You can mulch with whatever organic matter you have on hand or can easily (and cheaply) obtain - leaves, straw, bark, pine needles, grass clippings.....you name it. All will break down eventually and add nutrients to the soil and stimulate soil biology. They will also help to conserve soil moisture and moderate temperatures about equally as well.

Mulch derived from acidic materials - like bark or pine/conifer needles - really do not alter soil pH to any significant degree. That is a gardening myth that has no basis in reality and is very hard to quash :-) There is some slight leaching into the surface of the soil from the fresh product but not enough to be at all concerned about. As these materials break down with decomposition, they become virtually neutral afa pH is concerned.

Thanks very much for your reply. I think I will consider a mix of straw with pine bark over it. I´m also a bit worried by the fact that straw is an easy flammable product, so adding pine bark over can possibly help against that. Let´s see!

+1 for Gal's comments. The acidification thing is way overblown, as in don't even worry about it. Soil buffering capacity makes a mockery of a bit of acidic material applied at the surface-or anywhere in the soil profile.

+oM