Influence Of Site Condition And Stand Structure On The Undergrowth Characteristics Of Larch Plantation In The Liupan Mountains Of Northwest China

In order to control soil and water loss on the Loess Plateau,China has implemented a large-scale project of returning farmland to forests and grasslands since 1999.Both vegetation restoration and sediment control on the Loess Plateau have achieved significant results.But at the same time,artificial afforestation has led to prominent problems such as the degradation of undergrowth vegetation and reduced biodiversity.Based on this,this thesis is aimed at the key scientific issues of how different site conditions and stand structures affect the vegetation composition and diversity of the artificial forest under the Yellow River Basin.In North China’s Liupan Mountain,typical plantations of Larix principis-rupprechtii with different stand structures and site conditions were selected.Sample field,through field investigation and indoor analysis,to study the composition and diversity of different plant conditions(elevation,slope,slope position,aspect)and stand structure(density,forest age)on the vegetation under the Larix principis-rupprechtii forest Impact.The findings are as follows:1.The genus composition of the vegetation community under the Larix principis-rupprechtii forest in Liupan Mountain is the richest in Asteraceae,among which the dominant ones are Artemisia argyi.And Artemisia dubia var.Subdigitata,Artemisia sacrorum Ledeb.,Artemisia mongolica.,Etc.Fragaria orientalis Losinsk.Of the genus Rosaceae,and Carex tristachya.It is especially common with Leymus secalinus.,Especially the oriental strawberry,which has an important value of 1324.22 in the 46 plots surveyed.2.Site conditions have an important influence on the characteristics of undergrowth vegetation: the effect of altitude is the most significant.As the altitude increases,the coverage,richness,and biodiversity of undergrowth vegetation appear to decrease first and then increase.The degree is increased from 2300 m,and the richness and diversity are increased from 2800 m.The slope also affects the characteristics of the vegetation under the forest.With the increase of the slope,the richness and diversity of vegetation show a trend of first increase and then decrease,reaching the maximum in the range of 10 °-15 °,but the impact on the vegetation coverage Smaller;slope position and aspect have a greater impact on the characteristics of the vegetation under the forest.The slope position mainly affects species richness and diversity,and decreases with the rise of the slope position,that is,the bottom of the slope> the middle of the slope> the top of the slope.It has little effect on the coverage,while the slope direction mainly affects the coverage and diversity,which is shown as shady slope>semi-yin slope>semi-yang slope>yang slope,which has little effect on the richness.3.The forest structure also has certain effects on the characteristics of the vegetation under the forest: the impact of forest age is small,but the overall performance is that as the forest age increases,the vegetation coverage and richness both increase first,then decrease,and then increase slowly.,But the change in richness is small,and the diversity shows a trend of decreasing first and then increasing;the stand density has a greater impact on the characteristics of the vegetation under the forest,and the trend of richness and coverage first increasing and then decreasing.It reached the maximum at 1000-1200 plants / hm~2,but the effect of stand density on species diversity showed that as the stand density increased,the Simpson index Sp of the North American Larch plantation fluctuated greatly,but there was no obvious law,Shannon-The Wiener index Sw has small fluctuations.