This is one of the most common questions on the "Trees" forum so I suggest you try posting it there. From a landscaping/gardening perspective (not sure I know the difference and not sure I care), whatever you plant is going to be affected by the rocks. Rocks tend to absorb and reflect back heat, which can add stress to the life of neighboring plants/trees. It's not a deal breaker, but it is a factor. If you do not like the rocks, I would remove them. Rocks also collect dirt and debris between the spaces and then seeds get in and grow, so have to be weeded. Not too much different than dirt, but they are far from low maintenance.

From a landscaping perspective, what you are describing is sort of like a "mixed shrub border" which is an artful mix of shrubs, perennials and trees to create a harmonious view. There are many ways to achieve this, and with a "part sun" condition, you have a lot of options for plants. Just make sure you select ones that can take the conditions, and also as you are planning and executing your plan, take into account the mature size of the shrubs or trees. Don't plant them too close together or too close to the fence so that when they are mature, they do not look good and don't grow well because at that point they are too close. So a mixed border looks kinda sparse for the first few years. You can fill in with quicker growing annuals or other plants that you plan on yanking when the backbone plants get big enough.

What are the dimensions of the area?

I would be very sure that the plants you choose will do well in your climate and soil--conditions quite different from zone 5 in the east.

The rock is 6' deep on all sides. The yard is 60' in the back and 50' on the sides.

It would be troublesome to get rid of the gravel mulch since it continues under the fence and into the surrounding yards. If you got rid of it, you'd need some kind of curb-like barrier below the fence in order to keep the neighbor's gravel from spilling back into your yard. If you planted groundcover within the gravel mulch bed, it could spread and cover the mulch so that it wouldn't be seen. In general, the bed is not deep enough for shrubs unless they will be small and something that you keep clipped.

The yard is small. It's not likely that you would want to give up much of the interior lawn space. This pretty much suggests that tree planting will be primarily confined to the perimeter, with the corners of the back yard being the likeliest places to be planted first.

You like the fir tree because of the pyramidal shape with its foliage sweeping the ground? Keep in mind that with age, such a tree is going to become fairly wide at the bottom. In order to keep yard space, it would eventually mean removing lower limbs so that you could walk below it. Are you going to like it that way? It would either be that or having it consume a huge amount of your yard "floor" space.

Since landscape design is a PLANNING function, and you intend to make changes to the deck, why aren't you incorporating that now into the planning of the rest of the back yard .... so that all the things fit and work out in the end...?

1.) I agree the gravel is a bad idea. It tends to really heat up in the summer sun and gets mixed into your lawn.

2.) A lot of people seem to assume that you have to stick trees along the fence and and against the house. This limits your options and crowds trees. I think people should be more willing to think outside of the borders...you can put a tree in the middle of your lawn.

3.) I don't think you have room for a conifer. Most conifers look stupid if they lose their lower branches...if they keep the lower branches they would take up a lot of yard space.
4.) If you keep the gravel, the quickest "bang for your buck" would be planting prairie perennials in it. Liatris, Baptista australis, etc.
5.) Have you thought of planting vines along the fence? Put a trellis up against it. Be careful what vines you use, many vines are invasive. Doesn't use a lot of yard space but gives you a green backdrop and potentially flowers fast.

Is that gravel (i.e., uniform, decorative) or is it rubble left over from construction?

it's just so odd.. I've never heard of landscaping filler but if it's something the developer paid to install I'm sure a few more yards of sod would have been cheaper. What's under it? There must be a barrier to keep the line so straight? i would find out what the reason for it was. Drainage?? Does it have resale value? How would one get rid of it?

Are you anywhere near Denver? If so, visit the Denver Botanical Garden for some ideas of plants and styles, including a kids' garden and this may help with ideas of what you like. Right now you have such a wide open request that it's difficult to make suggestions. I agree with Yardvaark that you need to plan the deck along with planning the backyard. Installation can be in stages, but the plan should incorporate everything. For instance, tree placement and selection will depend on where your deck is and whether you want it in sun or shade. Will you be irrigating the lawn? If so your planting choices need to consider the amount of water. How old are your kid(s) and how long will the play structure be there? What will follow - do your kid(s) like soccer or baseball or dress-up type play? Do you need storage space for a lawnmower, trash cans, yard toys, etc?

