Pine trees will have an acidic soil beneath them, and it may be very dry, too. Investigate acid-loving plants like blueberry, lingonberry, cranberry,etc.
Under the other trees comfrey would probably grow, but oregano is heat and sun-loving. Tansy, maybe would grow, depending on light.
What you have to look out for is raising the level of the soil around the tree trunk, which will kill most trees, and also having problems with roots. Many tree roots will seek out nourishing soil areas, and take over beds. Give it a try, and see what grows for you.

We have some herbs growing under fruit trees and that seems to work out. As the trees get bigger the herbs will spread out toward the light and die off where the shade is too deep. Some of the conifers have currants growing under them as part of a guild and that happens naturally. With the strong sun we have the currant would get too much sun and die so they survive in the shade of the pinon and also provides shelter for animals and birds.

Take a look at what is in the woods where you live. That will often give a clue about what herb or flower likes to live with what tree.

Fireraven9
Gutta cavat lapidem (Dripping water hollows out a stone) - Ovid

Oregano will grow fine under trees here. Tansy I think would need more light. Comfrey and tansy, however, are quite invasive, weedy, exotic plants - do you really want them? Comfrey is surprisingly not on state noxious weed lists, though it may be listed in certain counties. Tansy is a noxious weed in Colorado, Minnesota, and Washington.

A good way to get around the competition of tree roots is to keep the herbs in containers which are partially plunged into the soil. Roots can get into the surrounding soil through the drainage holes which provides some cushion on watering requirements. We get lots of nice 5 to 15 gallon containers from landscapers and our farmers' market customers for nothing. Containers also keep invaders in check.

One of our good customers, an orchid enthusiast and outstanding horticulturist, does this. Most of his yard is under a huge canopy of valley oaks, Q. labata.

Strawberries.....

This is where strawberries grow naturaly, in the leaf litter on a forrest floor. They have a very shallow root system and do well in semi shaded positions.

I had strawberries under a dwarf cherry and they did ok in semi-shade. I disliked trying to pick strawberries underneath the low tree branches so I put in sweet woodruff. Sweet woodruff likes shade, is shallow rooted and spreads quickly so I only needed to put a few plants in for dense groundcover, reducing the risk of damage to the tree roots. It has a wonderful scent, both foliage and flowers, and can be used for tea and flavoring.

Well, the first thing I would do is to try to find out what grows naturally under those trees in your area (if they are native plants, what grows under simular native types if not). It is normal that we want to incorporate some of our favorite herbacias species and decorative flowers etc. into our space, but I would definately attempt to do so in mix with native species and grasses etc. You will find that some trees do not allow very many things to grow around them (remember that "ALL things garden") and that some find it particularly beneficial to have specific grasses and herbacious plants closeby. If you cut out all the low juniper bushes from around a Mariposa tree, it will die. The only place you find your better protein quality grasses during a severe drought is under an acacia, a pecan tree will not let much at all grow under it by use of the tannin it produces dripping with rain water onto the surrounding soil, etc.

Our plants grow in 'community' as much or more so as we do as Mollison would say. The one thing I would not do, from a permaculture standpoint, would be to plant only one or two types of plants under the trees or to only plant them and not also attempt to incorporate some of the edge species appropriate to them.

Oh, by the way, if you will loosen the earth some around the pine trees and let the shed needles lie you can grow the best great big, fishing type earthworms there and they are easy to get to by just pushing around the needle litter. Needless to say they are great for the soil too.

Hope that helps some, ENJOY!! DD

Read the book "Forest Gardening".