A study reveals that deciduous trees' roots remain active in winter
26 comments
·March 22, 2025hoeoek
Cool! As a forester, this is interesting to see being researched. Many models in our field link biomass growth strictly to seasonal temperature thresholds, often considering trees to be 'growing' only when mean daily temperatures exceed 5 or 10 degrees Celsius for a consecutive week in spring, and 'idle' otherwise. So basically not accounting for this new "off-season growth", older research are overlooking a bunch of details and insights into growth dynamics. Using coniferous/decidious species as random effects in models has shown to have an effect - this might be why.
abakker
Its interesting because last year I did an experiment where I put ~6" of wood chip mulch and slow release fertilizer over the root zones of several trees (climate 6a), and now that its spring, every tree that got the thick coat of mulch has leafed out or budded significantly more than those that just got fertilizer. (sample size of around 10 trees in bad dirt in boulder. YMMV)
0xbadcafebee
I mean, could have been the fertilizer, or could have just been an insulating layer?
zdragnar
Since OP mentioned both with and without the mulch got fertilizer, it's definitely insulation.
They also mentioned "bad dirt" as well, so there's a very good chance the mulch also helped with moisture retention.
y-c-o-m-b
I always assumed the roots kept growing, so I didn't know that wasn't already an established idea. That kind of strikes me as strange and interesting. I figured it was common sense?
This was extremely evident by the red maple on our curb destroying the sidewalk even through the winter months. Even my dwarf magnolia tree has a notable increase in its trunk size in its dormant phase.
destitude
This is still in temperate forests. It still isn't clear to me if this is true where frost lines are feet below the surface. How can the roots grow in frozen soil?
mapt
> “Our results demonstrate that the above-ground and below-ground parts of a tree follow separate calendars, allowing for underground growth to be prioritized in winter and aerial growth at the beginning of spring,” says CREAF researcher Paolo Zuccarini, a co-author of the study. This divergence could offer a strategic advantage: in winter, while the rest of the tree is dormant, its roots store reserves of carbohydrates and nitrogen-rich substances, such as proteins and amino acids. Thus, when the tree ‘reawakens’, it will have enough nourishment for leaves to bud and photosynthesis to resume, which is essential for trunk and branch growth. “It’s kind of like having building blocks ready to use in the spring, when the priority is to produce leaves so that photosynthesis can start again,” explains Zuccarini.
Okay this part makes sense.
> Its findings suggest that forest soils have a greater carbon sink capacity than was previously believed, as they accumulate carbon all year long rather than only when trees are more active and their leaves are photosynthesizing.
This does not. They're not accumulating carbon in winter because they're not photosynthesizing carbon dioxide into glucose in winter. They're using stored carbon to continue cell division (not to mention bribing bacteria & fungi to build a rhizosphere with which to harvest nutrients).
darkerside
Probably misinterpretation. They don't accumulate carbon, but this activity depletes carbon reserves, increasing capacity to accumulate carbon in the summer months.
zdragnar
Sadly, roots respire- meaning that depletion of the carbon reserves happens by releasing CO2 (in addition to building lignin). It's only when they photosynthesize that plants produce more O2 and absorb more CO2 than they release.
londons_explore
This seems like the logical result... Underground where temperatures are less extreme, there is no good reason to reduce growth.
taeric
My mental model for deciduous trees was that they drop their leaves as a form of biological warfare against the shrubs below. I'm also growing to the idea that it is a way to lower their footprint against winds in the winter.
Would be neat to see more studies like this that look at the way they grow. Reminds me of the fun video that talks about where they get their mass. Related heavily to how and where people lose weight.
moate
In your mind, how does dropping leaves harm the shrubs? Wouldn't it allow for more light to pass down to the forest floor? It feels like the tree's response to shrubs was "grow taller to maximize sun exposure"
I feel like the conventional wisdom that this is a response to environment(conserve energy/lower wind resistance) make more sense than "offensive deterrent for competing plants" even more so when you consider that every leaf dropped is biomass that the tree had already taken in and utilized, but now it's giving it up. Maybe a pro-symbiotic move whereby dropping the leaves provides shelter/biomass for beneficial insects that could provide root aeration or soil enrichment would be another reason?
Maciek416
I think conserving energy in cold months is close to the biggest factor.
Regarding the dropping of biomass, in both deciduous and evergreen species, some of the substances from the retiring leaves/needles are reclaimed by trees ("retranslocation") and pulled out of the leaf before letting go of the leaf. In species like pines it'll be the second or third (or older, sometimes much older) retiring needles and in species like maple or beech it'll the be the entire foliage. Mass useful to soil ecosystems still falls but the tree grabs what it can in the late months of the year, hence the color change.
