Complex sentence: Building work across the Scilly Isles continued, expanding to include the neighbouring island of St Mary's, and at least 540 oak trees from South Wales were dispatched to the islands in early 1550, since the islands lacked suitable sources of timber of their own.
Split into simpler sentences: Building work across the Scilly Isles continued, expanding to include the neighbouring island of St Mary's. At least 540 oak trees from South Wales were dispatched to the islands in early 1550, as the islands lacked suitable sources of timber of their own.