Wow, -9c in the sub-tropics? I dont think we get that very often in our 'alpine' regions here...
We had our coldest morning in 5 years today, with a chilly 4.4c, but by the time I left for work it was t-shirt weather...
Just twice a century (or a bit more) we had -9º C, but I had to mention this because a forest should live "forever" ;-)
Usually frosts are -4º C, or some years -7º C, but with a good grove of trees, water ponds, rocks and so, we should be able to keep the trees growing. Dont you think?
Today we had -1º C. Winter starts in 4 days
I agree that Eleagnus is a very tough family. Start with Oscar's So-Shang, Taiwan Sweet Olive, Goumi and the regular Autumn Olive. Most need male and female, but I think all are very forgiving in their care, fertilization and water requirements and bear heavily.
Great, we dont have any of these trees, will have to get seeds
I would also stick in a self-pollinating carob, Red Shahtoot Mulberry (its dwarf and non-weedy - must be grafted), maybe Japanese Raisin, Loquats, Nuts (Pecan, Chestnut) and for a long term project I would stick in a few Bunya nuts near a fence line.
Great for this non-weedy mulberry!: we have japanese raisin seeds, some loquat (here we call them níspero) trees too (near the forest garden), they will be fine; and there are some normal nuts and almonds, we have to get some non-grafted pecan, etc. Very nice this bunya (Araucaria bidwillii), I loved it