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The “bones” and “circulatory systems” of large portions of critical California catchments appear increasingly impacted by degradational processes analogous to osteoporosis and hardening of arteries in humans.  Such downhill processes in humans are associated with aging, among other factors.  Catchment degradation is similarly associated with long (over-)exposure to human lifeways played out in ignorance of incremental impacts.  Now these cumulative historical impacts are increasingly compounded by the effects of anthropogenic climate change happening before our eyes – and other senses, e.g., the color-coded intensities of smoke-filled air many of us have inhaled for weeks or months of recent years.  We who access information beyond what our immediate senses and memories tell us about the effects of climate change in our lifetimes subject ourselves to even greater yet perhaps well-founded gloom.

I chortled when I read the title and lead to this Feb 6, 2022 New York Times piece, 

Climate Change Enters the Therapy Room: Ten years ago, psychologists proposed that a wide range of  people would suffer anxiety and grief over climate. Skepticism about that idea is gone. 

‘Thought to myself, “yeah, I can relate”, but didn’t stop to read it until a few days later.  That was after I finished reading the below article that I had begun reviewing some time ago, and realized I was relating only too well.

Dwomoh, F. K., J. F. Brown, H. J. Tollerud, and R. F. Auch. 2021. Hotter drought escalates tree cover declines in blue oak woodlands of California. Frontiers in Climate 3:689945.  

Dwomoh and colleagues pulled together a deliciously complex set of analyses that is truly admirable in both its thoroughness and exposition.   But their findings are a bummer.  That would be true for folks solely concerned with the existing and potential biodiversity of blue oak woodlands.  

But when you make the connection that oak and other woody and perennial root systems, along with associated soil ecological systems/ structures, serve as essential ecohydrological conduits along the paths from the ground surface, where precipitation falls … through the vadose zone … to bedrock aquifers … to downstream alluvial aquifers … feeding baseflows supporting aquatic biodiversity … as summarized in my last post, well then, you just might feel like jumping out of your skin over this.

Blue oak woodlands W. of Red Hills BLM ACEC, Tuolumne Co. April 20, 2019

Click images to expand

Produced by Dwomoh, contractor to USGS and colleagues at the U.S. Geological Survey (USGS) Earth Resources Observation and Science (EROS) Center, Sioux Falls, SD, this 2021 report is open access and a must-see for its compelling and revelatory graphic exhibits.   [I do love that spicy EROS acronym.]  It is so information-rich that encapsulation can barely do it justice, but cutting to the chase:


Our results revealed elevated decline in tree cover in blue oak woodlands during the major 2012–2016 drought. Overall, ∼1,266 km2, constituting about 37% of the cumulative tree cover loss in the 32-year study period, were lost during the five-year drought. Additionally, ∼617 km2, constituting about 28% of the cumulative tree cover conditional change in the 32-year study period, were recorded during that drought. The record decline in tree cover in blue oak woodlands specifically in 2015–2016 occurred in the fourth and fifth year of a multiyear drought beginning in 2012 that resulted in significant tree cover losses due to fire and non-fire causes in the context of a hotter drought than seen in prior decades. Our findings have important implications on the long-term vulnerability of this iconic vegetation community, and its ecosystem goods and services. The unusual increases in both fire and non-fire related tree cover declines during this drought event portend that the compounding effects of fire and climate variability may enable rapid vegetation shifts in the studied region. More specifically, our findings signify that blue oak woodlands may be vulnerable to extreme climate events and changing wildfire regimes. Here, we present early evidence that frequent droughts associated with climate warming may continue to affect tree cover in this region, while drought interaction with wildfires and the resulting feedbacks may have significant influence as well. As a result, efforts to conserve the blue oak woodlands, and potentially other vegetation communities in the Western United States, may benefit from consideration of climate risks as well as the potential for climate—fire and vegetation feedbacks.  (Dwomoh and colleagues 2021)

Given the weather patterns we’ve been witnessing the past couple years, their findings are cause for concern.  BTW, yes, they did use the word “iconic” there and I’ll buy that.  But wait, there’s more …

