( ( Several species ) ( ( are ( considered ( to ( be ( ( serious threats ) ( to ( native vegetation ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Several) (NNS species)) (VP (VBP are) (VP (VBN considered) (S (VP (TO to) (VP (VB be) (NP (NP (JJ serious) (NNS threats)) (PP (TO to) (NP (JJ native) (NNS vegetation))))))))) (. .)))
Several species are considered to be serious threats to native vegetation.
(ROOT (S (NP (NNP Overharvesting)) (VP (VBZ is) (NP (DT a) (JJ serious) (NN threat)) (ADVP (RB particularly)) (PP (TO to) (NP (JJ aquatic) (NNS species)))) (. .)))