Done a little more research on the Pawlonia it seems like there is a bit of conflicting information about it. Some suggest that it is not a
root nitrogen fixer after all. Some websites claim that its leaves fix nitrogen - something I have not come across before? This seems to be a characteristic of some tropical nitrogen fixing plants. Perhaps there is someone out there who can enlighten us? Anyhow, it seems like it is used extensively in China in Agroforestry situations to increase the yields of companion crops. That suggests potential suitability for forest garden type situations.
Dj, yes I agree I suppose we are all pioneers at the beginning. I guess it means we all potentially could make significant contributions/ and mistakes!!! in working out how to do it in our own particular set of circumstances. We are really lucky here in Devon UK as Martin Crawford has blazed a trail and shown how it can be done in the conditions we have in the UK. So it is easy for us here to see how well his designs works in practice and therefore feel confident to follow his recommendations. his two
acre demonstration garden is about fifteen years old and is very impressive. Lots there on you tube if you want to get a feel for his garden. Furthermore I haver found that his various
books are excellent resources in helping you to design a garden - highly recommended.
http://www.amazon.co.uk/Creating-a-Forest-Garden-ebook/dp/B003Z9JMYI/ref=sr_1_10?ie=UTF8&qid=1363083139&sr=8-10
There is a chapter in this book devoted to designing the nitrogen fixing plant aspect of a forest garden. The principles that he uses are described very clearly although they are expressed in the context of a cool temperate climate I imagine some of those principles will be universal. However for the detailed application of those principles in different circumstances adaptation will no doubt be necessary.
The main issues to consider with the designing nitrogen fixing in a forest garden situation, as I understand it are:
1 That most nitrogen fixers are quite light demanding - (elaeagnus is a rare exception)
2 if the cover of nitrogen fixing plants need to be 25 to 40 percent ( in a sunny situation) 50 to 80 percent (in shady situations). To get this kind of cover you need to fill much or most of you under-story/shrub layer with nitrogen fixers - you have to start sacrificing a lot of this very valuable space to nitrogen fixing plants when you might prefer to use that space for edible or other kinds of yields . Therefore it makes sense to get your nitrogen fixing done way up in the over story.
3 This conclusion is even more convincing when you also consider that: If you use nitrogen fixers in a sunny situation you need only half the area to be covered by nitrogen fixing plants compared to those in a shady situation.
Anyone wanting more detailed information on nitrogen fixing plants might benefit from this:
http://www.agroforestry.co.uk/publorders.html which is Martin Crawfords website where you could get a booklet called:
Nitrogen-fixing Plants for Temperate Climates
by Martin Crawford
2nd rev Edition, 1998. ISBN 1-874275-38-6. A4, 89 pages.
Plants which fix nitrogen (ie utilise nitrogen from the air) are some of the most useful plants in agriculture, horticulture, forestry and agroforestry. Their use can lead to much reduced fertiliser usage, lower losses of soil nitrogen through leaching, and improved soil fertility through increased soil organic matter.
Most people only know of the legumes as nitrogen-fixers; however, there are several other plants groups which do so, notably the so-called actinorhizal plants (including alders, Elaeagnus, sea buckthorn) which are mostly of temperate origin and better-suited to cool temperate climates.
This directory describes the different groups of plants which fix nitrogen, including the legumes, the actinorhizal plants, liverworts, and lichens. Most fixation occurs via a symbiotic relationship with bacteria in root nodules, and the nodulation status of temperate genera are listed, with notes on cross-compatibility between different strains of bacteria and different genera.
The nitrogen contributions which N-fixing plants can make are discussed, and an overview of the different uses given, including their use in forest and fruiting gardens as well as in forestry and agriculture. The main parts of the directory describe over 450 different species and their in-depth uses. This includes tables, organised by plant type, showing conditions required and uses of all species.
Not sure if this would be of any help to you in Colorado dj?
I won't be around for a while as I'm off to work on the forest garden - no internet access there. So keep up the good work