It is believed that permafrost degradation will lower the water table and dry out surface soil, changes that should adversely affect alpine grasslands – but according to analysis by researchers in China that's not necessarily so. Warming might also extend the growing season of plants and thus accelerate nutrient cycling.

There is a wealth of literature on the effects of permafrost degradation on alpine grasslands that compares vegetation characteristics of quadrats in plots set on different permafrost zones. However, these areas are difficult to access because of the lack of suitable road networks, so the number of plots that have been studied is quite limited. The results obtained have also been affected by local factors such as topography. And while techniques like microwave remote sensing are useful tools for measuring surface soil moisture over a large area, their spatial resolution is too low to study the effects of permafrost.

Shuhua Yi and colleagues studied the effects of permafrost degradation at basin scale by deriving the limiting factor of alpine grassland growth for different types of permafrost over a semi-arid basin on the north-east edge of the QTP. The datasets used were 1-km resolution fractional vegetation cover (FVC), and land-surface temperature (LST) from "MODIS" Aqua products. The limiting factor of growth transitioned from energy in the extremely stable and stable permafrost zones (which exhibit a positive relationship between FVC and LST) to water in unstable permafrost and seasonal frost zones (which show a negative relationship).

The results suggest that permafrost degradation produces both adverse and beneficial effects. For alpine grasslands on the extreme stable and stable zones, warming can extend the growing season and thus accelerate nutrient cycling, both of which benefit vegetation growth. This result was published in Environmental Research Letters (ERL). A semi-humic basin nearby was also studied; the relationship between FVC and LST was found to be positive for all types of permafrost zone.

The team's results show that the effects of permafrost degradation on alpine grasslands depend on the stage of degradation and the climate region. Overall, future warming seems to benefit alpine grasslands on the QTP.

The researchers now plan to use a process-based biogeochemical model (the Terrestrial Ecosystem Model) to investigate the overall effects of climate change, permafrost degradation and grazing on the alpine grasslands of the QTP. They hope their results will help local governments to set up appropriate regulations that will aid in both protecting alpine grasslands and assuring the well-being of herders in a changing climate.