Study On Multi-function And Trade-off Of Subtropical Plantation For Soil And Water Conservation

With the gradual strengthening of human consensus on forest ecological service functions,the original single timber production function can no longer meet the needs of social development.Jiangle County in Fujian Province is a typical area of southern Chinese fir(Cunninghamia lanceolata)plantation management.It has objective requirements for the realization of multifunctional management of plantations,especially soil and water conservation.In this study,the soil physicochemical properties of pure and mixed Chinese fir plantations were analyzed using stand data and soil profile data.Based on the data of precipitation,soil,remote sensing,etc.,the soil conservation in the study area was quantitatively analyzed based on the Revised Universal Soil Loss Equation(RUSLE),and the priority protected area was determined based on the vegetation restoration characteristics of the harvested land.Based on the data of second-class survey of forest resources,random forest algorithm and inflection point function were used to construct random forest models to analyzed the factors that affect the structure characteristics of the understory.The factors were divided into three categories,namely human factor,stand status factor,and site condition factor.Based on the collection of a large number of relevant literature data,the water conservation function of typical plantations in the study area was analyzed using the measured hydrological data from the sample site and referring to the typical comprehensive water storage capacity method.The relationship between natural water-holding capacity and biomass of vegetation structure components in plantations were analyzed using the method of total biomass harvesting.Finally,the four functions of soil conservation,water conservation,wood production,and carbon sequestration were analyzed on the stand scale using the measured hydrological data of the plot and existing volume models and biomass models.The main research conclusions are as follows:(1)The physical properties of the 0-20 cm soil layer are the main factors affecting the growth of pure Chinese fir plantations,especially the 0-5 cm.The chemical properties of deep soil are the main factors affecting the growth of Chinese fir plantations,especially the 40-60 cm.Soil available phosphorus content and organic matter content are the key soil characteristics for the growth of Chinese fir plantations.In general,the soil quality of Chinese fir plantations improved first and then degraded with the development of the stand.There were significant differences in the distribution pattern of soil properties between pure and mixed Chinese fir plantations.In addition,the differences in chemical properties between pure and mixed plantations are significantly greater than the difference in physical properties.Mixed tree species can improve soil conditions,especially chemical properties.(2)The soil erosion intensity is light in most of the study area,but there is strong erosion locally.Mild and moderate erosion contribute greatly to erosion.Soil erosion area and erosion of 15-25°with a maximum,followed by 8-15°and 25-35°.Soil retention per km~2 of woodland and sparse vegetation is relatively high,which is significantly higher than other land cover types.The area of the trace should be minimized when designing the operation.The average restoration time of Jiangle plantation is nearly 4years,and the average vegetation cover management factor is 0.729.Except for severe erosion,the erosion modulus of other erosion grades increased first and then decreased with the increase of slope.For the second-and third-level key protected areas,broad-leaved forest type has the largest area.(3)Compared with the traditional method,the inflection point function method is more suitable for identifying important variables in the prediction of understory properties.The main factors affecting the structure characteristics of the understory are landform type,altitude,slope,humus layer thickness,soil layer thickness,stand origin,dominant tree species,canopy density,stand age,average DBH,average tree height,number of trees trees per mu,and accumulation of forest stand per mu.The most important influencing factors are altitude,humus layer thickness,stand age,and number of trees per mu.(4)The total water conservation capacity of Jiangle's main forest ecosystem is 6.08×10~8 m~3,and the water conservation capacity per unit area is 3 245.78 m~3/hm~2.Among them,the canopy interception is4.98×10~8 m~3,accounting for 82.04%.For canopy interception,pure broadleaf plantation accounted for the largest proportion(34.10%),followed by pure Chinese fir plantation(26.53%),and mixed plantation accounted for the smallest proportion,only 6.15%.Combined with canopy interception,litter water holding capacity,and soil water storage capacity,the pure broad-leaved plantation has the strongest water conservation capacity,accounting for 31.30%.The maximum values of canopy interception and soil water storage in most plantation types occur at altitudes ranging from 300 to 600 m.As the altitude increases,the amount of forest water conservation generally decreases.(5)The wood production and carbon sink functions show a significant increase with the elevation factor(P<0.001),and the rate of increase in wood production function is greater(slope k=1.91).In general,with the development of stands,the function of wood production increased,but the function of water conservation decreased significantly.The trade-off value between the pure Chinese fir plantation is relatively small,while the mixed Chinese fir and Michelia macclurei plantation and the pure Pinus massoniana plantation are relatively large.Wood production and soil conservation functions,wood production and water conservation functions of the mixed Chinese fir and Pinus massoniana plantations all show great comprehensive benefits.The comprehensive benefit of soil conservation and water conservation functions of pure Chinese fir plantation is greater,while mixed Chinese fir and Pinus massoniana plantation is smaller.In summary,the purpose of this study is to analyze the multiple functional benefits of typical subtropical plantation types and the effects of stand characteristics and site conditions on their functions,in order to provide theoretical support for multifunctional forest management.