Abstract:

Aims: Competition can affect the growth of individual trees and is a key factor that shapes the structure and drive the dynamic change of forest communities. It plays an important role in population spatial distribution patterns, population dynamics and succession process. For endangered plants, intraspecific and interspecific competition can be driving factors that cause plant mortality. Forestry management departments can formulate targeted conservation strategies based on the predicted competition sources. In order to explore endangered reasons and provide protection measures, the intraspecific and interspecific competition of a wild Michelia wilsonii (yellow lily-tree) population at Zhougong Mountain in Ya’an was studied.

Methods: The intraspecific and interspecific competitive relationship was analyzed, competition radius was determined by gradually extending range method, and competition index (CI) was calculated by using the Hegyi competition model.

Results: A radius of 10 m was the most reasonable competition range of the M. wilsoniipopulation in this study, which best reflects the intensity of intraspecific competition. The mean competition index of individuals in the small and medium diameter class (3.97 and 3.14, respectively) was greater than the total mean competition index (2.68). The competitive pressure of M. wilsonii primarily came from the intraspecies, and the intraspecific competition (348.72, 62.52%) was stronger than that of interspecific competition (209.03, 37.48%). In addition, as the diameter class increased, the intraspecific, interspecific, and total competition indices decreased. This indicated that as M. wilsonii individuals became larger, they were released from competition, and they became a dominant species of the population. The intraspecific and total competition also peaked at 7.5-12.5 cm and 32.5-37.5 cm, respectively, while interspecific competition peaked only at 32.5-37.5 cm. Of the 21 competitive trees in this population Cunninghamia lanceolata, Prunus conradinae, and Ilex hylonoma were the most important. The relationship between diameter at breast height (DBH) and competition index of M. wilsonii was approximately an exponential function (CI = 3.8907e^-0.048x, R² = 0.1087, P < 0.01), with the competition index decreasing continuously with the increase of the objective trees’ DBH. When the DBH reached 30 cm, the competitive intensity plateaus.

Conclusion: Individual M. wilsonii in the small and medium tree stages were clustered and influenced by strong intraspecific competition. Individuals entering the old tree stage, were subjected to strong interspecific competition, and sporadic individuals grew vigorously. To better protect M. wilsoniipopulation, the relationship among forest competition, spatial patterns, and population renewal should be fully considered in stand protection and management. Appropriate human intervention measurements for the small and medium diameter class should be carried out to promote the regeneration of small and medium trees, to reduce the competitive exclusion among plants, and accelerate plant growth and conservation of population.

Key words: endangered plants, Michelia wilsonii, intraspecific competition, interspecific competition, competition index