Study On Dynamics Of Stand Growth,Biomass And Plant Diversity In The Eucalyptus Plantations

In recent years, Eucalyptus plantation has been developed rapidly in Guangxi Province, which has accelerated economic development.To make sustainable development of Eucalyptus plantation, it is necessary to have a better understand on forest growth, biomass and undergrowth. In this paper, the study site is situated on the sprout regeneration and stock regeneration of Eucalyptus plantation at the similar site sondition in Qinzhou city, each regenerate way set three repetitions.Through the investigation on the forest growth and plant diversity during2008.1～2012.1,the dynmic changes of growth, biomass and plant diversity in two regenerate ways of Eucalyptus plantation were analyzed, and effect of two regenerate ways on stand structure, growth characteristics, biomass, productivity and plant diversity were stated. The results were as follows.Regenerate ways of Eucalyptus plantation have some effect on stand structure:(1)The DBH total increment of Eucalyptus plantation in sprout regeneration is bigger than that of stock regeneration; the height increment of Eucalyptus plantation in sprout regeneration is higher than that of stock regeneration; the stand structural diversity of Eucalyptus plantation in stock regeneration is not smaller than that of sprout regeneration until the fifth year.(2)The LAI,MELA,TD,TR,Kand LD of canopy have no obvious differences between sprout regeneration and stock regeneration in Eucalyptus plantation.Forest growth of Eucalyptus plantation has been impacted by regenerate ways, and the growth laws of sprout regeneration and stock regeneration in Eucalyptus plantation showed as follows:(1)The DHB of Eucalyptus plantation in sprout regeneration is similar to its height in growth laws, but after the first year’s growth peak, they turn to the lowest point in the fifth year with the obvious falling; Compared to Eucalyptus plantation in sprout regeneration,stock regeneration has the growth peak in the second year.(2)The volume current increment of two regenerate ways peaked at3years old, although it steady declined after that, it is still higher than that of the first year.(3)With the increasing of DHB, tree height of Eucalyptus plantation in sprout regeneration and stock regeneration increased, the DHB and tree height capacity index has a strong positive correlativity.(4)The five years’old of Eucalyptus plantation in sprout regeneration were significantly greater than stock regeneration in DHB, height, individual volume increment and total volume increment whose respective rates are28.78%、12.84%、75.71%、64.06%.Biomass and productivity of tree layer are affected by regeneration ways in eucalypt stands:(1)Except the stand density of Eucalyptus plantation in sprout regeneration (1433stem/hm2) is significantly lower than that of stock regeneration (1533stem/hm2), the biomass of average individual, biomass of tree layer and productivity of sprout regeneration are considerably higher than those of stock regeneration. For example, in the fifth year, the higher rates respectively are52.38%、42.30%、42.30%.(2)The coeffieient variation of biomass is2.23%～9.79%among sprout regeneration, and the range is3.08%～26.78%in stock regeneration.Regeneration ways influence undergrowth plant functional group as followings:(1)The vegetation composition and dominant species are found to change considerably between sprout regeneration and stock regeneration of Eucalyptus plantation. Melastoma dodecandrum Lour.,Mussaenda kwangsiensis H.L.Li,Clerodendrum cyrtophyllum Turcz. and Lygodium japonicum (Thunb.) Sw. were the dominant species in stock regeneration of shrub layer Eucalyptus plantation, and Phyllanthus reticulata Poir.,Lygodium japonicum (Thunb.) Sw. and Cratoxylum cochinchinense (Lour.) B1. were the dominant species in sprout regeneration of shrub layer.(2)The plant species of Eucalyptus plantation in stock regeneration are higher than those of sprout regeneration with the respective rates of28.57%、7.41%、83.33%in herbaceous layer (HL), shrub layer (SL), and arbor layer (AL), but the plant species of Liana(Li) is higher than that of stock regeneration with12.50%.(3)The plant species of Phanerophytes (PH), Hemicryptophytes(H) and Chamaephytes(Ch) of Eucalyptus plantation in stock regeneration are higher than those of sprout regeneration with11.43%、40.00%、37.50%. Regeneration ways impact undergrowth plant diversity as follows:(1)In600m2, the species richness in sprout regeneration and stock regeneration of bush layer are28.33±2.52and30.67±1.15, the species richness in sprout regeneration and stock regeneration of herb layer are5.67±1.53and5.67±1.15,but their difference are not obvious (2)The Simpson index in sprout regeneration of bush layer is much higher than that of stock regeneration,but the C index in stock regeneration of herb layer is much higher than that of sprout regeneration,there are obvious differences between them.However, their Simpson index of herb layer is similar.(3)According to β diversity index, the Jaccard index of Eucalyptus plantation in sprout regeneration and stock regeneration is close; the Cody index and community diversity of stock regeneration are slight higher than those of sprout regeneration.(4)The community similarity of Eucalyptus plantation in sprout regeneration and stock regeneration range from59.38%to76.47%and from62.16%to66.67%. The community similarity ranges from50.75%to70.42%between sprout regeneration and stock regeneration of Eucalyptus plantation.