Holdridge life zone system

[Arnoldw]

Hello,

I am looking for definitions of the classes used in the Holdridge life zone system. I have looked at some of Holdriges writings but I have not been able to find a clear definition of the classes he is using in his system. For example what is the difference between dry and rain tundra? Is it just the humidity of is there a change in vegetation and faun as well? Is there anyone here that can explain the system to me in greater detail or point me to an article that includes the definitions?

Thanks in advance for any help you can give me.

Arnold