You probably never thought about it but Autumn is natures drive mode. The glories of Spring and Summer have gone and nature is taking over to produce LeafMould.As the cold weather starts is believed corky growths start to block sap flowing to the leaves. This combined with cold weather changes the leaf colours. Slowly now they will start to drop. This is natures recycling program!The leaves drop to the ground forming a natural mulch around the plants roots.If this is left in place it all breaks down to form Leaf Mould. This then feeds the plant from next Spring onwards. Below is Japanese Maple Smoky just starting to change its Leaf colour. In a week or so this will be bright crimson and then the leaves will drop and mulch the roots. Leave them around the plant if possible as food source for next Spring and summer. If on the grass or paths obviously you have to clear them up. So trees in grass you really should clear the grass from around the roots to at least 2 foot. Do this and you can then rake the leaves onto this cleared area and leave them there. If you want to clear all leaves then you should make or buy LeafMould and add to the cleared area in Spring. To make your mulch go further you can add Compost Bark,Manure and a little topsoil.Top this mulch up every year and you should have the healthiest most stunning trees.The tree will be well fed more moisture will be available to the plant, This means in hot weather the tree will not become stressed and an unstressed tree produces better Autumn leaf colours and holds onto the leaves longer. A small amount of effort pays big dividends