Effects of key forest management practices and climatic factors on the growth of Populus tomentosa plantations in the North China Plain

• Adding irrigation and fertilization reduced the effect of CMI on tree growth. • The relative importance of management factors was higher than climate factors. • Irrigation was the most important factor at the young stage. • Both the effects of CMI and planting density increased with stand development. This study aimed to provide sustainable management recommendations for long-term poplar plantations in the North China Plain (NCP) within the context of climate change. Within the NCP, through primary literature and field surveys, we collected tree growth data of 2515 individual trees from monoculture stands of Populus tomentosa with different stand ages (1–40 years). Using linear mixed effects models, we examined the effects of different management practices (planting density, irrigation, and fertilization) and climatic factors (mean air temperature and climate moisture index) on tree growth at different stand ages. Results showed significant effects of all management practices on tree growth across stand ages. Also, the relative importance of management practices was higher than climatic factors. The effects of planting density and growing season climate moisture index (CMI) on tree growth gradually increased with stand ages. In contrast, no significant effect of growing season mean air temperature on tree growth was observed regardless of stand ages. Irrigation was the most important factor impacting tree growth in young stands. In addition, we found that irrigation and fertilization reduced the effect of CMI on tree growth in young stands. The relative importance of planting density and CMI did not differ for younger trees. However, the relative importance of planting density was higher than CMI in middle-aged and mature stands. We also found that the biologically mature age of unmanaged P. tomentosa stands in the NCP was about 15 years. In conclusion, our study highlights the importance of forest management practices and climatic factors for long-term poplar plantations in the NCP. Especially, planting density and moisture were critical factors for managing poplar plantations. The findings of this study can be relevant for intensively managing fast-growing tree plantations in other water-limited areas.