Effects Of Improvement Of Pinus Massoniana Low-benefit Forest On Soil Physical And Chemical Properties And Stand Biomass

In this paper,based on reseaching soil physical and chemical properties of pinus massoniana low-benefit forest which have been rebuilt before 20 years and determinating the stand biomass by method of yield,interaction process between vegetation and soil in different reconstructive times,by different restoration measures is revealed,and effects by different restoration measures on soil nutrient,stand biomass and soil erosion are evaluated,that is to provide theory for improvement and ecological resilience of low-benefit forest.The results show that:The results of changes of soil physical properties concerning reconstructive times(3a and 20 a) and changes of soil major nutrient concerning reconstructive times(6a and 20a)show that:taking the soil depth of 0～20 cm for example,in early years after rebuilding,the benefit of soil melioration is obvious comparatively,but with the increasing reconstructive times,the changes of soil physical and chemical properties is smaller than that in early years,and some physical and chemical indexes appear descending trend even,possibly because forest is disturbed and its process of self-fertilization is restricted.With regarding to the different treatment(treatmentⅠ:Pinus massoniana -low density-fertilizing; treatmentⅡ:Pinus massoniana-high density-no fertilizing;treatmentⅢ:pinus elliottii -low density-no fertilizing;treatmentⅣ:pinus elliottii-high density-fertilizing and ck),in the soil depth of 0～20 cm, improveming effect on soil physical and chemical properties of ck is more obvious than that ofⅠandⅡ.All in all,in the wood land rebuilt,there is no significant difference betweenⅢandⅣ,so doⅠand,butⅢandⅣare better obviously thanⅠandⅡ;in the soil depth of 20～60 cm,the difference of soil physical and chemical properties in different treatment is not significant(P＞0.05).For soil bulk,porosity and soil water holding capacity of the different soil layers(upper layer:0～20 cm,lower layer:20～60 cm) in the same treatment,the change trend of forest land rebuilt and ck is same,the upper layer's soil bulk issmaller than that ofthelower layer's,the upper layer's soil porosity is more than the lower layer's soil,the upper layers' soil water holding capacity is better than the lower layer's;In addition,the distribution of soil nutrients which show obvious change with the increasing of soil depth,and the soil nutrient condition of surface is significantly better than lowers.These reflect that, during the recovering of vegetation,the effect of reducing soil bulk,increasing soil porosity and water conservation ability,increasing soil fertility and so on is obvious on the surface.There is difference in now arbor density of Pinus massoniana forest of different treatment,from 2150 to 4350 trees/hm~2.And with the arbor density increasing,the basic law shows that:under branch height and crown density increase too,respectively from 6.41m to 7.82m,from 0.55 to 0.80,but their average height,average DBH and crown area gradually decrease,respectively from 9.98m to 11.72 m,from 7.77cm to 10.26 cm and from 1.94m to 2.26m.In addition,the biomass of different planting density varies significantly which ranges from 112.67 t/hm~2 to 170.56 t/hm~2.The arbor density ofⅣis 3950 trees/hm~2 and the biomass of arbor stratum which is 170.56t/hm~2 is largest.It doesn't illuminate that:the greater arbor density,the greater its biomass.For the community biomass,the difference among the arbor,the shrub,the herb,the litter and the whole stand is significant at the 0.01 level in the different treatment.With regarding to biomass of the total stand(184.14 t/hm~2) and the arbor(170.56 t/hm~2),treatmentⅣis the largest of all,which is significantly larger than other treatment,andⅢis the second;For the shrub and the herb,biomass of ck is the lagest among all the treatment,which are10.54 t/hm~2 and 1.50 t/hm~2,and it is significantly larger than others.In the different stand stratum of one treatment,the biomass proportion of the arbor is the largest,which ranges from 87.95%to 92.63%.For soil and water conservation forest of Pinus massoniana,biomass of the arbor is larger,because arbor density is too large,which leads to growth inhibition to the undergrowth certainly,and all the stratums can not effectively intercept rain water.According to the correlation analysis of undergrowth and impact factors,there were significant positive correlation between undergrowth biomass and soil non-capillary porosity,capillary water holding capacity,SOC,available K;there were significant negative correlation between undergrowth biomass and soil bulk,stand crown density;but t there is no correlation with others.Forest rebuilding impacts the soil erosion critically,soil erosive modulus descents significantly by changing the surface vegetation,soil physical properties and nutrient condition.The amount of soil erosion is different by different treatment:the erosion modulus of ck stand is minimum,being 6.68 t/km~2,and theⅢ(8.52 t/km~2)and theⅣ(8.93 t/km~2)are smaller than theⅠand theⅡthat are 15.43 t/km~2,16.78 t/km~2.The amount of soil erosion and the impact factors are selected to carry out correlation analysis. Soil erosion modulus is significant positive-correlation with soil bulk density at the 0.01 level;and negatively correlates with minimum water holding capacity,soil organic matter,total nitrogen; hydrolyte nitrogen,the total vegetation coverage,undergrowth vegetation biomass at the 0.05 level;and negatively correlates with the soil total porosity,non-capillary porosity,soil maximal water holding capacity,capillary water holding capacity,available potassium at the 0.01 level;and is not significant correlation with other factors.