I don't have all the facts, Larry, but the person who helped with the initial landscaping of our property told me that my North Carolina clay was slightly high in Ph to start with so never dig pine needles or the center part of trees into it, or it would further raise the Ph. So it raised a red flag when I saw my friend had mulched with sawdust. I don't know if he had the same type soil or the same Ph to start with, but I do know, he lost all the plants from the bed where it was used in that year and in subsequent years. There may have been other circumstances, i.e. drought, other things added to the soil, etc. I have used sawdust from ground out tree trunks before but added lots of nitrogen, topsoil, and other organic matter so that the sawdust had completely turned into soil....and then checked the Ph before planting. I believe even though it may be aged the decomposition of sawdust will still take a lot of nitrogen out of your soil, be attractive to termites, and not be as beneficial to your soil as bark. It could very well be that matting prevented both rain and oxygen from reaching the soil. A person speaking to our club mentioned that too deep of a layer of mulch during a drought year prevented water from reaching the roots of the daylilies. They were landscapers who also advised against double ground hardwood mulch that has both the center part of the tree and the bark as it also has a tendency to mat down and not allow water to flow thru it. That is why it is used....to starve out weeds. So I have always stuck with pine bark....worms love it....and water can flow thru it. For faster decomposition of sawdust into soil, I would think lime would be needed in clay soils. I'm not an expert...just repeating a few things that I have learned along the way on what to avoid. And the center part of the tree with the cellulose is on the "do not use" list here. I once had delivered some garden compost that I believe had a lot of sawdust in it, that came with termite larvae....not a good thing to buy! The firm that delivered it had so many complaints that year, they went back to another firm with more expertise in composting. And if a company can't tell me the Ph of garden soil they are delivering, they will not receive my business.