A method of harvesting a row of small trees, including the steps of: advancing at least one rotating spiral (141 to 146; 351, 352) and horizontally spaced guide member, forming an inlet passage of a harvester head (120; 320) of a tree harvester, to engage the stems and/or foliage of the trees in the row; cutting the stems of the trees by a base cutter on the harvester head (120; 320); conveying the trees, maintained in a substantially vertical position by the, or each, rotating spiral (141 to 146; 351, 352) and spaced guide member, to a location above a rotating chipper drum or chopper drum for engagement by at least one pair of nip rollers (131, 132; 378); and feeding the trees downwardly to the rotating chipper drum or chopper drum by the, or each, pair of nip rollers (131, 132; 378), while maintaining the trees in the substantially vertical position; and wherein the chipper drum or chopper drum is rotatably driven by at least one drive means about a first axis, the nip rollers (131, 132, 378) are rotatably driven by the at least one drive means about respective substantially parallel second and third axes, vertically spaced above the first axis, and the first, second and third axes are disposed substantially parallel to the direction of travel of the tree harvester, and are upwardly inclined to the horizontal from a leading end to a trailing end, so that the, or each, pair of nip rollers (131, 132, 378) are operable to maintain a stem of a tree being harvested in a substantially vertical position, while feeding the tree downwardly through the chipper drum or chopper drum (121 and wherein the relative rotational speeds of the nip rollers (131, 132, 378) to the chipper drum or chopper drum are selected so that the nip rollers (131, 132, 378) progressively feed the stems of the trees downwardly and rearwardly relative to the chipper drum or chopper drum as the tree harvester continuously advances along the row of the trees. advancing at least one rotating spiral (141 to 146; 351, 352) and horizontally spaced guide member, forming an inlet passage of a harvester head (120; 320) of a tree harvester, to engage the stems and/or foliage of the trees in the row; cutting the stems of the trees by a base cutter on the harvester head (120; 320); conveying the trees, maintained in a substantially vertical position by the, or each, rotating spiral (141 to 146; 351, 352) and spaced guide member, to a location above a rotating chipper drum or chopper drum for engagement by at least one pair of nip rollers (131, 132; 378); and feeding the trees downwardly to the rotating chipper drum or chopper drum by the, or each, pair of nip rollers (131, 132; 378), while maintaining the trees in the substantially vertical position; and wherein the chipper drum or chopper drum is rotatably driven by at least one drive means about a first axis, the nip rollers (131, 132, 378) are rotatably driven by the at least one drive means about respective substantially parallel second and third axes, vertically spaced above the first axis, and the first, second and third axes are disposed substantially parallel to the direction of travel of the tree harvester, and are upwardly inclined to the horizontal from a leading end to a trailing end, so that the, or each, pair of nip rollers (131, 132, 378) are operable to maintain a stem of a tree being harvested in a substantially vertical position, while feeding the tree downwardly through the chipper drum or chopper drum (121 and wherein the relative rotational speeds of the nip rollers (131, 132, 378) to the chipper drum or chopper drum are selected so that the nip rollers (131, 132, 378) progressively feed the stems of the trees downwardly and rearwardly relative to the chipper drum or chopper drum as the tree harvester continuously advances along the row of the trees.