Review and Prospects of Frozen Soil-Vegetation Interaction and Climate Effects in the Three Rivers Source Region

Abstract

The interaction between frozen soil and vegetation in the Three Rivers Source Region （TRSR） affects the local climate by changing the characteristics of soil water and heat and the exchange of energy and water between the land surface and atmosphere， which challenges the ecological security in this region.This paper reviews the characteristics of frozen soil， vegetation and their trends， the process of frozen soil-vegetation interaction， and their climatic effects in the TRSR in the past few decades.On this basis， some future directions prospect.The main cognition is as follows： The TRSR is a combination zone of seasonally frozen soil， continuous and discontinuous permafrost.The vegetation type is diverse， including alpine meadow， alpine steppe， alpine wetland， and alpine desert.The growing season is short， and the phenology is greatly affected by altitude， air temperature， precipitation， and light condition.Under the influence of global change and human activities， the frozen soil and vegetation in TRSR have changed rapidly in the past few decades.As for the frozen soil， soil temperature increased significantly； permafrost shrunk， and the area of seasonally frozen soil expanded； the active layer thickness and thawing period of permafrost increased， while the maximum freezing depth and freezing period of seasonally frozen soil decreased.As for vegetation phenology， the regreen-up stage was advanced， the fade stage is postponed， and the growing period is extended； at the same time， the structure and function of the alpine vegetation ecosystem have also changed significantly.There is a strong interaction between the frozen soil and alpine vegetation in TRSR.The water and heat state of the soil， the temperature and humidity conditions of the soil are the critical bond between frozen soil and alpine vegetation.On the one hand， the freezing/thawing state of frozen soil and soil hydrothermal processes are closely related to the growth of alpine vegetation； on the other hand， through changes in vegetation characteristics and ecosystems， the vegetation located in the upper boundary of frozen soil affects soil temperature and moisture， then reacts to the formation and development of frozen soil.As the two typical underlying surfaces in TRSR， frozen soil and alpine vegetation are organic whole in the land-atmosphere interaction.By influencing local energy distribution and water processes， the variation of frozen soil and alpine vegetation affects regional precipitation， air temperature， energy budget， local circulation and water vapor cycle.Therefore， it is necessary to consider the influence of the two synergistic changes on regional climate.By using observations， machine learning models， land surface process models and regional climate models which coupled with dynamic vegetation models， further researches on the internal relationship between the soil freezing/thawing process and the alpine vegetation change in the TRSR will further improve the understanding of the future changes of frozen soil and alpine vegetation.

Keywords

• three rivers source region
• frozen soil
• vegetation
• climatic effects