hmm, seems like Access only wants you to refer to fields one level of nesting down. The following works:
SELECT s.*, sn.SurvT, sn.CE, sn.SD, sn.Dec, sn.Tapr, sf.*
FROM ((Species s RIGHT JOIN species_abundances sa ON s.ID = sa.SpeciesID)
RIGHT JOIN Lars_seedling_morph_nursery_data_Biotropica...