring trees that have been removed.

Tilden Park, October 2016. East Bay Regional Park District has radically thinned this area to distances of 25 feet between remaining trees. This area is about 2 miles away from any residential structures. Cal Fire defines “defensible space” as 100 feet around structures.

There are two major reasons for increased wildfire hazards.  More than 50% of the increase in areas burned by wildfire in the American West is attributed to climate change.  The expansion of residential development into forested areas—called the Wildland-Urban-Interface (WUI)—is the second factor:  “Between 1990 and 2010, almost 2 million homes were added in the 11 states of the western United States, increasing the WUI by 24%.”  35% of wildfires in the WUI since 2000 were in California, more than any other state.

What is the new management goal?

Whereas past policies were designed to maintain forest conditions to historical conditions, this is no longer considered a realistic goal.  The recommended goal is now “supporting species compositions and fuel structure that are better adapted to a warming, drying climate with more wildfire.”  Sounds like planting tree species that are adapted to new climate conditions, doesn’t it?

The other, equally important new goal is to reduce the vulnerability of communities to wildfire by “changing building codes to make structures more fire-resistant…and providing incentives, education, and resources to reduce vulnerability to future wildfire.”  The only tree removals that make sense to the authors are those immediately around residential communities, “strategically located to protect homes and the surrounding vegetation.”  That is the principle of creating “defensible space” immediately around structures:  “fuels management for home and community protection will be most effective closest to homes…where ignition probabilities are likely to be high.”

Source: Cal Fire

These strategies are called “transformative resilience,” which “refers to planned fundamental change in response to drastically altered disturbances that have the potential to create broad-scale, systemic shifts in ecological states or radical shifts in values, beliefs, social behavior, and multilevel governance.”  The authors of these policy recommendations acknowledge that such rapid and radical shifts in social and ecological transformation are rare and difficult to achieve.  We certainly agree with that observation.

The urgently needed paradigm shift

Public policy and conventional wisdom is wedded to the past.  The public is unable or unwilling to acknowledge the realities of climate change.  They remain committed to “restoring” the landscape to an imagined pre-settlement ideal in the distant past.  And public land managers remain committed to creating that fantasy landscape, by destroying existing landscapes and using herbicides to do so.  They destroy the trees of the future and plant the trees of the past.  And they destroy trees miles from any residential properties while property owners resist the creation of defensible space needed to protect their homes.

The authors of the NAS publication clearly state the risks of continuing down that path:  “[Such policies] may be the easiest, most familiar path with the least uncertainty, but this approach is short-sighted and could come at the cost of adaptation to future wildfire as climate change continues.”

They also urge the public to wake up to this new reality:  “Some ecosystems will survive and thrive as they adapt to novel future conditions, but not all.  Embracing rather than resisting ecological change will require a significant paradigm shift by individuals, communities, and institutions and will challenge our conservation philosophies.”

Our safety and the future of our land are at stake.  We must take our heads out of the sand and look forward instead of back to a past that is long gone and will not return.  Since climate change is causing more wildfires, destroying more trees than necessary to achieve fire safety is counterproductive because deforestation is the source of about 10% of carbon emissions contributing to climate change.

(1) Tania Schoennagel, et. al., “Adapt to more wildfire in western North American forests as climate changes,” Proceedings of National Academy of Sciences, May 2017

(2) Wikipedia

Guest article about FEMA projects by a student of the forest

A few days ago we received a comment from a fellow tree-lover and student of the forest that deserves our attention.  He visited the project areas that may soon be cleared of all non-native trees and expressed his opinion of this planned devastation.  With his permission, we are posting his comment as an article.

His name is Deane Rimerman and he describes himself as “Hybrid Car Geek, PNW Landscape Restorationist, Web Builder, Arborist, Writer, Poem Performer, Life-long Photographer & Audio Engineer” on his website.  


Frowning Ridge before "vegetation management"
Frowning Ridge before “vegetation management”

Yesterday I toured the Oakland hills for the first time since I visited it a week after the 1991 fires. That torched landscape turned me into a lifelong student of the forest. So after my visit back to those hills yesterday I started reading everything I could about these FEMA plans!

In the interest of providing the most value I’ll focus on what’s not been mentioned yet in the debates I’ve read on this website thus far. Primarily it revolves around moisture and the value of tall standing trees for the purpose of capturing fog drip during the dry season.

