Effects Of Shrubs On The Loess Plateau And Their Deforestation On The Growth Of Artificial Pinus Tabulaeformis

Plants and the environment was the unity of interaction.Study for response strategies of plants to environmental changes had become a hot spot research of ecology.Pinus tabuliformis was excellent tree species to build shelterbelt and commercial timber forest.It had a significant share in the forest resources on the Loess Plateau and played an important role in local economic development and environmental protection work.The saplings of P.tabuliformis would be nursed when they were moderately shaded by the shrubs at initial planted stage.Compared with the saplings of P.tabuliformis,the shrubs had stronger ability to adapt the environment and grew faster at later planted stage,which leaded to closed forest and affected the growth of the saplings.The closed forest would make the saplings die in high numbers and affected the sustainable development of the artificial forest if the artificial tending measures couldn't be timely taken.How about the growth 'regularity of the saplings at this stage?How would the habitat factors(such as light intensity,air temperature and soil condition)change?What should people do to adjust the community structure and promote the growth of the saplings?However,there was less research to these questions.The artificial saplings of P.tabuliformis were set as objects,which were planted in Malan forest on the Loess Plateau in 2008 and planted in 3 habitats:the edge of the shrubs,the central of shrubs and shrub-cutting release area.Habitat conditions,characteristics of crown shape,the growth characteristics of vertical direction,growth conditions of the current-year trunk,branch and leaf of the artificial saplings were systematically investigated and analysis.Main conclusions in this paper were:(1)The artificial saplings of P.tabuliformis planted in the central of shrubs were shaded by the shrubs.The air and soil temperature in the forest were lower than the outside,but the soil under the saplings had more water and nutrients.The measure of shrub-cutting alleviated the shading effects and set off a series of changes of habitat condition adverse to the growth of the artificial saplings,such as soil temperature rising,soil moisture decreasing and the decomposition of organic matter.The saplings of P.tabuliformis planted in the edge of the shrub lived in the habitat with good soil condition and adequate sunlight.(2)The results showed that the tree height of the saplings in the 3 habitats were not significantly different from each other.The basal diameter,crown width,the number of year of the branch with green leaves,living crown ratio of-the saplings were changed with the same pattern across the three habitats.They were ranked as the edge of the shrubs>shrub-cutting release area>the central of the shrubs.However,the height under branch showed an opposite pattern among 3 habitats.The characteristics of the crown shapes of the saplings planted in the central of shrubs differed insignificantly with those in shrub-cutting release area,but significantly with those planted in the edge of the shrubs.(3)The distribution of basal diameter for the artificial saplings of P.tabuliformis in 3 habitats(the edge of the shrubs,the central of shrubs and shrub-cutting release area)was investigated and the results showed that the basal diameter of the artificial saplings was more concentrated in the edge of the shrubs and the central of shrubs,but more discrete in the shrub-cutting release area.The number of the saplings growing well was less and most saplings' basal diameter was at the lower levels in the edge of the shrubs and shrub-cutting release area.The growth of basal diameter of the saplings was event and at a generally lower level in the central of shrubs.(4)There were more branches and leaves at the top and base of the saplings,but fewer in the middle in the saplings lived in the edge of the shrubs.Influenced by the shrubs,the growth of the branches and leaves of the saplings mainly concentrated at the upper canopy in the central of shrubs,which made the position of the canopy of the saplings move up.The measure of shrub-cutting was good for the growth of branches and leaves growing in base canopy of the saplings,which compensated the shrubs'inhibitory effect to the saplings and made the position of the canopy of the saplings move down.The branch-leaf ratio of the new branch at the outermost layer of canopy gradually decreased from the saplings' top to base in the edge of the shrubs and shrub-cutting release area,but kept a relatively stable low level in the central of shrubs.(5)The growth in current-year of the saplings planted in the edge of the shrubs was not significantly different with those above the shrub,and was significantly more than those saplings below the shrubs.With the increase in altitude intercept between the saplings and the shrub,there was a reducing in the growth of the current-year trunk,branch and leaf of P.tabuliformis.In order to adapt to the low light environment,the saplings below the shrubs would take some bionomic strategies,such as allocating more biomass to the growth of length than to the growth of diameter in current-year trunk and branch,reducing the branch-leaf ratio and increasing specific leaf area.The measure of shrub-cutting promoted the growth in current-year of the saplings(especially those below the shrubs)to a certain extent.(6)After analyzing the correlation among the traits of current-year trunk,branch and leaf,results showed that the leaf area and the total leaf area on the branch were positively correlated with the branch diameter,the total leaf area on the branch was mainly determined by the number of the pine needles on the branch;The specific leaf area had a positive correlation with leaf area,but a negative correlation with the leaf dry weight;the leaf area was significantly related to the leaf thickness.