| The Narrow-crown clone of Robinia pseudoacacia cl. Zhaiguan was newly selected fromBlack Locust population, which has the characteristic of fast growing, good stem form andsmall branching angle (≤35°). In this paper, the biological characteristics and growthperformance of the individual tree and stands of the Black Locust Narrow-crown clone werestudied, and the following results and conclusions were achieved.1. The Black Locust Narrow-crown clone individual grows much faster than the normal BlackLocust, it has the diameter of 17cm, height of 16.4m and the volume of 1.1949m~3 at the age of9 year, which is 22.55%, 83.33% and 175.49% more than that of the normal Black Locustrespectively. it also has good morphological characteristics with branching angle of 34°, factorquotient of 0.67 and average length between rounds of branches of 89cm, which is respectively13°less, 0.19 more and 16cm longer than that of the normal Black Locust respectively. Thesemorphological characteristics were performed in higher stability and with little influence byspacing.2. The 9 year old Black Locust Narrow-crown clone, growing on sandy soil in the ancientreaches of yellow river, had a so well developed root system with its distribution horizontallyextending to 6.6m along east-to-west direction & 5m along north-to-south direction, andvertically extending to 2m below the earth surface, and however its root system mainlydistributed in the soil layer of 0～40cm deep in the earth. In vertical, the roots with thediameter≥15mm mainly distributed in the soil layer of 20～40cm below the earth surface whilethe roots with the diameter＜15mm mainly distributed in the soil layer of 0～20cm below theearth surface, of which the fine roots with diameter＜1mm (for absorption function) mainlydistributed in the soil layer of 0～20cm below the earth surface. In horizontal, the amount ofroots with the diameter≥5mm decreased with the increasing distance away from stem while theamount of roots with diameter＜5mm firstly increased then decreased and then increased againor firstly decreased then increased and then decreased again with the increasing distance awayfrom stem, of which the fine roots with diameter＜1mm (for absorption function) mainlydistributed in the soil between 0.5m and 1.5m away from the stem.3. The 9 year old Black Locust Narrow-crown clone tree had biomass of 161.7kg with the biomass of above-ground parts and root system taking 83.18% and 16.82% respectively.Among the biomass of above-ground parts, each part takes 57.55%(stem)＞38.14%(branches)＞4.31% (leaves). Among the biomass of root system, each part takes 87.13%(main root)＞10.66%(first-class lateral roots)＞1.84%(second-class lateral roots)＞0.37% (third-class andother lateral roots). The 9 year old Black Locust Narrow-crown clone stands in differentspacing had biomass of 149.83t/hm~2 (2m×4m)＞144.57t/hm~2 (2m×3m)＞114.93t/hm~2 (3m×4m).4. For the 9 year old Black Locust Narrow-crown clone tree, the DBH had high growth rateduring the first 4 years after planting with the maximum annual increment & mean annualincrement of 2.6cm and 1.9cm respectively, the height had high growth rate during the first 4years after planting with the maximum annual increment & mean annual increment of 2.6mand 1.4m respectively, the annual increment & mean annual increment of volume continuallyincreased year by year and reached the maximum value of 0.02418m~3 & 0.01187m~3respectively at the age of 9 years, and seemed keeping on increasing in the coming year.5. For the 9 year old Black Locust Narrow-crown clone stands in different spacing, thestanding volume was 96.28m~3/hm~2 (2m×4m)＞90.05m~3/hm~2(2m×3m)＞75.61 m~3/hm~2 (3m×4m).the annual increment & mean annual increment of standing volume increased year by year andreached the maximum value of 19.48 m~3 & 10.01 m~3 respectively at the age of 9 year for thestand in spacing of 2m×3m. However, for the 8 year old normal Black Locust stand in spacingof 2m×3m, the annual increment & mean annual increment of standing volume increased yearby year and reached the maximum value of 3.35m~3 & 1.83m~3 respectively at the age of 8 yearwhich are only 17.2% & 18.28% of that of Black Locust Narrow-crown clone.The above mentioned results or conclusions indicated that the Black Locust Narrow-crownclone simultaneously has the advantages of fast growing, good stem form, narrow crown andwell developed root system, so that it is a good cultivar for establishing fast-growing &high-yielding timber plantations, tree & crops intercropping system, ecological protectionforests as well as "four-sides" greening, which could produce not only high quality timbers butalso provide with ecological protection and ornamental purposes. |
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