underplanting

from The Collaborative International Dictionary of English v.0.48

Underplant \Un`der*plant"\, v. t. [imp. & p. p. {Underplanted};
   p. pr. & vb. n. {Underplanting}.]
   To plant under; specif. (Forestry), to plant (young trees)
   under an existing stand.
   [Webster 1913 Suppl.]