| In this paper,the degraded artificial shelter forest of Populus simonii Carr.in Ordos area was taken as the research object.The physical and chemical properties of stand structure,growth process,soil bulk density,soil moisture,soil mechanical composition and soil nutrients were studied.Understanding the growth and structure of the stand,revealing the growth law of the stand,and analyzing the characteristics of the soil under the forest provide a theoretical basis for the rational management and sustainable development of the Populus simonii Carr.stand in the study area.The results show that:(1)The distribution of height and diameter of Populus simonii Carr.stands in the study area is asymmetrical single-peak mountain distribution,and the number of trees increases first and then decreases with the increase of tree height and diameter.Tree height distribution ranged from 4 to 14m height class,and concentrated in 7 to 10m diameter class,accounting for 76.9%.Diameter distribution ranged from 2 to 12cm diameter class,and plant number distribution ranged from 6 to 9cm diameter class,accounting for 66.9%of the total.(2)The total growth curve of height,diameter and volume of Populus simonii Carr.in the study area showed an "s" shape,showing a”slow fast slow" continuous growth characteristics.The trend of change is similar,the total growth is low and the growth speed is slow.(3)The growth process of height,diameter and volume of Populus simonii Carr.in the study area can be divided into:0?5a is the early growth period(slow growth);5?15a is the fast growth period(fastest growth);15?25a is the slow growth period(slow growth);after 25a is the late growth period(very slow growth,tend to be gentle).Volume growth slightly lagged behind tree height and DBH for about 5 years.The growth of height,DBH and volume of Populus simonii Carr.in each region mainly concentrated in the fast-growing period;the height and diameter of trees reached the quantitative mature age before and after 15 years,and the volume reached the quantitative mature age before and after 20 years.(4)The soil bulk density of forest land in the study area ranges from 1.4312 to 1.5582g/cm3,and increases with the deepening of soil layer in the depth of 0?60cm;the soil moisture content is in the range of 2.2?9.9%,and increases with the deepening of soil layer in the depth of 0?60cm;the distribution of soil particles is mainly in the range of(2?2000 ?m),and the distribution of soil particle size is relatively concentrated,showing non-uniform distribution,and the mechanical composition of soil is sand particles Mainly.(5)The content of organic matter in forest soil in the study area ranged from 1.0884 to 3.9762g/kg;the content of total nitrogen in soil ranged from 0.0546 to 0.2680g/kg;the content of available nitrogen in soil ranged from 2.4111 to 4.7589mg/kg;and the content of available phosphorus in soil ranged from 0.3814 to 0.9225mg/kg.The content of soil organic matter,total nitrogen and available nitrogen increased with the deepening of soil layer,while the content of available phosphorus did not change significantly with the deepening of soil layer.(6)The growth of Populus simonii Carr.was negatively correlated with soil bulk density,and positively correlated with soil water content,organic matter,total nitrogen and available nitrogen,but not with pH value and available phosphorus content.Soil available nitrogen,organic matter,total nitrogen and soil bulk density had greater impact on stand growth,while soil water content,pH value and available phosphorus had less impact on stand growth.Soil bulk density,water content,organic matter,total nitrogen,available nitrogen and available phosphorus contents were significantly different in different regions,but the pH value had no significant difference. |
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