Apparatus and method for processing wood fibers

A refining member comprising a refining body with a refining surface comprising first and second refiner bars separated by first and second refiner grooves, respectively. The first refiner bars extend from a radially inward position to a first radially outward position. The second refiner bars extend to a second radially outward position that is nearer to an outermost part of the refining body than the first radially outward position. The second refiner bars have a longitudinal length from about 0.6 cm to about 10 cm. The first and second refiner bars have a respective first and second maximum height extending upward from a floor of a respective, adjacent first or second refiner groove. The second maximum height is at least 0.35 mm less than the first maximum height. The first refiner bars are adapted to refine wood fibers and the second refiner bars are adapted to break up fiber bundles.