The oak tree illustration is simple, yet incredibly detailed. Trees are common motifs for wedding invitations: they can represent vitality, strength, shelter, looking to the future. And they can also, of course, be more literal: depictions of the venue — in this case, a ranch in Calistoga, California — or they can be emblematic of a place special to the couple. The tree motif can embody all of these characteristics and connections.
This design is so clean and sophisticated. Because it has a lot of white space and isn't overly ornate, the little details really shine. The script has wonderful (in some case, overlapping) flourishes, and the custom double border really highlights the texture of the thick paper stock.