N addition decreased stand structure diversity in young but increased in middle-aged Metasequoia glyptostroboides plantations

Abstract

Nitrogen (N) addition has a pronounced impact on tree growth and forest function, but its effects on forest structure diversity are seldom studied. In this study, we measured leaf N and phosphorus (P) stoichiometry, and diameter at breast height (DBH) in both young (N limitation) and middle-aged (P limitation) Metasequoia glyptostroboides plantations under the N addition in the east coast of China, and DBH growth difference (coefficient of variation of DBH growth, CVDBH) and horizontal structure diversity (Gini index of DBH, GDBH) were also calculated. Both CVDBH and GDBH decreased in the young but increased in the middle-aged stand along N addition gradient. In the young stand, N addition increased leaf N:P ratio and relieved N limitation, which resulted in a decrease of horizontal structural diversity via promoting small trees growth and increasing individual DBH uniformity. In the middle-aged stand, N addition significantly increased leaf N:P ratio and strengthened P deficiency, where horizontal structural diversity increased via limiting small trees growth and increasing individual DBH inequality. Overall, our findings imply that the effect of N deposition on stand structure is complex during the plantation development, which can be used to develop guidelines for the management of forests at different growth stage in the east coast of China.

Keywords

• N addition
• Stoichiometry
• Horizontal structure diversity
• Metasequoia glyptostroboides