I meant to mention that mulching with fine material can have a significant impact on gas exchange, and ultimately, the amount of oxygen needed to drive root function and metabolism. Deprivation of O2 resulting from using fine materials as mulch shows up most often in soils that drain poorly and during prolonged periods of rain. When root growth is robust, symptoms become more evident/get worse.
Sawdust might repel water and prevent it from soaking in, or cause soils to retain water already IN the soil for longer periods, but it won't "suck" moisture from soils.
Moist mulch piled against woody stems also cause phloem stress due to a lack of gas exchange between inner and outer bark. With a compromised phloem, roots become malnourished and loose efficiency taking up water and nutrients.
Uncomposted sawdust also produces a LOT of heat if it is piled high enough. Temps of moist sawdust just a few inches thick can reach up to 140*, with 120* being hot enough to kill many temperate species of woody material.
Mn toxicities are also common if you use uncomposted hardwood as mulch.
Al
