wont a trees canopy block most of the light in those tree grows?
Yes and no.
Sure you lose some light due to the shade, but (as long as the canopy is not too thick), you more than make up for it because natural sunlight is so intense.
To me, natural shade is a good thing for an outdoor guerilla gro - it helps keep the plants small. Small is ggod for outdoor guerrilla gro.
I am trying two outdoor guerrilla gros right now - I have 16 seedlings growing in two three gallon buckets that have been painted green and hidden in some big oleander bushes at a vacant house. In about six weeks when they start to flower, I will cull the males, and then hope that the outdoor sunshine ripens up some good buds. Yes, they are heavily shaded, but they are still growing very well. The shade is actually kinda handy because it prevents the soil from drying out so fast. I have to sneak over there at night and hand water the soil about every 3-5 days (it is really really hot here now)
If I get just 4 oz.s outta those two 3 gallon buckets, I will be very happily stoned.