There are all sorts of environmental factors that influence the kelp community.  There is light, substrata, sedimentation, nutrients, water motion, salinity, and temperature.  Outside factors caused by humans are harvesting, oil spills and pollution.  Grazers can cause disturbance to the kelp bed.  One popular grazer would be that of the purple and red sea urchins.   These two can cause a devastating effect.  They can eat away the entire forest and it will then be known as an urchin barren.  This can take years to overcome.