Concern about natural regeneration of valley and especially blue oaks dates back to the late 1980s.  Status reports focused on blue oak sapling recruitment near the end of the 20th century ((Swiecki and colleagues 1997, Swiecki and Bernhardt 1998) suggested concerning trends.   More recent studies of blue and black oak seedling recruitment at 24 experimental gardens in the southern Sierra Nevada and western Tehachapi Mountains during 2012 and 2013, paired with modeling studies (Davis and colleagues 2016) indicate a sensitivity at that seedling stage to Climatic Water Deficit (CWD), defined as follows:

CWD is the difference between calculated potential evapotranspiration and actual evapotranspiration, and thus integrates solar radiation, air temperature, humidity, and available soil water to provide a measure of time-variant drought stress seedlings are likely to experience during establishment.  (Davis and colleagues 2016)

As might be anticipated, exceptionally hot, dry conditions took a toll on seedling establishment.  Davis and colleagues point to “windows of opportunity” for seedling establishment that appear to be shrinking with climate change.  

But I’d say the same is generally true for nearly all the native plant species comprising a hypothetically more diverse (pre-colonization) blue oak woodlands than exists today.  Ecological restoration in general, especially on uplands, may nearly always be expected to be more successful during episodic wet years.  Provision for being able to “jump on” opportune conditions and respond to other contingencies must be factored into restoration planning, but will doubtless only become more challenging as weather patterns become more erratic.  

For example, the snow dumped on us in late December 2021 prompted me to order creeping wildrye seeds that week with an eye on drainage swales (it’s notoriously slow to propagate by seed but not easy to get otherwise).  By the time they arrived in mid-January, I had concluded from weather forecasts they must be started in irrigated flats, if at all.

Davis and colleagues acknowledge,

Overstory vegetation and nurse plants could potentially expand the availability of establishment sites by reducing summer sunlight and heat stress, an effect not accounted for in our experimental design or establishment niche models but documented for oak establishment in both California and Mediterranean regions (Callaway 1992a, Gomez-Aparicio et al. 2006).  

(Davis and colleagues 2016)

Pacheco State Park April 7, 2010

Click images to expand

From my perspective, fundamental problem #1 for blue oak woodlands regeneration is that the domination of their understories by nonnative annual grasses has transformed soil ecohydrology in the root zones.  This relationship was inferred long ago in container studies (Gordon and colleagues 1989) but subsequent field evaluations proved more challenging to sort out, given the methods of the time (Gordon and Rice 1992).  Later, a combination of container and field studies reaffirmed the original concern about soil water potentials altered by annual plants – the nonnative annual grasses quickly consuming soil water resources each spring (Gordon and Rice 2000) but additionally the concern that adult trees shade out saplings, also observed by Swiecki and Bernhardt (1998).  Swiecki and colleagues (1997) and Swiecki and Bernhardt (1998) also pointed to grazing impacts.  For photos of annual rangelands that have lost most or all of their oak and other woody components, see my July 2021 post.
Oak Adaptation Advantage via Fungi

Michael Allen (2015) offers a bright prospect for oak resilience to climate change in that, 

Oaks are among a select group of trees that form both arbuscular mycorrhizae (AM) and ectomycorrhizae (EM) (Egerton-Warburton and Allen 2001).

Note that those are the two predominant types of mycorrhizal relationships; there are others.  As alluded to in blog post #14. Who Values Catchments More Than CA? with regard to the “wood-wide web” and doubtless elsewhere on Rainfall to Groundwater, such mycorrhizal relationships between/among plants and soil fungi are fundamental to the soil ecology/ nutrient fluxes supporting healthy plant associations, but also to soil ecohydrology and catchment functions.  

Allen continues,

Members of the Fagaceae [oak family] are among the most ancient of plants that formed EM, between 100 and 200 million years ago.  Oaks also retained their ability to form the original, primitive AM that evolved with the invasion of the land, somewhere between the Ordovician and Silurian Periods (Redecker and others 2000). This means that oaks are able to take advantage of a wide range of mycorrhizal fungi that have a multitude of different strategies for dealing with environmental variability. Oaks form AM during drought years and up hillsides, in largely inorganic soils, and when their roots extend into grasslands where AM predominate (Querejeta and others 2007). In stands where large amounts of organic matter accumulate and N is largely immobilized, oaks will form EM with a high diversity of fungi, including many with the ability to break down organic N and transfer it to the plant (Bledsoe and others 2014). Oaks will switch between AM and EM mycorrhizae depending upon the location, season and yearly precipitation (for example, Querejeta and others 2009).

