Are Oak trees allelopathic?

dandy_line (Z3b N Cent Mn)

This topic is sure to create a lot of interest I'm sure. I didn't know what Allelopathic was until sometime in the last year. But now I think I have a good basis for allelopathic behavior from oak trees on my property. The story:

I bought this place just five years ago, 2 acres on a beautiful river with about two dozen spectacularly large(90') red and white pines. A few white Birch, and lots of Ironwood, Chokecherry, Poplar and a few Blueberry and Snowberry . Plus fifty or more large mature red and white oak. There is a nice house, two heated garages, and land that is mostly native, unmowed Pennsylvania Sedge. Along with many other native wildflowers like: Yellow Bellwart, Sarsasparilla, Columbine, Geranium, Trillium, Anemones, Mianthemums, Thalictrum, Rudbeckia, Helenium, Asters, and more I can't think of right now.

But the oak trees had over a period of fifty years or so cornered all the shade, and me, not fond of them in the first place, immediately started the removal process. Also eradicated some poplars, one giant Basswood and a lot of the Ironwood. But when I moved in there were no young pines or birch.

The canopy was opened up and I immediately started seeing new plants like: Viburnum dentatum, Diervilla lonicerra, and lots of Elderberry.

Over this time I also planted more than 400 native shrubs and trees to flourish in the sun now available.

But now, about four years after the major removal process began, I am seeing hundreds or thousands of small pine seedlings, which only started this summer. No birch as of yet, and a few black cherry. So, my thinking is that the oaks had prevented any pine germination all that time, and not just because of the lack of sunlight. Note that the shade had been removed starting 4 years ago and it is only now this year that the pine seedlings surfaced. And they are becoming a real nuisance too.

So, just my musings on whether oaks are really more evil than we thought.




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gardengal48 (PNW Z8/9)

I'd hardly use the word "evil" when describing a plant with allelopathic properties :-) It is just a natural adaptation, much like the ability to vine or climb or the production of thorns. A great many plants - not just trees - have allelopathic properties to some degree but they are often directed at specific plant species - their primary competition in the wild - rather than broad generalists like the walnuts. And some species of oaks do have some of these properties. But since both red and white oaks (both native species themselves) are common to mixed forests that include eastern white pines. I am not at all sure that oak allelopathy is the sole cause of the lack of development of the pine seedlings. I'd think excessive shade and lack of water available within the established root system of the oaks was just as likely a determining factor as was the presence of the oaks themselves and any potential allelopathic effect.

Your position is a bit confusing - you consider the oaks 'evil' yet consider the proliferation of the pine seedlings appearing after their removal a 'nuisance'. So what exactly is it you are looking for?


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docmom_gw(5)

It is also possible that the germination process for the pines is very slow and the first year or two takes place out of site. It might be that once there was adequate light and moisture, it still took a long time for the seedlings to become visible. Trillium plants, for example, take 7 years to go from seed to flowering plant.

Martha

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WoodsTea 6a MO(6a)

Oaks are somewhat allelopathic, though less so than, say, black walnut. Perhaps it's some mixture of that plus what gardengal48 says -- competition for sunlight/water. It would make sense that some time might be required for allelopathic compounds in dead leaves/roots to break down. It could also be weather: a warmer/colder or wetter/drier season that favors pine germination.

You're wanting something more open/diverse? If so I would think continual disturbance would be necessary in your neck of the woods.



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Campanula UK Z8

I have english oak in my woodland (Quercus robur) and, while it does offer a canopy of dense shade, there are numerous early spring carpeters growing under the canopy. Allelopathy is an interesting phenomenon - I am beginning to suspect that nearly all plants have a degree of allelopathy once I started thinking of plants as communities rather than isolated specimens. A sort of throwback to my old veggie growing days where we talked ofcompanion pairings, both favourable and not (alliums always featured prominently) I imagine that the obvious contenders such as black walnut are allelopathic to a wider range of plants but would be unsurprised to learn that allelopathy occurs on a wider spectrum and, along with the microbial life of the soil, interacts on a contingent basis as the environment changes. In other words, not a fixed syndrome but one which can be triggered into play much like enforced dormancy or even gender changes.

A boring dreary english afternoon - do feel free to pass by these ramblings.

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wisconsitom(Zone 4/5)

Campanula, I think you're likely onto something. Just as with mycorrhizae, a group of organisms once relegated to the sideline of what's going on in numerous plant communities, but now understood to be everywhere and of immense significance to forest health. I suspect that acid precipitation across parts of Europe, leading to declines in the suitability of the site for the microorganisms, is behind recent and widespread tree health declines there.

And the almost unbelievable findings in terms of an almost "neural network" linking the trees within a stand to one another via these same hyphal strands is beyond cool. no reason why we wouldn't be equally ignorant about the allelopathic thing.

+oM

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wantonamara Z8 CenTex

I am beginning to suspect that some trees are allopathic to their own kind or maybe a mature tree has eaten up a certain nutrient in the soil that is needed by the young seedlings to thrive. I am trying to encourage red Spanish Oaks ( Quercus buckleyi) and they Never ever come up close to the parent. I now make my brush piles down hill from the parent to create deer protection, soil, water and compost capturing structure to encourage sproutage. I used to think under the canopy was a good place but it did not bear fruit.. Juniperus ashei have no problem spouting under the oaks. Can you tell, I have never studied plants except in my own school of The Outback Academy. Someone please give me a scientific explanation so I can sound smart in the future. LOL.

A glorious sunny make believe spring day, 76F

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Embothrium(Sunset Climate Zone 5, USDA Hardiness Zone 8)

A common, easily seen factor is competition through shading.

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wisconsitom(Zone 4/5)

Oddly enough...or not odd at all as it's turning out... individual trees in the forest can actively shunt nutrients, not only to others of their kind, but across species and genera. This via the hyphal network of those fungal species involved in mycorrhizal relationships with the trees. I already knew momma tree could send photosynthate and other materials to little baby tree of same species, but now it's turning out these fungi are far more likely to cross-connect with a range of species. Trees, in this sense, really and truly could be said to communicate with one another. Very likely, many of the same processes are underway in grasslands too. So long as the substrate has not had one or more nutrient levels unnaturally hyped up via overuse of fertilizers, these organisms will be present, quietly doing their work.

+oM

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wantonamara Z8 CenTex

Here the baby will not sprout unless it is a distance from the oak canopy. But it is not a shade issue because under the oak canopy gets more light than under a cedar canopy where they do sprout. the winter time has the oak loosing its leaves. Cedar come up like a vengeance under the oaks and end up out competing the oak.

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WoodsTea 6a MO(6a)

You might find the introduction of this paper interesting:

Effects of germination inhibition on the dynamics of Quercus ilex stands

It's not about your specific Q. species, but they find some evidence of auto-allelopathy. They don't really get into the why of it. I can imagine that it might be advantageous for new seedlings to be some distance away so that they are not competing with the parent for resources.

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wantonamara Z8 CenTex

Very interesting. My woods are in transition but it is a non burnt fire dependent ecosystem that has been historically over grazed and now "managed" by a dilettante.. God knows what stage of disturbance it is in.

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