nitrogen fixing trees for cold temperate drylands (in USA)

Hello,

I am out in south Central Washington state. The base ecosystem is a mixed ponderosa pine and Gary oak forest, with occasional Douglas Fir.

65cm of precipitation annually, mostly in the form of snow
low temps around -10C, high temps 44C
Altitude 650-670 meters
4 months of no rain on average through summer (June-September)

Currently I am working with these legumes:
- Alfalfa/Lucerne (dryland ladak variety)
- Crimson Clover (home-grown spreading variety)
- Black Locust (Rabina suedoaccacia)
- Deerbrush (Ceanothus Interrimus, native bush, leguminous pioneer)

Looking for Leguminous trees to populate swales and provide intermediate shelter for young fruit trees. Having a hard time finding any that seem like they could stand up to this variable conditions. Does anyone here have much experience?

Any ideas are much apreciated.

Thanks!
Andrew

EDITED at request of author to modify thread title (John Polk)

I live just south of Bend so similar conditions. Might look at caragana (siberian pea).

serbian pea, autumn olive, goumi, silverberrry, seaberry

I second the caragana. How about buffaloberry (Shephardia argenta)? Native at least to the east side of the Rockies and the northern Great Basin region and grows up to 12 feet tall. As you are in pine country, what about the native bitterbrush (Purshia tridentata). I've seen it growing in shallow soils in Wyoming, mountainous areas of Nevada and sagebrush steppe on some sites in eastern Oregon. It's a non-leguminous nitrogen fixer and is not as tall as buffaloberry.

I would try some common "mimosa" Albizzia julibrissin. It should be hardy to zone 7 at least. It's often critiqued as an invasive in the East, but rarely spreads much in the West because the trees require a long summer to mature seed, and the seedlings also need reliable moisture the first season to germinate and establish. That said, established trees are quite tolerant of drought and I have seen them growing in unirrigated conditions in OR and CA. Nodulation is prolific and occurs even in seedling pots without inoculation. The tree casts a useful light shade, coppices readily, and is good forage.

Interesting I didn't know bitterbrush was a nitrogen fixer. I have removed most of it from my property because it is so flammable.

Russian Olive
Mountain Mahogany (Cercocarpus spp.)
Siberian Seaberry or sea buckthorn (hippofae)
Not a tree but a nitrogen fixer and medicinal herb; mongolian astragalus (astragalus mongholicus).

One possible "problem" with Russian olive (Eleagnus angustifolia) is that is considered a noxious weed in some western states (Wyoming and Montana) for example. A person could create more problems for themselves by planting this species. That being said, the Russian olives on my land are tough, and provide a LOT of food for birds this time of year with their super abundant berries. The crabapples failed in my immediate area, and now the cedar waxwings are pounding the Russian olives out here in the valley as they are one of the few abundant food sources during this last nearly four week cold spell. I do find them to be a very resilient species as those that we've cut and had the stumps ground up still sprouted from the roots near the surface. Another thought for consideration is Amur maackia (Maackia amurensis). It doesn't appear to be as aggressive as black locust, is a leguminous nitrogen fixer, and likely will no overgrow many of your desired species. The wood is useful as post and poles- very rot resistant.

Here is a useful resource regarding this question:

thebestgardening.com - nitrogen-fixing-plants-chart.pdf