Land Use in Temperate East Asia (LUTEA):

Site Studies of Long-Term Ecosystem Dynamics

 

Dennis Ojima, Togtohyn Chuluun and Wang Yanfen

Natural Resource Ecology Laboratory, Colorado State University, USA

 

Abstract

 

Land use has a long history in Temperate East Asia, and much of the ecological landscapes have been shaped by the changing land use patterns in the past.  Long-term studies of the relationships between climate variability, ecosystem dynamics, and land use are needed to better understand the current and future ecosystem functioning.  Examples are provided from the Land Use in Temperate East Asia (LUTEA) study of interactions between nomadic land use and environmental conditions on the development of grassland ecosystems in the region for hundreds of years.  Land use intensification in China have resulted in overgrazing and degradation of grassland ecosystems, especially in the past 50 years.  In Mongolia, recent political and economic changes have resulted in an increased number of grazing animals.  These recent changes in Mongolia and long-term affects in China provides an opportunity to evaluate the resilience of the Mongolian steppe ecosystem to changing land use intensity.  The purpose of this paper is to analyze a long-term ecosystem dynamics and land use impact on ecosystem structure and function in this region.  Climate, soil (carbon, nitrogen and carbon isotopes) and plant (biomass, cover and diversity) relations have been studied in ecosystems of Temperate East Asia.  The results from two long-term steppe ecological research sites: Xilingole in China and Tumentsogt in Mongolia have been incorporated in this paper.  Grasslands at Xilingole and Tumentsogt are dominated by cool season grasses and soil carbon isotopic analysis shows that it has been for a long period of time.  Stipa and Leymus are the dominant grass genera.  Interestingly, Cleistogenes spp. were the only C4 species in the steppe ecosystems of this region.  Soil organic carbon and nitrogen levels were positively correlated with annual precipitation in Mongolia, but not in China.  However, there was a decreasing trend of soil organic C and N with increase of mean annual temperature.  Soil carbon isotopes were related better with annual precipitation than annual mean temperature, although there is some disagreement in China.  Soil carbon isotope distribution with the depth indicates a possibility that the Stipa site was more sensitive to past climate change than Leymus site in Xilingole and Tumentsogt sites.  The C4 plant cover and actual plant cover increased and plant diversity decreased with grazing in all research sites we studied.  A total soil organic carbon level decrease by about 25% was observed with heavy grazing at Xilingole research site.  A simulation model showed that 50 years of heavy grazing in summer period may result in such change in soil carbon level.  Future research in this region needs to focus on the integrated impact of changing political, economic and social forces controlling livestock management, maintenance of biodiversity, sustaining the steppe ecosystem integrity, and economic development of the region.   

 

The Mongolian steppe study was supported from a research grant from the US National Science Foundation Long-term ecological studies component of the Division of Environmental Biology and from support from the Chinese Academy of Sciences and the Mongolian Ministry of Nature and Environment and the Mongolian Academy of Sciences.