Nitrogen is one of the most important elements needed for tree growth and one of the hardest elements for trees to obtain. The problem is that nitrogen exists as a gas in its most basic form which is a state most trees can not utilize. There are a family of plants however, that can extract nitrogen from the air and deposit it in the soil. These plants are known as legumes, and the black locust or catalpa tree are examples of legumous trees found in this area.
The way most other plants can obtain nitrogen is when it is extracted from decomposing organic material. Once a leaf falls off a tree, certain decomposing fungi or bacteria begin breaking it down into its basic elements and nitrogen is converted into ammonium or nitrates which is a form of nitrogen that trees and other plants can absorb and utilize. Most leaves will completely decompose within a year’s time.
When you rake leaves and burn them you are unleashing green house gasses like carbon and causing denitrification as the nitrogen is released as a gas into the atmosphere. A better option is to mulch the leaves into dime size piece and use them to fertilizer your yard. You'll be surprised how a giant pile of leaves can disappear simply by running your lawn mower over them a few times. Other options would be to rake them into the forest and let them decompose which will enrich the woodland environment or take them to the county landfill and at no cost to you they will compose them into a carbon and nitrogen rich additive for your plants.
Article by FCFCDB
Nature note for 11/27/21