Preseason sunshine duration determines the start of growing season of natural rubber forests

Abstract

Plant phenology is essential for projecting changes in the ecosystem including growing seasons, plant communities and carbon storage. However, it is still unclear how the start of growing season (SOS) of tropical plants responds to climate change. This study examined SOS of natural rubber (NR) which grows in tropical areas using long-term satellite solar-induced chlorophyll fluorescence (SIF) data and nineteen monthly climate factors. “Phenofit” (a R package), Pearson correlation coefficient, random forest and structural equation modeling were used to extract SOS and find the relationship between SOS and climate factors at landscape scale. SOS mainly occurred during 53.3–69.9 day of the year, with a slight yet non-significant delaying trend (about 0.2 d/y) across more than 76% of the study area over 2001–2021. The sunshine duration (Sund), ground temperature at 20 cm depth and evaporation in June last year (pre-June) were the three climate drivers with substantial effects on SOS. Sund in pre-June played the most crucial role (r > 0.65, p < 0.01, variable importance exceeding 0.34 and the standardized path coefficient larger than 0.63), with lower sensitivity to SOS (approximately 0.32 ± 0.06 d/h) among the three climate drivers. SOS had a significant delay with the increase of latitude, and the rate of delay was significantly reduced. Whereas, with the increase of longitude, SOS had a significant advance but the advance rate had no significant change. This study provided a new insight distinct from non-tropical regions, elucidating that SOS in tropical areas is predominantly driven by preseason sunshine duration, characterized by a slight delaying trend. These findings advanced the understanding of tropical plant phenology within changing environments.

Keywords

• Phenology
• Natural rubber
• Climate driver
• Tropics
• Solar-induced chlorophyll fluorescence (SIF)
• Climate change