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The establishment of mixed-species forests with complex structures and high biodiversity has emerged as a key approach for enhancing productivity and maintaining the stability of plantation forests. However, how the mixing effect changes with stand development and climate variation is still unclear. Additionally, little is known about how the mixing effects vary between even- and uneven-aged mixed planting strategies based on the same species combinations and site conditions. In this study, we used dendrochronological methods to reconstruct 37 years of annual growth series for even-aged mixed plantations (EMs) and uneven-aged mixed plantations (UEMs) of Pinus massoniana and Castanopsis hystrix , as well as their respective monocultures at the individual tree (286 trees in total) level. We found that in EMs, the growth of P. massoniana and C. hystrix was 20.8 % lower and 26.2 % higher than those of their monocultures, respectively. However, the growth of P. massoniana remained unchanged during the first 17 years of mixing, after which it was significantly suppressed by C. hystrix. The growth of P. massoniana and C. hystrix in the UEMs was 20.8 % and 26.2 % lower than that in their monocultures, respectively. Remarkably, the mixing effect on the growth of P. massoniana shifted from suppression to promotion after 30 years of mixing. Furthermore, the relative growth of P. massoniana in the UEMs increased with dry season precipitation. These results indicate that transforming pure plantations into uneven-aged mixed plantations may be a crucial forest management strategy for enhancing tree growth and to improving adaptation to future precipitation pattern changes. However, in EMs, thinning should be conducted before fast-growing, shade-intolerant species experience intense light competition. • Even-aged mixture (EM) decreased the growth of both P. massoniana and C. hystrix. • Uneven-aged mixture (UEM) decreased the growth of P. massoniana but increased that of C. hystrix. • The growth of P. massoniana in the EM became suppressed after 17 years of mixing. • The growth of P. massoniana in the UEM became promoted after 30 years of mixing. [ABSTRACT FROM AUTHOR]

China's subtropical forests play a vital role in sequestering global carbon; therefore, it is critical to conduct a precise investigation of intra-annual wood formation in these ecosystems to clarify the mechanisms behind this. Two field experiments were established in Chinese subtropical forests to monitor weekly the intra-annual xylem formation of Pinus massoniana Lamb. from January to December 2015, using the recently developed micro-sampling approach. The effects of climate on wood formation were also assessed using linear or mixed models. Results indicate that there is an inactive period that might be semi-dormancy in subtropical pine ecosystems in January compared with the complete dormancy in temperate and boreal ecosystems and the fully active or short-term dormancy in tropical ecosystems. The duration of xylem formation of Chinese red pine in subtropical China in 2015 was 4–6 months longer than temperate and boreal forests. Moreover, trees were found to grow better during the dry season than the wet season, indicating that the Chinese red pine ecosystem is more strongly regulated by net energy than by environmental factors. Our findings indicate that China's subtropical pine forests may benefit from the expected longer dry seasons, possibly leading to better forest growth and improved carbon sequestration under continued climate warming. [ABSTRACT FROM AUTHOR]

It is critical to investigate the effects of competition and climate on forest growth as they are main forces affecting forest dynamics. However, in subtropics of China such a study has never been conducted. Here we conducted a pioneer study to evaluate the effects of competition and climate on growth of Chinese red pine (Pinus massoniana) in mixed forests of subtropical China along a broad latitudinal gradient (23°N∼32°N). Twenty-three plots (20m × 20m) were randomly selected from 11 sites and competition and tree radial growth data were collected. Principal component analysis (PCA) was used to detect the potential spatial pattern in site-specific standard tree-ring chronologies during the common period (1990-2015). The linear mixed-effect models (LMMs) were employed to quantify the relationships between cumulated basal area increment (5, 10, 15, 20 and 25 years) of subject trees and six distance-independent competition indices. The relationships between tree radial growth and climate were evaluated by response analyses. Finally the best predicted competition index and climate factor were employed in a full model and their relative importance were calculated. The PCA results allowed classifying the mixed forests into southeastern and northern groups along the Nanling Mountains and Wuyi Mountains. LMMs results revealed that competition pressures mainly come from density and size of larger individuals. Response coefficients demonstrated that precipitation in September and sunshine duration in October influenced trees radial growth of southeastern group and northern group respectively. Our results clearly showed that effects of competition on tree radial growth decreased from southeast to north while effects of climates increasing over this large spatial scale. This is the first attempt to clarify the effects of competition, and further quantify the contributions of competition and climate on tree radial growth in China subtropics. Our finds will certainly contribute to a better policy-making for sustainable forest management. [ABSTRACT FROM AUTHOR]