Although there are many examples of restoration projects in which a subset of the characteristics of the native system have been successfully restored, typically there are critical ecosystem attributes that recover very slowly.
Plant species diversity is one such attribute.
Native plant species richness and diversity in restored ecosystems is usually much lower than in comparable undisturbed ecosystems, and may take decades or longer to approach undisturbed ecosystem levels. This is particularly true in grasslands, where it has proven relatively easy to restore the dominant C 4 grasses, but it is difficult to establish the diverse C 3 forb populations that characterize most undisturbed grasslands. Most grassland restoration efforts occur on former agricultural fields, where soil resources have been homogenized. In contrast, most natural communities are characterized by a high degree of spatial heterogeneity in resources, which is assumed to enhance plant species diversity. We contend that the problem of low plant species diversity that plagues most restoration efforts is due to the slow conversion of an ecosystem from a spatially homogeneous to a heterogeneous state of resource availability.