Most of the net transport of mass and energy between an ecosystem and the atmosphere occurs through the turbulent wind. As discussed in the last two chapters, turbulence varies greatly in its properties depending on where and when it occurs, but it also exhibits coherency and organization in its motions. Both the variable and coherent aspects of turbulence are induced by features of the earth’s surface; especially by topographic features, such as the location of hills, mountains, and valleys, and canopy characteristics such as depth and roughness. From a theoretical perspective, it had been reasoned since the groundbreaking work in 1954 by Andrei Monin and Alexander Obukhov that near-surface shear forces, in the neutral surface layer above a horizontally homogeneous land surface, could not sustain vertical divergence in the momentum flux. This led to the inevitable conclusion that surface fluxes must be conserved as a function of height in the surface layer, which in turn led to the concept of a “constant flux layer.” In the late 1950s and early 1960s several research groups took up the aim of validating these theoretical predictions – an aim that required careful observations above flat, simple terrain. The initial experiments conducted in Kansas (and later in Minnesota) in the late 1960s did indeed validate the predictions and this validation has withstood numerous subsequent tests and debates. As referenced in the paper cited above from Kaimal and Wyngaard, after more than 30 years of testing, the tenets of these early experiments are still widely accepted and used.