How a drought affects trees depends on what’s been holding them back

Hmmmm…I wonder if this has any ramifications for treemometersTM, aka tree-ring circuses ~cr

How a drought affects trees depends on what’s been holding them back

In cold, harsh environments, drought can actually benefit the trees by extending the growing season

Peer-Reviewed Publication


Whitebark Pines

(Santa Barbara, Calif.) — Droughts can be good for trees. Certain trees, that is.

Contrary to expectation, sometimes a record-breaking drought can increase tree growth. Why and where this happens is the subject of a new paper in Global Change Biology.

A team of scientists led by Joan Dudney at UC Santa Barbara examined the drought response of endangered whitebark pine over the past century. They found that in cold, harsh environments — often at high altitudes and latitudes — drought can actually benefit the trees by extending the growing season. This research provides insights into where the threats from extreme drought will be greatest, and how different species and ecosystems will respond to climate change.

Many factors can constrain tree growth, including temperature, sunlight and the availability of water and nutrients. The threshold between energy-limited and water-limited systems turns out to be particularly significant. Trees that try to grow in excessively cold temperatures — often energy-limited systems — can freeze to death. On the other hand, too little water can also kill a tree, particularly in water-limited systems. Over time, many tree species have adapted to these extreme conditions, and their responses are broadly similar. They often reduce growth-related activities, including photosynthesis and nutrient uptake, to protect themselves until the weather improves.

“Interestingly, the transition from energy- to water-limited growth can produce highly unexpected responses,” explained Dudney, an assistant professor in the Bren School of Environmental Science & Management and the Environmental Studies Program. “In cold, energy-limited environments, extreme drought can actually increase growth and productivity, even in California.”

Dudney and her colleagues extracted 800 tree cores from whitebark pine across the Sierra Nevada, comparing the tree rings to historical records of climate conditions. This climate data spanned 1900 to 2018, and included three extreme droughts: 1959–61, 1976–77, and 2012–15. They recorded where tree growth and temperature showed a positive relationship, and where the relationship was negative.

The authors found a pronounced shift in growth during times of drought when the average maximum temperature was roughly 8.4° Celsius (47.1° Fahrenheit) between October and May. Above this threshold, extreme drought reduced growth and photosynthesis. Below this temperature, trees grew more in response to drought.

“It’s basically, ‘how long is the growing season?’” Dudney said. Colder winters and higher snowpack often lead to shorter growing seasons that constrain tree growth. Even during an extreme drought, many of the trees growing in these extreme environments did not experience high water stress. This surprised the team of scientists, many of whom had observed and measured the unprecedented tree mortality that occurred at slightly lower elevations in the Sierra Nevada.

Dudney was curious whether drought impacts growth in just the main trunk, or the whole tree. Without more data, the trends they saw could be a result of disparate processes all responding to the drought differently, she explained. Fortunately, whitebark pine retains its needles for roughly eight years. This provided additional data that could address this question.

The researchers shifted their attention from dendrology to chemistry. Atoms of the same element can have different weights, or isotopes, thanks to the number of neutrons they contain. Several aspects of a plant’s metabolism can influence the relative abundance of heavy, carbon-13 and light, carbon-12 in tissues such as their leaves and needles. These changes provide a rough guide to the amount of water stress a tree experienced during drought. This was a boon for the researchers, because isotopic data from the pine needles spanned drought and non-drought years.

Analyzing needle growth, carbon and nitrogen isotopes revealed that the whole tree was affected by the threshold between water-limited and energy-limited systems. Trunk growth, needle growth, photosynthesis and nutrient cycling responded in opposite directions to drought above and below the threshold between energy- and water-limited systems.

The future of whitebark pine is highly uncertain. The species — recently listed as threatened under the Endangered Species Act — faces many threats, including disease, pine beetle infestation and impacts from altered fire regimes. It’s clear from this research that drought and warming will likely exacerbate these threats in water-limited regions, but warming may be beneficial for growth in energy-limited environments. “This research can help develop more targeted conservation strategies,” said Dudney, “to help restore this historically widespread tree species.” Indeed, the pine’s range encompasses a diverse region, stretching from California to British Columbia, and east to Wyoming.

