A boreal forest (taiga) is a biome that is much less rich than a temperate deciduous forest. There is less biomass per area in a boreal forest as this biome is able to support much less life.
The reason for this stems from the climate of the two biomes. A boreal forest has a climate that is much harsher than that of the temperate deciduous forest. The boreal forest has very low temperatures where temperate forests have extended periods of warm weather. The boreal forest gets most of its precipitation in the form of snow.
Because of these things, plants are less able to grow in the boreal forest. This causes the soil to be less rich as well.