Studt On The Growth And Ecological Function Of Different Age And Multi-layer Forest Of Pinus Massoniana And Castanopsis Fissa

Pinus massoniana Lamb is one of the main fast-growing timber species in southern nationwide.The management of large-scale pure forests cause a series of problems such as declining soil quality,reducing biodiversity and productivity.The near-natural modification of Pinus massoniana Lamb pure plantation is consider to be an alternative to solve these ecological problems.As a result,it can effectively maintain the natural growth capacity of the forest,promote the ecological stability of the forest,and improve the sustainable management of the Pinus massoniana Lamb plantation.Based on the investigation of 4 different densities of 42a Pinus massoniana Lamb-Castanopsis fissa mixed forests（T₁:3000 plants/hm²,T₂:2500 plants/hm²,T₃:1667 plants/hm²,T₄:1250plants/hm²）and a Pinus massoniana Lamb pure forest（control check,CK）,the growth laws of mixed forests,soil physical and chemical properties,water conservation capacity and the diversity of mixed forest after 13a were analyzed.We constructed an evaluation system of Pinus massoniana-Castanopsis fissa mixed forests with ecological function as object evaluation,made a systematic exposition on the effectiveness of near-natural modification of Pinus massoniana plantations.There by,the optimal management density for interplanting Castanopsis fissa under the overmature forest of Pinus massoniana was selected,which providing a theoretical basis and technical support for the modification and sustainable management of artificial coniferous pure forest.The main research conclusions are as follows:（1）The growth at DBH（diameter at breast height）of Pinus massoniana Lamb under different interplanting densities varied between9.18-10.75 cm,followed by T₂>T₁>CK>T₃>T₄;the height of Pinus massoniana varied between 5.33-7.83 m,followed by CK>T₂>T₃>T₄>T₁.The growth of Castanopsis fissa with different interplanted densities varied between 12.98-17.25 cm,followed by T₄>T₃>T₂>T₁;the height of Castanopsis fissa varied between 17.55-19.75 m,followed by T4>T3>T2>T1.A stand growth model of age-diameter at DBH and age-height of Pinus massoniana Lamb have been investigated,in which the Chapman-Richards and Power equations could better describe the DBH and height of Pinus massoniana Lamb.At 54a,the diameter classes of Pinus massoniana Lamb are mainly distributed in 55cm and 60cm,T₂and T₃are accounted for a higher proportion.The forest stock volume of the mixed forest of Pinus massoniana-Castanopsis fissa forest is between 365.36-606.47m³/hm²,and the forest stock volume、biomass and carbon storage of T₂and T₃is significantly higher than other treatments.（2）The effects of different interplanting densities on the soil physical and chemical properties of Pinus massoniana-Castanopsis fissa mixed forest mainly affected the 0-20cm soil layer.T₁possess the optimal soil bulk density and total soil porosity.CK possess the higher total nitrogen content,total phosphorus content,available phosphorus content and instant phosphorus content.The soil organic matter content of T₄is higher than other treatments,and T₂possess a higher content of soil hydrolyzed nitrogen.（3）Different interplanting densities affected the water conservation capacity of the Pinus massoniana-Castanopsis fissa mixed forest.The CK litter layer（3.52cm）was thicker than other treatments;and the litter volume（3.04t/hm²）of CK was significantly higher than other treatments except T₁;T₃possess the maximum water holding coefficient（245.69%）and CK possess the maximum water holding capacity（6.12t/hm²）.（4）Pinus massoniana interplanted with different densities of Castanopsis fissa affects the diversity of the understory vegetation.The Shannon diversity index and Simpson dominance index of the shrub layer in the T₄,T₃and T₂forests were higher than CK.The mixed forest has higher Pielou evenness index than CK.The Shannon diversity index,Pielou evenness index and Simpson dominance index of the herb layer showed that CK was higher than that of the Pinus massoniana-Castanopsis fissa mixed forest.The Shannon diversity index,Pielou uniformity index and Simpson dominance index in mixed forests were decreased with increasing interplanting density.（5）T₃treatment was the highest score in the comprehensive evaluation of ecological function of Pinus massoniana-Castanopsis fissa mixed forest with different interplanting density.The score of T₃and T₂treatment in carbon sink index is higher than that of other treatments,reaching the good grade.The soil condition index score decreases with increasing interplanting density,the CK score is the highest,which belongs to the good grade,and the T1 score is the lowest.The water conservation capacity index of T₁and T₃belongs to the good grade,which is better than other treatments.CK owns the highest score in species diversity ecological indicators,which belongs to a good grade,and T₁belongs to a bad grade.（6）Synthesis of evaluation indicators,T₃can not only produce more wood harvest,but also maintain a relatively good ecological function.There for,T₃is the best density for interplanting Castanopsis fissa under Pinus massoniana forest in our study.