Mycorrhizal fungi and planting tricks 

We are getting more and more information on how plants, shrubs and trees grow in association with other organisms in their ecosystem 

Yes: pollinators and biological control agents, as well as composters in the soil and the earthworms (earth workers) that aerate the soil and take well-produced organic matter deeper and deeper into the soil levels, where roots can pick up the nutrients. 
 
But over the past decade or more scientists have made some grand discoveries around the role of fungi, assisting plants (Watch Susan Simard’s TED talk How Trees Talk to Each other) 
 
Mycorrhizal fungi extending root zones of host trees and shrubs. They form Mycorrhizal networks that “connect” trees with each-other (sharing food, communication and warning neighbouring plants for bark beetle attacks etc).  
 
Some of the orchids would do so much better if the mycorrhiza is included in the orchid mix; The way to achieve that is by mixing in some old mix in the new mix, when replanting your orchids. 

When I dig native trees and shrubs (beech, rata, Pittosporum, kawakawa, etc) into the garden, I often make a short journey to a nearby native forest to grab a large bag of moist leaf-litter and humus from the top-layer of the soil. That material is likely to contain quite a few beneficial fungi, including some mycorrhiza, that would help with the establishment and subsequent growth of the native trees. It facilitates the up-take of phosphorus and Nitrogen. 

Trick is to get the fresh leaf-litter and use it as soon as you can: I tend to mix that biodiverse leaf-litter into the top layers of the soil where I plant the new trees.  

You can also use it as a moist mulch. 
 
Recent research in NZ (Ngā Kākano Whakahau) explored how to re-introduce native mycorrhizal fungi in restoration projects; replanting old paddocks with native trees is tricky!) One of the interesting findings was that – just like in forests – a succession of organisms (almost from fast-germinating “pioneers” to slower germinating later developing species) is crucial for establishment. 
 
That means that even Mycorrhiza have their time and place in the restoration and regeneration of forests! Maybe I should go to a young forest first and get some leaf-litter and humus from there before jumping straight to the old-growth forest!!