The findings also have implications more broadly. Approximately 21% of forests are considered energy limited, and an even higher percentage can be classified as water limited. So transitions between these two climatic regimes likely occur around the globe. What’s more, the transition seems to have an effect on nitrogen cycling. Trees in water-limited environments appeared to rely less on symbiotic fungi for nitrogen, which is critical for tree growth in harsh, energy-limited environments.

“Droughts are leading to widespread tree mortality across the globe,” Dudney said, “which can accelerate global warming.” 

Deciphering the many ways trees respond to drought will help us better predict where ecosystems are vulnerable to climate change and how to develop more targeted strategies to protect our forests.


Global Change Biology

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May 29, 2023 2:08 am

This morning I heard London described as a forest city. Left to its own devices it would revert back, that is true.

In my garden – located next to a relatively wild patch of common – an ash tree popped up out of nowhere 20 odd years ago and now is quite big and needs cutting back.

That’s my offset…

Ben Vorlich
Reply to  strativarius
May 29, 2023 2:35 am

Derby City council planted ash trees along the street where I lived. They did it just before a summer where there was very little rain. Most struggled to survive, I watered the one outside my house and it thrived th rest took a decade to get going.
Subsequently I had a problem every spring with Ash seedlings popping up where I didn’t want or need them

Reply to  Ben Vorlich
May 29, 2023 2:56 am

Life finds a way!

Reply to  Ben Vorlich
May 29, 2023 4:45 am

No good deed goes unpunished these days.

Peta of Newark
Reply to  Ben Vorlich
May 29, 2023 4:53 am

Derby Council are thus demonstrated to be insane:

Coming from NW corner of England (lots of rain and cool) I met Ash Trees in epic abundance.
i.e. They **love** lots and lots of water and patently don’t mind getting cold.
So wtf are they doing being planted in Derby City = one of the hottest and driest places in all of England?

In Cumbria they grew like weeds and triffids. What especially amazed me was how they were always the last trees to get the leaves in springtime and the firts to drop them in autumn YET – still managed to grow so fast and well.
In fact, they make their seeds (‘ash keys’ before they get their leaves on and in immense quantity

What doubly amazed every single year was when I went out to ‘mow my meadow’ to make winter cow-fodder silage was the incredible amount of ‘litter’ that fell out of them where they occurred around the edges of my fields.

I’d need to keep stopping the tractor and spend time clearing ‘winter fallen junk’ out the way of my mowing machine lest the god-awful stuff wrecked it.
I had huge numbers of Oak also and they never did any of the sort. Only the Ash ##

How did they grow so fast, in such a short (self imposed) season while making all those seeds and dropping the insane amount of twiggerey, dead leaves, junk and other litter onto the ground beneath them?
And quite sizeable branches too – ‘just fell out of them’ without any apparent harm at all

But their growth rate is last thing you’d want in a city – they’d undermine roads and houses causing incredible damage through subsidence and heave.
Even before all that litter they create gets onto roads and especially: dedicated cycle routes. It would be fatal for cyclists

wtf were Derby Council thinking when they chose Ash???!!!!???!!!
(I’m slightly familiar with Derby = Hotbed of Socialism)

## There’s the Farmer’s Almanac summer weather prediction.
In springtime, keep an eye on any Oak and Ash you have and note which one gets its leaves first
Then apply The Rule:

  • Oak before Ash = you’re in for a splash (relatively dry summer)
  • Ash before Oak = you’re headed for a soak (relatively wet summer)
Reply to  Peta of Newark
May 29, 2023 6:03 am

Know a decent tree surgeon?!

Reply to  Ben Vorlich
May 29, 2023 6:01 am

I have the same problem with Manitoba maple (Box Elder) and Carrigana, both of which are introduced species that can out compete many native species. The parent trees are on neighboring properties. Of course the native Quaking Aspen can be a problem too, without seeding. They like to break through my driveway.

James Snook
Reply to  Ben Vorlich
May 29, 2023 9:00 am

It’s not going to be a major problem much longer.

