Study On Ecological Benefit Assessment Of Different Vegetation Restoration Models In Lanlingxi Small Watershed

Based on former studies,we chose seven typical vegetation restoration models (chestnut plantation,oak forest,citrus plantation,masson pine forest,tea plantation, bamboo forest and mixed conifer and broadleaved forest) in Lanlingxi small watershed in the Three Gorges Reservoir Area as study subjects,choosing slope land as reference.A detailed study on ecological benefit assessment of conversion of farmland to forest in different vegetation restoration models in the study area was made and principal results were as follows:1.The herb plants were the main components of the numbers of species and individuals in soil seed bank.The size order of density in soil seed bank was:slope land(12042.67grain/m²),citrus plantation(10160 grain/m²),mixed conifer and broadleaved forest(5605.33 grain/m²),bamboo forest(3653.33 grain/m²),chestnut plantation(3642.67 grain/m²),tea garden(3626.67 grain/m²),oak stand(2005.33 grain/m²),masson pine forest(1045.33 grain/m²).Species richness of soil seed banks in different vegetation restoration models was caculated,and the result was as follows: chestnut plantation(23),mixed conifer and broadleaved forest(23),oak stand(21), masson pine forest(20),citrus plantation(16),bamboo forest(16),tea garden(14),slope land(11).The diversity of soil seed banks was in order of mixed conifer and broadleaved forest(3.19),oak stand(3.17),masson pine forest(3.12),bamboo forest(3.05),chestnut plantation(3.02),citrus plantation(2.72),tea garden(2.42),slope land(2.21).The similarity range of composing species between every two patterns was 37.50～86.67,but overall didn't exhibit a large heterogeneity.Among them,the similarity between slope land and other patterns was at minimum,but the similarity among chestnut plantation, oak stand and citrus plantation was larger than others.In these different vegetation restoration models,there were some similar species between soil seed banks and ground vegetation.In different vegetation restoration models,diversity of mixed conifer and broadleaved forest was restored rapidly,but the community structures of citrus plantation,tea garden were relatively simple.Although seed amount in models under less human disturbance such as mixed conifer and broadleaved forest,masson pine forest and oak stand was not large,their species richness and species diversity were larger than the others.On the premise of herb plants accounting for 88.1%,proportional composition of life forms of species in the former patterns was better than others.According to the maintenance and conservation of biodiversity of different vegetation restoration models in returning farmland to forest project in the Three Gorges Reservoir Area,masson pine forest and mixed conifer and broadleaved forest were better ecological forest models,and bamboo forest and citrus plantation were better economic forest models.2.In different vegetation restoration models,soil bulk density tended to increase with soil depth increasing.The order of soil bulk density was:chestnut plantation (1.865g·cm^-3),masson pine forest(1.815g·cm^-3),oak stand(1.795g·cm^-3),citrus plantation(1.725g·cm^-3),mixed conifer and broadleaved forest(1.53g·cm^-3),tea garden (1.51g·cm^-3),slope land(1.46g·cm^-3),bamboo forest(1.375g·cm^-3).The soil porosity sequence in size order was:bamboo forest(44.885%),tea garden(44.44%)＞mixed conifer and broadleaved forest(44.345%),slope land(44.3%),oak stand(33.7%),citrus plantation(32.25%),masson pine forest(30.4%),chestnut plantation(29.7%).The order of efficient water storage capacity was:bamboo forest(510.34t·hm^-2), mixed conifer and broadleaved forest(307.30t·hm^-2),chestnut plantation(305.80t·hm^-2), slope land(274.95t·hm^-2),masson pine forest(261.80t·hm^-2),citrus plantation (255.75t·hm^-2),tea garden(242.00t·hm^-2),oak stand(178.00t·hm^-2).The stable percolation rate was 0.03mm·min^-1 to 4.43mm·min^-1,the stable percolation rate was between 0.03 mm.min^-1 and 2.96 mm·min^-1.The stable percolation rate of oak stand and masson pine forest was the highest in A layer;and slope land was the lowest as 0.96 mm·min^-1.In B layer,the stable percolation rate of bamboo forest was the highest (1.02mm·min^-1);masson pine forest and mixed forest of conifers and broad-leaved trees were the lowest(0.03 mm·min^-1).3.The amount of litter of the three forest types(oak stand,masson pine forest,mixed forest of conifers and broad-leaved trees) in per unit area were 16.88 t·hm^-2,13.24 t·hm^-2 and 6.88 t·hm^-2,respectivly.The maximum water-holding capacity of the three patterns in per unit weight was:mixed forest of conifers and broad-leaved trees(2863.g·kg^-1),oak stand(2696.9g·kg^-1),masson pine forest(1796.0g·kg^-1).The relationship between the water capacity(water-losing capacity) of litter production and immersion time (water-losing time) was a logarithm function.The relationship between the water absorption speed(water losing speed) of litter production and immersion time (water-losing time) was a power function.4.Compared with slope land,soil and water conservation effects of different vegetation restoration models had been improved obviously,and the surface runoff trended to decrease.Among them,the surface runoff in the pattern of mixed conifer and broadleaved forest was the minimum(220.7 m³/hm²),which was decreased by 86.42% compared with slope land.The range of runoff coefficients of different models was 0.0195 to 0.0253,average being 0.0215,which was decreased by 83.72%compared with slope land.The soil erosion modulus in different vegetation restoration models trended to decrease and the range was 1608.87 t/km²Â·a^-1 to 1876.66t/km²Â·a^-1.The soil erosion modulus in bamboo forest was the minimum(85.8 t/km²Â·a^-1),which was decreased by 95.6%compared with slope land.Next came mixed conifer and broadleaved forest, which decreased by 93.1%.The maximum was tea garden(352.63 t/km²Â·a^-1).The research showed that most of the soil in study areas was a bit acidic,and nutrient content of soil organic matter,N,P,K,exchangeable Ca²⁺ and exchangeable Mg²⁺ trended to increase compared with slope land.The massion pine forest had the biggest increase in hydrolytic nitrogen(192%) and available phosphorus(129%).The chestnut plantation had the biggest increase in total nitrogen(354%),available potassium (176%) and soil organic matter(189%).The citrus plantation had the biggest increase in total phosphorus(810%).Variation range of exchangeable cation in different patterns was limited.5.Eleven factors(soil organic matter,hydrolytic nitrogen,total nitrogen,available phosphorus,total phosphorus,available potassium,exchangeable Ca²⁺,exchangeable Mg²⁺,pH,bulk density and non capillary porosity) were chosen as the evaluation index of the principal component analysis to evaluate the soil quality in different vegetation restoration models.Compared with the soil of slope land,the soil quality in seven models were better than slope land.The soil quality index of different models was respectively: masson pine forest(1.6170),chestnut plantation(1.0239),oak stand(0.7764),mixed conifer and broadleaved forest(0.2902),citrus plantation(-0.3007),bamboo forest (-0.7028),tea garden(-1.1719),slope land(-1.5320).The soil quality of models under less human disturbance such as chestnut plantation and masson pine forest was obviously better than those influenced by cultivation activities.So recommended ecological forest models in research area were masson pine forest and chestnut plantation,recommended economic forest models were citrus plantation and bamboo forest.