Study On Sustainable Management Techniques Of Eucalyptus Plantations In The Northwest Of Fujian Province

The community structure, water holding capacity of litter and soil, mixed mode, planting density, small terrain and other sustainable management techniques of Eucalyptus plantations in Yong'an Forestry Company were studied in this paper. The main conclusions were as follows:(1) Small-scale heterogeneity of nutrients index of different types of Eucalyptus Plantations were significantly different. The pH values of plots were between 4.28 and 5.12 which was the optimal range for Eucalyptus's growth. The organic matter content of Eucalyptus forests increased with the decrease of the soil depth, and the average content of three soil layers were 14.41 g/kg, 9.04 g/kg and 5.73 g/kg, while the total organic matter content was relatively low. Soil total N content ranged from 0.69 mg/kg to 2.02 g/kg and the total nitrogen content decreased with the increase of the depth, and the differences among various plots became small. The whole phosphorus content in soil changed little, but in a different study plots, the total P distribution is very uneven. Total potassium content increased with the deeping of soil depth, available K contents were generally more uniform in distribution. The contents of hydrolytic nitrogen, phosphorus and potassium increased with the increase of the soil depth while the change was even. Hydrolysable nitrogen's average content of the soil in different forest nitrogen content changed heavily, which was very poor in some plots. Total phosphorus content was rich and the K content of different Plots fluctuated largely in the range of 31.45 mg / kg to 185.72 mg / kg.(2) There were some different affection to growth and water conservation capacity because of the different mixed mode of eucalyptus plantation. The different mixed modes with different Eucalyptus species benefit the growth of eucalyptus, and seeing from the average DBH and average tree height, volume and accumulation on the growth there were many advantages. The growth order of the growth situation in different mixed modes of Eucalyptus was: E.grandis>E.grandis-E.grandis×E. camaldulensis Dehnh>E. dunnii-E.grandis(7:3)>E.urophylla×E.grandis>E.dunnii-E.grandis×E.camaldulensis Dehnh>E. dunnii-E.urophylla×E.grandis>E. dunnii-E.grandis (5:5)> E.benthamii >E. dunnii.In the 9 types of mixed plots, the E. dunnii-E.grandis mixed forest height layers water holding capacity was up to 14.03 t/hm2, The water holding capacity of E.dunnii-E.urophylla×E.grandis mixed and E.urophylla×E.grandis pure forest were followed, respectively to 10.54 t/hm2 and 10.05 t/hm2, E.grandis-E.grandis×E. camaldulensis Dehnh ranked 5 (8.96 t/hm2), E.benthamii , E.grandis, E. dunnii Eucalyptus pure site were respectively 8.63 t/hm2,7.73 t/hm2 and 6.76 t/hm2. Litter layer's water holding capacity was nearly 10 times to the height layers. The litter store in stands of E.urophylla×E.grandis was small, but its water holding retention rate reached 339.8%.Litter storage in E.grandis-E.grandis×E.camaldulensis was abandunce, the total fresh weight was 5 times to E.urophylla×E.grandis stands, but it was low in water holdup. Compar with the 9 community, the biggest water holding capacity was in the mixed of E.grandis-E.grandis×E. camaldulensis Dehnh, it up to 12.73 t/hm2. Water holdup was slightly larger in herb layer than shrub layer.In shrub layer the largest water holding capacity was the mixed of E.grandis-E.grandis×E. camaldulensis Dehnh (3.02 t/hm2), the smallest is the pure forest of E.grandis (0.67 t/hm2), herbal layer of water holding capacity is the biggest Dunn Eucalyptus - Giant Eucalyptus mixed (2.12 t/hm2), the smallest is E.benthamii eucalyptus plantations and E. dunnii-E.grandis mixed forest (0.43 t/hm2). The results showed that the water conserving capacity of mixed forests were larger than pure plantations.(3) Density of plantation was a very important factor for the impact of stand diameter and volume. DBH and height of low density were obviously bigger, and the stand volume increased with the increase of the density while the stand volume of the forests had the decrease trend when the density reached the level of 2700 ind? hm-2. The planting of eucalyptus plantations did not affect the species diversity of shrub and herb layer, neither was the density factor. But there were some differences in species component. Understory plants'harvest volume in density of 1950 ind·hm-2 was the largest, and the presence of litter was beneficial to the maintenance of soil quality.(4) From the altitude study we can see that the Volume of Dunn Eucalyptus forest decline with altitude increasing within 420-739m above sea level, and the diameter distribution situation in different altitudes were differently significantly. There was the largest number of species in low-elevation, while in the second place in the mid-elevation, and least at high altitude, but the number of understory plants in mid-elevation was biggest. The changing rules of the species diversity indexes and the even indexes were very similar, which were both decreased with the increase of the elevation.(5) There were different affections to height and DBH growth of Eucalyptus because of the different slope direction. The shady slopes benefit the growth of height, while the sunny slopes benefited the growth of the diameter. The affection of slope position to the growth of eucalyptus plantations in different slop direction was not consistent in the law. In the sunny slope, the trees grew best in the downhill than that in the uphill, which was 11.8% bigger in average diameter, and 42.8% larger in stand volume. There was no significant difference in growth situation between mid-slop and downhill, and the premier one was 4.02% smaller than that in the downhill. The forest in the uphill had the worst growth condition among all, and the difference of the average height was close to 2 meters, and the single tree volume in the downhill only reached the 70% of that in the downhill. In the shade slops, the growth situation was the best in the mid-slope, and difference of that in downhill and uphill ranged only from 4% to 10% level. The affection of small terrain for the growth of young eucalyptus plantations was very small. The existence rate of Eucalyptus trees in 1.5 year old was about 96% which had the small fluctuation, and the difference level of average DBH difference was only 0.02cm,and height with a difference of 0.24m. The Stand volumes were 7.8, 8.1 and 8.1 m3. In general eucalyptus plantations grew relatively well in the hill slopes and valleys, although the superiority of the growth was not that obvious.(6)Water and nutrients were two very important factors for the fast growing of Eucalyptus. Land preparation methods, species select, density control measures were focusing on maintaining soil fertility management to improve production and sustainable forest management model. In the forest nutrient cycle, nutrient cycling speed didn't catch up with the consumption speed of fast-growing eucalyptus plantations, so the sustainable development of forestry mainly depends on human supporting, which could provide material basis for sustainable development. In this study, using the principal component analysis method to analyze the main factors affecting the growth of eucalyptus plantations, the results showed that: in the northwester of Fujian the altitude was the biggest factor for the growth of topography, and the soil pH, organic matter factor in the content, field capacity and bulk density, porosity were all very important factors, and the mixed patterns and understory vegetation would also affect the sustainable management of this plantations.