It is not the saw as much as the chain/dirt interface. Dirt is death to cutting edges. The lower portion of a tree can have dirt lodged in the bark that will dull your chain quickly. The best solution is to get used to touching up with a file after stumping.
Some types of chain dull more quickly than others - full chisel tends to dull more quickly when it hits dirt than semi-chisel for example.
and then it is mostly clean wood. Just getting the loose stuff off will help. Exhaust also lbows dirt and dust onto the b/c and that gets dragged into the cut. lay a piece of heavy canvas tarp at base of tree and that will keep the dust down, and will also collect chips.