The Ecological Effect Of Different Mixed Afforestation Patterns In Degradation Limestone Mountain Of Yimeng Mountainous Area

In this study, we took the vegetation and soil under different mixed afforestation patterns of degradation limestone mountain in Yimeng mountainous area as the research objects, combined field survey and laboratory experiment as research methods and took the barren slope without afforestation as control. We studied the varying condition of some indexes under different afforestation models and ages, such as composition of vegetation species, characters of quantitative, vegetation diversities, biomass, soil bulk density, soil porosity, characteristics of infiltration, soil moisture conditions, soil organic matter, total nutrient, available nutrient content, etc. Meanwhile, the principal component analysis was used to do the comparative assessment of all indexes and the explore for the afforestation model which with the highest ecological effect that could provide references for the afforestation in limestone mountainous. And main results as follows:(1) With the extend of afforestation years, number of plant species and proportion of annual and biennial both decreased, and the presented trend of perennial herb was increased first and stabilized later. Among them, the acer mono maxim and ailanthus mixed forest had the biggest additional proportion, that means five years after the afforestation, the species of small semi-shrub and semi-shrub increased. In the year of 2013, the average coverage, height and density of herbaceous plant of the control and each mixed afforestation patterns were the biggest and decreased in 2011 and 2014. But the acer mono maxim and ailanthus mixed forest and robinia and smoke tree mixed forest both increased compared to 2013.(2) The variation rule of herbaceous plant biomass under each afforestation models in 2011,2013 and 2014 all were robinia and smoke tree mixed forest> acer mono maxim and ailanthus mixed forest> oriental arborvitae and acer mono maxim mixed forest> oriental arborvitae and forsythia mixed forest> the control. The plant important value concentrated year after year, Themeda japonica (Willd.) Tanaka was the main dominant species, secondary dominant species took obvious changes in three years and the succession of dominant plant under different afforestation models were nearly the same. With the extend of time after afforestation, the Simpson diversity index, Shannon diversity index and Jsw evenness index all decreased while the Margalef richness index presented volatility.(3) Five years after afforestation, the soil bulk density of different mixed afforestation models all smaller than the control. The soil bulk density of different forestland in three years ranked as the control> oriental arborvitae and forsythia mixed forest> oriental arborvitae and acer mono maxim mixed forest> acer mono maxim and ailanthus mixed forest> robinia and smoke tree mixed forest. The changes of soil porosity condition were contrast to the soil bulk density. In the same year after afforestation, there were big differences in initial infiltration rate of four afforestation models and robinia and smoke tree mixed forest had the maximum value. With the extend of the year after afforestation, the initial infiltration rate, the steady infiltration rate and the average rate all increased.(4) The soil organic content of each mixed afforestation models all higher than the control, and in 2011 the acer mono maxim and ailanthus mixed forest had the maximum value while the robinia and smoke tree mixed forest had the maximum value in 2013 and 2014. Under different mixed afforestation models, the soil total nitrogen and total phosphorus content both increased with the extend of the year after afforestation, and maintained stable from the year 2013 to 2014. The soil total potassium content was rich, except the decrease in oriental arborvitae and acer mono maxim mixed forest with the extend of the year after afforestation while other three mixed afforestation models all increased, all these four models had significant difference with control. The variation trend of the three total nutrient content and available nutrient content were the same.(5) We can conclude from the score of the principal component analysis and ranking results of the five afforestation patterns and fifteen combination in three years that the robinia and smoke tree mixed forest had the best ecological effect and the rest were as follows:oriental arborvitae and acer mono maxim mixed forest, oriental arborvitae and forsythia mixed forest and the control. The results of clustering methodology and principle component analysis were consistent thus could verify each other.