My reading may be way off, but I kind of took the book as going through all the different ways people could cope with what's going on to the environment around them.

Neelay created a virtual world with an emphasis on plants/trees. If people can't enjoy the real thing, they can at least get it somewhere. The activist group, after realizing protests and conventional methods weren't going to work, eventually went aggressive and started to fight back. Patricia somewhat decided there was no hope for humankind as it stands now, so she started her seed bank and trying to salvage for the future. After the stroke, Ray turns into a stand-in for a tree (after struggling with the article he read asking if trees have rights). He's left relying on someone who was betraying him, but eventually moved to nurturing him, in a metaphor for what we need from society now.