One thing the grandparent comment doesn't talk about much is the cost (in sugar) of both building and thereafter maintaining leaves and the related tradeoffs. Building a fully winter-tolerant broadleaf is more expensive sugar-wise than building a winter-interolerant leaf. A sugar maple in Quebec, where the season is shorter than (say) Oregon is going to compete in its niche better if it can attain surface area quickly at the start of the growing season, and that is better done with a winter-intolerant, more relatively delicate leaf. An evergreen leaf takes more time and mass to build and has to have more limited surface area or armor (cuticle) to tolerate such winters.
taeric
I'm largely going by what I see in my yard. If I want any of the ground shrubs to not die every year, I have to make sure they are not drowned in leaves.
Note that I'm not claiming the leaves are necessarily bad. They make pretty good mulch and such. But, without tending to uncover the smaller plants, they do a pretty good job of killing the things below the tree.
Maciek416
It affects seedling recruitment for sure. Some species love to start beneath leaf mulch and there is probably something out there that would colonize your leaf field hard and fast if it were given the chance. I collect red alder seedlings in timber clearcutting areas, and often find that they've had to twist/push their way through 6-12" of slash (clearcutting debris) to reach light and finally grow upwards. Quite a few conifers can push upward through many inches of needle duff as well.
jnellis
The bulk of roto-rooter calls to clear home sewer lines of tree roots happens during winter.
damnitbuilds
This seems like something that they could have and should have found out hundreds of years ago?
ledauphin
i'd read several state Ag agencies that have known this. It's why you keep watering newly planted trees even after their leaves fall, until the ground freezes. The roots will keep growing.
squircle
Not until its published? Have not read the article but I thought this was common knowledge.
Maciek416
Winter root growth is widely-observed amongst people who work with tree roots annually (bonsai hobbyists and professionals, commercial ornamental tree growers, especially propagation-adjacent roles) in milder temperate climates (eg: Pacific Northwest).
In my time studying bonsai (past 7-10y) in every winter (Jan-Mar) I've repotted (anywhere from partial to full bare rooting, partial to full root structure editing) many PNW-native deciduous trees (alders, bigleaf + vine maples, cottonwoods, etc) as well as non-PNW-native deciduous (birches, beeches, elms, maples, hazels, hornbeams, stewartia, bald cypress, cherries/plums, quinces, snowbells, etc). In somewhat-mild-and-milder climates there is always some root growth going on. Such winter root growth is much more aggressive in conifers, particularly pines, but also in spruces, cypress-family species (junipers).
Here's a diagram from a paper showing scots pine and rowan/ash adding either root or vegitative growth in various parts of the year:
Temperate trees collect or spend carbon in the warm parts of the year, i.e. between bud-break and mid-summer. In cooler parts of the year, they do various things: store it in the wood, move it around (redistribution + retranslocation), spend it (future-season buds + cambium + root expansion) or carefully avoid spending it (dormancy).
Even in these periods they're still collecting sunlight if they can, quite a few deciduous species can photosynthesize at least a little bit directly through their bark -- young twigs have much thinner bark even in trees that get very rough bark (eg: black cottonwood). And evergreens are collecting sunlight any time mild-or-warmer conditions are in play.
Trees are active in some shape or form any time they are able to be. If you live in USDA hardiness zone 7 or warmer and have trees/shrubs outside you can notice this more easily than in colder climates (where the grow/no-grow seasons are more sharply bounded). Roots are not the only thing expanding in winter. Take a picture every day of a branch on a deciduous or evergreen tree and you'll see bud expansion.
destitude
Yeah but they aren't making this clear and see people misinterpreting this not realizing that it is in temperate forests only. I don't see how any tree roots can be formed when frost line is feet below the surface.
naikrovek
I feel like I already knew this somehow. I'm sure I wanted to discover this as a child and cut a root during winter so that I could see if it healed. more likely I probably put the end of a root into some water with food coloring in it and came back later to see that food coloring had moved up the root.
mvdtnz
This is common knowledge. What a waste of time and effort.
aaron695
[dead]
When controlling invasive plants like honeysuckle using glyphosate, one of the more responsible approaches is to wait until all of the trees have lost their leaves in the fall and entered dormancy. The idea being that because the honeysuckle still has its leaves, you can safely use glyphosate on it with minimal to no impact on the rest of the ecosystem. I've always had my doubts (particularly due to studies on mycelium being exposed to glyphosate), but this is one of best practices that conservation departments recommend.
With this new study, it opens the possibility that trees may still have root absorption during the winter season. I feel like it is further evidence of how glyphosate likely always impacts the ecosystem and has no truly safe usage