Global warming increases risk of frost damage to trees

August 10, 2018 by Michael Keller, ETH Zurich
Frost damage to young beech leaves on the Zugerberg, taken on 24 April 2017 only a few days after a heavy frost. Credit: Christof Bigler/ETH Zurich

Climate change is bringing with it not only drier summers, but warmer springs too. This causes trees and shrubs to bud earlier, making them vulnerable to late frost, as ETH forest scientists have now proven.

During the hot summer months, humans and animals alike enjoy the shade offered by the leafy canopy of trees and shrubs. In order for deciduous woods to make maximum use of the growing season, when growth and reproduction are possible, they must bud early in the springtime. Climate change favours this: with rising temperatures, the growing season in Switzerland has generally shifted forward.

Frost frustration for trees

Yet this presents plants with a dilemma: while early leaf unfolding extends the period in which plants can grow, early budding also increases the risk of frost damage to leaves and blossoms. The heavy late frost around 20 April 2017 provides a striking example of this: after an extremely warm March and April, temperatures in the lowlands dropped well below zero degrees Celsius for several days – with dramatic consequences for vegetation, not least for Swiss fruit and vines.

Senior Scientist Christof Bigler and Harald Bugmann, ETH Professor of Forest Ecology, have now examined in more detail whether and how the frost risk has changed for the leaf unfolding of 13 European tree and shrub species in Switzerland over a period of 60 years. To this end, they analysed temperature measurements and 48,000 observations of leaf unfolding carried out by MeteoSwiss at 264 stations since 1951. The researchers reported on their results in Scientific Reports.

Increased risk – safety margins exist

Since around 1980, the time of leaf unfolding has shifted forward as a result of global warming, and the leaves and needles of some species are budding earlier, particularly at higher elevations. This means that the time between the last late frosts and leaf unfolding has shortened. "The risk of frost damage has therefore tended to increase," says Bigler.

Nevertheless, in most of the years studied, the last intense late frosts have occurred before the leaves have unfolded, leading Bigler and Bugmann to conclude that many European tree and shrub species have relatively large safety margins with regard to frost risk. Yet the safety margins are distributed unevenly, as Bigler explains: "Species that bud early at an elevation above 1,100 metres, such as larch, have the lowest safety margins."

Weakened vegetation

Even if springtime frost after leaf unfolding is relatively rare, every now and then above-average spring temperatures followed by intense cold results in frost damage to leaves and needles, as in April 2017, when Bigler observed that some affected spruces could no longer bud after the cold snap. "Since spruces have perennial needles, they can handle this – in contrast to deciduous trees, which often bud again." And yet some seedlings and saplings would have barely survived last year's frost.

Frost damage weakens trees. If the leaves bud again, they lack the required resources to grow taller and thicker and to form roots. This makes them less competitive, as can be seen in tree rings, which are narrower after such frost events.

A finely tuned moment

For plants, the time of leaf unfolding is a compromise between minimum frost risk and maximum vegetation period, and they adapt continuously. "The time of leaf unfolding has been fine-tuned over a very long evolutionary period," says Bigler. In spring, however, trees also react to the rising temperatures: when it becomes warm, frost is less likely.

Bigler and Bugmann assume that extreme late frosts will continue to occur in a warming climate, but the trend towards earlier leaf unfolding will continue for some time. A better understanding of how local trees and shrubs react to changing conditions will allow forest ecologists to estimate more precisely how quickly our forests will grow in the future and how species composition will develop.

Explore further: Broadleaf trees show reduced sensitivity to global warming

More information: Christof Bigler et al. Climate-induced shifts in leaf unfolding and frost risk of European trees and shrubs, Scientific Reports (2018). DOI: 10.1038/s41598-018-27893-1

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17 comments

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elevyn_11_
2.7 / 5 (3) Aug 10, 2018
If you're cold, they're cold.. bring them inside
rrwillsj
5 / 5 (1) Aug 10, 2018
Then we would have to ponder if "A Tree Grows in Brooklyn"?
Surveillance_Egg_Unit
1 / 5 (2) Aug 11, 2018
There are deciduous trees who drop their leaves, and there are the evergreens who should fare well in severe cold weather. In warmer climates, such as in Georgia and Florida, during a severely cold spell, many orange groves are found dousing/spraying the trees already laden with fruit and their leaves with water to build up ice, to protect the fruit and leaves from the cold wind, which is the real destroyer.
antigoracle
1.5 / 5 (8) Aug 11, 2018
More PATHOLOGICAL LIES from the AGW Cult and their PATHOLOGICAL "science".
Results indicated FALSE SPRING EXPOSURE DECREASED ACROSS THE U.S. OVER THE 94 YEAR RECORD.........PLANT COMMUNITIES AND AGRICULTURE WILL LIKELY TAKE ADVANTAGE OF EARLIER WARM TEMPERATURES, AND DECREASED FALSE SPRING EXPOSURE MAY ENHANCE ECOSYSTEM CARBON SEQUESTRATION ACROSS THE CONTINENTAL U.S.

Take a look at actual facts -- https://agupubs.o...GL059266
humy
5 / 5 (5) Aug 11, 2018
If you're cold, they're cold.. bring them inside

Bring forests inside?
rrwillsj
5 / 5 (4) Aug 11, 2018
"Only You Can Save a Forest From the Treacherous Lies of auntirtreacle!"
antigoracle
1.6 / 5 (7) Aug 11, 2018
"Only You Can Save a Forest From the Treacherous Lies of auntirtreacle!"

