this wood also tends to have a higher longitudinal shrinkage than the wood produced later so that a radial shrinkage gradient is established across the tree stem microfibril angle and wood density are directly related to stiffness a tree having higher microfibril angle and lower density wood will typically produce weaker lumber than one of the same species having lower microfibril angle and higher density warp in lumber assumes several forms that may be present singly or in combination as seen in fig1 and 2 crook and bow are the result of differential longitudinal shrinkage in various portions of sawn lumber one must differentiate between u201c longitudinal shrinkage u201d which is measured parallel to the fiber direction and u201c lengthwise shrinkage u201d which is measured parallel to the longitudinal axis of the board fig3 these may or may not be the same cup shown in fig4 is principally the result of variations in tangential shrinkage which tends to increase as one moves radially outward from the pith twist as illustrated in fig5 is normally the result of spiral grain in the log from which the lumber was sawn the days in which a highly skilled head sawyer made real time decisions as to how a log should be optimally cut have largely passed with the near disappearance of the huge old growth logs from the nation 39 s.