Hi Richard!
Looking at the picture you've posted it looks like the pines are over 10 years old and in my humble opinion they are better off being kept where they are.
First of all it's obvious there was a lot of work when they were planted there and it would be pity to see them gone after so many years.
Secondly, the soil could have a higher level of acidity already after so many years and I don't see any improvement in the near future (even though is still a controversy over the fact that pine needles create acidity in the soil).
Thirdly, I would use any other wood than pine or walnut in hugels. I'm in the second year now with my raised beds (in which I used only birch, beechwood and my favourites linden and poplar because they hold water a lot better) and I could say I'm more than happy with the outcome.
Now, it's up to you if you consider that you really need that space and you're absolutely convinced that it's worth to waste the energy that it took to bring up that little forest, there are methods of improving the soil with different cover crops (buckwheat, rye) and nitrogen fixers (Siberian pea shrub, Illinois bundle flower), but all these in time of course.
Keep us posted with your progress!
