The Process of Patchy Expansion for Bamboo (Phyllostachys edulis) at the Bamboo-Broadleaf Forest Interface: Spreading and Filling in Order

Bamboo (Phyllostachys edulis) expansion to native adjacent forests has become an increasingly serious problem; however, expansion patterns of bamboo are still lacking research, especially at a community scale. Quantitative research on bamboo expansion patterns plays a significant role in understanding the bamboo expansion process, as well as expansion prevention and control. We analyzed the change in expansion pattern, expansion index, and expansion rate of bamboo in the bamboo-broadleaf transition zone sample plots, specifically from 2017 to 2021 and from the bamboo forest (representing the late stage of bamboo expansion) to the bamboo expansion front (representing the early stage of bamboo expansion). We found that the expansion of bamboo is a patchy expansion, including inner filling patch, boundary expanding patch, transboundary leaping patch, expansion-infill mixed patch, and stationary patch. From the early stage of bamboo expansion (year 2017 and bamboo expansion front) to the late stage of bamboo expansion (year 2021 and bamboo forest), the type of bamboo expansion patches transitioned from boundary expanding patch to inner filling patch and boundary expansion-inner infilling mixed patch. Additionally, the expansion rate of bamboo showed a declining trend. From 2017 to 2021, the bamboo forest (position of 0-20 m) and expansion front (position of 60-80 m) declined by 0.53 m/2a and 0.47 m/2a, respectively. Our research reveals that bamboo expansion exhibits a patchy expanding process, characterized by a sequence of "first spreading outward and then filling inward", whether viewed from the type of expansion pattern or the expansion rate. This process involves continuous plaque addition, expansion, merger, and filling to complete the expansion of a bamboo population. These findings provide valuable insights into the process of bamboo expansion and have important implications for the management and control of bamboo forests.