Finally, as oak roots grow through fractures in the bedrock, their mycorrhizae grow with them. The roots remain within the fractures, but if the bedrock is weathered, the mycelial network actually grows into the granite matrix (Bornyasz and others 2005). …

Invasive grasses have a mixed impact on oaks. The presence of the grasses themselves reduces EM activity (Allen and Karen, unpublished data) and the oak roots that extend beyond the canopy into a grassland or seedlings that establish in the adjacent grasslands tend to be AM, not EM. While oaks form AM, this mycorrhizal association is not as effective for oak seedling growth as EM associations (Egerton-Warburton and Allen 2001). In addition, grasses carry fire more extensively and frequently than do widely-spaced shrubs. But, the fire is not as hot as in dense shrub stands, potentially resulting in lesser injury to mature oak trees. In the past, California Indian tribes burned the understory of oak stands, in part to sustain the harvest of mushrooms. Most of the mushrooms produced under these conditions are EM fungal sporocarps (Anderson and Lake 2013).

(Allen 2015)

Blue oak – foothill pine woodland fall color above Coulterville Dec 16, 2019

Blue oak, Pacheco State Park April 7, 2010

Mother Trees – Suzanne Simard

While it is partly implicit in what Allen observes about evolutionary advantages conferred oaks in utilizing a variety of fungal relationships, I would be remiss if I did not point out the brilliant observation by Suzanne Simard, made essentially as an aside in her 2021 Finding the Mother Tree: Discovering the Wisdom of the Forest:

… Maybe even more important was the fungi’s ability to reproduce rapidly.  Their short life cycle would enable them to adapt to the rapidly changing environment – fire and wind and climate – much faster than the steadfast, long-lived trees could manage.  … (Simard 2021 p. 185)

If I learned one thing in my undergrad mycology class, it was that the fungal (now) kingdom encompasses a vast array of life cycles and permutations thereof.  They definitely have some tricks up their sleeves.  And, as Simard points out, the rapid-turnover life cycles allow genetic evolution to proceed apace in contrast with much slower-growing and long-lived trees like blue oaks.  This would seem to confer more opportunities for rapid adaptive responses to rapidly changing climate.

However, traditional genetic evolution may not be the only game in town, as Simard reminded me at another point in her book when she describes the fluxes of resources from a Mother Tree through the mycorrhizal networks to her juvenile offspring and even non-kin in the vicinity: 

Their nascent roots drank from the nutritious soup supplied through her web.  The shoots received messages about her past struggles, giving them a head start.  (Simard 2021 p. 303)

Such “messages about her past struggles” is another “aside” but Simard seems to be suggesting potential epigenetics among the trees, operating through the mycorrhizal mycelial network(s).  Doubtless among the more difficult systemic phenomena to document under field or any conditions, but it does suggest another possible ray of hope for the resilience of blue oaks against climate change.

Moreover, Simard’s Mother Tree concept may indeed be applicable to blue and other oak woodlands.  She has campaigned to encourage Canadian foresters doing “salvage logging” to leave the oldest Mother Trees to nourish recovering forests.  She and her students have shown that even dying and dead Mother Trees transmit carbon and other resources through mycorrhizal networks to their offspring and even other species.  This is a whole other paradigm that contrasts decidedly with the emphasis on “competition”, including as keyword, in papers cited herein from the end of the 20th century.  Consider what this might mean for existing blue oak woodlands.

Despite historical threats mainly from clearing and grazing, canopy-dominants aging 150 to more than 400 years are still common in remnant old-growth blue oak landscapes, especially on rugged terrain in remote areas (Stahle et al., 2013; Reiner and Craig, 2011).

