▁as ▁b ison , ▁el k , ▁and ▁white - ta iled ▁de er , ▁ro amed ▁the ▁exp ans ive , ▁diverse ▁grass lands ▁before ▁European ▁colon ization ▁of ▁the ▁Amer icas . ▁For ▁ 1 0 , 0 0 0 - 2 0 , 0 0 0 ▁years , ▁native ▁people ▁used ▁fire ▁ann ually ▁as ▁a ▁tool ▁to ▁assist ▁in ▁hunting , ▁transport ation , ▁and ▁safety . ▁Ev idence ▁of ▁ign ition ▁sources ▁of ▁fire ▁in ▁the ▁tall gr ass ▁pra irie ▁are ▁over wh el ming ly ▁human ▁as ▁opposed ▁to ▁light ning . ▁Hum ans , ▁and ▁gra zing ▁animals , ▁were ▁active ▁participants ▁in ▁the ▁process ▁of ▁pra irie ▁formation ▁and ▁the ▁establishment ▁of ▁the ▁divers ity ▁of ▁gram ino id ▁and ▁for bs ▁species . ▁Fire ▁has ▁the ▁effect ▁on ▁pra i ries ▁of ▁removing ▁trees , ▁clear ing ▁dead ▁plant ▁matter , ▁and ▁changing ▁the ▁avail ability ▁of ▁certain ▁nut ri ents ▁in ▁the ▁soil ▁from ▁the ▁ash ▁produced . ▁Fire ▁k ills ▁the ▁v asc ular ▁t issue ▁of ▁trees , ▁but ▁not ▁pra irie ▁species , ▁as ▁up ▁to ▁ 7 5 % ▁( dep ending ▁on ▁the ▁species ) ▁of ▁the ▁total ▁plant ▁bi om ass ▁is ▁below ▁the ▁soil ▁surface ▁and ▁will ▁re - g row ▁from ▁its ▁deep ▁( up wards ▁of ▁ 2 0 ▁feet ) ▁roots . ▁Without ▁disturb ance , ▁trees ▁will ▁enc ro ach ▁on ▁a ▁grass land ▁and ▁cast ▁sh ade , ▁which ▁suppress