As an important component of the climate system, permafrost responds significantly to climate change, and its impact on the ecosystem cannot be ignored. In this study, we analyzed the temporal and spatial variation trends of the normalized difference vegetation index (NDVI) in Arctic permafrost regions and revealed the correlation between the active-layer thickness (ALT), soil temperature, and NDVI change. Using the partial correlation method, we assessed the ecological regulation service of permafrost to the ecosystem. The results showed that both the average annual maximum and summer NDVI values in the Arctic region followed a significant increasing trend from 1982 to 2015. The average correlation coefficient (ACC) between Arctic NDVI and ALT was 0.35, followed by the ACC (0.33) between NDVI and soil temperature at 7-28 cm depth, and had a lower ACC (0.31) at 0-7 cm ALT. When the precipitation and snow water equivalent (SWE) remained unchanged, the partial correlation between NDVI and ALT was 0.711, which was a significant positive correlation. It also showed that permafrost degradation was the dominant factor controlling Arctic NDVI increase, whereas precipitation and SWE had little effect. The study revealed the impact of permafrost on NDVI change, deepened our understanding of the importance of permafrost degradation for ecosystem services, and effectively filled the gap that tundra ecosystem services value has been ignored in the global ecological service value assessment.

As an important component of the climate system, permafrost responds significantly to climate change, and its impact on the ecosystem cannot be ignored. In this study, we analyzed the temporal and spatial variation trends of the normalized difference vegetation index (NDVI) in Arctic permafrost regions and revealed the correlation between the active-layer thickness (ALT), soil temperature, and NDVI change. Using the partial correlation method, we assessed the ecological regulation service of permafrost to the ecosystem. The results showed that both the average annual maximum and summer NDVI values in the Arctic region followed a significant increasing trend from 1982 to 2015. The average correlation coefficient (ACC) between Arctic NDVI and ALT was 0.35, followed by the ACC (0.33) between NDVI and soil temperature at 7-28 cm depth, and had a lower ACC (0.31) at 0-7 cm ALT. When the precipitation and snow water equivalent (SWE) remained unchanged, the partial correlation between NDVI and ALT was 0.711, which was a significant positive correlation. It also showed that permafrost degradation was the dominant factor controlling Arctic NDVI increase, whereas precipitation and SWE had little effect. The study revealed the impact of permafrost on NDVI change, deepened our understanding of the importance of permafrost degradation for ecosystem services, and effectively filled the gap that tundra ecosystem services value has been ignored in the global ecological service value assessment.

As the Arctic warms, tundra wildfires are expected to become more frequent and severe. Assessing how the most flammable regions of the tundra respond to burning can inform us about how the rest of the Arctic may be affected by climate change. Here we describe ecosystem responses to tundra fires in the Noatak River watershed of northwestern Alaska using shrub dendrochronology, active-layer depth monitoring, and remotely sensed vegetation productivity. Results show that relatively productive tundra is more likely to experience fires and to burn more severely, suggesting that fuel loads currently limit tundra fire distribution in the Noatak Valley. Within three years of burning, most alder shrubs sampled had either germinated or resprouted, and vegetation productivity inside 60 burn perimeters had recovered to prefire values. Tundra fires resulted in two phases of increased primary productivity as manifested by increased landscape greening. Phase one occurred in most burned areas 3-10 years after fires, and phase two occurred 16-44 years after fire at sites where tundra fires triggered near-surface permafrost thaw resulting in shrub proliferation. A fire-shrub-greening positive feedback is currently operating in the Noatak Valley and this feedback could expand northward as air temperatures, fire frequencies, and permafrost degradation increase. This feedback will not occur at all locations. In the Noatak Valley, the fire-shrub-greening process is relatively limited in tussock tundra communities, where low-severity fires and shallow active layers exclude shrub proliferation. Climate warming and enhanced fire occurrence will likely shift fire-poor landscapes into either the tussock tundra or erect-shrub-tundra ecological attractor states that now dominate the fire-rich Noatak Valley.