They can also be killed by other plants making the place where they grow too shaded, or taking all the nutrients or water. Therefore, plants compete with one another for survival. Plants per se, do not have what we commonly call a 'life-span'. Given optimum conditions, they can theoretically live for an indeterminate time. What does happen, however, is that as plants age they might be more inclined to break for example from drying or simply increased chance of being hit by some random accident.
Breakages can introduce disease-causing pathogens which can then move throughout the plant.
Environmental stresses, such as poor nutrition or extremes of temperature can cause dieback, and these areas of dead tissue might once again allow for entry of pathogens. Frequently when plants are stressed they seem to be noticed by insects who then finally finish them off. Gardeners often use plant propagation, which is basically taking a small part of a plant and growing it into an entirely separate plant. This smaller version of the original could be saved if something happens to the original parent plant. Argonne National Laboratory, Division of Educational Programs, Harold Myron, Ph.D., Division Director.