The Evaluation On Ecological Benefits Of Broad-leaved Species With Different Slope Positions After Forest Transformation

There are many low efficiency forests in Guangdong Province,which are needed to be transformated to increase forest productivity and water conservation capacity,and improve forest complexity and understory diversity.Seedlings of Michelia macclurei Dandy,Liquidambar formosana Hance,Elaeocarpus sylvestris(Lour.)Poir.,Schima superba,Michelia chapensis Dandy,Manglietia glanca Blume were introduced to upper,middle and lower slopes in a Cunninghamia lanceolata(Lamb.)Hook forest for transformation in Xiaokeng Forset Farm,Shaoguan City,Guanggong Province.We investigated tree growth(diameter,tree height and crown width),photosynthesis,chlorophyll fluorescence characteristics,leaf nutrient,diversity of understory vegetation,litter accumulation,soil physical and chemical properties(pH,organic matter,total nitrogen N,total phosphorus P,total potassium K,available nitrogen,available phosphorus,available potassium),soil microbial number and enzyme activity were studied.The results are as follows:1.After the forest transformation,the growth of the seedlings of each slope was improved.Among the six seedling species,growth of L.Hance and S.superba was greatest in the upper slope,and greatest growth occurred in L.Hance in the middle slope and occurred in M.Blume in the the lower slope.2.After the transformation,the soil physical properties of each slope improved,the soil bulk density and porosity were significantly improved,and in general,the soil physical properties in the lower slope were the best among the three slopes.3.During the period of forest transformation,the soil pH value,organic matter and nutrient content of each slope first decreased and then increased,and the soil organic matter and nutrient content decreased in the order of the lower slope > the middle slope > the upper slope.4.The activities of soil enzymes in different slopes increased with the decline of slope position,and they decreased first and then increased during the period of forest transformation.5.There was no regular pattern of nutrient content in seedling leaves at different slope positions: leaf C and K contents of M.Blume were the highest,leaf N content of E.sylvestris was the highest,leaf P content of S.superba was the highest at the upper slope;leaf C content of E.sylvestris was the highest,leaf N and K contents of M.glanca were the highest,leaf P content of M.macclurei was the highest at the middle slope;leaf C content of M.macclurei was the highest,leaf N and P contents of E.sylvestris were the highest,leaf K content of M.Blume was the highest at the lower slope.6.The organic carbon content and total K content of litter show the same trend at the three different slopes: The litter organic carbon content and total K content of the upper slope is significantly lower than those of the middle slope and the lower slope.The litter total N and total P contents decreased in the order of the lower slope > the upper slope > the middle slope.With the increase of time,the litter water holding capacity of the lower slope is the highest throughout.7.The important value of Panicum brevifolium and Dicranopteris dichotoma was higher than other species among all of these herbaceous plant communities at the upper slope,whereas D.dichotoma had the highest important value at the milldle and lower slopes,the important value of Smilax lanceifolia var.opaca was the highest among these undergrowth shrubs at the upper slope,and Litsea cubeba showed the highest importance value at the middle slopes,the important value of Litsea cubeba and Evodia lepta both was higher than the others.The diversity index of the herb layer of the middle slope and the lower slope was higher,whereas the diversity index of shrub layer at the upper slope was the highest.8.The result of Pearson correlation analysis showed that the soil moisture,capillary moisture capacity and capillary porosity were positively correlated with soil organic matter and nutrient content;soil pH,organic matter and nutrient contents were significantly or significantly positively correlated with catalase but negatively correlated with acid phosphatase.9.Overall,M.chapensis,E.sylvestris and M.macclurei were more adaptable to growth at the upper and middle slopes;M.glanca was adapted to the middle slope and lower slope environment and showed a stronger ability of carbon fixation and oxygen release,cooling and humidification.S.superba has a strong adaptability and certain adjustment ability to environmental changes,however,L.formosana has a poor growth performance in different slope positions.