If I keep adding mulch to my garden beds, will it not eventually increase the soil depth in that bed? And if it does, what happens to all the surface roots if I remove the mulch (soil)?

Adding about 2 inches of mulch to our garden beds prevents moisture loss, improves the soil condition, and prevents weeds from germinating. Natural wood mulch, composed of fine wood chips, ground up leaves and twigs, encourages worms and microorganisms to break down the material into nutrients which plants can absorb through their roots. This relationship between the soil organisms, decomposing organic material and plants creates a self-sufficient ecosystem if we, as the caregivers, don’t ruin it.

When you clean your garden beds in spring, lightly cultivate the surface material into the soil bed. How much light and water a particular bed gets can speed up or slow down the composting of the mulch. Some beds may need an inch of new mulch each year around mid-June or when temperatures heat up. Other beds may be slower and may only need additional material every other year. Application is not an auto-pilot garden chore.

Do not apply more than what is recommended. More is not better for preventing moisture loss or weeds. Thriving plants have deep roots in the soil rather than roots close to the surface. Overloading on mulch gives the plant a false sense of where the real soil is and can keep the hair-like roots away from microorganism activity. 

Related: How to improve your clay soil