Effect Of Environmental Factors On The Natural Regeneration Of Pinus Tabuliformis In The Songshan,Beijing

Pinus tabuliformis is an endemic tree species in China,and it is one of the important afforestation tree species in northern China.There is the only large area of natural Pine forest in the Songshan National Nature Reserve,Beijing.However,There are problems with the natural regeneration of P.tabuliformis.In this study,we focused on the Natural Forests and Plantations in Songshan Nature Reserve to investigate the natural regeneration mechanism of P.tabuliformis.Combining with 15 habitat factors,such as stand structure,topography,soil factors,litter factors,and human disturbance factors,the natural regeneration mechanism of P.tabuliformis were studied form the three stages of soil seed bank,seedling and sapling regeneration.The purpose of the study is to provide a scientific reference for solving the problems of regeneration and subsequent management of P.tabuliformis.The results of the study are as follows:1.The quantitative characteristics of the seed bank of P.tabuliformis in Songshan were as follows:litter layer>soil layer(0-5cm)>soil layer(5-l0cm).And the number of intact seeds was slightly more than the number of un-intact seeds.2.The environmental factors that significantly affect the regeneration density of P.tabuliformis seedlings were:proportion of large trees,stand density,herb coverage,elevation,slope,slope position,litter depth,and human disturbance factor.The regeneration density of P.tabuliformis seedlings was positively correlated with stand density and herb coverage(P<0.05),and negatively correlated with elevation and slope(P<0.01).The relationship between the regeneration density of seedlings and the proportion of large trees could be explained by a parabolic model(R2=0.31,P<0.01).The regeneration density of seedlings achieved the lowest level when the proportion of large trees took about 50%.There was significant difference between different slope position(P<0.05),which was represented as bottom slope>middle slope>top slope.The regeneration density of seedlings at different disturbance intensity followed this pattern:strong disturbance>moderate disturbance>light disturbance.When the litter depth was greater than 6cm,the regeneration density of seedlings was significantly reduced3.P.tabuliformis has different responses to environmental factors in seedling emergence and seedling survival stages.The environmental factors that significantly affect the regeneration density of P.tabuliformis saplings were:proportion of large trees,stand density,herb coverage,elevation,slope,slope position,soil pH,soil total P,and human disturbance factor.The regeneration density of P.tabuliformis saplings was positively correlated with elevation and slope(P<0.05),and negatively correlated with stand density and herb coverage(P<0.05;P<0.01).The regeneration density of saplings achieved highest level when the proportion of large trees took about 50%(R2=0.38,P<0.01).There was significant difference between different slope position,which was represented as top slope>middle slope>bottom slope.The regeneration density of saplings at different disturbance intensity followed this pattern:light disturbance>strong disturbance>moderate disturbance.Soil pH and total P content had a significant effect on regeneration density of saplings(R2=0.547,P<0.01;R2=0.533,P<0.01).4.Provenance and seed germination conditions were not the limiting factors for natural regeneration of P.tabuliformis.There were obstacles in the growth and survival stages of seedlings.After principal component analysis,the natural regeneration was mainly affected by terrain factor,soil nutrient elements and the vertical structure of stands.And the most significant factors were elevation,soil total P,litter depth,proportion of large(small)trees,crown index and soil moisture content.