From Ryzom Wiki
Poison is one of the seven elemental damage types.
Poison is the racial damage type of the Matis. The poison damage elemental spell can only be learned from a Matis magic trainer once a mage reaches level 125 elemental magic. It is generally the preferred damage type to use while in the forest, as creatures there tend to resist it poorly.
Most animals and most intelligent plants have no protection against Poison magic; exceptions are the Bolobi, Najab, Yelk, and Cratcha. Most kitin do have protection against Poison magic, though in the case of Kincher, Kirosta and Kinrey it's no more than against any other elemental damage type. Outpost guards in forest outposts are immune to Poison.
Protection from Poison
Matis player characters have a natural 20% protection from Poison damage. Any player can protect themself against Poison damage by wearing jewelry that gives additional Poison protection. You can have at maximum 70% protection, whether you're Matis or not.
You can also increase your chances of resisting a Poison elemental spell by wearing jewelry that raises your Forest resistance.
Non-magical Poison damage
Kirosta have a poison sting which does Poison damage, but this attack itself is physical and not magical in nature. That means Poison protection will protect you against it, but Forest resistance will not help you resist it.
Many bandits and tribes guards also have random elemental damage added to their melee and ranged attacks, including Poison. If you're hit with Poison damage that way, Poison protection will decrease that damage, but Forest resistance will not help you resist it.