May 29, 2023 2:21 am

This article will not be a surprise to readers of Peter Wohlleben and Colin Tudge….

Joseph Zorzin
Reply to  186no
May 29, 2023 5:34 am

Wohlleben thinks trees communicate with each other and enjoy a kind of socialism. I think he’s nuts, but what would I know, I’ve only been a field forester for 50 years?

Dave Andrews
Reply to  Joseph Zorzin
May 29, 2023 8:56 am

What? 50 years and you haven’t heard the trees talking to each other? 🙂

Joseph Zorzin
Reply to  Dave Andrews
May 29, 2023 9:48 am

Only when I have some excellent weed. 🙂

Right-Handed Shark
May 29, 2023 3:54 am

“Droughts are leading to widespread tree mortality across the globe,” Dudney said, “which can accelerate global warming.” 

And what about the droughts caused by inappropriate planting of trees?

Joseph Zorzin
Reply to  Right-Handed Shark
May 29, 2023 5:39 am

from that link:

A study in 2005 showed “about 30% less water flowed from the mature pine plantation than the pasture.”

yuh, that’s why wise forest managers thin such forests allowing more water to stay in the ground- and the best trees should be left to grow into high value timber- but that’s not to say that often the wrong species are planted- especially in urban environments, where they often plant the cheapest trees they can purchase

Reply to  Joseph Zorzin
May 29, 2023 7:44 am

Important to note that for at least some species/sites the impact of forest thinning on water balance is transient with expanding crowns and increased undergrowth returning evapotranspiration to pre-thin levels relatively quickly.

For example Bottero et al (citation below) found that to sustain improved water balance you have to thin heavy and often. When I compare the basal area and stand density index (SDI) they reported for their Minnesota site (red pine) it became clear water optimized thinning likely needs to be much heavier than timber optimized thinning. I’d be curious to hear your thought’s Mr. Zorzin for species/sites your familiar with in terms of how far past optimal silviculture thinning we would have to push it to have an appreciable effect on water balance for the majority of the time between entries.

Don’t get me wrong, as a forester I am all for increasing the amount of thinning, the benefits are numerous. However, I am concerned when thinning is described by climate activists as a “no-regrets” adaptation option. If we have to thin heavier and more often than silviculturally appropriate yields will go down, particularly in the larger high-value trees at later entries, which seems like a “regret” to me. At some point we also compromise ecological function as we transition from a closed canopy forest to a parkland. Parkland also has it’s own ecological function, so reasonable to have some on the landscape, but also need to maintain a decent amount of closed canopy.

Bottero et al. Density-dependent vulnerability of forest ecosystems to drought. Journal of Applied Ecology 2017, 54, 1605–1614.

Joseph Zorzin
Reply to  MJB
May 29, 2023 9:45 am

Well, I’m not a forest scientist- can only report what the “forest science” says- that evapotranspiration will return- usually fully in about a decade- more or less depending on many factors. I suspect fairly heavy thinning periodically is needed if the primary goal is to increase water yields. That’s what “watershed foresters” usually say- though I don’t agree that attempting to increase water yields should be the primary goal. Just my personal perspective- is that producing high value timber should be the primary goal even on watersheds- if done right, you’ll also get some improved water yields- and wildlife benefits- and it’ll look good too, if done right. Too often, logging isn’t done right- the down and dirty secret that forestry academics, industry and professional groups don’t like to talk about. In fact, most logging is still high grading- or just sloppy work. Really first class silviculture is very, very rare. I’ve been talking about this dirty secret for decades and it hasn’t made me popular in forestry circles. One negative regarding heavy cutting (for water yields or supposedly to get wildlife that prefers early succession forest) is that invasive species tend to enter the stand- especially on good soils. And when they arrive, they are a huge problem to get rid of. I used to have a theory that most forest thinning/harvesting should remove about a third of the basal area. I now go a bit more than that living in an area with a (just barely) biomass market- since they’ll take anything, which is good- to get rid of the very low quality wood- in order to leave mostly the best trees- which is sometimes called “crop tree” silviculture. By the way, just call me “Joe”- the Mr. thing makes me feel old, of course I am 73, but in my mind I’m still about 25. 🙂

