Study On The Cause And Regulation Of Low-Function Forest Of Pinus Massoniana, Cunninghamia Lanceolata In Guizhou

Pinus massoniana and Cunninghamia lanceolata are the main afforestation species in the south of China,they are widely distributed in Guizhou province.The results of the eighth forest resource inventory in China show that China has a large forest area,but low productivity and low quality.The average forest accumulation in China is 89.79m³/hm^2,which is 70%of the world average,and the average in Guizhou province is only 46.03m³/hm²,ranking 14th in China and51%of the national average.General Secretary Xi Jinping made clear requirements on improving forest quality.The State Forestry Administration listed the improvement of forest quality as the key content in the 13th Five-Year Development Plan.The area of C.lanceolata and P.massoniana forests in Guizhou Province is 163 and 1.6 million hm²,respectively.The low efficiency forests of P.massoniana and C.lanceolata are mainly caused by high density,poor site conditions,sparse and incomplete,etc..Improving the quality of forest stands is the focus and hot topic of the current research in the forestry industry,and it is also one of the important issues in the current development of forestry in China.According to the fourth secondary resource survey of P.massoniana and C.lanceolata in 12counties and districts of Guizhou province,the data of small classes and temporary sample plots and study plots of P.massoniana and C.lanceolata were investigated,and literature was reviewed to analyze the main causes of the formation of inefficient forests of P.massoniana and C.lanceolata in Guizhou province,including poor site conditions,excessive density,sparse and incomplete,and natural factors,etc..Therefore,it is a great significance to select three regulation technologies of tending,thinning,fertilization and replanting and replanting to influence the growth and undergrowth environment of P.massoniana and C.lanceolata plantation,and summarized the countermeasures for the low-efficiency forest reconstruction of P.massoniana and C.lanceolata plantation of three different types.Along the contour of randomized block design,four different thinning intensity treatments were carried out on 12-year-old P.massoniana and 18-year-old C.lanceolata plantation.The thinning intensity of P.massoniana was control?TPCK,0%?and mild?TPL,11%?.Moderate?TPM,22%?and severe?TPH,33%?,C.lanceolata thinning intensity as control(TC_CK,0%),mild?TC_L,17%?,moderate?TC_M,33%?and severe?TC_H,50%?,studied the effects of forest growth and understory environment after 4 and 3 years of thinning,respectively.Using three factors and three levels of L₃?3⁴?orthogonal experimental design,the poor site conditions of P.massoniana and C.lanceolata Plantations of different fertilization experiment,the growth status,soil nutrient and soil enzyme activities of each plot were measured in 3 and 4 years after fertilization,and reasonable fertilization ratio was explored.The Alus nepalensis,the C.lanceolata and the Ligustrum lucidum were replanted in the gap between P.massoniana and C.lanceolata,and studied the growth of trees and the change of under forest environment after replanting and supplementing.The results showed that:1.According to the data of the fourth secondary resource survey of P.massoniana and C.lanceolate in 12 counties and temporary sample plots and research plots,the basic data of the genesis analysis of P.massoniana and C.lanceolata low-efficiency forests were formed together,small classes with average breast diameter<5cm were screened out,among which 26,011 were secondary mixed forests of P.massoniana,17695 were mixed forests of C.lanceolata,25237were mixed forests of P.massoniana and 66634 were mixed forests of C.lanceolate,which are used to analyze low-efficiency forest genesis.?1?The proportion of mixed low-efficiency forests of P.massoniana and C.lanceolata in Guizhou was 35.77%and 19.67%,respectively,and that of pure low-efficiency forests was31.26%and 30.47%,respectively.?2?The main factors that formed the mixed forest and pure forest of P.massoniana in Guizhou were poor site conditions,accounting for 22.56%and 21.96%respectively,followed by excessive density,accounting for 6.85%and 4.19%respectively,followed by sparse defects,accounting for 4.96%and 4.10%respectively,the least affected by natural factors,the mixed forest and pure forest accounted for 1.39%and 1.01%respectively.?3?The main factors for the formation of mixed forests of C.lanceolata in Guizhou are high density,accounting for 9.26%,followed by poor site conditions,sparse defects and natural factors,accounting for 4.90%,4.17%and 1.34%,respectively.?4?The main factors affecting the low-efficiency forest of C.lanceolata pure forest were sparse and incomplete,accounting for 13.66%,followed by site conditions,high density and natural factors,which were 9.24%,7.15%and 0.42%,respectively.?5?The formation of low-efficiency forests of P.massoniana and C.lanceolata in Guizhou was also caused by complex terrain and concentrated rainfall,harvesting unreasonable,not timely renewal,technical factors and economic factors and so on.2.Tending and thinning has different degrees of promotion on forest growth,plant diversity and soil properties.?1?After thinning for 4 years,the average annual growth rate of volume per plant of P.massoniana TP_L,TP_M and TP_H was 3.53%,4.04%and 6.49%higher than that of TP_CK,respectively.After thinning for 3 years,the average annual growth rate of TC_L,TC_M and TC_H volume per plant was 1.14 times,1.32 times and 1.20 times respectively of TC_CK,and the growth was the largest with moderate thinning.?2?Short-term cutting did not significantly increase the stock volume of the stand,and there was no significant difference in the total stock volume?cumulative volume+thinning volume?of different thinning stands of P.massoniana and C.lanceolata.However,it can significantly improve stand quality and material composition,and increase the proportion of large and medium diameter grade specification materials.?3?The diversity of understory plants is also improved after thinning,and the number of species in the fourth year was the highest with moderate intensity.?4?Tending and thinning generally improved soil nutrient,enzyme activity and microbial quantity,reduced soil bulk density,and generally decreased significantly with the deepening of soil layer.Generally,moderate thinning intensity was the highest,but the peak values of nutrients,enzyme activity and microbial quantity were different in different months.For