Study On Structural Dynamic And Silvicultural System Of Conifer-broadleaved Mixed Plantation In Southern Tropical Montane Region

Conversion from timber-oriented plantation forestry to multi-functions oriented forestry calls for rational closed-to-nature forest management strategies and silvicultural systems. However, it has been demonstrated that the ignorance and hesitance of the targeted forest structures is the cause for the uncertainty of research on forest management benefits. The keys for the solutions to problems lie in how to make proper and effective forest management for adjustment of the forest structure and for the formation of the forest with high productivity,, but under the conditions and constrains of forest resiliency and sustainability to benefits long term multi-services function with high economic productivity. In this paper we focus on variability of structure of plantations with different layers in order to fill these information gaps. The objectives of the study were:(i) to investigate diversity and distribution patterns with four different stand layers;(ii) to assess the effects of different succession sera on the variability of structure and stability, and(iii) to evaluate how the growth of certain target species planted within the residual plantation understory are affected by the presence of different potential facilitator species.(iv) to provide structure management strategies and silvicultural systems corresponding for maintaining the sustainability of its plantation in subtropical zone in China.(1) We categorized all tree individuals into four layers according to tree height: the regeneration, lower, middle and upper layers. The results showed that(i) Individual distribution and species richness varied greatly among different stand layers. Species richness and abundance index increased firstly and then decreased with increasing stand layer.(ii) Tree diameter distribution showed significant differences among different stand layers. Tree individuals with diameter more than 20 cm dominated at the upper stand layer(tree height>15.6 m).(iii) Stand volume presented great variance along the stand layers. Although tree individuals at the lower layer contributed substantially to forest area at both plot and stand levels, their volume was less influential than larger trees because about 12.6% of the total tree individuals at the upper layer provided 46.5 % of total stand volume.(iv) Trunk slenderness was applied to represent the trade-off between relative growth rate of height and that of diameter. Trees with stem slenderness values smaller than100 and DBH more than 20 cm were predominantly located at the upper stand layer. The findings suggest that the features of vertical structure were useful for management of plantation.(2) By the method of substituting temporal serial with spatial serial, and taking six forest lands with different ages(10, 20, 30, 40, 50 and 60 years) in monoculture region as test objects, this paper studied the change characteristics of plant community structural characteristics during age stages. Totally 36 plots were measured. Species composition, DBH(diameter at breast height) distribution, abundance, species richness, diversity, and volume were quantified and compared among different age stages. The results showed that(i) Species richness and abundance index increased firstly and then decreased with increasing years.(ii) Tree diameter distribution showed significant differences among different stand layers. Tree individuals with diameter more than 20 cm dominated at the late age stages.(iii) Stand volume presented great variance along the age stages. Silvicultural practices play an important role in shaping the age stages dynamics of Masson plantation, resulting in differences in the structure of the community.(3) We used a field experiment to evaluate the effect of two facilitators, Castanopsis fissa and Magnoliaceae glance, managed with variable retention harvests(25%, 50% and 75% retention), on the development of two target species, Castanopsis hystrix and Erythrophloeum fordii, after a five-year period in a monoculture. The results indicate that the abundance, growth and aboveground biomass were relatively higher over a period of five years in plots planted with C. fissa compared with M. glance and that the target species performed best with 50% retention harvesting of C. fissa, with the greater establishment of the target species indicating a positive interaction. Moreover, the regeneration, LAI and soil conditions differed between the two facilitators in the variable retention harvesting treatments because of the different intrinsic characteristic of the facilitators. We conclude that facilitation by species in variable retention harvesting can shape the establishment of plant communities and that the amelioration of deterioration in microenvironment conditions can favor the development of target species.(4) The concept of forest development type(FDT) was designed to support forest management in ECTF. Considering the soil condition, It was more practical for forest management from the view of dominate tree structure, forest succession stage and tree selection, our study highlights the importance of having a good understanding of operation methods were adopted to match the different FDTs. It is intended to provide a useful idea and approach for further case studies on achieving the target stand and anticipating the benefit of muti-functions forest.