Greater variability in precipitation has been shown to alter the structure and function of tallgrass prairie plant communities. As much as 99% of the tallgrass prairie, however, has been converted for row-crop agriculture. Restoring cropland to prairie is a widespread practice to reverse agricultural ecosystem disservices, but few studies have examined how climate affects the development of functional group structure and diversity in restored prairie. We compared functional group composition of tallgrass prairie restored using the same methods in different years under contrasting precipitation conditions: average precipitation and drought. Plant species cover was measured for six years in both restorations. Plants were assigned one of eight a priori functional groups (warm-season graminoids, cool-season graminoids, annuals/biennials, spring ephemeral perennials, spring perennials, summer and fall perennials, legumes, and woody species). Plant species and functional group composition were visualized over time using non-metric multidimensional scaling (NMDS). Communities (species and functional groups) were compared using repeated measures permutational multivariate analysis of variance (PERMANOVA). Indicator species analysis (ISA) was used to identify species and functional groups with high fidelity and abundance to a specific restoration by age.
Results/Conclusions
Total plant composition was differed between the two sequences at each restoration age (PERMANOVA, P < 0.001). The two sequences retained separate community structure that moved in parallel through the NMDS ordination space. Functional group composition between the sequences began to diverge after prairies were restored for three years. Functional similarity in years 1 and 2 was due to the flush of agricultural weeds that dominate early in the restoration process, supported by annuals/biennials being the indicator functional group for the first two years. Legumes were the functional group indicator in year 6 in both sequences, but the overall composition and proportional cover of functional groups differed (PERMANOVA, P < 0.001) between the two restorations after annual/biennial dominance disappeared, suggesting that the occurrence of drought in the restoration year has a lasting effect on functional group composition. This study shows initial climatic conditions has a sub-decadal effect on both total species and functional group composition, and can cause distinct communities to develop over time in parallel trajectories.