Hi Amanda.
I think a lot of good points have been raised. I have some more, hopefully as good.
I would build intensively managed, slightly sunken beds, and use those as your islands of fertility that nurture the soil life. I would look at your property and decide where the wind usually blows from, and go to that edge of your property. If there are any on site, I would consider building a low wall on the bed's windward side out of any rocks you can scrounge, and building your slightly sunken bed in its shelter. It will likely act as an airwell, if there are air spaces sufficient to the task, and that will harvest water for your bed.
I would plant trees in this bed, probably something that fixes nitrogen and sheds its leaves, or that will coppice/pollard, such that you can harvest its biomass without losing the benefits of the tree as shelter. Food trees are an option as well, but obviously, choose based on your conditions.
Whatever trees and shrubberies you choose for this bed will slow the dessicating wind, transpire moisture into the air, leaving less carrying capacity to rip moisture away from the rest of your property. The shelter belt guild should also be designed to spread itself with minimal assistance, such that the sheltering effect keeps growing, making your work easier over time.
As to choice of species, I have read that deeply taprooted trees have been used in desert regreening projects where there is a deep watertable, as once the taproot reaches that water, it will thrive without watering, and depending on the species, will pull water up for the rest of the bed. Up north where I am, Sugar Maples perform hydraulic lift, raising the water table locally for themselves and those plants growing around them. Ideally, this is what your choice of tree would do.
Once the shelter bed is established, it will provide shelter for plantings downwind of it, and so on, and so forth.
Water harvesting is pretty key. I would keep in mind the downpours you can get seasonally, as mentioned by Nathaniel, I think, and think about making water harvesting depressions on-contour, rather than swales less-suitable for large volume rain events.
Honestly, if I was being minimalist about the rest of the project, I would put in the water harvesting features (long, shallow basins on contour) and then hill up rows of straw on the downslope side to trap sediment. In areas of increased rates of water flow, I would actually stake small rectangular bales on contour, especially in river beds that tend to look like rivers in rain events.
I think vetiver would be really awesome in rows on contour. If not that, then pretty much anything else that will survive in your climate, planted on contour (preferably on the downslope sides of your water capturing landforms) will hold the soil and sand in place, and nurture those soil critters that do all the actual soil-building work.
I think it crucial to think about not just water harvesting, but also the trapping of sediment from the wind and rain. The vetiver rows on contour (or whatever you choose that works in your area) would act as perfect sediment traps, but just laying some of that mesquite down on contour downslope of water harvesting features would result in sediment building up on the windward and waterward sides.
I also wonder if anyone in the position of turning lots of sand into soil has used bentonite clay or some other hydrophilic powdered clay as amendment to hold water longer and to break up the homogeny of nothing but sand. This in itself should make it easier for soil life to expand outside of the islands of fertility that your beds will represent. Covering that sand outside of your beds with whatever mulch you can, even just enough to block the sun from baking the sand, will reduce the heat island effect.
And as to that, I like Nathaniel's idea about sweet potatoes and watermelon. Anything termed "living mulch" like giant-leaved curcurbits will shade out the soil, too, and provide biomass after harvest. I would build a hot-season guild focusing on sweet potatoes, okra (they are complimentary in the garden), and watermelon, for starters. I would plug in as many companions to those as will fit without getting in eachothers' ways. I have included the link for the
List of companion plants that I go to most often. I figure that groups of plants that support eachother will only make your job easier.
All the best to you in your endeavours. Keep us posted, and good luck!
-CK
A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects.
-Robert A. Heinlein