( ( ( ( Fires , ) ( mainly ( caused ( by lightning ) ) ) ) , ) ( ( are ( ( a ( natural disturbance ) ) ( in ( temperate grasslands ) ) ) ) . ) )
(ROOT (S (NP (NP (NNP Fires)) (, ,) (VP (ADVP (RB mainly)) (VBN caused) (PP (IN by) (NP (NN lightning)))) (, ,)) (VP (VBP are) (NP (NP (DT a) (JJ natural) (NN disturbance)) (PP (IN in) (NP (JJ temperate) (NNS grasslands))))) (. .)))
Fires, mainly caused by lightning, are a natural disturbance in temperate grasslands.
(ROOT (S (NP (NP (NNP Fires)) (, ,) (VP (ADVP (RB mainly)) (VBN caused) (PP (IN by) (NP (NN lightning)))) (, ,)) (VP (VBP are) (NP (NP (DT a) (JJ natural) (NN disturbance)) (PP (IN in) (NP (JJ temperate) (NNS grasslands))))) (. .)))
Fires, mainly caused by lightning, are a natural disturbance in temperate grasslands.