What about creating a hybrid tree that combines spice AND gas into a single tree? When you click on it it could have options for Water, Pet, Harvest Gas, and Harvest Spice. The standard harvest limits would still apply, so if you can only harvest each tree once a day you choose gas or spice, if you can harvest each tree twice a day you could choose to harvest gas once and spice once, or a double harvest of one or the other. I think this would be a very diplomatic solution for the current situation in Ix, as well as the rest of Ur. Gas harvesters and spice harvesters could live in relative peace again.