 When foraging intensity increases , individuals become shorter each growing season due to the reduction in energy reserves from less photosynthetic production . One study determined that the ideal deer density in northeastern Illinois , based on T. grandiflorum as an indicator of overall understory health , is 4 to 6 animals per square kilometer . This is based on a 12 to 14 cm stem height as an acceptable healthy height . In practice , deer densities as high as 30 deer per square kilometers are known to occur in restricted or fractured habitat where natural control mechanisms ( that is , predators like wolves ) are lacking . Such densities , if maintained over more than a few years , can be very damaging to the understory and lead to extinction of some local understory plant populations . 