Regarding red pine- many red pine plantations were planted here in Woke-achusetts during the Great Depression- and few if any were ever thinned- resulting in very unhealthy forests since red pine doesn’t seem to “self-thin”- so you have extreme over density of pencil thin trees very susceptible to many diseases and pests. So, now the solution is to clearcut them- which is probably the only solution- but it’s unfortunate they weren’t thinned or they’d make nice forests. There is a small amount of native red pine in parts of the state. When I see a red pine, I usually leave it.

Matt Kiro
Reply to  Right-Handed Shark
May 29, 2023 6:19 am

Isn’t the world experiencing an overall greening? I would expect that trees are a good chunk of this growth. I thought the biggest area losing trees was the Amazon do to converting forest to agriculture, which isn’t drought . Maybe I’m not up to date on the latest numbers.

Reply to  Matt Kiro
May 29, 2023 6:39 am

The planet has been losing trees to human agriculture for about 6000 years. This followed a period of about 4000 years where boreal forests replaced glacial ice sheets. In geological time…just a couple of heartbeats of a hummingbird…

May 29, 2023 4:38 am

Their closing conclusions…

“Droughts are leading to widespread tree mortality across the globe,” Dudney said, “which can accelerate global warming.” 

Once again, imagining that climate change causes, is caused by virtually every weather outcome.
Closely followed by researcher(s) absurd claims to alleged benefits of their research.

“Deciphering the many ways trees respond to drought will help us better predict where ecosystems are vulnerable to climate change and how to develop more targeted strategies to protect our forests.”

Amazing that EurekaAlerts failed to mention where these researchers got all of their ‘results’.
From their file contains their tables of results:

“Tables and Figures


Table S1. Model comparison with various climate windows (includes precipitation and temperature terms) using AIC from generalized additive models (GAMs).



                              Model comparison

Weather window (both precip. and temp.) DF AIC

Annual (Jan 1 – Dec 31) 4 21079.65

Annual water year (Oct 1 – Sept 30) 4 21089.21

Fall-spring water year (Oct 1 – June 30) 4 21072.81

Spring and summer (April 1 – September 30) 4 21101.65

Summer (June 1 – September 30) 4 21106.16″

Yes, This is another alleged research based upon researcher programmed models and their “p hunting” so they can claim correlations.

Reply to  ATheoK
May 29, 2023 5:41 pm

Yes, This is another alleged research based upon researcher programmed models”
Yeah but that way they don’t have to go walking in all that weather and nature stuff.

Peta of Newark
May 29, 2023 5:04 am

What on Earth are these people doing inside ‘climate’ and ‘plant biology’

They have nothing but the simplest, niave and childish understanding of both = putting the two together is laughable & cringe-worthy/embarrassing in the extreme.

Are none of them gardeners in any way – do **none** of them even keep a cactus on their kitchen windowsill?
They haven’t got a frigging clue what they’re about.
Lord help us.

(I’m busy right now – will be back to explain more and Succulents are The Perfect Example that *anyone* can understand.)
most people that is

May 29, 2023 6:16 am

I never did have any faith in tree ring data. All they really indicate is a bad/good year for growth for a particular tree or species. Too many unknowable factors can influence growth.
A family of goats (or whatever) may use the shade and fertilize with their defecations.
An insect infestation could severely inhibit growth.
Defoliation by hail or wind can be devastating.
Just a few that don’t even include more distant influences such as smoke that reduces the available sunlight.
I think tree ring data, without this usually unavailable data, is for most purposes, practically useless.
It is a sad state of science that climate alarmism started with this crap and triggered a race for more such flimsy evidence. Evidence which neither constitutes proof or even builds a credible case. It certainly does not build a basis for prediction.

Reply to  rckkrgrd
May 29, 2023 8:40 am

Well Rocky, you are obviously wrong.
Detailed scientists like Dr. Mann can tell the average seasonal temperature by treemometers within a tenth of a degree without needing to know any of that trivia….actually more accurate than the temp variation from the airport to my house by real thermometers….


