Trauma can provide more healing than wild growth when enough ppl are affected by the Fountain of Light proc. In a 25 man raid the hot can heal all 25 ppl at the same time when they stay close to each other.
More info about valanir vs trauma:
http://www.mmo-champion.com/threads/...S-Resto-weapon
"On fights like BQL, Marrowgar, Sindragosa, Festergut, and even Putricide (P3) to an extent, Trauma will outperform Val. On fights like LK, Deathwhisper, Valithria, Rotface and Princes, Val will outperform Trauma."
Each healing effect (including hot ticks) has a 1% chance to proc Fountain of Light. A druide that is healing the raid has per second a chance of around 10% to proc Fountain of Light which gives the trauma hot a up time of around 60%.
Sadly the 45 sec interal cd on warmane makes trauma currently worthless and nobody seems to care about the bug... :(