The oldest trees in the world are Bristlecone pine trees

Bristlecones live so long because of several factors that give them the advantage. They can live in poor soil so there isn't much underbrush to allow fires to burn. They grow in an arid climate of the White Mountains between altitudes of 9,000 to 11,500 feet, where few other plants can grow. Bristlecone pine needles are replaced every 20 to 30 years, instead of the usual 3 to 4 years for other pines, so they require less water and fewer minerals. Their trunks are impervious to most insects, and they have the ability to let part of the tree die when there isn't enough water.

The old stump to the left was 3,200 years old when it died in 1676. The trees don't decay when they die because the area is so dry and cold that there are no insects. The wood will lay on the ground for centuries.