Controlled Burn

Centered at a point up to the spell’s distance, trees with an average trunk diameter of 1 ft sprout up to 15 ft tall filling a 100 ft square area.  Trees are offset 5 ft from the edges of the spell's area of affect, spaced 10 ft apart, and will not grow beyond the height of a ceiling when cast indoors.  The trees may share a space with a medium or smaller sized creature and can share a space with a structure that has room for the tree. Trees will not grow where solid structures, such as stone pillars, occupy their space, however, they can grow over any surface.

When cast, and on subsequent turns if the caster maintains concentration, the caster may select a tree within line of sight and cause it to burst into flames. At the beginning of each of the caster's turns, all trees within a 15 ft radius of a burning tree burst into flames. Trees can burst into flames only once. A creature or wooden structure within 5 ft of a tree when it bursts into flames takes 2d8 fire damage. Any creature starting their turn within 5 ft of a burning tree must make a Dexterity check against a DC of 11 plus the spell slot level this spell was cast at. Upon failure, the creature receives 1d8 fire damage. A successful roll results in no damage. Wooden structures within 5 ft of a burning tree receive 1d8 fire damage every round. After more than half of the trees are burning, any creature starting their turn in the spell’s area of affect takes 1d4 fire damage from smoke inhalation. 

The fire burns itself out within 20 minutes and the area becomes difficult terrain for 1 hour. The fire may spread beyond the spell’s area of affect if the caster loses concentration before the fire burns out.   Preexisting trees of similar size or smaller than those grown by this spell are treated as if they were grown by this spell and can be caused to burst into flames. Significantly larger preexisting trees are treated as wooden structures and can be subjected to fire damage.

When you cast this spell using a spell slot of 5th or higher level, line of sight is not required for selecting the tree that bursts into flames. When you cast this spell using a spell slot of 6th or higher level, you may choose two trees to burst into flames each round.