 diversity. Most the time when we're talking about diversity, we're talking about species diversity. But as plants in a single population age, they change in size, vigor and productivity. That's just as important to the animals that depend on those plants. I think about problems in our forest and sagebrush systems, but a great example of this phenomena is our urban forests. Take a look around and notice the number of great, stately old trees. Now most trees have a lifespan similar to humans. Are there as many sapling trees as there are kids in the human population? Well, there ought to be. A plant population's vitality depends on there being a number of different ages in the population. Young, old and in between. Each of them in turn serve the needs of the different plants and animals that depend upon them. From the University of Wyoming Cooperative Extension Service, I'm Eric Peterson.