Evaluation On Cultivation Regimes Of Eucalyptus Industrial Plantation In Leizhou Peninsula

Eucalyptus (Eucalyptus spp.), with the features of fast growing and favorable wood quality, has been widely used in the industrial plantation forest in Lei Zhou Peninsula Area, Guangdong Province, China since 1950s, with great investment returns and social and ecological benefits. However, problems, including site degradation, productivity and stand stability decline, have emerged in the growing of the species in the past decades, which has been curbing the increase of benefits from the growing of this tree species. This study focused on the stand production, investment returns, and site quality dynamics under current silviculture regimes, aimed at providing optimal strategies for future management of plantation forest of this tree species. The major results are:(1) The site quality of eucalyptus industrial plantation declined obviously under current management regime employed in Leizhou Peninsula. In spite of the currently intensive investment in site preparation, fertilization and other management measures, the yield of the plantation declined gradually, and the physical and chemical characteristics of the soil deteriorated to some extent.(2) The wood yield of eucalyptus industrial plantation varied under differnt cultivation regime. The wood yield of the vegetative regenerated plantation stands was markedly higher than that of planted ones. Wood production differed dramaticly between clones of the species, with the ranging of production from highest to lowest of DH32-22 (23.6 m~3/hm~2·a) , LH1, U6, SHI and W5 (18.81 m~3/hm~2·a) . Between cultivation areas variations in wood production were also detected, with the highest in the southern area (25.5 m~3/hm~2·a) , intermidiate in the central area (21.2 m~3/hm~2·a) , and lowest in the north area (18.6 m~3/hm~2·a) . The optimized monoculture plantation growing regime produced better thancurrently used ones in terms of wood output.(3) The investment returns from the plantation varied soundly between cultivation regimes. Financial analysis indicated that the investment returns from vegetative regenerated stands was much higher than that from planted ones, suggesting that vegetative regeneation a favorable approach after first rotations. Investment returns differed obviously between stands of different clones of eucalyptus. The order of clones produced highest to lowest returns was DH32-22, LH1, U6, SH1 and W5. Sound differences in investment returns were also detected between growing areas, with the best in the southern area, intermidiate in the central area, andthe lowest in the north. While the returns from optimized cultivation regime was not as good as the other cultivation regime using now, the returns of it was also very high.(4) Tree stump decomposition promoting approach produced ideal results for the management of regenerated eucalytus plantation forest. Retaining stump on cutover site and accelerating the decomposition by chemicals benefited the growth of the trees in the following rotation thanked to the improvement of soil physical and chamical properties. Sound effectiveness in stump killing, decomposition promoting and site improvement was found with the method of overal spray of a new, self-developed chemical compound. Mixing acacia (Acacia crassicarpa) in the plantation of eucalyptus improved soil fertility, with acceptable wood production and economic benefit. Intercropping between eucalyptus and other crop had better economy returns and maintained soil fetility. The improvement of microclimate in intercropping system was achieved, which produced higher crop yield. Wider spacing and inter-stripe space was an optimal regime for the intercropping system.(5) The optimimal regimes for eucalyptus industrial plantation forest management in Leizhou Peninsula were developed based on the evaluation of new techniques and regimes with the consideration of economic returns, ecological and social benefits. Our results suggested that harmonization in the economic and econological benefits in the management of eucalyptus plantation would be achieved under our new optimal silviculture regimes, which would contribute to sustainability of eucalyptus plantation management. We suggest that rotation between eucalyptus monoculture and mixture with acacia be employed in the northern area, considering the need for long term fertility maintaining;Intercropping regime should be favored in most central area of middle and south area to produce better economic, econological and social benefits.