If you don't officially do a 1031 exchange, then this is barter, and barter is taxable according to all the normal rules as if it was money. Suppose you bought lot A 10 years ago for $50,000 and it is now worth $100,000. You trade it for lot B which also has a present market value of $100,000. You have bartered away lot A for $100,000 and you must realize that and report it as a taxable capital gain ($100,000 sales price minus $50,000 basis = $50,000 capital gain). Then your basis in the new lot would be $100,000 (the amount reported as proceeds in the barter sale of lot A equals the barter cost of lot B.)
