Effects of bamboo invasion on forest structures and diameter–height allometries

Forest structure is fundamental in determining ecosystem function, yet the impact of bamboo invasion on these structural characteristics remains unclear. We investigated 219 invasion transects at 41 sites across the distribution areas of Moso bamboo ( Phyllostachys edulis ) in China to explore the effects of bamboo invasion on forest structural attributes and diameter–height allometries by comparing paired plots of bamboo, mixed bamboo-tree, and non-bamboo forests along the transects. We found that bamboo invasion decreased the mean and maximum diameter at breast height, maximum height, and total basal area, but increased the mean height, stem density, and scaling exponent for stands. Bamboo also had a higher scaling exponent than tree, particularly in mixed forests, suggesting a greater allocation of biomass to height growth. As invasion intensity increased, bamboo allometry became more plastic and decreased significantly, whereas tree allometry was indirectly promoted by increasing stem density. Additionally, a humid climate may favour the scaling exponents for both bamboo and tree, with only minor contributions from topsoil moisture and nitrogen content. The inherent superiority of diameter–height allometry allows bamboo to outcompete tree and contributes to its invasive success. Our findings provide a theoretical basis for understanding the causes and consequences of bamboo invasion. • Bamboo invasion decreases mean and max DBH, max height, and TBA, but increases mean height and stem density. • Bamboo has a higher scaling exponent for diameter–height than trees, indicating a competitive advantage for light. • Invasion reduces the bamboo scaling exponent but indirectly increases that of trees by increasing density. • A high wetness index promotes bamboo and tree allometry.