I'm doing some excavation around the base of a Garry Oak in preparation for a new dry-stacked retaining wall and pathway. The tree is about 100 years old and when the house was built in 1968, back fill was piled behind the tree and the back part of the trunk became buried in soil. (see pic) As this part of the trunk has been buried in dirt for such a long time, I'm wondering if I might be exposing the trunk to danger by exposing it. I'm also encountering a few roots, max 1.5 inches thick and am wondering if it is OK to cut these. Your thoughts are appreciated.
That is one nasty back fill, and a high risk tree to do it to. Good post. The roots you are finding are not structural, and it looks like you have a fair bit more digging to do before you find the root flare and structural roots. I recommend having an area risk assessing arborist by. The typical Garry Oak failures we see are as a result of decayed roots resulting from anaerobic soil conditions, Armillaria root rot, or a combination of those and other factors.
Yes, trees that are to be retained with reassurance are never subjected to cuts or fills. As the roots go, so goes the top. Most fully developed trees and shrubs have more root than top. Roots grow in the existing soil conditions, new soil conditions brought on suddenly may kill the roots. And the tree.
Thanks ryansenechal and ron b. I've had the arborist over twice to evaluate the safety of the oak regarding a potential renovation to that side of the house. His advice was to hand dig any nearby footings. When asked about the roots, he was equivocal, but suggested cleanly severing roots rather than maiming them. My most pressing concern, as I am in the middle of repairing the retaining wall, is regarding the back fill that surrounds part of the trunk. My instincts tell me that I could carefully remove the soil and hopefully the trunk will harden after having been buried all these years.
If new roots have been produced higher on the trunk - in response to the previous fill - do not dig below the level these occur at. Or remove these.
If you have a permit to excavate that close to the Oak, the terms in Victoria/Saanich/Esquimalt/Oak Bay are that a Certified Arborist performs any cuts and excavation within the critical root zone (18x DBH). A *proper* second opinion is a root collar examination with air spade, sampling for decay on critical roots, evaluating overall risk followed by recommendations on actions. Any recommendations beyond that, specifically those of the internet variety, are a shot in the dark at best. Prescription without proper diagnosis is malpractice -- this forum is famous for it.
It's hard to know when I'm digging if roots are from the snowberry or photinia that surround the oak. Regardless, I'm just going to disrupt as little as possible for this retaining wall. I didn't know I was going to need a 2nd opinion before renovations, (our Certified Arborist failed to mention that) but our reno plans are on hold anyway. The tree is within the building envelope, so technically, I'm not obligated to keep it, but we like it and are trying to do the right thing. This tree stuff is serious business, but it's great to protect our heritage trees. In Vancouver, off-shore buyers are removing all the trees from their lots. A 200 fine is nothing to them.
I suggested a 2nd opinion based on the Arborist's recommendation that you perform the work. That's not typically how we do things, as per bylaw and liabilities. If you would like to review the Victoria Tree Preservation Bylaw, it is available here -- http://www.victoria.ca/common/pdfs/bylaw05-106.pdf
It seems to me your problem is, if exposing the trunk will harm the tree. To the contrary. The trunk should never be buried in the soil. Exposing the trunk can only strengthen the tree, not to weaken it. It is good thing to do. By doing that you can also find out if there is any damage to the trunk, that could otherwise remain undiscovered and cause problems in the future. If there is, it should be assessed and dealt with appropriately. The roots that you may encounter above the root flare are not structural roots so cutting them will not create any safety risk. You may find helpful (although not entirely relevant to your problem) the information at http://www.dirtdoctor.com/view_question.php?id=484
Thanks for the link, ryansenechal. Am glad that Victoria has these bylaws. Sundrop, Thanks for the great link. I'm inclined to think, if there has been back fill, even though it was 40 years ago, to try to remove it. I did that today, being careful not to damage the softened trunk. At about 1 1/2 feet down, I encountered a few small 1/2 inch roots that had started growing from the trunk. As you suggest, they are probably not essential. I will proceed carefully. I've remarked, since moving to Victoria that most Garry Oaks appear to be coming straight out of the ground, i.e. have no root flare. Is this a species trait or have people been burying the flare?
