Assuming that your first mulch is an organic material such as bark or wood chips, I don't think so. I did something similar. I added new compost a year or two later and the original mulch was only partly decomposed. So I "stirred" the two together so that the compost was available to the plants easily, then put new mulch on top of that to protect the compost from the sun.

It is my opinion that you would want to avoid stirring these two into the soil where the decomposition would bind nitrogen during the process. However, current thinking is that if the decomposition takes place on top of the soil, only the contact layer of soil is affected.

If you are using a non-organic mulch then yes, I do think you will want to try to remove it.

Rosefolly

Heck...I do this every year. I lay down a layer of newspaper long the edge to re-establish the border edge and throw down more mulch and compost or what ever on top of what is there. I have never worried about binding up nutrients because they are going to break down again eventually and in the mean time there is plenty of good stuff around. People used to be concerned with blackspot in the mulch and so on but that has apparently not proven to be a real problem. It all rots eventually. If the mulch is too fine-bark fines in particular-and too deep It can keep water from getting into the ground. I use woodchips and manure and dont have any problems with that.

patricia

I've been laying down new hardwood mulch on top of old mulch every year for 25 years....we started out with clay soil and now the dirt is like black gold. Besides, mulch is waaay too expensive to remove.

Another added plus...earthworms! My beds are full of 'em. They like the cool, mulched beds.
-terry