Do you know what cultivar it is? A good number of JM's have a rather narrow, vase-shaped habit - the crown never gets particularly wide - and some are even quite columnar in habit. Before you undertake some random pruning exercise, it would be a good idea to identify how YOUR tree would normally prefer to grow :-) In general, JM's are approached with a very light hand when it comes to pruning. You just want to enhance the growth habit, not really alter it. Some light canopy thinning, removal of any dead wood and maybe the removal of a lower or wayward branch or two. btw, what is all that growth from the base? Are those root stock shoots (below the graft union)?? That would be where I would focus any pruning efforts for the time being - just get that cleaned up so you have a clear trunk upto where the major branching begins.

By the look of the surrounding landscapes, you appear to be in a pretty sunny and hot location. I would substitute an organic mulch for the rocks - better for the tree in terms of insulating the roots against the heat of the sun (and reflected heat from the rocks) as well as a greater ability to retain soil moisture.

Just an FYI but full-on sun in hot and possibly dry climate (SoCal??) is not a great situation for Japanese maples. Prepare for your tree to experience some ongoing climate stress which could affect the way it grows and develops.

And any further pruning suggestions we might consider would need clearer, close up photos of the areas of concern.

Due in part to the potentially tough situation if It were mine I wouldn't do anything at this point. If a few branches start rubbing or die later then I would probably do something about those. Often after these trees develop for a time and become dense on the outside small interior branches die and dry out, can actually be just snapped off.

in my world.. all touching crossed branches are removed ... one or the other ... looking at which is heading in the direction you prefer ... [not knowing where you are.. i dont know when you do that]

which brings us to the question of what is your goal with this tree ...

do you want a bare trunk for a number of feet .. if so.. you would start taking some of the lower branches .. to expose said trunk ... i would never go whole hog and just denude it up 5 feet ... pruning.. in my world.. is a lifetime project ... do a few.. wait a year.. etc ...

'

which leads us to another issue.. of whether this is a grafted plant.. and whether any of those very low branches are coming from understock.. and not the same plant as above ....

i see a palm tree behind .... lol .. where are you ..

i am surprised you had no leaf loss on such a large transplant ... surrounded by heat retaining stone .... you must have done something right ...

soooo lets discuss what your goals are ...

ken

I agree that it seems like a hostile environment for Japanese maples.

I would be careful about suddenly exposing too much trunk to the sun. Like Embrothrium, I'd leave it alone for the most part for now. I don't see any major crossing branches and the lowest leaves look just like the rest so it doesn't appear anything is coming from below the graft.

mike

think I see another issue..it's planted too deep..don't see any basal flare..

planted too deep.

what cultivar?

I am going to assume it is just plain old acer palmatum. It needs crown raising.... Bad!

see link

==>>>http://hort.ifas.ufl.edu/woody/documents/raising.pdf

It also looks to have a co-dominant leader, so will need subordinate pruning as well (after you perform crown raising).

1. Photos are not close enough to determine if it is planted too deeply or not. Root flare may not be visible due to the rock mulch.

2. Any familiarity with Japanese maples would indicate that "crown raising" is not a requirement for these trees. Many selections grow with very low branching systems and in many cases that is a very desirable trait. I would be concerned about the growth emerging from very low on the trunk - if a grafted form, it needs to be removed. If non-grafted, it still needs cleaning up or the result will be more of a shrub than a tree.

3. Japanese maples (really ALL maples) are a decurrent species in that they do not develop a leader. So concerns about "co-dominate leaders" are irrelevant. And since they are relatively small growing trees, that sort of branch formation - extremely common with many cultivars - pose few of the structural concerns or issues their much larger growing cousins may exhibit.

I personally, would remove the Y in the branch (I did on mine). You should remove a good deal of the lower branching seen on this tree, unless it is supposed to be columnar. Overall, the gravel is a bad idea because it reflects sunlight onto the tree causing leaf damage. In severe cases it may reflect enough heat onto the tree to completely defoliate it.