Sun Burn

klimbinfool

klimbinfool

Location
magalia california
Ok , we all know how sunburn on trees is caused, but can someone explain what is really happening.With the ever growing varieties of Maples, I'm finding that we have to be very picky about what we take along the trunk and how much is atken from the Western exposure, other wise we find sunburn occuring. For example , if you take a 4" dia tree and cut a 1 1/2 " dia limb off the trunk at waist height they seem to sun burn from the cut down.Whats happening there ? Is there something occurring from that cut down to the root system ? doesn't always burn from the cut up.

thanks
Greg
 
Greg, that is a good question. The only answer I know is that, when the hot mid-day sun heats the bark and fluid up and then sets quickly, the drastic change in temp causes the bark to crack and even split. I once was told that this is accelerated when the season is changing. Anyone heard other reasons?
 
Greg, I fyou have a 4" DBH tree, the circumference is about 12". You cut off a 1.5" dia limb and you just made a hole in the cambium that's about 12% of the circumference. That's a huge interuption of the cambium. What you're seeing might be dieback from the wound and not have anything to do with sunburn. Could you try doing some subordination on a control group to see if that makes a difference?

I think it was Don Roppollo who did his MS work on frost cracks in transplants. If my fuzzy memory is correct, he found that the biggest variable for cracks or not was watering the trees well, especially in the fall. The trees he looked at were near Milwaukee so they have a real winter.

Tom
 
Greg

I don't know if this helps but in the winter, bark cracking can be a problem caused but the rise and fall of temps. At night the temps drop and cause fluids in the tree to thicken. Then when the sun rises, the side that is getting sunlight tends to warm up quicker causing the fluids to expand and crack the tree. In the late fall we would always wrap our newly planted trees to help insulate the trees from sudden temp changes. This seemed to stop most the problems that we were having. If you are seeing signs of bark cracking in the spring, the cause may not be from previous pruning, but from a hard winter.
 
I've talked with Janna Beckerman at the U of MN about that article. I don't believe that using tree wrap has anything to do with reducing frost cracks.

Let me know what you think about this. If tree wrap, which is kraft paper with a layer of goo inside. If tree wrap is such a good insulator would you wear a jacket made of it when it gets cold? Now, it might work OK in Mesa, but, believe me, even on a night like tonight in the Twin Cities, you'd be darn cold. If tree wrap were made by Marmot, it would be a blanket of 600 fill prime down. If it were made by 3M it would be Thinsulate. The catch with insulation is all that it does is capture heat. If the tree is cold during the day, no amount of insulation will keep it "warm".

I would like to see a control group study in a cold winter climate to show the effect of tree wrap. So far, all I've ever heard is ancedotal folk tales being repeated.

Shigo says that frost cracks can always be tracked back to a wound of some kind. Maybe a mower bight or a broken root. Maybe a bad pruning job.


Tom
 
Good point

I agree that tree wrap can only capture heat.

We have a whole different problem with sun burn here in Az as I am sure you can imagine. Citrus being the main one.

Juiceman
 
I see it mostly on south to west exposures after line clearance work.

Not knowing when that work was done in the season, I can only guess as to the cause (s).

Since Greg is seeing it in Chico, CA can we assume that it is not the huge swings in temp we see up here? Maybe ask Greg?

I've touched bark exposed to the sun for long peoriods of time and it can get quite warm. Is there any data as to what temps cambium of given trees can endure for hours at a time?

Another thought for Greg, do you know the seed source for the cvs being used by Chico? Could it be that this is, say, an OR or WA adapted cvs and you need something developed for your heat?
 
Tom,
Thanks for mentioning what Shigo says, I've been waiting to see if anyone would bring that up. I recall Alex saying that on numerous ocassions. After hearing this I started looking closely at "frost cracks" and many times I have found visible defect some where in or near the crack.

Greg,
In reference to your original post; I have dug up trees of the size you mention that had similar symptoms. Most of the time there was a large root that had been cut during transplanting. This usually was in direct vertical alignment with the cut branch. I first started looking for this after hearing Shigo talking about this very topic.

As for the Citrus trees, I think the above applies to "burn" on the lower trunks. In this situation I think there will be a prior injury which may or may not be visible. I have seen numerous citrus that had "burn" on limbs. It has been a few years since I worked in FL but if I recall correctly most of it was in conjunction with heavy pruning. Many times the "burn" injuries are expanded to near by pruning cuts.
 
Tom

Here in Az heavy pruning on citrus in the months leading up to summer can be deadly. We do all of our citrus pruning right about this time of year. Many customers want to control the growth of there citrus by the old apple orchard method. Bascially extreme pruning. I have seen many citrus trees prunned this way and they are fried. The bark has peeled leaving exposed cambiam layer. The old time method to protect the trunk is to paint the trunk of the tree. This of course causes numerous of other problems and is generally not recommended in most cases. The best solution is not to raise the canopy more than a foot above ground, and to limit thining cuts by 10%.

So Greg, I guess there is a direct correlantion with heavy pruning and sun injury. At least on smooth barked trees here in the desert.
 
Thanks for your replies guys.

John, thats good idea and I belive we are trying to find the most suitable Acers for our area. Temp changes can be very radical here. For example last year we went from the 40s and 50s to 100s in one week . We all died of heat exhaustion.

Eric, I would agree with you and the root cuts inline with the limb or limbs removed , but it always seems to be on the South to West side of the tree. I couldnt see the guys who are planting always pruning the roots on thats side of the tree. However , your point is valid and is somthing to keep in mind for future reference. I always like to try and find out ( why ) somthing is happening .

Tom,
CAmbium disruption is a point brought up in our discussion about sun burn. I would have to agree with this . However , it may be a combination of both disruption and the baking heat.The tree is vulnerable at this area, but I'm not really sure until I do more pruning tactics like you mentiond.

I've been experimenting on some rgoups by just heading back the lower limbs. One that we know will eventially come off Leaving them for trunk dia. and shade.unfortunalty , some of these limbs are larger then we want to leave. Because of future visability, peds, traffic, height and everything else that goes along with street trees, these limbs will get or have gotten much larger then we would have liked them .Therefore resulting in larger cuts. Co dominant trunks, included lower scaffold are some of other reasons for larger cuts. 10,000 young trees are at are beck and call and we can only visit a third of them , if that , each year.

I appreciate your input and ideas. If you have anymore information I would like to hear it. More the merrier

Thanks
Greg
 
What about the 60+ year old trees after ROW work?

I've seen them with textbook cuts at 20-40 ft and dieback in line with the sun.

My gut feeling is that severe trimming in hot dry condittions can lead to cambial dieback in thinbark.
 
thats true John. I have seen some of that to, especially on Camphore and some Holly Oaks. We dont have many 60 year old maples yet , At least the newer varieties anyway. However, we have many old Silver Maples that never seem to have the ablility to compartmentalize after a lager cut and of course they are no longer aprt of our street tree program.

Greg
 
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