Producing on an Alaska south facing steep slope

I just moved to a home in Palmer Alaska, My back yard is overgrown in small birch tree's, 1.5-2 inches thick, 20' tall and between 10-20 inches apart.  The slope behind the house is steep perhaps 20% grade, and composed of a dense amount of fill stones between 1.5 and 2.5 inches in diameter.  There is  little earth but it's present.  I'd like to encourage bio diversity on 1/2 of this slope (about 1/2 acre) and garden on the other.  I'm barley a beginner when it comes to gardening.  In the end I'd like decrease some of the non-edible's and increase the native edibles around the area. (blue-berries, raspberries, salmon berries, watermelon berries, high and low bush cranberries.   We are getting ready to head into the  cold season and last night was our first frost. so I'd like to plan out my work for next year.  Due to the very long growing days and a short growing season I understand that gardening around here can be very productive, in somewhat of a sprint.  I was thinking i could do some terracing on the slope to get the gardens in.  I'd be happy to listen to any suggestions, or follow links to already developed information if you'd be willing to share.  

Some specific questions:
1.  would it be better to mulch the birch or keep them whole for a type of hugaculture, there thinner then I think are optimal.
2.  what are good ways to increase the amount of earth on this slope?
3.  I'm planning on harvesting berries from around the area, starting them, and then planing them.   Is there a better way to garner these plants?  that puts me about 3 years out from my first berry production.
4.  I'd like to do this in stages, is there a natural progression i should be focusing on?
5.  is there a better time of year do the clearing of trees?
6.  What are the questions I should be asking that I'm not?  (I'm super new to this).

Thanks for the help and suggestions.

I'm not a fan of having trees near gardens. It seems like they suck fertility and moisture from the garden. My general strategy is to not plant a crop for a distance equal to the height of the tree. So no attempts at gardening within 20 feet of a 20 feet tall tree. Many species of berries will produce fruit next summer if transplanted this fall.

What direction does the slope face?

I personally would mulch the birch let it degrade into soil  as for the berry bushes they all transplant from the roots so don't bother with seeds, roots and or hard wood cutting should work better.

David

I have a pretty small plot (1acre), my urban setting has some restrictions flattening the trees. So I'm working with what's available.  I'd prefer more land but I'm working withing the confines of civilization.

Thank you both for your input.