This asks a rhetorical question in passing which has a rather delightful answer:
What tree nourishes us without fruit?
Everything which photosynthesizes nourishes us with oxygen, whether or not it fruits.
Or, if “nourish” means “provide food or medicine”: Acer saccharum nourishes us with its sap; Cinnamomum verum and Cinnamomum cassia flavor our food with their bark; the roots of Sassafras albidum flavor drinks and its leaves thicken sauces; Cinchona officinalis and Taxus baccata yield essential medicinal compounds from their bark; the flowers of Hibiscus rosa-sinensis make a delicious drink; the leaves of Moringa oleifera are edible and packed with nutrients. Those are only the trees which nourish us directly; anything which flowers gives us honey through bees; many species of tree return atmospheric nitrogen to the soil to enhance the growth of nearby crops.
This asks a rhetorical question in passing which has a rather delightful answer:
Everything which photosynthesizes nourishes us with oxygen, whether or not it fruits.
Or, if “nourish” means “provide food or medicine”: Acer saccharum nourishes us with its sap; Cinnamomum verum and Cinnamomum cassia flavor our food with their bark; the roots of Sassafras albidum flavor drinks and its leaves thicken sauces; Cinchona officinalis and Taxus baccata yield essential medicinal compounds from their bark; the flowers of Hibiscus rosa-sinensis make a delicious drink; the leaves of Moringa oleifera are edible and packed with nutrients. Those are only the trees which nourish us directly; anything which flowers gives us honey through bees; many species of tree return atmospheric nitrogen to the soil to enhance the growth of nearby crops.