Both are bad for humans in terms of the smoke generated.

For the forest environment, many forests rely on naturally occurring forest fires as part of its normal life cycle. Some trees and plants only have their seeds erupt when exposed to fire or the aftermath of fires. Fire helps clear out the underbrush regularly while older trees survive with little damage.

However, once humans start living near forests, they don't want them to catch on fire. Fires are stopped before they can clean out the forest. They also start diverting all the water elsewhere and cut down the old large trees for their own usage.

Now we have dry conditions and an overgrowth of underbrush due to a lack of fires. This makes any forest fire much larger and hotter, able to burn even the largest trees that typically survive fires.