I once worked with a forester named Rudolph Becking on studies that show 200 foot tall old growth redwoods can capture up to 7 inches of fog drip during the dry season. The biggest tallest eucalyptus,and pines, invasive or not also have the ability to do this. And if we’re talking about fire safety don’t we want to increase humidity in soil and in the air during the hottest driest times of the year? If the answer is yes, that can be done by protecting sites that are most exposed to fog in the dry season.

Frowning Ridge after 1,900 trees were removed from 11 acres in 2004
Frowning Ridge after 1,900 trees were removed from 11 acres in 2004

Also eucalyptus are huge water users only when they are young and exposed to full sun, but like most trees, once in a closed canopy forest they consume far less water during the dry season compared to open canopy forests.

Point being, we need to maintain landscapes that don’t dry out because plant and tree diversity won’t thrive and really aggressive invasive weeds will take over if we don’t intentionally map out and seek to protect the highest existing levels of soil moisture. The SF Bay Area climate is very arid.  If a time of drought were to coincide with this fire hazard removal plan, we could have a mass die-off native species and an even greater shift to drought tolerant non-native weeds that will eliminate most biodiversity.

And regardless of drought, desert like alterations to the landscape is what happens when we lose too much shade and moisture all at once. Many native plants growing under semi-shade conditions right now can’t survive if all the non-natives are clearcut or near clearcut as proposed in this plan.

Also what is missing from this landscape is lots of tall dead trees that act as bioreactors for flora fauna and rhizo diversity. Tall dead trees are like a bank account for future healthy soil, homes for so many birds and bugs too. There is a great poverty of standing deadwood on this landscape, yet no significant mention of snag retention and snag creation in this plan.  If we cut down all the largest live and dead standing trees there will be no large downed log recruitment for another century and that would be a misguided tragedy that will further impoverish the soil.

In a word: DIVERSITY.  You don’t have to cut down all the trees to increase diversity. We could have thousands of us spending every winter in these hills replanting hundreds of different species of native plants, as well as clearing weeds away from existing native plants in a low-impact site-specific way.  This of course is a labor intensive approach and humans have been manipulating these hills for thousands of years in very labor intensive ways.

In my view we’ve neglected these lands for too long and it’s about time we get back to all of us working together as volunteers meant to cultivate a garden of biodiversity with an eye toward carbon absorption and keeping as high as possible soil moisture and air moisture in order to prevent catastrophic fires.

But instead in this plan we see the usual lazy, super aggressive approach in which a forester, whose job is to cut down forests, is asked to solve our problems. And without any site-specific observation of fog drip and areas of high soil moisture in the dry season we log the forests as quickly and cheaply as possible thinking if we do it severely enough we won’t ever have to come in and fix anything ever again.

The homeowner version of these two approaches is akin to one homeowner who makes their landscape beautiful with hard work and lots of hands-on low impact cultivation of plant and tree diversity without herbicides. And then we have the other lazy homeowner who hates his yard and weedwacks his yard to bare ground every other year thinking once he does it one more time (and even more severely this time with extra herbicide) he won’t ever have to do it again.

And habitat-wise, if we inoculate eucalyptus and pine with heart wood rot to create cavities for habitat we will help fuel the whole food chain, not to mention create homes for myriad species.

And to all the folks who say these hills were mostly shrub oak and grassland I say that natural ecosystems in this region were mosaics of conifer and hardwood woodlands amongst mosaics of shrublands and small grassy meadows and it was all maintained by humans who for thousands of years used fire to maximize productivity in traditional cultivation areas. Those cultivation practices were based on specific sites where species grew best. The current plan as proposed is the antithesis of this. The current plan treats the whole landscape as if there’s very little variability of moisture levels and species compositions.  It’s as if the planners know more about growing corn in Iowa than they do about growing an ecosystem in the arid San Francisco Bay Area.

Frowning Ridge 2013
Frowning Ridge 2013

Lastly, the Monterey Pine is entirely native to a landscape that’s less than 100 miles away. And yes some of these pines might be a hybridized New Zealand variety but so what?

I’ll have more to say on all this soon… Maybe a whole website or book perhaps? 🙂


Remember that public comments are due by June 17, 2013.  You may submit written comments in several ways:

  1. Via the project website:
  2. By email:
  3. By mail: P.O. Box 72379, Oakland, CA 94612-8579
  4. By fax: 510-627-7147

These public lands belong to you and the money that will be used to implement these projects is your tax dollars.  So, please tell the people who work for you what you think of these projects.