A locking headplate for an adjustable saddle tree includes opposed, hingedly connected plates for securing to a saddle tree head portion, a rotatable displacing element for displacing the hingedly connected plates inwardly or outwardly, and at least one supplemental locking mechanism for selectively preventing rotation of the rotatable displacing element. The hingedly connected plates include apertures for receiving a portion of the rotatable displacing element therethrough, the apertures defining at least one cross-sectional dimension that is greater than a corresponding cross-sectional dimension of the rotatable displacing element. Saddle trees and saddles incorporating the locking headplate are provided.