This word for a cluster of trees or a clod of soil may come from the Dutch for "lump"
... Galaxies, too, 
tend to clump together in clusters, which in turn may be parts of superclusters ... 
1580s, "lump; cluster of trees," from Middle English clompe "a lump" (c.1300), 
from Dutch... [DOC] [TLE] What does lump mean - Definition of lump - Word finder [PAR] When it rained the water would cascade down the banks and wash great lumps 
of soil into the road.