Abstract: We examined the status of gap diameter/height ratio (D_EG/H) of Larix principis-rupprechtii plantations in Guandi Mountain, and explored the canopy structure and light factors of D_EG/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 D_EG/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 correlation between canopy structure and light factors and seedlings and saplings. The D_EG/H values of L. principis-rupprechtii 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 (T_tdr), scattered radiation (T_tdf), and total radiation (T_tot) showed a trend of gradually increasing with gap sizes, while leaf area index (LAI) exhibited a trend of gradually decreasing, with a pattern of T_tot>T_tdf >T_tdr 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.

Key words: gap diameter/height ratio, canopy structure, understory light environment, the growth of seedlings and saplings