A locking headplate for an adjustable saddle tree includes opposed, hingedly connected plates for securing to a saddle tree head portion and a rotatable displacing element for displacing the hingedly connected plates inwardly or outwardly, wherein the rotatable displacing element assists in retaining the hingedly connected plates in a set spaced-apart configuration when not being rotated. The locking headplate further includes at least one supplemental locking mechanism for selectively preventing rotation of the rotatable displacing element. The locking headplate further includes a supplemental motion restrictor for restricting outward motion of the opposed hingedly connected plates to a desired range of motion. Saddle trees and saddles incorporating the locking headplate are provided.