Early Summer Temperature Variation Recorded by Earlywood Width in the Northern Boundary of Pinus taiwanensis Hayata in Central China and Its Linkages to the Indian and Pacific Oceans

Simple Summary This paper analyzed the different relationships between earlywood and latewood as well as total tree-ring growth and the climate factors and reconstructed 106 years of May-June mean temperature (T-MJ) in the Tongbai Mountains based on the earlywood width chronology of Pinus taiwanensis Hayata. It also analyzed the linkages to the Indian and Pacific Oceans. This paper found that earlywood width chronology has better response to the climate factors than latewood width and total tree-ring width. This study also found that the main limiting factors that restrained radial growth of Pinus taiwanensis Hayata in the Tongbai Mountains were May-June mean temperature and mean maximum temperature. The reconstructed T-MJ series have a better reliability and are significantly negatively correlated with sea surface temperature (SST) over the tropical Western Pacific Ocean and Indian Ocean and are significantly positively correlated with SST over the subtropical Pacific Ocean. Finally, the periodic fluctuations of T-MJ in the Tongbai Mountains might be related to the quasi-biennial interannual oscillation of SST over the Indo-Pacific equatorial region (QBO). The results of this study are significant for further understanding and exploring forest growth and climate change in the climatic transition zone. The Tongbai Mountains are an ecologically sensitive region to climate change, where there lies a climatic transitional zone from a subtropical to a warm-temperate monsoon climate. The northern boundary of Pinus taiwanensis Hayata is here; thus, climate information is well recorded in its tree rings. Based on developed earlywood width (EWW), latewood width (LWW) and total ring width (RW) chronologies (time period: 1887-2014 year) of Pinus taiwanensis Hayata in the Tongbai Mountains in central China, this paper analyzed characteristics of these chronologies and correlations between these chronologies and climate factors. The correlation results showed that earlywood width chronology contains more climate information than latewood width chronology and total ring width chronology, and mean temperature and mean maximum temperature in May-June were the main limiting factors for radial growth of Pinus taiwanensis Hayata. The highest significant value in all correlation analyses is -0.669 (p < 0.05) between earlywood width chronology and May-June mean temperature (T-MJ) in the pre-mutation period (1958-2005) based on mutating in 2006. Thus, this paper reconstructed May-June mean temperature using earlywood width chronology from 1901 to 2005 (reliable period of earlywood width chronology is 1901-2014). The reconstructed May-June mean temperature experienced eight warmer periods and eight colder periods and also showed 2-3a cycle change over the past 105 years. The spatial correlation showed that the reconstructed series was representative of the May-June mean temperature variation in central and eastern China and significant positive/negative correlation with the sea surface temperature (SST) of the subtropical Pacific Ocean and the tropical Western Pacific Ocean and Indian Ocean from the previous October to the current June. This also indicated that May-June mean temperature periodic fluctuations might be related to the quasi-biennial oscillation (QBO) in the tropical Western Pacific Ocean and Indian Ocean. The results of this study have extended and supplemented the meteorological records of the Tongbai Mountains and have a guiding significance for forest tending and management in this area.

Automated summary

This paper analyzed the relationship between tree-ring growth and climate factors using the earlywood width chronology of Pinus taiwanensis Hayata in the Tongbai Mountains. It found that the earlywood width chronology had a better response to climate factors compared to the latewood width and total tree-ring width. The study also identified the main factors affecting radial growth and reconstructed May-June mean temperature using the earlywood width chronology. The results showed significant correlations with sea surface temperature over the Pacific and Indian Oceans, suggesting a potential link to the quasi-biennial oscillation. The findings provide important insights into forest growth and climate change in the climatic transition zone.