(S (S (S (PP (IN After) (NP (NP (NP (BASENP (DT a) (NN year)) (PP (IN of) (BASENP (JJ turbulent) (NN weather)))) (PP (IN in) (BASENP (NNP Mexico)))) (CC and) (NP (BASENP (NN destruction)) (PP (IN of) (BASENP (PRPD their) (NN habitat)))))) (COMMA ,) (S (NP (DT the) (NP (NP (BASENP (NNP Monarch) (NN butterfly)) (PRN (LRB -LRB-) (BASENP (NNP Danaus) (NN plexippus)) (RRB -RRB-))) (NN population))) (VP (MD could) (VP (VB be) (ADVP (ADVP (RB down) (PP (IN by) (NP (QP (ADJP (ADJP (RB as) (JJ much)) (IN as)) (NN 50)) (NN %)))) (PP (TO to) (NP (BASENP (NN 60) (NN %)) (BASENP (DT this) (NN year))))))))) (COMMA ,) (S (BASENP (NNS experts)) (VP (VBP say)))) (PERIOD .))