20:54 Nov 25, 2009 

it refers to the fact that plants, shrubs, undergrowth, subcanopy, or however you want to call it, grows on its own, as opposed to coltura forestale, which implies trees being cultivated like a crop (planted, tended, and harvested). So while the trees are planned, these instead are spontaneously occurring, in a way. That is my guess at least.

20:07 Nov 25, 2009 

but where does it mention plants, Tone?

19:57 Nov 25, 2009 

I think these are basically two concepts - one is "scarti dai processi di lavorazione delle colture forestali" and the other is ""scarti dai processi di lavorazione delle piante spontanee" because "colture spontanee" is probably an oxymoron. By that reading, the Italian is rather poorly written.