No one can save the rrwillsj jackass from its ignorance.
mtnphot
5 / 5 (8) Aug 11, 2018
Antigoracle. If you got out of your basement more often you would see this is true. With a warmer spring, plants break dormancy early. They are susceptable to a sudden cold snap, I have seen it many times; one doesn't need a scientific paper to tell me. This is why I said you need to get out more so you can see the effects of climate change for yourself, rather than relying on Infowars for your information..
antigoracle
1 / 5 (7) Aug 11, 2018
Antigoracle. If you got out of your basement more often you would see this is true. With a warmer spring, plants break dormancy early. They are susceptable to a sudden cold snap, I have seen it many times; one doesn't need a scientific paper to tell me. This is why I said you need to get out more so you can see the effects of climate change for yourself, rather than relying on Infowars for your information..

Another Chicken Little Jackass brays. If only it could get its head out of its rectum and magically grow a brain, it might just be able to read and comprehend actual science and facts.
https://agupubs.o...GL059266
Maggnus
5 / 5 (7) Aug 11, 2018
Another Chicken Little Jackass brays. If only it could get its head out of its rectum and magically grow a brain, it might just be able to read and comprehend actual science and facts.
https://agupubs.o...GL059266
Interesting that he provide a link to a study that supports global warming and provides support for the results of this study while at the same time seeming to denigrate the poster he is attacking. Great study by the way!
antigoracle
1.5 / 5 (8) Aug 11, 2018
Another Chicken Little Jackass brays. If only it could get its head out of its rectum and magically grow a brain, it might just be able to read and comprehend actual science and facts.
https://agupubs.o...GL059266
Interesting that he provide a link to a study that supports global warming and provides support for the results of this study while at the same time seeming to denigrate the poster he is attacking. Great study by the way!

Another Chicken Little Jackass brays.
NOT interesting that this Jackass cannot read, far less comprehend, the fact that false springs has been DECREASING over the last 94 years.
Surveillance_Egg_Unit
1 / 5 (5) Aug 12, 2018
And by the way, trees are usually adaptive to environmental changes. They may drop their leaves, but a new set grows when conditions are more favorable, And don't forget that trees and other plant-life are capable of EVOLVING for weather and water considerations, just as animals have been evolving for millions of years.
SteveS
5 / 5 (6) Aug 12, 2018
And don't forget that trees and other plant-life are capable of EVOLVING for weather and water considerations, just as animals have been evolving for millions of years.


How many generations of trees do you think that will take? How many hundreds of years?
rrwillsj
5 / 5 (1) Aug 12, 2018
Oh Steve you are asking S_E_U_W_E_R the wrong question. He? She? It? is a typical denier shill. Incompetent at numeracy in addition to being illiterate.

Egghead counts using his fingers and toes. You would think the poor dear would at least be able to count to 24 that way? However, SEUseless needs to use one of it's digits to count the others. So, totally confused trying to figure base 23.

Undoubtedly to be found in the same playpen as auntie-oralroberts.
SteveS
5 / 5 (2) Aug 12, 2018
Oh Steve you are asking S_E_U_W_E_R the wrong question.


Not at all, If he wants to play with the adults he has to answer questions like an adult.
RealityCheck
1 / 5 (2) Aug 12, 2018
@Surveillance_Egg_Unit.
trees are usually adaptive to environmental changes. They may drop their leaves, but a new set grows when conditions are more favorable, And don't forget that trees and other plant-life are capable of EVOLVING for weather and water considerations, just as animals have been evolving for millions of years.
The problem is not so much the adaptation, it is the RATE of change which 'overwhelms' the adaptation process insofar as HUMAN livability/sustainability during this RAPID change due to AGW exacerbating prior settled/tolerable global weather patterns/conditions/systems. Consider cost/upheavals caused to humans globally, even as we speak! Drier/longer/more frequent/extensive , 'back-to-back' drought/rain/storm 'catastrophic' events displacing millions, costing billions, not easily recovered/absorbed before catastrophe strikes again. Not to mention diseases/pests/parasites, unseasonal weather events in areas not previously so affected. Rethinkitall.
RealityCheck
1 / 5 (2) Aug 12, 2018
@antigoracle.
More PATHOLOGICAL LIES from the AGW Cult and their PATHOLOGICAL "science".
Results indicated FALSE SPRING EXPOSURE DECREASED ACROSS THE U.S. OVER THE 94 YEAR RECORD.........PLANT COMMUNITIES AND AGRICULTURE WILL LIKELY TAKE ADVANTAGE OF EARLIER WARM TEMPERATURES, AND DECREASED FALSE SPRING EXPOSURE MAY ENHANCE ECOSYSTEM CARBON SEQUESTRATION ACROSS THE CONTINENTAL U.S.

Take a look at actual facts -- https://agupubs.o...GL059266
My customized computer system cannot establish a secure connection to that site at the moment (probably because I'm in the middle of reconfiguring my computer system for added new equipment and all the necessary new settings/authorizations etc haven't been sorted out yet). So can you tell me if the global situation was discussed at all therein, even in passing/comparison etc? Can you post it again including more contextual data and any 'qualifiers' used (if any)? Thanks. :)

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