Many Garry Oaks in the area have been growing well before the lots were developed, or redeveloped or re-landscaped. So in answer to your question, yes, many of them have had root crowns buried. The most important follow up from your excavation is that you monitor the newly exposed bark for signs of splits in the bark or plates sloughing off, fruiting bodies forming or insects penetrating the bark. Keep an eye on the crown density while your at it. These are the early indicators that things are going wrong.
Progress Am making progress with uncovering the trunk. As you can see from the pic there was indeed at least one root circling the trunk - a potential strangler. Haven't found the flare yet and may not be able to go that far due to the the grade of the adjacent walkway, but hopefully the tree will be happier with what I've done.
It is not true that you always want to remove fill that has been in place around a tree for some time. If you find a substantial tier of new roots made in response to the fill you do not want to cut these off. These would indicate the tree has survived the change in grade and grown a new tier of roots in order to cope with it. Cutting these off now would just serve to create a new crisis for it.
Thanks Ron B, I guess it depends what you call substantial. I've uncovered tiny roots of a few mm and few new roots of about 1- 1.5 cm, and these are circling the trunk, which, I understand could choke the trunk as they increase in size. There is already some minor indentation into the trunk from these circling roots. I heard from the arborist yesterday "These type of adventitious roots, can often indicate that the original roots of the tree have started to deteriorate due to the fill and the tree is putting out new roots to compensate. While these new roots can keep the tree looking healthy, they tend to not offer as much support as the original structural roots." So, structurally speaking he said it was OK to cut those off but to monitor the tree during high wind to check for stability--i.e. any new movement in the trunk base. Regardless, I don't seem to have reached the root flare yet and likely won't be able to get that far due to the grade of adjacent pathway. Thanks again for your thoughts.
Small girdling roots I would remove. What should be retained, if encountered, is a whole set of substantial roots all on the same, higher level than the original flare - that are obviously a start on replacing that original set.
If I were you I would shade the exposed part of the trunk for a year, without obstructing air movement. It could help a smooth transition back to natural conditions. “Sometimes I come across a tree which seems like Buddha or Jesus: loving, compassionate, still, unambitious, enlightened, in eternal meditation, giving pleasure to a pilgrim, shade to a cow, berries to a bird, beauty to its surroundings, health to its neighbors, branches for the fire, leaves for the soil, asking nothing in return, in total harmony with the wind and the rain. How much can I learn from a tree? The tree is my church, the tree is my temple, the tree is my mantra, the tree is my poem and my prayer.” - Satish Kumar
Thanks for your thoughts Sundrop--and the poem. Combining the oak's location between two houses, shade from the remaining backfill and it's own canopy there won't be much sun on the newly exposed trunk.
Note also that leaving it in a well, with the rest of the roots still under fill does not do the whole job. If it seems like it would still benefit from being returned to the previous grade all the accessible fill soil should be taken off.
Yes. I'm wondering about the well I've created. I did not reach the root flare but have stopped digging because, as has been suggested, new roots formed above the flare might be vital to the tree's health. I have removed some new roots that were wrapped around the trunk. I can't remove all the backfill because that's simply too big a job, wouldn't jibe with the adjacent landscape, and it probably has become a resource for the roots. I would estimate that it's about 15 yards of soil. It would have to be removed by hand as the arborist has discouraged the use of heavy equipment above the tree roots. The backfill has been there since 1968. The tree, according to the arborist is about 100 years old. I sure hope I haven't damaged it. I'm going to line the well with stones (? plus also landscape cloth) to keep the soil and snowberry at bay and will probably apply crushed gravel on the surrounding ground as with the adjacent walkway. I'll post more pics soon.
