Patterns of Tree Species Composition of Secondary NaturalVegetationa long an A ltitudinalGradient on Earthy-rockyMountainous Area inW estern Shanxi Province

The pattern s of dom inant spec ies and ligneous plant commun ity d iversity w as analyzed at different a l-t itudinal grad ients in the ea rth-rocky m ounta inous area in w estern Shanx i P rov ince. The resu lt are as fo llow s:the dom inan t species had regu lar change in different altitud ina l grad ients; the species r ichness o f a ll the ligneousplants decreased w ith the incremen t o f altitude. The tree species richnessw as h igh in the commun ity o f h igh a lt itude, but the shrub spec ies richness w as h igh in the commun ity of low a ltitude. In most a ltitude the richnessof shrub species w as grea ter than that of arbor spec ies. The β diversity o f arbo r layers w as b ig in h igh altitude,how ever the β diversity of shrub layer decreased w ith the increm en t o f a lt itude. In the ?? diversity research, theCody index andW h ittaker index w ere stud ied in the commun ities o f th is reg ion. The resu lt ind icated that the ??diversity index w as low am ong the communities of ne ighbor ing a ltitude, but the index increased w hen the d istance w as high be tw een the commun ities. The resu lt show ed the value of ?? diversity ind icesw as m ax im al in thereg ion of about 1 650 m a lt itude.