Canopy characteristics under different gap diameter/height ratios of Larix principis-rupprechtii plantations and their effects on the growth of seedlings and saplings
We examined the status of gap diameter/height ratio(DEG/H)of Larix principis-rupprechtii plantations in Guandi Mountain,and explored the canopy structure and light factors of DEG/H of different grades and their effects on the growth of seedlings and saplings regenerated under gaps.We classified gap size into five grades based on DEG/H:Ⅰ(0.1-0.4),Ⅱ(0.4-0.7),Ⅲ(0.7-1.0),Ⅳ(1.0-1.3),Ⅴ(1.3-1.6).We analyzed the changes in canopy structure and light factors under different gap grades,the correlation between canopy structure and light factors,the impacts of gap size on regeneration density and growth indicators of seedlings and saplings,and the cor-relation between canopy structure and light factors and seedlings and saplings.The DEG/H values of L.principis-rup-prechtii plantation were roughly distributed between 0.17 and 1.52,with the highest number of gaps within the range of 0.4-0.7.Canopy opening(CO),direct radiation(Ttdr),scattered radiation(Ttdf),and total radiation(Ttot)showed a trend of gradually increasing with gap sizes,while leaf area index(LAI)exhibited a trend of gradually decreasing,with a pattern of Ttot＞Ttdf＞Ttdr under the same gap sizes.The growth indicators of L.principis-rupprechtii seedlings at grade Ⅰ were the largest(average ground diameter of 2.40 cm,average height of 2.69 m),while those of saplings within the forest(CK)were the highest(average ground diameter of 4.15 cm,average tree height of 5.04 m),followed by grade Ⅴ(with an average diameter of 3.41 cm and an average height of 3.34 m).The growth indicators of Picea asperata seedlings and saplings were the highest at grade Ⅳ(the average ground diameter of seedlings was 1.31 cm and an average height of 0.47 m;the average ground diameter of saplings was 4.03 cm and an average height of 2.89 m).Our results indicate that canopy structure and light environment conditions are the best when the ratio of gap diameter to height is at grade Ⅴ,and the conditions at grades Ⅰ,Ⅴ,and Ⅳ can provide an optimum living environment for the establishment of seedlings and saplings in the gaps of L.principis-rupprechtii forests.
gap diameter/height ratiocanopy structureunderstory light environmentthe growth of seedlings and saplings
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