## 4 Discussion  
### Effects of Plant Size and Stubble Height on the Plant Growth and Root Sprouting Ability  
Stubble is an effective technical measurement and widely applied in plant cultivation [36; 37; 38]. The main functions of stubble are to break the apical dominance of plants with sprout ability, promote the formation of new branches and root sprouts from adventitious and dormant buds/new shoots on the residual parts and root system, and increase the number of new branches and root sprouts due to more nutrients being allocated to the growth of branches and root sprouts [27; 39]. Our results showed that there was no significant interaction between plant size and stubble height on the growth of the plants, new branches and root sprouts, and the number of new branches and root sprouts. These findings were inconsistent with the hypothesis (1) that the growth and sprouting ability of _A. elata_ will be affected by the interaction of plant size and stubble height. In the following, we discuss the effects of plant size and stubble height on the growth and sprouting ability of _A. elata_, respectively. Many previous studies have indicated that plant sprout regeneration is closely related to plant size (e.g., diameter at breast height and stump diameter, etc.) [20; 21; 23]. One year after stubble treatment (in 2018) in our study, the number of new branches and root sprouts of large plants were significantly higher than those of the small plants, and the plant growth (plant basal diameter growth) also showed the same trend. On the one hand, our results were partly consistent with previous studies that the sprouting ability of some tree species increased with the increase in stump size (e.g., stump diameter) [24], and the larger plants showed better sprouting ability. On the other hand, the growth of large plant basal diameter also showed better performance, which was conducive to the subsequent development of the plant [15]. Therefore, when using the stubble method to promote the growth and sprouting ability of _A. elata_, large plants should be preferred for stubble treatment. Stubble height (i.e., stump height), an important factor which is easily controlled by humans in stubble treatment, has been widely used in recent years to affect plant growth and sprouting ability in forest management and artificial cultivation [23; 40; 41]. In our study, the stubble height had a significant effect on the basal diameter of new branches and the growth of plant basal diameter. These results revealed that the stubble height mainly affected the horizontal growth of new branches and the plant itself. Compared with non-stubbled _A. elata_ plants, the number of root sprouts of stubbled plants was significantly higher. This finding supported that the stubble treatment could facilitate the regeneration of root sprouts of _A. elata_. Furthermore, previous researchers have found that the optimum stubble height on the growth and regeneration of trees or shrubs varies greatly among different species [26; 27; 39]. Our results indicated that the plant growth and sprouting ability of _A. elata_ also varied among different stubble heights. The new branch basal diameter and plant basal diameter growth significantly decreased with increasing stubble height, and the short stubble height treatment was most beneficial to the plant and new branch growth of _A. elata_. The stubble technique has been applied to rejuvenation of the senescent plants [42]. Based on our findings above, when using the stubble technique to rejuvenate _A. elata_, the large plant with short stubble height (6-15 cm) treatment was the optimum stubble method. This result was consistent with the hypothesis (2). In addition, we reviewed the root sprout regeneration of stubbled _A. elata_ plants after three growing seasons (in November 2020) and found that there was no significant difference in the number and growth of root sprouts of _A. elata_ between the two plant sizes and among three stubble height treatments.