Lifestream

The flow of life throughout the world, which primarily nourishes the land with the mana for plantlife to grow - and by extension, all other organisms. While invisible in the physical plane, it is as clear as day in the spirit world. 
It is possible to temporarily corrupt parts of the lifestream with excessive negative energy, especially when using magic: the most grievous offendors are magics that twist the souls of the unwilling, damaging them (such as necromancy) and all forms of chaos magic .
In the same vein, it's possible for a person to actively improve and empower the lifestream in an area with positive energy. Even something as mundane as human kindness contributes.