Mr Ed
May 29, 2023 7:04 am

Are there any photos of these tree rings that illustrate what this group has found?
And are there comparative dendro pics of say a redwood or sequoia rings of the same period but at a different elevation? I’m not doubting this but just interested.

We’re currently seeing an outbreak of a douglas fir beetle Dendroctonus pseudotsugae that
seems to be associated with the severe drought of the past couple of seems
to be in both overgrown and well thinned parcels.

May 29, 2023 8:14 am

Calling the Whitebark Pine endangered is a stretch. Their definition of ‘endangered’ must include the degree of difficulty associated with getting to the locations where they grow!

May 29, 2023 10:12 am
Peta of Newark
May 29, 2023 10:44 am

Drought helps the trees for the same reason cacti and succulents exist so comfortably where they do:
why (supposedly) the Amazon Forest existswhat explains a lot of Global Greeningexplains why farmers do ‘crop rotation & fallowing‘beautifully illustrates soil erosion….. and probably….why the underside of a large conifer tree in my garden becomes a veritable Hot Spot during the night
Are humongous blobs of water, deeply ridged/crevassed, are insanely prickly, grow very nicely thank you in places of permanent drought and often have pretty miniscule root-systems compared the size they can get to

So how do they do it?
Reason: Their food and water is ‘A blowing in the wind
Obviously CO2, that’s easy
But also their water – every molecule of water comes as = Carbonic Acid – one or more molecules of CO2 wrapped in a little ball of water
But what also comes in the wind (your primary-school teacher was ‘economical with the truth’) is what we’d call ‘Pollution’
You know what I mean by that = Every variation of dust, smoke, acid (rain) stinks & smells, smut, grot, bird mess and anything else that could possibly Blow In The Wind

And that is why the prickles are there – also the characteristic ‘shape’ of them = ridged & crevassed
Yes OK the prickles might stop critters from eating them but errrr, there aren’t (m)any critters where cacti usually habituate. By definition.
So why do they put up such epic defence against being eaten?

Because the prickles act as fur/hair does on animals, it slows down the wind as it blows over them.
This not least reduces evaporative water loss but also – the prickles ‘filter’ the air by slowing it down and all that airborne grot/pollution ‘condenses’ into the ridges and furrows of the body of the plant,
And it eats them

Similarly water vapour at night. The prickles encourage condensation, which runs down into the crevasses and the cacti ‘drink’
They are very good at that and is why they don’t have large root-systems typically. Only usually just enough to stop them falling over.
They are Filter Feeders and how many of those exist in the aqueous environment?

Cacti are land-bound Coral

Sooooo, what exactly is to stop other plants doing anything similar?
It’s what supports/feeds/nourishes the Amazon Forest not least. And That Stuff came from the very place that a cacti would call ‘home’ = the Sahara desert

Ain’t that beautiful? – Need I say more.
What’s nice is how it so completely trashes the Hockey Stick

Back to my Hot Spot Tree in my garden on The Fen.
This is an answer to what puzzled me when I first ever visited the place =
How do farmers on The Fen grow some very water-hungry things like potatoes, beet and beachball-cabbages without using Irrigation and Rain-guns – of in fact any sort of AddedWater throughout the growing season?
While back ‘home’ 80 miles away near Newark – rain-guns are visible horizon-to-horizon and they work all through the summer – even on crops of wheat/barley let alone all the spuds they grow there.

Because, through the night, my tree is ‘drinking’ the air.
it is getting all the water it needs for ‘tomorrow’ by condensing water-vapour on its pine-needles (just like cactus prickles) and it is the Heat of Evaporation being so released that keeps the air in/under the tree as warm as it is through the night.

Grasses do similar BUT, they don’t have the size/bulk and handling capacity of a large tree.
Hence why the grass is soaking wet in the morning while the leaves, branches, bark and trunk of the tree are Bone Dry
The tree sucks up every drop and in doing so lifts night-time temps by 3°Celsius

Pennies: Drop now
…….It’s why Henry 8th, chopping England’s forest (and most of NW Europe’s trees) as he did, triggered The Little Ice Age
Night time temps plummeted – hence day time temps took ‘that much longer’ to warm up and often, never did. Hence the ice.

