Study On Ecosystem Services Of Planted P. Tabulaeformis Forest In The Loess Hilly Region

In this study, to select the young to mature typical planted P. tabulaeformis forest in theLoess Hilly Region, taking restored shrub-grass vegetation after clear-cutting offorest(hereinafter referred to as clear-cutting land) and abandoned land as control, based onthe method of space instead of time and long-term located observation, the ecological servicesfunction and its dynamic changes of planted P. tabulaeformis forest were systematicallyreached, and the value of ecosystem services were valued. It can provide the basis andguidance for ecosystem management work of planted forest in the Loess Hilly Region.In thisstudy, the main conclusions as following:(1)In the material production. Planted P. tabulaeformis forest had a strong materialproduction capability and potential.9a,23a,33a,46a planted P. tabulaeformis forest ecosystembiomass were24.62t·hmx^-2,68.31t·hmx^-2,102.70t·hmx^-2,173.43t·hmx^-2, and the growth of the treelayer biomass was the main reason for stand biomass growth; Control of clear-cutting landecosystem biomass is44.67t·hmx^-2, only the1/4of46a mature planted P. tabulaeformis forest.The typical planted P. tabulaeformis forest maintain a high productivity in near mature forestand mature forest period indicating that reasonable regulations can extend the time of higherlevel of productivity.(2)In the accumulation of nutrients and maintain soil. Cumulative nutrient was poor inplanted P. tabulaeformis forest, but it reached a certain level at the beginning of afforestation,and nutrient accumulation in planted P. tabulaeformis forest gradually increased with thegrowth of forest age;46a mature have cumulated the elements of N, P, K are589.50kg·hmx^-2,21.80kg·hmx^-2,304.37kg·hmx^-2, slightly higher than the clear-cutting land. Soil organic carbonand N element content(0－100cm) of planted P. tabulaeformis forest are increasing at firstand then decreasing trends with the forest growth,and about to peak in the near mature forestperiod; Soil P and K content are decreasing at first and then increasing trends with the forestgrowth; Soil nutrient condition in clear-cutting land is better than46a mature planted P.tabulaeformis forest. With the increase in soil depth, soil organic carbon and N content wasgradually reduced, but the element content of P and K are essentially independent of the depth of soil layer.(3)In carbon sequestration and oxygen release, the planted P. tabulaeformis forest had astrong capacity for carbon sequestration,9a,23a,33a,46a ecosystem carbon reserves were78.81t·hmx^-2,102.30t·hmx^-2,147.95t·hmx^-2,154.41t·hmx^-2, in which soil carbon was highproportion (43.43%to86.02%) and the plant layer carbon proportion were significantlyincreased with the growth of forest age (from10.62%to49.72%) and the litter layer carbon isabout5.00%. The46a planted P. tabulaeformis forest ecosystem carbon sequestrationpotential was93.42t·hmx^-2and the clear-cutting land ecosystem carbon sequestration potentialwas34.05t·hmx^-2; In the composition of the carbon sequestration potential of planted P.tabulaeformis forest ecosystem, carbon stored in living plant biomass and surface litter wasthe main form(92.80%) and carbon stored in soil was low; So improve soil carbon storage isthe key to increase ecosystem carbon sequestration potential. Soil carbon density was the firstincreased and then decreased trend with the increase of the C/N ratio, the peak in the C/Nratio of about10; soil C/P ratio and the C/K ratio increases in favor of soil carbon storage;soil bulk density is smaller, more conducive to soil carbon storage. Planted P. tabulaeformisforest ecosystem annual carbon sequestration rate was the first increased and then decreasedtrend with the forest age growth, in which the average annual carbon sequestration rate inmiddle aged forest period was the highest (3.70t·hmx^-2)and mature forest period was the lowest(0.50t·hmx^-2).(4) In the water regulation and soil conservation functions, from middle age to matureof P. tabulaeformis forest, the annual interception rate by canopy increased tended to increase(from17.00%to29.70%), and the mean interception rate of canopy of P. tabulaeformis wasabout5times of clear-cutting land; The mean stem flow rate is2.80%, and the relationshipwith age and annual precipitation are not obvious; Annual interception by litter is about9.70%, which are remained stable with forest age and have no significant difference fromclear-cutting land; The mean soil water storage (0x^-300cm) in P. tabulaeformis forestland is420.10mm (139.20mm less than the clear-cutting land and decreasing in rate of1.80mm·a-1with the age of forest. The capacity of water conservation in planted P. tabulaeformis forestwas lower than clear-cutting land, and the annual water conservation in the young forest,middle aged forest, near mature forest and mature forest period respectively were2301.95m3·hmx^-2,2377.28m3·hmx^-2,2285.48m3·hmx^-2,1948.79m3·hmx^-2, and canopy interceptionand soil evaporation were the main factors to affect the forest water conservation. planted P.tabulaeformis forest had a good function of soil conservation, and the highest soil loss (duringthe young forest) was only750.40kg·hmx^-2·a-1, and no soil and nutrients loss after the middleaged forest essentially; Soil erosion was not serious in clear-cutting land too. (5)In the purify atmosphere and biodiversity conservation functions, the capability ofpurify atmosphere of planted P. tabulaeformis forest ecosystem was gradually increased withthe forest growth, and various functions of46a mature forestwere about6times ofclear-cutting land. Species richness and biological diversity index of tree layer in Planted P.tabulaeformis forest were at a low level, but those in the shrub layer and herbage layer werehigh.Planted P. tabulaeformis forest ecosystem species richness was28³8, the Simpsonindex and Shannon-Wiener index ranged between0.50⁰.62and1.15¹.58; Thedifferences of species richness and biological diversity index between planted P.tabulaeformis forest and clear-cutting land were not obvious.(6) Valued the7ecosystem service indicators(including provide organic matter,accumulated nutrients, sequestrate carbon and releasing oxygen, water conservation, soilconservation, atmosphere purification, biodiversity conservation) of planted P. tabulaeformisforest, the average annual value of ecosystem services in young forest, middle-aged forest,near mature forest and mature forest pierod respectively were35.97thousand Yuan·hmx^-2,45.33thousand Yuan·hmx^-2,38.81thousand Yuan·hmx^-2,32.43thousand Yuan·hmx^-2, in whichthe three functions economic value of water conservation, carbon sequestration and oxygenrelease, biodiversity conservation are more prominent; Provide the organic matter of timberand fuelwood accounted for only6.00%to15.00%, showing that deforestation blindly to getthe timber and fuelwood only obtain a small part of the stand value of ecosystem services, andmore service value will thus suffer losses.