The fork assembly for lumber stackers includes a plurality of mechanized arms. Each mechanized arm includes a biasing assembly that provides a movable carrying surface onto the arm upper surface Such movable carrying surface is for example in the form of an endless belt, that biases an object deposited onto the arm towards a distal end thereof. The fork assembly according to the present invention prevents smaller pieces of lumber to rise when the fork assembly is retracted above a lumber stacker elevator during deposition of the lumber from the fork assembly to the elevator's platform. The present invention further allows creating stack of lumbers having different configurations.