D.C. Code § 16-1113

In an action to recover vacant and unimproved lots of ground it is not necessary, in order to maintain the defense of adversary possession, to show that the premises in controversy had been enclosed; but if it appears that the property had been assessed for taxation to the defendant, or those under whom he claims, and that he or they had regularly paid the taxes on the property and were the only persons who had exercised control over the property for a period of fifteen years before the bringing of the action, the facts shall be the equivalent of possession by actual enclosure.