干旱区生态环境知识资源中心

In 1997 the USDA Agriculture Research Service (ARS), Hydrology Laboratory began collecting remotely sensed ground, aircraft, and satellite data on the physical and biological states of two semiarid ecosystems (grass and shrub) typical of the Sevilleta Long-Term Ecological Research (LTER) site (New Mexico. USA). Remote sensing measurements were made at Sevilleta in May/June and September/October of 1997, 1998, and 1999. Radiance measured at ground and aircraft platforms was 12 to 40% higher for a 30 x 30 m area at the shrub site when compared with the grass site. Landscape surface temperatures that were similar in the morning were 3 to 5degreesC higher under the shrub when compared with the grass site by 1300 h local time. The shrub site had a lower LAI indicating less surface cover and giving a greater soil contribution to the total radiance measured. These differences could have significant effects on the energy and water balances of the Sevilleta if shrubs continue to expand at the expense of the grassland.