I am interested to know if anyone out there in permies land has used Amur maackia (Maackia amurensis) as a nitrogen fixer as they've developed their food forest/woodland. What kind of success have you had? I am told or have read that this a very tough tree; nitrogen fixing, drought tolerant, and tolerates alkaline conditions. I know a city forester in central Wyoming was promoting this tree for residential use as it was tough as nails and could take the hurricane force winds, dryness, and alkali. This would seem to make it very suitable for the western states ( at least east of the Sierra/Cascades) and northern plains (USA). It seems to fit the bill as to being one of the larger nitrogen fixers that Paul Wheaton bemoaned as lacking in one of his podcasts about developing food forests. Our subtropical and tropical friends have a huge selection of woody nitrogen fixers. We in the cold temperate region of North America are more limited as to the variety of species we can use to provide long term nitrogen fixation in developing food forests. The wood is supposed to be good for fenceposts and uses such as that. It seems to have a lot of potential in providing nitrogen over a long period of time since it is relatively long-lived and grows taller than Caragana arborescens so it wouldn't be shaded out as quickly as Caragana would be as trees grow around it. Perhaps this is a plant we in the Northern Rockies should promote as a forest development "helper".

Maackia amurensis is a fairly common street tree in the Portland, OR metro area, and widely available at local nurseries. Both of those facts would tend to suggest easy culture. Sounds like a good one to play with.

As to your comment that the cold temperate region of North America is limited for large, long-lived N+ species, some of the following are native or proven in cold temperate N. America, and some of the others are sure worth trying:

Trees:

Several Robinias including R. neomexicana, R. pseudoacacia, and R. viscosa.
A bunch of alders, including A. incana, A. cordata, A. rugosa, and A. tenuifolia.

Large Shrubs:

Multiple species of the genera Elaeagnus, Hippophae, and Shepherdia that are pretty popular in Pc circles, notably E. umbellata, H. Rhamnoides, and S. canadensis, all hard to at least -40º F.

Equally hardy species of Myrica.

And then there are some pretty hardy (Z4-5) species in Cercocarpus and Ceanothus.

Really quite a smorgasboard!

Thanks, Leonard.

Interesting that Amur maackia grows well in rainy Portland. Talk about adaptable! It does sound as if Amur maackia has some real possibilities for helping build soil fertility as I develop my food forest (Helena area-northern Rocky Mountains zone 4 with psychotic spring weather).
Checked on the Robinia species and it looks as if Robinia psuedoacacia could work in this area as well. Are there any readers here in western Montana who are growing this? Interesting how it is adaptable to pH up to 8 or so. I see people are using or trying to use it in Idaho a few hundred miles from here. Robinia neomexicana looks more suitable for southern Rocky Mountain permies to grow. Robinia viscosa has some possibilities but the thorns sound NASTY!

Am using or will plant this spring, all three suggestions you listed Elaeagnus umbellata and Hippophae rhamnoides in limited amounts to see how they adapt to the Helena valley. Using plenty of Sheperdia argentea. I have a few old, poor condition specimens on the property but there are plenty in the area which tells me they would thrive with a bit of TLC, especially light ( the existing ones are badly shaded by overgrown Russian olives).

Myrica pennsylvanica sounds most interesting. I like the fact it's from a plant family unlike so many of the nitrogen fixers.
My experience in the Great Basin/high plains, Bighorn Mts. country earlier in my life makes me a bit doubtful about Cercocarpus and Ceanothus. Cercocarpus always appeared on very shallow soils with lots of rocks or very calcareous outcrops in Wyoming. Ceanothus was clearly a pioneer species in burned forest areas so the pH (too low) would be out of whack for my site. Still, thanks tons. Matching plants to particular sites is always a challenge.