Ask Mr. Smarty Plants

We were very interested in your stated purpose of "re-creating a mini-ecosystem so that all the parts help each other." This is a laudable purpose and well in line with our basic precepts of sustainable gardening with native plants. However, centering this arrangement on Carya illinoinensis (Pecan) which, as you pointed out, not only creates a lot of shade but also emits substances (juglones) to eliminate and kill competing plants around it, makes the process somewhat more difficult. However, we will try to find some research information on these subjects and help you come to your own conclusions.

Temperate climate permaculture plants - this discusses nitrogen-fixing plants and how they work, but most of the listed plants are non-native. We will go through and pick some plants native to the Austin area that might work in your situation.

PerennialSolutions.org All Nitrogen Fixers are Not Created Equal

Please note this paragraph in that article, which reinforces our determination to recommend only native and non-invasive plants in every situation.

"It’s interesting to note that many of the most hated naturalized species turn out to be incredibly efficient nitrogen fixers. In fact the “high” nitrogen fixtures category is a rogues gallery of successful dispersive species, like Russian olive (Eleagnus angustifolia), kudzu (Pueraria lobata), and Scotch broom (Cytisus scoparius). I decided to use the database to generate lists of native and non-native nitrogen fixers and categorize them by their efficiency."

Here is a list of the nitrogen fixers we found that are native to Travis County. Notice that all belong to the family Fabiaceae, including our iconic Texas bluebonnet.

Acacia angustissima (Prairie acacia)

Amorpha fruticosa (Indigo bush)

Astragalus crassicarpus (Groundplum milkvetch)

Lupinus texensis (Texas bluebonnet)

Apios americana (Groundnut)

Now, on to the juglone problem. We have 2 previous Mr. Smarty Plants answers on juglones, with links to lists of plants that resist them. Again, these are not all going to be native.

Previous answer from Maryland.

Previous answer from San Antonio

And, although we didn't find a book specifically on the juglone-resistant native plants, we did find this article from SF Gate Home Guides, which included this paragraph: