Regional MODIS analysis of abandoned agricultural lands in the Kazakh steppes

Abstract

The institutional consequences of the Soviet Union's collapse in 1991 have been greatly underestimated as a significant forcing on the boundary layer through changes in land surface phenology. Upon independence, Kazakhstan lost the centralized agricultural planning, crop subsidy system, and access to international markets that the Soviet Union had been providing. These institutional changes led to substantial decreases in livestock populations, especially sheep, and in arable land area cultivated, especially rain-fed spring wheat in northern Kazakhstan. As a result the fallow fields reverted to weedy species and idle pastures produced denser grass cover. In this case study we used MODIS imagery from three consecutive growing seasons (2001-2003) to study the processes that occur after arable land has been abandoned, a process that is often underestimated in carbon cycle modeling, but which is especially important in central and northern Eurasia. We selected two study regions in northern Kazakhstan: one in the Kazakh forest steppe ecoregion and another in the Kazakh steppe ecoregion. Within each region we visually determined a spring wheat area, and an area with other land cover. We then constructed land surface phenology models based on MODIS imagery from March 2001 through October 2003 and accumulated growing degree-days (AGDD) calculated from the NCEP/NCAR Reanalysis data. Comparisons among these phenology models provide insight into the land cover change trajectories that have occurred since large areas of arable land have gone fallow. Furthermore, we determine the change in parameters based on different land cover percentages. We have shown that abandoned arable lands green up before croplands that are plowed for planting in the last week of May. This may explain, in part, the greening trend that has been observed over northern Eurasia by other investigations