| Farmland shelterbelt refers to a special shelterbelt planted around farmland and aimed at protecting farmland ecosystem,which is an important part of shelterbelt.Its main function is not only to resist natural disasters,but also to improve the microclimate in the field,create favorable conditions for the growth of crops,and ensure stable and high yields of crops.Due to the constraints of history,location,transportation and other factors,the yield of crops along the old course of the Yellow River is not high,which leads to people’s low living standards,and economic development lags.Build a scientific system of farmland shelterbelts can be of great significance to improve crop yields,increased protection forest ecological,economic and social benefits.In this paper,the main research object is the poplar farmland protection forest on the old course of the Yellow River.42 forest belts were selected in the Huangfan area to investigate and determine the topographic factors,soil properties and tree growth conditions,and then the types of site conditions were divided.On this basis,the standard wood of typical site was analyzed.Analyzing the growth characteristics of the DBH,the tree height,and the wood volume;combined the biomass measurement of each organ,analyzed the growth rule of poplar shelterbelt under different site conditions,and evaluated its growth adaptability.The research results are as follows:(1)Site condition analysis of the old course of the Yellow RiverThe terrain in the study area is gentle,the elevation is assembled at 2.5-10m,the slope is assembled at 0-4°;the average bulk density of the soil is 1.35g/cm~3;the soil texture is mainly silty grains;the average pH value is 7.57,which is weakly alkaline;the soil organic carbon content is low,which average value is 1.82 g/kg;three variaties of soil available nutrients as alkali-decomposed N,available P and available K in the study area are all at level VI according to the standard;the average forest age of the shelter belt in the study area is 9.2a,and the average breast diameter is 24.91 cm,the average tree height is 16.05m.And the east-west forest belt grows better than the north-south forest belt.(2)Classification and evaluation of site typesSix dominant factors for site classification were screened out:soil texture,saturated moisture content,Total N content,forest growth,pH value,and micro-topography;combined with the specific geographic location and topographic features of the study area,the study area was defined as The main site type area of the old course of the Yellow River,and 42 plots are divided into 5 site types by 6 dominant factors,including 2 site type groups,and the top area of the alluvial fan contains 3 site types,which are high silt loam characteristic areas(I),sand loam soil characteristic area(II),silt loam soil characteristic area(III);alluvial fan slope area contains two types of site,namely sand loam characteristic area(IV),sand loam characteristic area(V)two site types.Site conditions are ranked from well to poor as I,II,III,IV,and V.(3)Analysis of the growth process of poplar shelterbeltThe growth characteristics of poplar trees are notably distinguished under different site conditions,and the performance overall is that the top of the alluvial fan is greater than the alluvial fan slope.At the 10th age,the total growth amount of different diameter types of wood breast diameter from large to small is ranked as III>I>II>IV>V,the largest is the site type III,the average breast diameter is 20.73cm,the smallest is the site type V,and the breast diameter is only 12.13 cm;tree height total growth order from large to small is I>III>II>IV>V,the largest is site type I,the average tree height is 19.45m,the smallest is site type V,the tree height is only 12.43m;volume growth The order of the total amount is III>I>II>IV>V,the largest is site type III,the average volume is 0.427087m~3,the smallest is site type V,and the volume is 0.061407m~3.(4)Fitting of growth equation of poplar shelterbelt and division of growth periodThe growth prediction model of poplar shelterbelt under various site conditions shows that the DBH and tree height growth of poplar shelterbelt show"slow-fast-slow"S-shaped growth trend,and volume growth shows"slow-fast"J-shaped growth trend.The commonly used tree growth equations such as power function type,exponential type,quadratic polynomial regression model,cubic polynomial regression model,and Logistic growth equation are used for fitting.The effects are significant.The P value of all equations is less than 0.001.The R~2 of the model is superior to 0.8.The logistic growth model and cubic polynomial regression model have the best fitting effect amoung all the models.According to the Logistic growth equation,the growth period of the shelterbelt can be cut into pre-growth period,fast-growing period and late-growth period.The fast-growing starting point of the tree height is the earliest,and it enters the fast-growing period from the 4th tree height on average;the average breast diameter enters the fast-growing period is 5.8a;the volume is the latest,and the average is 10a.Site type I standard trees have DBH,tree height,and volume earlier than other site type standard trees and enter the fast-growing period,and the total length of the fast-growing period is short,and the poplar mature time is earlier than the other three site types.(5)Research on biomass characteristics of poplar shelterbeltThe aboveground biomass of poplar shelterbelts in different site types are:No.I 280.34kg,No.II 382.80kg,No.III 336.45kg,No.IV 309.95kg,and No.V 157.12kg.The biomass allocation ratio of each organ of poplar is about the same under different site conditions,which is expressed as trunk biomass:branch biomass:leaf biomass=73.5%:20%:6.5%.The best fitting model of the biomass of each organ is W=aDb,which belongs to the CAR type.The model interpretation degree R~2 is greater than 0.5,and the correlation between simulated stems and branches is significant,and the correlation between simulated leaves and whole plants is extremely significant. |
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