example,the peak values of soil bacteria and fungi in P.massoniana plantation were in September and March respectively.?5?With the change of months,the total number of soil microorganisms under P.massoniana forest showed a trend of decreasing first,then increasing,and then decreasing under different thinning intensities,the largest number was 3614.834×10⁵cfu·g^-1 in September,and the TP_M was1.65,1.33,and 1.18 times higher than that of TP_CK,TP_L,and TP_H.The total number of microorganism under C.lanceolata forest is basically the same as that of P.massoniana.?6?Thinning improves soil enzyme activity.With the change of seasons,different forms of enzyme activity are different,and there were significant differences between different thinning intensities,some of which were not significant.However,with the increase of soil layer,there is a significant decrease in the trend of the trend,and the moderate enzyme activity of moderate thinning is much stronger.?7?Reasonable management density is beneficial to increase the carbon storage of soil,if the density is too small,it will reduce the carbon storage of soil layer.Although the low density increases the growth of trees,it has no significant impact on the carbon storage of forest ecosystem.?8?The principal component analysis method was used to comprehensively evaluate the indicators after thinning,and the results showed that the 12-year-old P.massoniana plantation and the 18-year-old C.lanceolata plantation had the highest scores in moderate thinning,indicating that moderate thinning management is more suitable.3.Fertilization improved soil nutrient status under P.massoniana and C.lanceolata forests,and the short-term soil nutrient content continued to increase,the effect of high-level P fertilizer mixed with N fertilizer or K fertilizer was the most significant.?1?Fertilization applied to N3P1K3,which had better breast diameter and tree height growth in P.massoniana plantation,with an average annual growth rate of 13.64%and 11.63%,respectively,and the N2P2K3 and N3P1K3 treatments of C.lanceolata plantation with better breast diameter and tree height,the average annual growth rate was 9.64%and 7.94%,respectively.N element has a significant effect on the height growth of P.massoniana.The impact on the volume per plant is different.The growth of N3P3K2 and N3P2K1 is the largest,and the growth is 0.0103m³ and 0.110 m³,respectively.The impact on unit area is slightly different.?2?Fertilization increased the contents of soil organic matter,total nitrogen and alkali-hydrolyzed nitrogen,however,there is no significant effect on soil organic matter in P.massoniana plantation.NP had a significant effect on organic matter of 0²0cm in C.lanceolata plantation,P had a significant effect on organic matter of 20⁴0cm,and N had a significant effect only in 2013.There was no significant difference between soil total nitrogen and alkali-hydrolyzed nitrogen in P.massoniana and C.lanceolata plantation on fertilization.?3?In December of the third years after fertilization,the activity of alkaline phosphatase in0-20cm soil layer was significantly promoted by N and P,and N,P and K in the 20-40cm soil layer had significant influence on the activity of soil catalase,and the expression patterns and effects were different in different months.There were no significant changes in catalase,urease,and sucrase.?4?Soil organic matter of P.massoniana plantation was positively correlated with alkali nitrogen and positively correlated with total nitrogen,alkaline phosphatase and invertase after fertilization;Soil organic matter,total nitrogen and alkali hydrolysable nitrogen were negatively correlated with urease and catalase,and alkali hydrolysable nitrogen was positively correlated with total nitrogen,and was positive with alkaline phosphatase and invertase,There was a positive correlation between soil enzyme activity and catalase and invertase,but there was a certain difference in the expression and correlation of soil nutrient and enzyme activity.?5?According to the comprehensive evaluation by principal component analysis,FP4?N2P1K2?treatment performed better after fertilization in P.massoniana plantation,FP3?N1P3K3?treatment performed better after fertilization in Chinese fir plantation,and FP9?N3P3K2?was ranked second in P.massoniana and C.lanceolate.?6?C.lanceolata forest is not sensitive to fertilization,and more reasonable improvement measures should be formulated according to factors such as the age of inefficient C.lanceolata forest,site conditions and undergrowth vegetation.Soil enzyme activity has no obvious change rule under the influence of fertilization and seasonal changes,which needs to be further explored.4.Replanting promoted the growth of stand DBH,but there was no significant difference,which had a significant impact on tree height,volume per plant and volume per unit area,and the plant diversity under the forest was significantly improved.Moreover,due to the replanting transformation measures of broad-leaved tree species?eucalyptus and privet?,the content of total nitrogen and alkali nitrogen in the replanted plots increased significantly in the 0-20 cm soil layer of the P.massoniana plantation,and the organic matter did not change significantly.The organic matter and alkali nitrogen content increased not significantly,and the total nitrogen increased significantly in the contrastive plots.The contents of total nitrogen,organic matter and alkali-hydrolyzed nitrogen in the soil layer of 0²0cm of C.lanceolata plantation were increased.The low-efficiency forests of masson pine and fir with high density were reformed by tending and thinning measures to promote the growth of stand and improve the environment under the forest,which effectively promoted the good development of the ecosystem and performed well in moderate thinning.High level N fertilizer,P fertilizer and medium level K fertilizer had good effect on the low-function forest of P.massoniana,and can also be used as one of the effective measures for the transformation of P.massoniana.After fertilization,the undergrowth environment of C.lanceolata has been improved significantly,but it had no significant effect on the growth of C.lanceolata.This may be the result of many factors such as competition between understory grass and shrub and the utilization of fertilizer and nutrient.Replanting can improve the growth of stand,improve soil nutrient and quality under the forest,and increase the plant diversities.Tending and thinning?fertilizing and replanting can be used for reference for the same type of inefficient forest.