sentences:  It grows on a variety 
  of soils from moist silts, gravels, and sands to rich humus, loams, and occasionally clays.Black cottonwood is a pioneer species that grows best in full sunlight and commonly establishes on 
  recently disturbed alluvium.Seeds are numerous and widely dispersed because of their cottony tufts, enabling the species to colonize even burn sites, if 
  conditions for establishment are met.