This is a great idea for establishing trees and bamboo pipes can be used. Small holes are drilled along the sides and buried straight into the ground or at an angle to let the water seep in higher first as it falls down the tube. Compared to having drip emitters on top of the ground, deep pipe irrigation allows the water to reach deeper into the soil and encourages deeper roots and has proven higher rates of survival!
Studies in this pdf show how trees in the desert survived after a three year drought. For those who wish to help reforest hills and landscapes, this would be a good idea to reduce water usage and encourage survival. Water can be hand delivered and poured in or setup on drip systems.
I posted the pdf over at a social networking site for permaculture I setup. The download link for the pdf can be found here - http://permacultureslo.ning.com/forum/topics/deep-pipe-irrigation
More information can be found here - http://www.aridsolutionsinc.com/page/page/1988794.htm