(Dwomoh and colleagues 2021)

Applying Simard’s forest Mother Tree concept to blue oak woodlands suggests that the vicinities of ancient blue oaks may be ideal locations to establish restoration plantings of acorns.  And not just acorns, but suites of suitable native woody and perennial species, including nurse species, to reestablish above- and belowground ecological and ecohydrological integrity.  But we also need to tackle those rangelands now devoid of woody species.

Pacheco State Park April 7, 2010

Oaks as Catchment Keystone Species 

I may be the first to refer to oaks as “catchment keystones” and I look on rather breathlessly as blue oaks seem to be declining in advance of any concerted efforts to recover the innate diversity and ecohydrology of their birthright woodlands.   But I am not the first to refer to blue oak as a “keystone” species.

That would be Rice and colleagues (1993).  Equally noteworthy is their citation of Paine 1980, which should definitely be considered a “golden oldie” in conservation science – with particular reference to marine ecosystems but concepts more broadly applicable.  He did not actually use the term “keystone” but it is implicit in that piece.

… response to environmental change is especially critical for threatened “keystone” species (sensu Paine 1980) because loss of these species may result in the loss of entire communities …

… Taken together, these considerations demonstrate that blue oak is an important keystone species; a species whose loss would have impact far beyond a simple reduction in species diversity within the Quercus genus.  …

(Rice and colleagues 1993)

While they were referring to ecosystems, I say that blue oaks are also ecohydrological, or catchment keystones.  The evidence strongly suggests that blue oak woodlands are threatened by climate change and that suggests that the remnants of these catchment keystones merit an “emergency” restorative response to halt that decline before it crosses yet another “threshold”, beyond which recovery may be impossible.

I trust I sufficiently emphasized in my last post that the catchment restoration I emphasize here can help support salmonids through the lower, hotter reaches of their domain.  While salmonids represent only a few of the aquatic species of concern, their requisite environmental conditions do render them focal species for conservation encompassing the needs of many other species.  And that is to say nothing of associated terrestrial biodiversity that would be supported through catchment restoration on blue oak woodlands.

San Luis Reservoir & wind turbines from Pacheco State Park April 7, 2010

Back to the Pathways to 30×30 Draft Report

‘Should come as no surprise that my recent spate of blog posts was prompted by our California Natural Resource Agency’s 30×30 process.  I got seriously tired of all my earnest input going into CNRA’s black hole, never again to be seen or heard from.  I’ve asked them to consider my recent posts as part of my input to their process.  Given past experience, I expect to be disappointed with their output.  And I don’t expect many will read this or my other posts.  I actually can’t care about that at this point.  Expressing these concerns is my own form of therapy for coping with what I see coming down.  At least it’s out there and at some point, someone else may pick up a thread.

Revisiting that draft definition in the Pathways to 30×30 draft report, I suggest a potential tweak.

Conservation Definition for 30×30:

Land and coastal water areas that are durably protected and managed to support functional ecosystems, including ecohydrology, both intact and restored, and the species that rely on them.

If I knew for certain that “ecohydrology” is included in their concept of “functional ecosystems”, those additional words would be unnecessary.  But the draft report suggests that, despite that this integrative, interdisciplinary field has been around for a couple decades now, CNRA and the agencies it encompasses remain clueless about it, having invested all their resources in engineered approaches.  Appearances suggest that will remain true for this planning document purported to take us to 2030.

In a state whose water resources are increasingly challenged by climatic uncertainties, ignoring ecohydrology and nature-based initiatives to apply it – specifically catchment restoration – and especially after indicating they would go all-in on “nature-based solutions”, I can only reiterate the point I made in last July’s post

Given California’s pressing water issues, doesn’t it seem prudent / responsible to at least consider all possibilities?

Put another way, given the dire need and consequences, it does seem downright irresponsible to simply ignore potential options – even if you don’t (yet) understand them.

Deputy Secretary Norris reminded us during the Feb 1st 30×30 Public Feedback Virtual Meeting that, as the name implies, this planning document is meant to serve us for the next eight years.  That is precisely why, as a lifelong Californian, I expect a bit more foresight from this document than the rather timid strategies spelled out to date.  

