Forest and Thicket - Loop Hero
Forest and Thicket are field cards that increase the hero's attack speed by 1% and 2% respectively. At first it looks like Thicket is twice as good but it is actually better than that if you also use the River card that doubles the effect of the connecting land cards.
Where to place them
I'm not sure if it's just luck but I seem to draw more forests than thickets, so my strategy is to make sure every thicket really counts. Here is a setup I like:
The river zigzags like this and thickets are placed on the tiles that connect with three rivers. This gives the hero a 12% attack speed bonus (4% + 4% + 4%) for a single thicket tile. The forests are placed on the tiles that connect with only one river.
The Storm Temple card will destroy any forest or thicket in it's path to make them burned forests. Those give a 0.5 magic attack bonus instead of the attack speed bonus. Attack speed is better so I make sure to have a good look before placing a temple.
What about the necromancer?
The necromancer still benefits from attack speed, one could even argue it is one of his most important statistics. In his case, it becomes summon speed until the maximum amount of summons is reached.
The higher the necromancer's attack speed (summon speed) is, the more important the max skeletons statistics become. You always want to be summoning new minions, the necromancer's melee attack is too weak.
That +100% attack speed bonus won't be of much use if you can only summon two skeletons. Ramp that up to five skeletons!