| Rapid-growth and high-yield plantation has brought significant economic benefits,while a series of relevant ecological problems, such as biodiversity, soil fertility, and stabilityof forest ecosystem, have become topics of academic arguments. Eucalyptus occupies a highproportion of plantation in South China, and Hainan is one of the most concentrated areaswhere the Eucalyptus pulp forest was planted in China. Casuarinas equisetifolia is one ofimportant shelter forest tree species in the southeast coastal areas in China, and it was plantedin a large area in the coastal area of Hainan.Hainan Danzhou Forest Farm, Eucalyptus plantation, and Hainan Wenchang ShanyaForest Farm, Casuarinas plantation, were chosen as the target study areas, and the contrastsample plots adjacent to the farms were selected to analyze the changes of tree growth andphysicochemical properties of soil through the investigation data of artificial forest soil andplant community. Assessment the influence of artificial forest planting on soil fertility, andanalysis the effects of environmental factors on plantation growth, which provided thescientific basis for the sustainable development of plantation in HainanStudy on the influence and response of Eucalypt plantation growth on soil fertility, theresults showed that:(1) The average volume increments of a single Eucalyptus tree and per hectare of1a-to-5a Eucalyptus plantation was0.0066,0.0177,0.324,0.0246,0.0215,0.0019m3and9.95,26.56,48.59,36.84,32.32,2.91m~3/hm~2. The volume increments increased from1-to-3-year old and3-year old Eucalyptus tree reached the largest,4-year old more and thegrowth significantly slowed down in5-year old. According to the change trend of averagevolume increments, the turning point of average volume increment was most likely to occurin the5-year old, and then decreased. At present,5-year or6-year cutting cycle was short,and it can be delayed1-2years to7-year or8-year, which can improve the timber yield andpulp quality.(2) With the increase of tree age and volume growth, the soil water content of1-to-5-year old Eucalyptus plantation appeared to have a decline trend; that is10.73%,9.89%,9.34%,8.95%and7.19%respectively. Plantation transpiration water consumption and soilwater consumption increased, and short-term rotation Eucalyptus plantation might lead to adrop of soil water. Soil permeability declined with increasing stand age, and the permeabilitywas improved after Eucalyptus tree was cut down.(3) With the increase of tree age and volume, soil organic matter contents of1-to-5-year old Eucalyptus plantation increased gradually. The soil organic matter contents ofnon-short-rotation Eucalyptus plantation and Cocos plantation were close to5-year oldEucalyptus plantation, and significantly higher than1-year old Eucalyptus plantation, whichmeant that Eucalyptus plantation is conducive to the surface accumulation of soil organicmatter. Eucalyptus planting may result in the decrease of soil alkali-hydrolysable nitrogenand available phosphorus. There was an obvious surface accumulation of alkali-hydrolyzablesoil N, and no obvious impact on soil available potassium.The alkali-hydrolysable nitrogen contents of layers significantly declined with theincrease of tree age, and the N contents of1-to-5-year old Eucalyptus plantation were fewercompared with the contrast sample plots, non-short-rotation Eucalyptus plantation and Cocosplantation. The soil available phosphorus contents of different layers decreased with theincrease of Eucalyptus tree age. The available potassium contents of1-year old Eucalyptusplantation were least in all soil layers, and the contents of2-to-4-year old Eucalyptus forestwere close to non-short-rotation Eucalyptus plantation and Cocos plantation.Study on the influence and response of the Casuarinas plantation growth on soil fertility,the results showed that:(1) Planting Casuarinas can improve soil fertility of bare sandy land. The organic mattercontents of0-20cm and30-60cm depth in soil layers of Casuarina woodland, glade,grassland and bare sandy land were14.87,11.19,10.94,6.56g/kg and11.38,5.84,8.40,6.226g/kg respectively. Soil organic matter content of forest land was significantly higherthan glade, grassland and bare sandy land. Planting Casuarinas had an accumulation of soilorganic matter, and it was objectively helpful for the improvement of the soil nutrient.For the same slope Casuarinas plantation, contents of alkali-hydrolysable nitrogen,rapidly-available potassium and available potassium in different soil layers declined with theincrease of the elevation. There was an obvious surface accumulation in all sample plots. Thecontent of rapidly-available potassium in bare sandy land was last but one, just higher thanthe Casuarinas woodland soils in middle slope, and contents were the least ofalkali-hydrolysable nitrogen and available potassium in the bare sandy land.(2) Compared to the grassland and bare sandy land，the Casuarinas plantation maybeconsumes more soil water. For the same slope, the soil water contents gradually decreasedwith the increase of elevation, and the contents of upper slope, middle slope and lower slopewere5.73%,3.16%and2.70%respectively. The soil water content of grassland was7.50%,bare sandy land6.27%, much higher than Casuarinas plantation.(3) Planting Casuarinas would not bring negative influence on the soil permeability, and it might have a little improvement on woodland soil permeability. At the same slope, thepermeability of Casuarinas plantation had slightly change with elevation and grow amountincreasing, but the difference was not significantly. Casuarinas plantation had the same soilpermeability with contrast sample plots, grassland and bare sandy. |
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