There needs to be some aspirational vision here, not reliance on generalized niceties that were old a decade ago.

Climate Resilience – Key Objective #3

Per the Pathways to 30×30 draft report, Key Objective #3 is:

Conserve places that help California achieve carbon neutrality and/or build climate resilience

CNRA seems to have carbon down, to the extent that they understand a few things about sequestration.  But the document seems woefully weak on climate resilience, which I assume to mean resilience to climate change.  I imagine I’m repeating myself but perhaps that’s because I haven’t really been heard.  So here goes again:

Climate change appears to be diminishing the snowpack we’ve long depended on for detention storage (again, see Retention vs Detention Storage).  But there is one huge existing opportunity to create more detention storage – restore degraded catchments!

Those of us paying attention may be forgiven for hearing the alarm bells and sirens going off and feeling some exasperation that even the supposedly most progressive state in the union seems to be pussy-footing around with mediocre policy statements like the Draft Pathways to 30×30 document.

Is it unreasonable to expect at least aspiration toward excellence from our “progressive” government?


Verna Jigour, PhD



Allen, M. F. 2015. How oaks respond to water limitation. Pages 13-22 in R. B. Standiford and K. L. Purcell, tech. cords, editors. Proceedings of the seventh California oak symposium: managing oak woodlands in a dynamic world. Gen. Tech. Rep. PSW-GTR-251.  U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station, Berkeley, CA. 

Dwomoh, F. K., J. F. Brown, H. J. Tollerud, and R. F. Auch. 2021. Hotter drought escalates tree cover declines in blue oak woodlands of California. Frontiers in Climate 3:689945.  

Gordon, D. R., J. M. Menke, and K. J. Rice. 1989. Competition for soil water between annual plants and blue oak ( Quercus douglasii ) seedlings. Oecologia 79:533 – 541.

Gordon, D. R. and K. J. Rice. 1993. Competitive effects of grassland annuals on soil water and blue oak (Quercus douglasii ) seedlings. Ecology 74:68-82.  

Gordon, D. R. and K. J. Rice. 2000. Competitive suppression of Quercus douglasii (Fagaceae) seedling emergence and growth. American Journal of Botany 87:986-994.  

Macon, D., T. Schohr, D. Schmidt, and M. M. Garbelotto. 2020. Recent blue oak mortality on Sierra Nevada foothill rangelands may be linked to drought, climate change. California Agriculture 74:71-72.

Paine, R. T. 1980. Food webs: linkage, interaction strength and community infrastructure. Journal of Animal Ecology 49:666-685

Reiner, R. and A. Craig. 2011. Conservation easements in California blue oak woodlands: testing the assumption of livestock grazing as a compatible use. Natural Areas Journal 31:408–413.  

Rice, K. J., D. R. Gordon, J. L. Hardison, and J. M. Welker. 1993. Phenotypic variation in seedlings of a “keystone” tree species (Quercus douglasii): the interactive effects of acorn source and competitive environment. Oecologia 96:537–547.

Simard, S. 2021. Finding the Mother Tree: Discovering the Wisdom of the Forest. New York. Alfred A. Knopf. 

Stahle, D. W., R. D. Griffin, D. M. Meko, M. D. Therrell, J. R. Edmondson, M. K. Cleaveland, L. N. Stahle, D. J. Burnette, J. T. Abatzoglou, K. T. Redmond, M. D. Dettinger, and D. R. Cayan. 2013. The ancient blue oak woodlands of California: longevity and hydroclimatic history. Earth Interactions 17:1-25.  

Swiecki, T. J., E. A. Bernhardt, and C. Drake. 1997. Stand-Level status of blue oak sapling recruitment and regeneration. Pages 147-156 in N. H. Pillsbury, J. Verner, and W. D. Tietje, technical coordinators, editors. Proceedings of a symposium on oak woodlands: ecology, management, and urban interface issues; 19–22 March 1996; San Luis Obispo, CA. Gen. Tech. Rep. PSW-GTR-160.  Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture, Albany, CA.

Swiecki, T. J. and E. A. Bernhardt.. 1998. Understanding blue oak regeneration. Fremontia 26:19-26.