Lastly, Gus showed us structures that he and his students have built over the years to shade plants. The goal is to examine light levels and assess plant productivity across a range of light exposures. One might think that plant growth and biomass production would decline at low light levels, but apparently significant reductions in light can be tolerated by Arctic vegetation with little to no loss of productivity. The pivotal point here turns out not to be light per se, but instead the proportion of light coming as direct versus diffuse radiation. Plants are pretty efficient in using diffuse radiation for photosynthesis and biomass growth, so there is not a direct correlation between shade treatments and biomass growth.