Growth Characteristics and Influencing Factors of Emmenopterys henryi Root Sprouts

Emmenopterys henryi Oliv., belonging to the genus Emmenopterys in the family Rubiaceae, is a rare and endangered second class state-protected plant in China. The population size of wild E. henryi has declined rapidly due to habitat destruction, overex-ploitation, and poor natural regeneration. Using variance analysis, multiple comparisons and principal component analysis, the growth characteristics and main influencing factors of E. henryi root sprouts were investigated and analyzed. The results showed that the number of E. henryi root sprouts decreased with increasing age, and one-year-old root sprouts showed the highest mortality. Height and stem base diameter both showed exponential equations with monthly increases in the age of root sprouts. Most root sprouts generated southeast of (120°-150°) and within 2 m of their mother tree, and growth occurred mainly from exposed roots with a diameter of 2 cm and a length of 30 cm. The height of the root sprouts was influenced less by orientation around the mother tree, but more by the diameter and length of the exposed roots from where the sprouts generated. Compared with other sides, root sprouts growing south of the mother tree showed significantly larger stem base diameters and reached a maximum at 168.75°. The crown breadths of the root sprouts from the east and west were larger than those from the north and south. Morphological indices, including height, stem base diameter, and crown breadth of the root sprouts, declined with increasing distance from the trunk of the mother trees. The morphological indices firstly increased and then decreased with increasing diameters of the exposed roots, with the height and stem base diameter of the root sprouts reaching a maximum when the diameter of the exposed roots was 6.5 cm. The indices showed a reverse trend with increasing length of the exposed roots. The mortality of the root sprouts beyond the crown of the mother tree was larger than that under the crown. Principal component analysis indicated that light conditions, soil organic matter content, gravel coverage, and moderate artificial interferences were the main factors promoting E.henryi root sprout growth. To maintain development and realize natural regeneration of the E.henryi population, the canopy density of E. henryi should be reduced and artificial cultivations increased.