For the purpose of constituting an adverse possession, founded upon a written instrument or a judgment or decree, land is deemed to have been possessed and occupied in any of the following cases:
Where a known farm or a single lot has been partly improved, the portion of the farm or lot that has been left not cleared or not enclosed, according to the usual course and custom of the adjoining country, is deemed to have been occupied for the same length of time as the part improved and cultivated.
N.Y. Real Prop. Acts. Law § 512