As far as the rocks go, do you like them? Do they continue onto the other side of the fence? Is the area weedy? Do your kids play in the gravel or throw it? If you like the border as is, leave it. If you don't like it or it has problems such as weeds or it being thrown, and the gravel continues under the fence, I'd remove it to within a few inches of the fence and reinstall the border to keep the few inches of gravel contained. This will keep the base of the fence dry and reduce soil splash onto the fence. Then you can plant outside of that. If you want a border of plants, it will need to be deeper, at least in some spots such as the corners as was suggested above. You also can plant a deeper border on one or two sides and go without a border on the remaining side(s) and place the kids' play structure there, closer to the fence. Also consider planting for the kid(s) - a bean teepee or a large arching shrub such as a forsythia or Physocarpus/ninebark or Philadelphus/mock orange that makes a great fort as well as breaking up the expanse of fence.

"A lot of people seem to assume that you have to stick trees along the fence and and against the house. This limits your options and crowds trees."

Users don't usually want tree trunks in the middle of places that might be used for play or other activities, or where the trunk or foliage canopies are likely to obstruct desirable views beyond (which usually the back half of one's back yard is.) It's the same principle as avoiding posts and columns in the central area of a building room. Usually, users want these spaces free and clear.

Kitasei, the rocks are not actually landscaping filler. They are river rock mulch (as opposed to wood mulch) on a prepared shrubbery bed, separated from the lawn by metal edging. It's extremely common in the Denver metro area. When properly planted, these rock mulched beds are quite beautiful. It's just a different look from that seen on the east coast.

ColoradoLime, you haven't mentioned your elevation. From what I am reading about the Abies koreana 'Horstmann's Silberlocke', it's mature width is 10-12', which might fit in a corner of your bed, however, it's not recommended above 6000 ft.

If you're at a higher elevation, you might take a look at some of the Juniperus scopulorum cultivars. There are a number of very slender (3-4' wide) choices. You could even do a grouping of 3 in a corner with a groundcover at the base. Denver Botanic Garden has 2 beds with 3 surrounded by perennials. Stunning!

One observation I would like to share - our daughter and her family are in a new home in Castle Rock, with an almost identical backyard setting as yours. ALL of their adjoining back-fence neighbors have planted trees within 2 feet of their own fences. As a result, our daughter isn't planting any. They are surrounded by trees! It appears that yours is also a new development. Just something to be aware of.

Some things to consider (keeping in mind your elevation):

Evergreen shrub - dwarf pinyon pine

Evergreen tree - Picea glauca 'Pendula' (weeping white spruce) - 20-24' tall x 3-4' wide. This would be striking in the corner and definitely something your neighbors are not likely to plant.

Evergreen tree - Juniperus scopulorum 'Woodward'

Deciduous shrub - 'Mini Man' dwarf Machurian viburnum (good for small beds)

Deciduous shrub - Spirea - there a many cultivars that remain small enough for your space and have lots of color during the summer and the fall.

Perennials - too many choices to even list. Perennial heaven here!

Have fun!

With regards to the stones, gravel, rock material, there really is no right or wrong. If you like them and they serve a purpose for you, then leave them. But just be aware that they will create a micro-climate where they will absorb and reflect heat, which will affect which plants can grow and thrive planted next to them. I have similar rock around the front of my house with southern exposure. Some plants do OK there, others do not. I would suspect, for example, that clematis would not do well there because it needs to have it's roots shaded. That's the advice, think about the effects of the sun, rocks, fence, neighbors, use of the yard, heights, views, etc. before you buy and plant. You choices should start with what function you want them to play and what conditions you want them to be able to survive in, and hopefully thrive. That's the first step in narrowing down a tree choice.

I would not feel cheerful looking at naked fence and rocks. You could start by doing something like this.

I don't really like the rocks either. Removing them would be a big task. Do you need low water plants?

I'm not sure if there is an easy solution to this but have you experienced using garden design software. There are plenty of resources online, but to be honest some are difficult to use. Maybe they could assist in your project.

This looks like it's probably a thread that has been abandoned by the OP. She hasn't been back to react to any comments in nearly 10 days (or any of the comments I posted on Oct. 6!)