Soil Physical and Chemical Properties of Five Subtropical Forests in Lingao of Hainan

With 5 types of typical forests as research object, the physical and chemical properties of different types of forests were analyzed by sample plot investigation method. The results showed that： the soil total porosity was the highest in the Casuarina equisetifolia forest （46.168%）, but the lowest in the Encalyptus robusta forest （39.46%）. The soil capillary porosity was the highest in the Acacia mangium forest （22.57%）, but the lowest in the secondary forest （18.95%）. The soil water content was the highest in the C. equisetifolia forest, with a mean value of 27.85%, but the lowest in the secondary forest, with a mean value of 4.34%. The soil pH values were in the range of 4.81-6.59, the soils in the A. mangium forest, C. equisetifolia forest and E. robusta forest were strongly acidic （pH 4.5-5.5）, and the soils in the secondary forest and C. nucifera forest were weakly acidic. The soils had organic matter contents in the range of 0.34-28.68 g/kg, and showed an order of A. mangium forest〉C. equisetifolia forest〉E. robusta forest〉secondary forest〉C. nucifera forest, with a decreasing trend with the soil depth increasing. The soil total N contents were in the range of 0.10-1.63 g/kg, the A. mangium forest showed the highest soil total N contents, while the C. nucifera forest exhibited the lowest soil total N contents; the soil total P contents were in the range of 0.21-1.74 g/kg, and the E. robusta forest had the highest soil total P contents; and the soil total K contents were in the range of 0.16-2.15 g/kg, and the A. mangium forest exhibited the highest soil total K contents. The soil available P contents were in the range of 0.98-132.46 mg/kg; and the secondary forests had the highest soil available P contents; and the soil rapidly available K contents were in the range of 3.03-27.35 mg/kg, and the C. nucifera forest exhibited the highest soil rapidly available K contents. The soil ammonium N contents were in the range of 1.38-5.15 mg/kg, and the nitrate N contents were in the range were in the range of 0.56 -3.51 mg/kg. The A. mangium forest showed the highest soil nitrate N contents （with a mean value of 2.29 mg/kg） and ammonium N contents （with a mean value of 3.93 mg/kg）. For the same forest type, with the increase of soil depth, the nitrate nitrogen and ammonium nitrogen content also showed a decreasing trend.

Forest Community Structure and Species Diversity of Eight Forest Communities in Wenchang City

The research took different forest communities in Wenchang Satellite Launch Center as the research object and selected 8 forests to explore species diversity, evenness, and dominance of forests. The results showed that species diversity tended to be volatile upon forest communities; semi-mangrove species was the richest, as high as 2.38, followed by natural secondary forest and mixed forests. Plant evenness from high to low was as follows： herbaceous layer〉shrub layer〉tree layer. Natural secondary forest was higher in canopy density, and fewer in herbaceous plants; diversity and evenness were lower than shrub layer. Mangrove forests held lower dominance, and dominance showed insignificant differences among species.

Biomass and Nutrient Accumulation Characteristics of Young Stands of Alnus cremastogyne

To investigate plant biomass and nutrient distribution and accumulation in organs of Alnus cremastogyne at different ages from 1 to 4 years, the biomass, N, P, K, Ca, Mg, Fe and Zn were tested. The results showed that the average biomass of the whole tree and the biomass of leaf, branch, stem, and root were in positive correlation with tree age, but the growth rate of biomass had a decreasing trend with the tree age increasing, and only the biomass proportion of the trunk in the whole individual plant showed an increasing trend with age. The contents of nutrient elements in organs showed an order of N 〉 Ca 〉 K 〉 Mg 〉 P 〉 Fe 〉 Zn ; and the contents of N, P and K were higher in the leaf than in other organs, and the contents of Ca, Mg and Fe in the root were higher than in other organs. The accumulations of N, P, K, Ca, Mg and Zn were the highest in the trunk, and that of Fe was the highest in the root. The annual net accumulations of N, P, K, Ca and Mg in the average trees from 1 to 4 years old were 17.07, 40.79, 95.82 and 106.71 g, respectively, and the annual net accumulations of microelements （Fe and Zn） were 335.04, 577.26, 1267 and 1525.27 mg, respectively.