I noticed that Sepp plants a lot of trees in between his hugelkultur raised beds. Is there a reason for this? Could this negatively effect the plants growing in the hugel beds? Should there be a size limitation? Thanks for your insight!
In his book Sepp Holzer Permaculture I believe he talks about using the fruit trees as windbreaks (protection) for the Hugel beds. I think they also feed off of the natural fertilizer supplied BY the hugelkultur beds since lots of hydration and fertility sink in to the valleys between the Hugelkultur beds.
I theorize (no practical experience, my few Hugelkultur beds are only a few months old now), that the biggest issue you would see is if the tree shaded the bed enough to preclude some varieties of plants from being able to thrive under their foliage.
That being said, this is yet more valuable small microclimates (the tree will provide some frost protection, will gather condensation and drip it on the plants, stimulate shade-loving plant-growth, etc.)
In my area (arid High Desert), I think trees intermingled in Hugelkultur will be a boon, because my evaporation rate is so intense.
If your area is wet or has high rainfall, then slowing evaporation is not as big of a deal.
I encourage you to read Sepp Holzer Permaculture, I really enjoyed it. I was also crazy enough to listen to the 20 hour Podcast review Paul did. (you can read the book in under 10 hours).
I also enjoyed the review and it was good to hear other peoples interpretations of the concepts in the book as well.