Taiga organisms experience an extremely short growing season and cold winter temperatures; but within the growing season, environmental conditions vary considerably among sites, ranging from cold, wet, black spruce forests on north-facing slopes to extremely warm, droughted sites on south-facing bluffs. Thus the environment ranges from conditions close to the northern extreme of tree growth through mesic conditions not unlike those of temperate forest ecosystems (except for generally lower soil temperatures) occurring at the ecotone between forest and dry temperate grasslands. There is a similar large breadth of conditions through succession. Within the taiga fire is an extremely important process with a return time of 50–100 years. On river floodplains, active erosion and deposition also result in a mosaic of communities of differing successional ages. Early in succession, following fire in the uplands or formation of new silt bars in the lowlands, soils are warm and conditions are favorable for the activity of plants, microorganisms, soil fauna, and above-ground herbivores. Gradually, through succession, nutrients become bound up in live and dead organic matter; and the soil is insulated and becomes cooler, resulting in decreased activity of most organisms. In summary, although the taiga contains forests growing under cold, nutrient-deficient conditions, it also includes a diverse array of other forest types not unlike those found at more temperate latitudes.