Tue, Aug 03, 2021:On Demand
Background/Question/Methods
Tallgrass prairie restorations tend to have lower biodiversity than native prairies, particularly biodiversity of forbs. Many seeded forb species fail to become established or persist long-term. Seeded grasses are often identified as suppressing seeded forbs. In most restorations, grasses are seeded at relatively high density, while forbs are seeded at relatively low density. Previous research from earlier years of the same experiment discussed here found that increased forb seeding density increases richness of sown forbs, but has not examined how dynamics change over time as the community matures. We ask: (1) To what extent does seeding density constrain establishment, abundance, and diversity of sown forbs? (2) How does increasing forb seeding density influence succession? Free State Prairie, an experimental tallgrass prairie restoration, was established 2014 in eastern Kansas on a former athletic field. It consists of 18 123m2 plots arranged in three rows. All plots were seeded with the same density of 10 native grass species (~8894.839 g PLS/ha). Treatments varied only the seeding density of 31 forb species: no forbs; a standard density of forbs for restoration (~2648.5 g PLS/ha); or twice this standard density (~5297.14 g PLS/ha). Cover surveys were conducted annually from 2014-2020.
Results/Conclusions Based on analysis of data from the first 7 years of the experiment, the cover of sown species significantly increases over time, while the cover of non-sown species, particularly grasses, significantly decreases. Abundance-weighted floristic quality also increases with time, likely due to the shift in composition from non-sown to sown species. Doubling forb seeding density increases both the cover and richness of sown forbs (both by an average of around 25%), but does not increase overall richness. Consistent with previous research, seed limitation appears to constrain diversity of sown forbs. Seed limitation also appears to constrain sown forb cover, an effect not seen in previous research at this site. Succession from a community dominated by less-conservative nonsown grasses to one dominated by more-conservative sown forbs occurred similarly as long as forbs were seeded. Increased forb seeding density may be beneficial to maximize the diversity and cover of sown forbs, however doubling forb seeding density does not double either richness or cover, suggesting diminishing returns.
Results/Conclusions Based on analysis of data from the first 7 years of the experiment, the cover of sown species significantly increases over time, while the cover of non-sown species, particularly grasses, significantly decreases. Abundance-weighted floristic quality also increases with time, likely due to the shift in composition from non-sown to sown species. Doubling forb seeding density increases both the cover and richness of sown forbs (both by an average of around 25%), but does not increase overall richness. Consistent with previous research, seed limitation appears to constrain diversity of sown forbs. Seed limitation also appears to constrain sown forb cover, an effect not seen in previous research at this site. Succession from a community dominated by less-conservative nonsown grasses to one dominated by more-conservative sown forbs occurred similarly as long as forbs were seeded. Increased forb seeding density may be beneficial to maximize the diversity and cover of sown forbs, however doubling forb seeding density does not double either richness or cover, suggesting diminishing returns.