## 5 Conclusions  
We discuss the impact of future climate on Arctic ecosystems by simulating vegetation growth at a tundra site and a forest site. In this study, we simulated the changing trends of NEE and GPP of the tundra and needle leaf forest in Alaska from 1992 to 2014 and their future changes by 2100 using the LPJ-GUESS model. Our results showed that the LPJ-GUESS model is a useful tool to simulate the NEE and GPP for these two land cover types. During the past decades, the GPP showed a faster-increasing rate in the needle leaf forest site than in the tundra site, and the carbon uptake rates for the two areas fluctuated considerably, with nonsignificant increasing trends. Under the future emission pathways, the GPP values of the tundra and needle leaf forest were also higher, while the carbon uptake showed no significant increasing trends in the future. Under the future emission pathways, the GPP of the high emission SSP5-8.5 scenario increases faster and NEE decreases faster. In this study, we utilized the LPJ-GUESS model to simulate vegetation growth and carbon exchange processes in Alaska. The model validation period was relatively short, spanning only from 2004 to 2008, which may not fully capture the impacts of long-term climate change on the vegetation ecosystems. Additionally, while LPJ-GUESS is a well-recognized ecological model, its structure and parameter settings may not entirely reflect the complexities of the world. **Supplementary Materials:** The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/land13050632/s1](https://www.mdpi.com/article/10.3390/land13050632/s1)]([https://www.mdpi.com/article/10.3390/land13050632/s1](https://www.mdpi.com/article/10.3390/land13050632/s1)), Text S1. The supporting information contains detailed information of FLUXNET data; Text S2. The supporting information contains detailed information of CMIP6 data; Text S3, The supporting information contains detailed information of Supplementary data; Figure S1. Relationships among GPP, NEE and CO2 concentration, Precipitation, Solar radiation, and air temperature for ATQ tundra site under SSP2-4.5 (a,c) and SSP 5-8.5 (b,d); Figure S2. Relationships among GPP, NEE and CO2 concentration, Precipitation, Solar radiation, and air temperature for PRR needle leaf forest site under SSP2-4.5 (a,c) and SSP 5-8.5 (b,d). **Author Contributions:** [PERSON]. ([PERSON]) is responsible for the design of the project, revision of the paper, and acquisition of funding; C.L. ([PERSON]) is responsible for the implementation of the project, analysis of data, and drafting of the manuscript; [PERSON] is responsible for the collection and analysis of data. All authors have read and agreed to the published version of the manuscript. **Funding:** This work was supported by the National Natural Science Foundation of China grant 42161058. **Data Availability Statement:** Land cover data were downloaded from the website [PERSON], Gong, [PERSON], [PERSON], Bai and Liang [27] ([[https://doi.pangaea.de/10.1594/PANGAEA.913496](https://doi.pangaea.de/10.1594/PANGAEA.913496)]([https://doi.pangaea.de/10.1594/PANGAEA.913496](https://doi.pangaea.de/10.1594/PANGAEA.913496)), accessed on 12 April 2023). The climate data and validation data were downloaded from the website ([[https://fluxnet.org/data/download-data/](https://fluxnet.org/data/download-data/)]([https://fluxnet.org/data/download-data/](https://fluxnet.org/data/download-data/)), accessed on 12 April 2023).