Thanks Henry. thanks for nothing.
Apart from famine, war and pestilence.
(See what ‘sugar-poisoning’ gets you…….)

Peta of Newark
Reply to  Peta of Newark
May 29, 2023 11:26 am

Groan: I missed the soil erosion bit

OK. The Fen is made of, what was, sea bed or at very least, loads & loads of silt and sediment washed into the ancient swamps and bogs that comprised The Fen 200+ years ago.
The soil is thus ‘very fertile’

Soils around Newark are a hideous mix but, there’s a lot of Glacial Till = clay and some (very sharp) sand. The sharpness of that sand is a killer – it so easily turns into concrete.
(Similar to Caliche Soils although the chemistry is a world apart)
Relentless ploughing and fertilising since end-WW2 now means they are very nutrient deficient.
Even before so much Glyphosate gets dumped into/onto them.
(That’s how Glyphosate works – it induces nutrient deficiency. It is not an actual ‘killer’ – just a slow strangler)

So why farmers around Newark (and everywhere) use so much irrigation is to ‘flush’ the soil
i.e. The get what nutrition is in the soil moving and within reach of the plants’ roots.

But on The Fen there is no such requirement – the soil is soooo rich that any/all trace-elements the plants need are ‘right there’ ready and waiting.
So, plants on The Fen can simply get away by condensing water vapour throught the night and using what comes in anyway with their CO2

Hence and by very definition, if farmers near/around you or anywhere are using, or need to use, ‘irrigation’, they are operating on highly eroded soil.
I say ‘highly’ because to greater extent, the plants themselves can compensate by putting out more/bigger/longer roots.

But obviously that can only work for so long until it becomes ‘resource negative’ and it is then that irrigation becomes necessary.
Irrigation ‘extends the reach’ of the plants’ roots if you like. yes?
Don’t eat the food grown there. It will be Nutrient Deficient and it will make you ill. Mentally as well as physically.

See why I said your primary school teacher lied to you.
By omission admittedly but as we see – Primary School Teachings are what powers all of Climate Science

Reply to  Peta of Newark
May 29, 2023 6:19 pm

Are humongous blobs of water, deeply ridged/crevassed, are insanely prickly, grow very nicely thank you in places of permanent drought.

Wrong. Cacti grow in areas with very seasonal rain. The only ones with grow in a permanent drought area live in the Atacama desert.

Their food and water is ‘A blowing in the wind

Wrong. Their food is in the substrate in which they grow and their water comes from mainly from rain.

You know what I mean by that = Every variation of dust, smoke, acid (rain) stinks & smells, smut, grot, bird mess and anything else that could possibly Blow In The Wind

And that is why the prickles are there – also the characteristic ‘shape’ of them = ridged & crevassed

Wrong. The spines are there for protection from grazing and/or from protection from intense sunlight. There are many cacti without spines. How do they collect air-borne food?

They are very good at that and is why they don’t have large root-systems typically. Only usually just enough to stop them falling over.

Wrong. There are many cacti with massive root systems used as storage organs and they often grow right next to shallow rooted species.

Similarly water vapour at night. The prickles encourage condensation, which runs down into the crevasses and the cacti ‘drink’

They are very good at that.

Wrong. Any dew condensing on the spines may be able to sustain a few species such as those in the Atacama which experience intense daily fog but even that is not enough to ensure their survival as no seedlings are to be found in the area. It obviously was a wetter area in the past. Now they are doomed to extinction due to lack of rain.

May 29, 2023 1:57 pm

Wait, wot? Are you telling me that “tree” isn’t just scientific shorthand for “treemometer?”

Tom Abbott
May 30, 2023 4:59 am

So the tree ring science isn’t settled.

Aren’t we spending Trillions of dollars based on tree ring science?

Why would we do such a stupid thing? That was a rhetorical question.

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