Plant community and ecosystem properties in a semi-arid grassland chronosequence

Ecosystem recovery in semiarid and arid regions is often slow, variable, and discontinuous.  Low water availability limits plant establishment and growth, resulting in patchy plant cover and heterogeneous nutrient distribution.  The objective for our research was to assess the state and rate of recovery of both plant community and ecosystem variables over a chronosequence of recovering semiarid grassland enrolled in the Conservation Reserve Program.  We sampled 2, 7, and 18 year-old fields that were seeded with either a native or non-native seed mix.  Within 18 years, species composition shifted from a species rich annual forb community to a perennial grass community with lower richness if the field was planted with non-native species.  18 year-old CRP fields planted with native species more closely resembled uncultivated shortgrass steppe in functional composition, plant density, and basal cover than those planted with non-native species.  Above and belowground net primary production, basal cover, litter, and ion exchangeable nitrogen increased in CRP fields over time.  Aboveground net primary production on 18 year-old CRP fields was nearly double that found for uncultivated shortgrass steppe.  Attributes associated with high ANPP included low species and plant density, low tissue quality, and increased spatial heterogeneity of roots and soil nutrients.  Drought conditions during the second year of the study indicated that high ANPP could not be maintained under dry conditions. Drought also resulted in a reduction in plant density and species richness.  Knowledge about the processes and variation associated with recovery will lead to an enriched understanding of how ecosystems assemble and function in semiarid regions.