Hi
First a few conversions for those of us who use English units. You have 4,000 m^2 of land, about an acre. At an elevation of 920 m, or 3,000 feet. Your warmest times are between 15-20 C or 60-72 deg F. You get 7 to 8 cm of rain per month, which is 3 inch a months (36 in a year). 2 meters of snow is about 6 feet. And lastly 10cm of soil is an average of 4 inches of soil before you get to gravel. OK. I think that is it.
Let me just say one thing, I love Spruse (Sitka, Englmans, Blue, etc). I like the way it looks, and how prickly it is and just everything about it.
So, I am going to make a suggestion. You know Spruce grows well up there. Why not plant some more. If they are sub-alpine or alpine they will grow ultra slowly, I get that, so it may be 6 or 7 decades before the timber is merchantable. However, not everyone is in a situation where you can grow bananas and oranges. You can try, but it may be more efficient to try other things that will be as bountiful as a permiculture farm in Florida. Remember, we are encouraged to look at a problem as a solution.
The keys to growing a lot of fruits and vegetables is sun, soil, water and some time with each. You have lots of water but little else. At first I was going to say, you need to build the soil. That is still true, but the method may be a little unconventional. I would normally tell you to chip up some of the dead wood and put that all over your property, then take the rest of the dead wood and make hugel piles. However, you have no soil to cover the beds (yea, you can truck it in). I would say, plant your Spruce on a grid 4ft x 4ft (1.5mx1.5m) everywhere on your property (use seedlings, not seeds). What ever grows, grows, what ever dies, dies. Do not water these trees (you get enough rain). Now, Your soil can only hold so much water before it gets to the gravel. This is fine, because it will come out in a stream for the neighbors down hill from you. However, you do want more water to be retained on your property. This will be done with years of soil building. This building must be slow and steady say 1/3 of an inch (1cm) per year.
So, what can build the soil, and what is usable to you or trade able (
sell able) or others over the next 60 years? Let's look at the trees themselves. You can cut branches and collect cones and make Christmas wreaths. I am not sure people will like such a prickly wreath but it is worth a try. Another thing is, you could create a Spruce nursery, that grows seedlings of Spruce and other local trees. You could become the local Spruce expert or even the regions expert silviculturist. Neither of these things will build the soil, however.
So, we come to the dead trees on the ground. Some, I would inoculate with the local edible mushroom species. They like the shade an damp areas, the forest is great for that. Some of the other dead wood I would chip up and broadcast throughout your new forest of Spruce. Apply it sparsely and do not cover with soil. Eventually this will decay and become spongy pieces of soil. Do that every year with the dead wood. No dead wood? Cut down a tree or two and make some chips. Shear the trees and chip up the branches. You may leave 1 or two dead trees (snags) standing for habitat for wild animals. Eventually, the logs you are using for the mushrooms will be unusable. Chip these up as well and fall a few trees for the next generation of mushrooms. You can also become a local expert on mushrooms.
Want to build the soil even more? have animals
poop on your land. Here I would say, since you are up in the mountains, you are far from big population centers. Because of that, I would say you have a few choices to get animals to poop. You can do wild animals or you can try your hand at animal husbandry. Now there is a bunch written about keeping animal in this forum and in other places. They talk about the virtues of cows, pigs,
chickens and so on. However, at your temperature range and elevation you may need to winter your animals for 6 months instead of the usual 4 months out of the year. It is generally maintained in permaculture circles to use a paddock shift method of pasturing your animals, which may be a little difficult to do in a forest, but your grasses will get eaten.
I would actually recommend fertilizer (and soil) be carried onto your property by wild animals. This is done by planting things that will grow in a forest at 3,000 feet elevation in acidic soil. These things should be plants that
deer, bear,
voles, moles and any other Czech mammal, bird, reptile or amphibian like to eat or gets eaten by. I live in the Northwest (Washington State) and I would plant Huckle berries, salmon berries, black berries,
dandelions (for the
rabbits) and rabbits for the raptors and so on. In a young forest I would place a few perches for the raptors, then as the trees get tall, the poles would not be needed. Put bits of string and other things out so that birds have extra materials to build their nests with. Try to satisfy their needs several feet from the house, you will not want a bear barging in your front door asking for dinner. You may even plant a thick row of Spruce or two around your house to keep larger mammals away from your house. Make a few piles of 2 -3 inch (5 - 8 cm) diameter rock a foot high or so as habitat for reptile friends. If you are a hunter, you could probably shoot a deer every once in a while on your property, but you do not want to tell the deer that this is a dangerous place to go. A deer on your property every 3 or 4 years would probably be best. You could also get rabbit and other small game almost continuously.
OK, What if you do this for 20 years and the soil gets thicker but it is not very dense with nutrients and still a bit acidic? In the northwest, we have stands of second growth Douglas fir that, if it is in poor soil it can make white truffles (very expensive). I do not know if a similar thing will happen for a second growth stand of Spruce at 3,000 feet. My point is, you may find more advantages to your situation 20 years from now as well, you simply need to be open to what the land is telling you.
Now, for those hugel piles. In this string, I see people recommend against it. That is up to you. The closest thing I would do, is have a South facing hugel green house. That is like a keyhole garden, where the entrance is on the south side of the garden. On the North, East and west side, I would pile rocks. This "U" shaped pile of rocks would act as a thermal mass for the plants within the keyhole. If South means down hill, then bring the level of the wood down. In other words, make the key hole entrance the highest point of the garden, to allow water to come in and be collected by the rotting wood. Some plants that do better in cooler weather will do great, and over the years you can get adventurous and experiment. Hugel beds build soil well, but like I said, you need dirt (or soil) to begin with. Shipping soil in to cover the beds makes for some expensive vegetables. Try to make soil on your property.
What about swales at the top of the property (and throughout)? Swales are a good idea for places that have a lot of soil for rain to soak into. Every month, this ground gets about 3 inches of rain on 4 inches of soil. Digging down (on contour or not) at the high side of the property, I would be a little worried.
First, It will not help with the water table of your ground. You basically have a 4 inch water table and another table 150 feet down (your well depth). A swale at the top may help the level you need to pump from in your well, but your land will not get any more continuous water feed that a swale usually provides.
I might even worry a little about a land slide. If I were to do anything on the uphill side, I would place a gabion (on contour), particularly if there are any channelized areas. I would use rocks found on the property. After a few years of catching some soil up there, you can bring some down further onto your property.
Did I tell you that I love Spruce?