Abstract
Cunninghamia lanceolata (Lamb.) Hook. has been widely planted in subtropical China to meet increasing timber demands, leading to short-rotation practices that deplete soil nutrients. However, increased nitrogen (N) deposition offsets soil N depletion. While long-term experimental data investigating the coupled effects related to short rotation practices and increasing N deposition are scarce, applying model simulations may yield insights. In this study, the CenW3.1 model was validated and parameterized using data from pure C. lanceolata plantations. The model was then used to simulate various changes in long-term productivity. Results indicated that responses of productivity of C. lanceolata plantation to increased N deposition were more related to stand age than N addition, depending on the proportion and age of growing forests. Our results have also shown a rapid peak in growth and N dynamics. The peak is reached sooner and is higher under higher level of N deposition. Short rotation lengths had a greater effect on productivity and N dynamics than high N deposition levels. Productivity and N dynamics decreased as the rotation length decreased. Total productivity levels suggest that a 30-year rotation length maximizes productivity at the 4.9 kg N ha−1 year−1 deposition level. For a specific rotation length, higher N deposition levels resulted in greater overall ecosystem C and N storage, but this positive correlation tendency gradually slowed down with increasing N deposition levels. More pronounced differences in N deposition levels occurred as rotation length decreased. To sustain C. lanceolata plantation productivity without offsite detrimental N effects, the appropriate rotation length is about 20–30 years for N deposition levels below 50 kg N ha−1 year−1 and about 15–20 years for N deposition levels above 50 kg N ha−1 year−1. These results highlight the importance of assessing N effects on carbon management and the long-term productivity of forest ecosystems.
Highlights
Nitrogen (N) is the element that has the greatest limiting effect on plantation productivity [1]
Site Description The C. lanceolata plantations that were evaluated in this study are located at the experimental area of the Huitong National Forest Ecosystem Research Station (NFERS), Hunan Province, southern China [31]
The results showed that of the productivity of C. lanceolata plantation in response to increased N deposition were more related to stand age than N addition depending on the proportion and age of growing forests
Summary
Nitrogen (N) is the element that has the greatest limiting effect on plantation productivity [1]. In many areas, forest ecosystems have experienced increased atmospheric N deposition in recent years [2,3,4,5]. In most forests in subtropical China, the current rate of N deposition ranges from 18 to 73 kg N ha year, and this is expected to increase in coming decades [6,7,8,9]. The increase in N that is deposited in forests will increase soil N content and, stimulate increased productivity over the short term [10]. N deposition could meet the N requirements of these forests, excess N will result in a nutrimental burden and offsite environmental effects [5,11,12]. Balancing the N supply and the demand for tree growth in these forests is critical for optimizing productivity, sustainability, and environmental protection [13,14]
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