Ice-Bubble Donut Rings Around Inundated Tree Bases: Observations and Speculations

Flooded GTR with ice cover and ice-bubble donut rings around tree bases

Flooded GTR with ice cover and ice-bubble donut rings around tree bases

 

Following a recent cold snap here in the Eufaula, AL area, I cruised over to the Bradley Unit GTR (in Stewart Co., GA) of the Eufaula NWR to take a few ice-habitat photos.  As I crunched around breaking through the thin ice cover (i.e., 1/8- to ¼-inch thick), I noticed a series of donut-like rings of tiny bubbles encapsulated in the ice around the bases of several small and large trees which were inundated by 4 to 12 inches of water in the managed GTR pool.  I took several photos of these ice-bubble donut rings, as I could not recollect ever having seen these types of features before. 

Overcup oak tree with an ice-bubble donut ring

Overcup oak tree with an ice-bubble donut ring

 

 Although I’ll let the photos speak for themselves as to the appearance and apparent character of these ice rings, clearly lots of questions and speculations occurred to me as to how these features were formed, and what significance they might have in the grand scheme of things. 

Small tree with ice bubble ring at base

Small tree with ice bubble ring at base

 

As I ruminate about these ice-bubble rings, keep several things in mind and remember:  1) Mark Twain’s comments about science and speculation; 2) the fable about the five blind men and the elephant; 3) the admonition about “… another beautiful hypothesis killed by the ugly facts…”; and, 4) Sherlock Holmes’ postulate “When you have eliminated the impossible, that which remains, however improbable, must be the truth.”   Fortified with these insights, I’ll try to give a brief overview of some of the ideas that have occurred to me.  I also hope to expand on these ideas (and presumably correct them as necessary) in a lengthier module format, but for the moment, here goes. 

Tiny bubbles in the ice layer

Tiny bubbles in the ice layer

 

 Three potential (and very preliminary) causative scenarios have occurred to me regarding these ice-bubble donut rings. 

Tree base with moss cover, moss capsules, and ice

Tree base with moss cover, moss capsules, and ice

 

 First, solar insolation on the bole of a tree may produce enough heat to facilitate the transport of oxygen gas (i.e., potentially produced by the lower portions of the tree’s stem via cambial photosynthetic activity) throughout the root system.  In order for this gas to move through the roots, apparently there must be some openings in the root system to the exterior for some of the gas to escape.  Possibly there is a zone of gas escape openings in the root system located underneath the zone of tiny bubbles encapsulated in the ice above the ground surface and water column.  Potentially these root system gas escape openings located close to the tree stem would function somewhat as pressure relief valves to allow gas flow to continue past this zone and on to the tips of the live root system. 

Rings of ice bubbles around the bases of a large and a small tree

Rings of ice bubbles around the bases of a large and a small tree

 

Second, in a situation similar to item one, stem heat and gas transport via the root system may warm a soil zone around the base of a tree to the extent of the outer limits of the ice-bubble donut ring.  This “warm zone” may facilitate the growth and metabolism of soil/leaf litter/water column organisms such as algae, bacteria, cyanobacteria, and/or fungi.  Oxygen and/or other gases may or may not be released by the tree root system in this zone. 

Hand trowel (12 inches long) on ice at base of tree for scale to indicate relative size of ice bubble ring

Hand trowel (12 inches long) on ice at base of tree for scale to indicate relative size of ice bubble ring

 

Third, heat generated by insolation of the tree stem and transferred to the water column may cause oxygen and/or other gases to effervesce in the water column and form the ice bubbles. 

From a technical standpoint for some of the issues raised above, the reader is referred to comments and references contained in Water Relations of Plants and Soils by P. S. Kramer and J. S. Boyer.  (1995, Academic Press, Inc.).  See especially the comments on page 154, including the references to Grosse et al. 1992, Schroeder 1989, Dacey 1981, 1989, and Sorrell 1991. 

 

Habitat view for an ice-bubble “cloud” associated with a dead and downed submerged log

Habitat view for an ice-bubble “cloud” associated with a dead and downed submerged log

Somewhat as a complication and/or a clarification to the speculations about the ice-bubble donut rings associated with some of the tree bases, I also saw and photographed a series of ice-bubble “clouds” associated with inundated dead and downed log features occurring on the forest floor.  I doubt that tree stem heat and/or tree photosynthesis issues are involved with these ice-bubble clouds, so for the moment, we’ll have to scratch our heads together about the cause and significance of these ice features. 

Close up view of an ice bubble “cloud” associated with a submerged dead log

Close up view of an ice bubble “cloud” associated with a submerged dead log

 

Questions: 

1. Where did the gases encapsulated in the bubbles come from?  Some potential sources seem to be: a) gas escape from fine (or larger) tree roots; b) gas escape from root mycorrhiza; c) soil bacteria; d) aquatic algae and/or bacteria; and/or, e) gases already in the water column. 

2.  What causes the non-bubble zone, and its width, immediately adjacent to the tree stem? 

3.   What causes the radial width of the ice-bubble zone, and is this related to the size of the tree stem? 

4.  What limits the outward extent of the ice-bubble zone? 

5.  What gases are encapsulated in the ice? 

6. What influence might a moss cover on the base of a tree stem have on this ice-bubble phenomenon? 

Related Phenomena (?): 

1.  Is the moss growth that is often found on the lower portions of tree bases influenced by insolation heat derived from the tree stem? 

2.  Are snow melt-rings around tree bases related to these potential gas transport issues? 

3.  Do the root wad features on the root systems of sweetbay magnolia (Magnolia virgniana) and/or tupelo gum (Nyssa sylvatica var. biflora) trees serve as heat receptors (i.e., via insolation) to facilitate oxygen transport throughout their root systems? 

4.  Do the hypertrophied lenticels on the roots of the above tree species serve: a) as oxygen intake points when the lenticels are exposed above the water surface; and, b) as relief valve release points for oxygen (and other gases) when the lenticels are located below the water surface, thus potentially facilitating oxygen transport to the rest of the root system? 

5.  Do the knees on baldcypress (Taxodium distichum) tree root systems also serve as heat receptors to facilitate oxygen transport throughout the root system? 

6.  Is there a critical distance relationship between the location of individual baldcypress knees (i.e., based on heat and gas transport properties) if these knees do act as oxygen “pumping/lift stations/transfer points” between the tree trunk and the outer limits of the tree’s root system?      

 7.  Does photosynthesis and consequently oxygen gas production occur on the surfaces (i.e., cambial layers) of cypress knees located above the water surface? 

 8.  Do buttressed tree bases and fluted roots function to provide more heat for tree stem/root system gas transport purposes than do non-buttressed tree bases (i.e., because of more surface area exposed to insolation)? 

 9.  Is there some “non-random” orientation of tree bases, fluted roots, cypress knees, etc. such that the surfaces of these features can capture more insolation to provide more heat for root system gas transport (i.e., especially during the “winter/non-growing season)? 

 10.  What are the cooling effects, if any, of moss growth on tree bases in relation to the capture and transfer of solar insolation? 

 11.  How important is the sun’s insolation heat at a tree’s base in relation to: a) heat generated by photosynthesis; b) light reaching the tree bark cambium layer; and, c) the shading (i.e., light reduction and/or wave length impacts) of moss growth on tree bases? 

Ice bubble donut ring

Ice bubble donut ring

 

For now, this seems like enough to “mentally chew on”.  Bon appetite !! 

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