| In this paper,five Robinia pseudoacacia forests with different stand densities(1125,1475,1900,2675,3050 plants/hm2)in Caijiachuan watershed of Western Shanxi Province were selected as the research objects.Through collecting meteorological data,measuring wood seized feet,trunk analysis,and measuring soil moisture status in different forest lands,the variation regularity and research of growth indices(DBH,height,volume,biomass,stand volume,stand biomass,stand biomass,stand productivity)of individual and stand of Robinia pseudoacacia forest with different densities at different forest age stages(3-30 a)were studied.The temporal variation characteristics of soil moisture in different seasons and years(2005-2018)were studied.Based on the analysis of the correlation between soil moisture and tree growth,the water production function of Robinia pseudoacacia plantation was established,and the stand density was regulated based on this function,which provided theoretical support for 'determining the reasonable stand density of Robinia pseudoacacia at different age stages under the existing soil moisture conditions in the study area.The main conclusions are as follows:(1)The interannual and seasonal variations of soil moisture in the study area are consistent with the annual precipitation.The seasonal variations of soil moisture can be divided into four periods:stationary period,fluctuation period,accumulation period and regression period.Stand density had a significant effect on soil water storage(P<0.05).Soil water storage of low density(1475 plants/hm2)was significantly higher than that of high density(more than 1900 plants/hm2)of Robinia pseudoacacia.With the increase of stand age(3-30 a),the inhibition of stand density on DBH,tree height and total volume of Robinia pseudoacacia increased gradually,and the most obvious effect was DBH and volume..(2)Within the density range of 1125?3050 plants/hm2,stand density had significant effects on the growth indexes of Robinia pseudoacacia(P<0.05).For a single tree,the higher the stand density,the smaller the DBH,tree height,total volume growth and the smaller the total biomass per plant,the earlier the intersection point between the average growth and the successive growth(i.e.,the shorter the rapid growth period);for stand,the greater the stand density,the greater the total volume,total biomass and productivity of the stand.(3)According to stand age,stand density and annual soil water storage,the water production functions of DBH,volume,biomass,stand volume and stand biomass of Robinia pseudoacacia were constructed respectively,and the correlation between annual soil water storage and forest growth was clarified.Through analysis and calculation,it is suggested that the annual increment of Robinia pseudoacacia stand volume should not exceed 2.6 m3/hm2 in order to achieve the balance of water supply and water consumption in the study area.Taking this management objective as an example,the reasonable stand density range of Robinia pseudoacacia forest in 10-25 years of age is as follows:the reasonable stand density of 10 years of age is 2106 plants/hm2;the reasonable stand density of 15 years of age is 1350-1419 plants/hm2;the reasonable stand density of 20 years of age is 985-1072 plants/hm2;and the reasonable stand density of 25 years of age is 2106 plants/hm2.The range is 771-863 plants/hm2.In summary,using the water production function constructed by stand age,stand density and annual soil water storage capacity can effectively determine the reasonable density range of various ages of Robinia pseudoacacia,and provide theoretical guidance for the control of Robinia pseudoacacia density in the study area. |
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