This relationship has now been successfully modelled for the first time, revealing its sensitivity to climate change.

Ningning Zhang and colleagues from Nagoya University, Japan, have predicted that the larch trees will not be able to survive even the most optimistic climate change scenario of a 4 °C increase in summer temperature in Siberia by the year 2100.

"We found that the larch-dominated boreal forest–permafrost coupled system in Siberia would be threatened by future warming of 2 °C or more," Zhang told environmentalresearchweb. "However, our simulations also show that, even with 4 °C warming, some tree species can still survive, but with considerable loss of biomass."

To perform their calculations, the researchers had to develop a new model because previous models had not succeeded in simulating forest–permafrost coupling. They came up with a dynamical vegetation model that includes coupling with the permafrost hydrological process. The model considers the dynamics of boreal forest on a species level, taking into account 44 tree species. It also includes the vegetation process coupled with seasonally varying hydrological processes of permafrost (i.e. melting and freezing).

"This coupling process emphasizes the two-way effect of the permafrost hydrological process and the physiology of vegetation via soil moisture condition and evapotranspiration," said Zhang.

This work was made possible because of 10 years of in situ observational study on the larch boreal forest–permafrost region in Siberia, which provided sufficient data to force, tune and validate the model. The researchers had also previously succeeded in modelling the boreal forest in Siberia using their dynamic vegetation model (FAREAST model) without the forest–permafrost coupled system. "A permafrost model (FSM) has also been developed recently, including soil freezing-thawing processes," said Zhang. "The time was right to integrate these two models and also incorporate the in situ observational data."

The researchers now plan to introduce another typical permafrost hydrological process into the model, which Zhang believes will be even more challenging. "We want to include alas in the model," said Zhang. "Alas is a steep-sided depression formed by the melting of permafrost, which may contain a lake. Alas is a very complicated process, and it plays an increasingly important role in the forest–permafrost system. Our current model describes a self-recovering balanced system, but once alas is introduced, the balance of the system may be damaged."

The scientists published their work in Environmental Research Letters.