Chronic anthropogenic disturbance causes prolific resprouting and dwarfing – A case study of a widely distributed subtropical tree

Chronic anthropogenic disturbance (CAD) comprises the additive effect of multiple anthropogenic stressors that lead to subtle but continuous alterations to the structure, composition and functioning of natural ecosystems. However, this effect has been little studied at the tree species level. Here, we examined CAD effects on Chinese beech (Fagus engleriana), a common species in northern subtropical forests that utilizes both vegetative resprouting and seeding as regenerative modes. We computed an index of CAD for each plot based on livestock grazing intensity, wood extraction and miscellaneous resource use. Over 60 20 × 20 m plots, we measured the height and DBH of a total of 1261 Chinese beech individuals (21.02 ± 13.06 per plot, [mean ± SD]), including 593 adults (9.88 ± 4.89), 576 saplings (9.60 ± 8.91) and 92 seedlings (1.53 ± 3.91), and assessed the proportions of each that exhibited resprouting (0.91 ± 0.11, 0.69 ± 0.29, and 0.09 ± 0.25, respectively). CAD was associated with a greater number of individual trees and a proliferation of stems, and with a greater proportion of resprouting seedlings, but had no effect on adult-sized stem DBH. Chinese beech thus appears generally tolerant of CAD, which may ultimately result in its increasing contribution to the maintenance of forest biomass. CAD was also associated with shorter adult and sapling stems, but taller resprouting seedling stems, implying that CAD induced dwarfism as Chinese beech matures. Further analysis showed that the proportion of resprouting was related to small scale wood extraction and miscellaneous resource use, but not to grazing. In the context of better understanding cryptic effects of CAD, our findings show that CAD can alter tree morphology and regenerative processes. These coppicing-type effects of CAD on tree morphology structure are typically associated with higher community biodiversity in managed forest coppice, and future work should investigate the biodiversity consequences of CAD at our study site. Our study shows that CAD has important implications for forest resource utilization, planning, and management, with effects on forest biomass and carbon storage in human-modified landscapes.