# As the Growing Season Progresses, the Key Driving Factor of Vegetation Growth Shifts From Spring Phenology to Temperature in the Cross‐Border‐Region of Northeast Asia

## TL;DR

As the growing season progresses in Northeast Asia, the main factor driving vegetation growth shifts from spring timing to rising temperatures.

## Contribution

This study reveals how the influence of spring phenology on vegetation growth changes over the growing season in a cross-border region.

## Key findings

- The start of the growing season advanced by 0.22 days per year from 2001 to 2020.
- Vegetation growth increased significantly at a rate of 2.3 × 10−3 per year.
- The positive effect of an earlier growing season faded and turned negative during the peak and late growing seasons.

## Abstract

Spring vegetation phenology reflects the dynamics of ecosystems and the status of vegetation growth. Earlier spring phenology can promote vegetation growth by extending the length of the vegetation growing season, thus improving the productivity and carbon sink function of terrestrial ecosystems. However, the stage‐specific effects of spring phenology and climate change on vegetation growth are yet to be effectively explained. Taking the Cross‐border Region of China, Democratic People's Republic of Korea, and Russia (CRCDR) as an example, we utilized the Normalized Difference Vegetation Index (NDVI) as a proxy for vegetation growth and extracted the start date of the growing season (SOS) from NDVI to characterize spring phenology and explored the relative importance of SOS and climate factors on vegetation growth. Results indicate that from 2001 to 2020, the SOS in the CRCDR region advanced at a rate of 0.22 days per year, and vegetation growth increased significantly at a rate of 2.3 × 10−3 per year. However, the drivers of vegetation growth varied across different stages of the growing season. In the early growing season, an advanced SOS significantly promoted vegetation growth in forest and grassland, but this facilitative effect gradually diminished and turned inhibitory during the peak and late stages, during which warming became the primary driver of vegetation growth. Notably, the positive influence of SOS persisted until the fifth month of the growing season in forest but only until the fourth month in grassland. The results of this study supplement those of studies on vegetation growth in the CRCDR, elucidate the effects of the SOS on the dynamic process of vegetation growth, and offer insights into vegetation ecosystems.

During the early growing season, the advanced SOS significantly promoted vegetation growth, but this promoting effect weakened and gradually shifted to a suppressive effect during the peak and late growing seasons. At the peak and late of the growing season, warming becomes the primary driver of increased vegetation growth.