There are a multitude of reasons why tress and shrubs die. Causes range from insect damage to a natural death. This blurb is in regards to live trees and shrubs that need to be removed. I am not a big fan of stump grinding unless the tree is dead. If any part of the root system is alive, in most cases, you will be fighting sucker growth from them for years, depending on plant species. The most complete but labor intensive method is physical removal of the stump and root system. I have pulled more stumps than I care to count. Then I found the selective broad leaf herbicide 2,4-D. Leave about 8 inches of stump above the ground. Drill several holes in the stump with the largest drill bit you have (I use a 1 inch wood bit) and pour in 2,4-D. Usually the stump and root system will be dead within a month. Then you can grind the stump without the worry of sprouting roots. 2,4-D: http://npic.orst.edu/factsheets/2,4-DTech.pdf