( ( Forested ecosystems ) ( ( ( play ( ( a ( key role ) ) ( in ( the ( carbon cycle ) ) ) ) ) globally ) . ) )
(ROOT (S (NP (JJ Forested) (NNS ecosystems)) (VP (VBP play) (NP (NP (DT a) (JJ key) (NN role)) (PP (IN in) (NP (DT the) (NN carbon) (NN cycle)))) (ADVP (RB globally))) (. .)))
Forested ecosystems play a key role in the carbon cycle globally.
(ROOT (S (NP (NP (DT A) (JJ primary) (NN role)) (PP (IN of) (NP (NP (NNS decomposers)) (PP (IN in) (NP (DT an) (NN ecosystem)))))) (VP (VBZ is) (SBAR (IN that) (S (NP (PRP they)) (VP (VBZ cycle) (NP (NN matter)) (PP (IN by) (S (VP (VBG returning) (NP (NN carbon) (CC and) (JJ other) (NN matter)) (PP (TO to) (NP (DT the) (NN ecosystem)))))))))) (. .)))
A primary role of decomposers in an ecosystem is that they cycle matter by returning carbon and other matter to the ecosystem.