wide enough edges. Mitigation There has been a fair amount of controversy surrounding the practice of mitigation, which is the destruction of protected or endangered species and habitats, such as vernal pools, on the condition that whatever entity (business, land manager, etc.) is destroying the habitat will undertake the construction of a replacement habitat to "mitigate" their impacts. This concept is difficult to apply to vernal pools, which represent a tremendous habitat value- but are difficult to successfully replicate using construction methods (as mentioned above). Thus, it has been very controversial to apply mitigation strategies to vernal pool systems due to the obvious risks inherent in trying to reconstruct this kind of habitat. Although, some agencies are now requiring two replacements for every vernal pool that is destroyed, in order to compensate for the low quality of man-made habitat. Soils Vernal pools can form anywhere that a depression fills with rainwater, leading to low nutrients and low levels of dissolved salts. They are underlain with an impermeable layer of claypan, hardpan, or volcanic rock allowing for water retention. In many instances they contain grasslands that form over a variety of soil types containing silts and clays often covered by a layer of interwoven fibrous roots and dead leaves. The soil types present tend to relate to the local soil types and hydrology of the pool. Finer soils such as clay, silt, and muck are more common in perched situations, whereas pools which are more connected to the water table have more coarse soils like sand or gravel. Soils in vernal pools often reflect their inundated conditions, leading to low chroma horizons, mottling, and anoxic decay. They can develop hydric soils which are typical of flooded areas, including accumulations of organic matter, but this may not happen in drier areas. In some cases there is a hard pan layer which causes the retention of water in the pools. The hardpan clay basin accumulates water due to the small particle size and therefore reduced porosity. This permits flooding and development of vernal pools. Flora In vernal pools, flowering occurs simultaneously because of the seasonality of favorable conditions. Vernal pool ecosystems may include both cosmopolitan species and endemic species adapted to unique environmental conditions. These conditions include moisture gradients, salinity gradients, and reduced levels of competition. Microtopographical gradients also contribute to species distribution in vernal pool communities, where plants that flower sooner in