Can several people explain to me [per the advice given here in another thread regarding not adding soil on top of the root area of a mature Bridalwreath Spirea shrub] about adding soil on top of the root area of a tree [in my case a common type of spruce]. In our strata we have a raised earth berm of 20 years duration separating the grounds from the street, and on that berm various conifers have been planted, most of which have fortunately done well. I have only been here about 4 years so have not seen the whole picture. It is irrigated, but tends to be dry and now very root-bound. Mainly substantial cypress and cedar type hedgings and trees, and pines grow on it. Sorry for not being more specific, but I don't know all the tree types here well, being originally an East Coaster. A previous owner also planted some spruce behind our unit, on the berm, which have grown substantially, 30, 40 feet tall and maybe 4 or 5 of them...to help protect from traffic sounds and street view, etc... A couple of years ago our landscaper's worker excavated some soil away from our unit's foundation [it was mainly spent mulch and dry and powdery, but some heavy clay earth too, and I wanted room to spread some bark nuggets as a trim] and dumped it on the berm, around several of the spruce root area, fairly close to the trunk but not up against it... it was not a huge amount of earth, but maybe 2 or 3 wheelbarrows full altogether. I wondered about it at the time. It is still there, piled in some lumpy bunches about 4 inches high, around the spruces' general tree root area. The roots, however, extend further out than that, and are visible further down the berm and well exposed to air and not covered, etc... One spruce is now dead or dying, and needs to be removed -- this happened gradually over this past year. A result of the earth-dumping? The dead one is leaning rather drastically to one side, and a still-healthy-looking spruce is also leaning dramatically in the same direction, and leaning on the dead one... the landscaper says he can remove the dead one but I am wondering what will happen to the living one. The root area does look a bit loose on the windward side. We have high winds in this area when in a windy cycle, and our theory is that the wind loosened the trees -- this happened during this year. There are several tall narrow crowded-in spruces with them, which should perhaps be removed too, which don't look too thriving but I think it's owing to over-crowding -- the dumped soil is not in their root zone. In fact, the dumped soil is not specifically under the dead tree at all, but in the general area... Should we remove the soil, along with the dead and non-thriving trees, or do you think it is not really a factor... it isn't a huge amount. Curious.
Pictures of the area in question would help in determining what might have caused the tree to die. But in taking a guess as to what you have posted I would say a combination of factors were to blame and most likely the tree being partially uprooted by a strong wind sounds to be the most likely suspect. spruce trees grow deep tap roots and feeder roots about as long out ward as the tree is wide. These roots can become exposed to the sun (soil surface) over time do to soil erosion as well as just over all size. But as long as this happens over time is is normally not an issue for the tree. But being on a berm with the tree being on such a lean makes me think that the main trunk might have snapped under ground if not fully but slightly were as the other living tree did not (saved via leaning on the now dead one) Adding soil around shrubs and trees can be done (it is done with mulches all the time) but should not be done to drastically (no more then 6 - 12 inches tops at any one time. Massive changes in soil grade (like when building and landscaping for a new home) can cause issues for a mature tree or shrub and cause it's death and thus it is recommenced that a barrier be put around the bases of such trees to protect them.
That relieves my mind a lot, but I will prepare some photos and upload them tomorrow. I would say there has been soil erosion on that berm owing to the fact it was man-made to start with, 24 years ago, and goodness knows with what materials underneath... my husband is saying he is betting that a lot of the trees are going to die, owing to the lack of nutrients as the roots get bigger and more entangled, within 10 years... but I'll upload photos.
This is a situation where you might want to look into some erosion prevention if you really like your trees (I'm guessing there are better options than turf but I haven't drank any tea/coffee yet so I can't think of any). Maybe some sort of ground cover or some shrubs on the side that gets the most wind to add a little to the stability of the structure. I would not do anything too close to the base of your trees though on that front. If it is man made and eroding then clearly this can and will happen again to your trees the next time you get weather like that. If you want the rest of your trees to be less spindly then yes you will need to cut down on the overcrowding. You want a good amount of space between the trunks I believe? Also make sure they do not try to dig the roots out when they remove the dead one - those roots will help with the erosion thing even if they are no longer alive and they will damage your live trees if they are close enough for the roots to be tangled as your husband suggests.
