( ( ( ( ( Seeds ( usually ( germinate ( in spring ) ) ) ) , ) but ) ( ( ( the survival ) ( of seedlings ) ) ( is ( low ( due ( to ( their ( susceptibility ( to shading ) ) ) ) ) ) ) ) ) . )
(ROOT (S (S (NP (NNS Seeds)) (ADVP (RB usually)) (VP (VBP germinate) (PP (IN in) (NP (NN spring))))) (, ,) (CC but) (S (NP (NP (DT the) (NN survival)) (PP (IN of) (NP (NNS seedlings)))) (VP (VBZ is) (ADJP (RB low) (JJ due) (PP (TO to) (NP (PRP$ their) (NN susceptibility) (S (VP (TO to) (VP (VB shading))))))))) (. .)))
Seeds usually germinate in spring, but the survival of seedlings is low due to their susceptibility to shading.
(ROOT (S (NP (NN Seed)) (ADVP (RB dormancy)) (VP (VBZ ensures) (SBAR (IN that) (S (NP (NNS seeds)) (VP (VBP germinate) (ADVP (RB only)) (SBAR (WHADVP (WRB when)) (S (NP (NP (NNS conditions)) (PP (IN for) (NP (JJ seedling) (NN survival)))) (VP (VBP are) (ADJP (JJ optimal))))))))) (. .)))