phenotypically....the physical and observable structural makeup can change within the confines of the living time of an organism. however, I believe the genetic code to remake that morphological change will take more time. How much....that's evolution - the success of the individual species is inherent it is ability to adapat and in the translation of that adaption into a genetic code. that is genetic change and not adaptive change.
say for example you break your leg and you are in a cast for 12 weeks....your immobilized leg will undergo singnificant reduction in muscle mass (atrophy), and I expect under microscopic analysis your bones will also change structurally. these are adaptive, not evolutionary processes. The babies that my sperm produces will not have a changed genetic code for an atrophied and emaciated legs muscle and bone less adapted to being weight bearing.
Adaptive changes will only become evolutionary changes once they are an expression of the genetic material, and not a mere response to an environmental condition. Environmental conditions come and go. genetic change has to make certain that it is an absolute competitive advantage to propogating that genetic material. So, in the case of trichome production and THC concentration, the adapative change may be significant differences from the genetic map, but until the genetic map has "mutated" to include this as a "trait" it will remain as an environmental adaption.
I go back to my example of the cheetah and the thompson's gazelle. an individual cheetah that is able to chase down thomson's gazelle more successfully will propogate its genetic material. That behaviour will be passed along, but only those offspring that are capble of tolerating the higher body temperature will have the probability of higher survival success. Somewhere along the line, that same animal will have to experience a genetic map that carries the gene that is programed for the allowance to withstand a higher internal body temperature.
As we are "manipulating" environmental conditions, and we can complete many many generations, it is "theoretically" possible to pursue those traits that we prefer. there is much more to say here....and I will continue to read and think....I'm having SOOO much fun with this....I truly do believe I have gone over the edge! hahahahaha.
***EDIT*** taken from CC article entitled Pot Potency.....
Marijuana is unique from an evolutionary standpoint in being the only plant in history that in some cases has been grown and bred for over two decades under nothing but artificial light. It is very likely that there have already been some genetic changes that have taken place as a result of this. All plants, especially cannabis, will quickly adapt to a new habitat by adding or dropping traits over successive generations. With breeders doing potentially as many as three or four generations per year, over 20 years there is great opportunity for drift from original genotypes.