The LB3 map component occurs on Relict Glacial Lakebeds where sphagnum moss dominates the plant community.  It occupies the zone between the shallow water table, sweetgale (Myrica gale) or sedge dominated component (LB2) and the deeper water-table shrubby component (LB4).  It is common on its own or in a complex with LB2.  LB3 component is relatively infrequent on the lowlands.

LB3 can be considered the Relict Lakebed bog component.  'True' bogs are ombrotrophic systems, with deep sphagnum mats that perch rainwater above the regional groundwater table.  On the Kenai Lowlands, sphagnum-dominated units frequently have a significant contribution of groundwater that has recently been in contact with mineral soil, and thus can be termed 'poor fens' and are not really bogs.  Additionally, bogs contain relatively un-decomposed, still recognizable plant remains, whereas in fens plant remains are at least somewhat decomposed.  Often these LB3 components consist of relatively thin, un-decomposed sphagnum mats perched atop a deeper, more decomposed layer of peat.  Occasionally a thick un-decomposed sphagnum mat occurs at a spring where a constant supply of water encourages thick sphagnum mat development.