Effects of surface fire on species diversity of understory plant in Pinus sylvestris var. mongolica forests in Hulun Buir sandy land of Inner Mongolia.

The species diversity of understory plants of three stands including no surface fire,surface fire occurred in the current year and surface fire occurred 12 a ago in Pinus sylvestris L.var.mongolica Litv.forest in Hulun Buir sandy land were investigated with multi-scale modified Whittaker plots(1 000 m2).The results show that the DBH difference of all trees in each stand is very significant(P0.01).The understory vegetation coverage has extremely significant difference in the three stands at 1 m2 scale(P0.000 1) and that of the stand with surface fire occurred 12 a ago is the lowest(32.0%).At 1 and 10 m2 scales,the α diversity of understory plants exhibits significant difference(P0.05),and the understory species richness of the stand with surface fire occurred in the current year is the highest.The α diversity of different functional groups,including woody plant,gramineous plant and forb has a little difference at small scales.The β diversity of understory plants increases continuously as time goes on and that of stand with no surface fire is the highest.The results of detrended correspondence analysis(DCA) show that there are more understory species in the stand with surface fire occurred in the current year and understory plants distribute from drought to hygrophytic habitat along water gradient.Therefore,it is suggested that the understory plant diversity of Pinus sylvestris var.mongolica forest only responses to surface fire significantly at small scales and trends to be uniform as time goes on,and the understory vegetation has the ability to resist surface fire disturbance.