After reading this chapter, you may end up with a false impression that you have mastered nature rendering completely. If this is the case, I suggest you close the book, go for a walk, and then return to your reading when you are done. Go out to a meadow, river, or a park and take a look around. You will soon discover how nature's complexity is far from being tamed by graphics programmers, and some doubt it will ever be mastered. Given its fractal complexity, nature will always need more resources and more involved algorithms, effectively remaining one of the main challenges for programmers for years to come.
This chapter, along with the references provided in Appendix E, have just scratched the surface of what is certainly going to be an extensive subject in graphics programming. The more familiar you become with these subjects, the more competitive you will be.