Hey there
Can a Defiler cast spells if there are no living things around him? Here I of course specifically means plants, but if he is in the middle of a desert where nothing at all grows can he then still work his magic?
Say he is in the same desert with his party, can the lifeforce he draws from them be enough, then it is still going to be painful?
Thanks in advanced

Apparently, microbes living in the ground & air around the defiler are enough to power his spells to an extent. However, if he is in a completely barren area like the Deadlands or The Grey, then yes, said defiler is S.O.L.

The deserts of Athas have living things, just not very many of them, and thus have a considerable modifier on the radius of the defiling effect, the details have never been quite right, the math never perfect, but it works well enough and we have some good suggestions about adapting it to 4e on the other thread.

Yep, what Hendell said: the radius of defiled land just increases, sometimes significantly.
Also, defilers cannot draw lifeforce from living creatures, only plants, so members of the party (nor animal life) cannot fuel a wizard’s spells (though, yes, they do feel pain when defiling spells are cast). Only dragons can draw from living creatures.

Dragons and members of the Leech PrC…

Technically any Defiler that can learn to use Obsidian to channel the life force can use animals to power spells, although there is some suggestion that psionics are involved in the process or at least needed to properly configure the obsidian orb. The Dragon swallows the orbs and carries them around in a gal bladder or stomach it is unclear on that count as well. The process of learning to use the orbs is included in the dragon apotheosis although there is some suggestion that it is a separate sub component, or even a prerequisite stage of learning.