forest fire-secondary problems?

Answer 1

Secondary effects of forest fires include the loss of vegetation that protects the soil. As a consequence the fire-affected sites are often degraded by wind and water erosion. Increased water runoff also leads to disastrous floods and landslides, affecting drinking water availability and quality, or leading to siltation of reservoirs.

Answer 2

Depends on the fire intensity, fuel loading, fire-dependence of the ecosystem, and presence of exotic species.
Occasionally with high fuel loads, fire can spread into the crown and kill mature trees instead of opening necessary gaps in the understory. Other problems include post-fire invasion (and often type conversion) by invasive plants--cheatgrass taking over sagebrush steppes in the west is a major example; it moves in post-fire and changes shrubland to grassland and increases fire frequency.