Best way of planting tree in soil of forest garden.

Hi, Usually when i plant trees in forest garden , i first make a circle of stones , i kill all the herbs inside the circle and then i plant the tree in the middle of the circle and then i put mulch over the soil.

But i saw that a farmer makes a little mountain of soil and plant the tree in the middle, and then around the mountain in bottom he make a whole around the mountain so it can store water.

I was wondering which is the best? way of planting trees in the soil?
Which is a better design that can retain more water for more time? so i dont need to irrigate my plants so frequently?

Also i was wondering which is the purpose of making a mountain of soil? anybody knows?

To capture more rain runoff you can dig a large basin for each tree, and put the excavated soil on the downhill side. To avoid drowning the tree if it rains a lot, you can leave or make a mound of soil at the bottom of the basin, in which to plant the tree.

This website has lots of information about harvesting rainwater in the landscape: http://www.harvestingrainwater.com/

Here are pictures showing ways to plant trees in a dry region: