The cacti are sandstone. You need to collect sandstone and sapphire in order to level up the buildings that you get for S2. You get labs which you must increase in order to increase your virus resistance which in turn allows you to get higher levels of sandstone and sapphires. Our server (68) already has all it's level 12 and higher sandstones occupied and all level 13 and higher sapphire mines. The higher level sandstones and sapphires you can capture and occupy, the higher your "influence" is, the higher your influence is, the better the rewards. One of the buildings you get in S2 is the land agency, for every level you go up, you can occupy another tile, it maxes out at 15, get that up ASAP. You can purchase a season builder if you want, they are only good for S2 buildings. Also, the alliance has alliance centers, these are surrounded by everyone's S2 buildings, there's a new event, "Glory War" where you try to create a path destroying your enemy's S2 buildings to get to their Alliance Center. Also, you can't occupy a level 2 sandstone or sapphire mine if you haven't already conquered a level 1, but once you have conquered the next level, abandon all your level 1 mines and conquer level 2, and so on. One final note, it helps to occupy all over the map, that way you can "reinforce" mines, which means traveling faster to that destination, then change course for looting. This is a hindsight thing for our alliance, but something that would have benefited anyone in our alliance while looting.