Influence of seed mixture and hydrological regime on the establishment of a diverse grassland sward at a site with high phosphorus availability

Published source details Gilbert J.C., Gowing D.J.G. & Bullock R.J. (2003) Influence of seed mixture and hydrological regime on the establishment of a diverse grassland sward at a site with high phosphorus availability. Restoration Ecology, 11, 424-435.
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Summary

High phosphorus (P) availability in soil is associated with low grassland plant species diversity. This study investigated whether creation of a diverse sward is possible on a soil with very high P concentrations at a grazing marsh in southeast England. The experiment summarised here assessed the efficacy of sowing a commercial seed mixture designed to achieve a sward similar to British National Vegetation Classification (NVC) Cynosurus cristatus (crested dog’s-tail)–Caltha palustris (marsh marigold) grassland (NVC code MG8).

Study site: The study was undertaken on the grazing marsh at the Wildfowl and Wetland Trust's (WWT) Wetland Centre, Barn Elms, London.

Seeding treatments: Three different mixtures of the same five constant grasses from the MG8 community species were trialed: sweet vernal Anthoxanthum odoratum, crested dog’s-tail Cynosurus cristatus, red fescue Festuca rubra, Yorkshire-fog Holcus lanatus, rough meadow-grass Poa trivialis. Red fescue was varied in its proportion of the mix (10, 40 and 70%) with the other four species (kept in the same relative proportions) making up the remainder. Seed was sown at 25 kg/ha in unreplicated plots (each about 15 × 15 m) with 10, 1 m² quadrats randomly located in each.

Monitoring: Species and percentage cover estimates in each quadrat were recorded each June over 3 years. The location of the quadrats were recorded to enable an estimation of the water regime. The percentage cover estimates were entered into a vegetation analysis program which compares the vegetation to that of NVC floristic tables.

Hydrological regime: A network of ditches intersects the grazing marsh and influences the water table. A hydrological model was produced to predict the water table depth.

In the first 2 years the proportion of red fescue in the seed mixture was related to the similarity of the vegetation of MG8, but by year 3, seed mix composition had ceased to have a significant effect on similarity. The seed mixture containing the highest proportion of red fescue had the greatest similarity to MG8, and was also related to the water regime. By the third year, drier quadrats had almost no similarity with MG8, whereas wetter quadrats had similarity coefficients between 30 and 50.

By the third year the effect of seed mix composition became much less evident with the water regime a significant factor influencing cover of each species e.g. rough meadow-grass Poa trivialis, sweet vernal Anthoxanthum odoratum and Yorkshire fog H.lanatus appeared positively related to drought stress.

Conclusions: The composition of the seed mixes sown, affected the establishment species within the sward in the first year after sowing. After 3 years the composition of the seed mixture ceased to be an important factor with plant species cover and distribution most strongly affected by the water regime. The vegetation was less diverse than predicted from germination tests and decreased in diversity over the monitoring period. This was perhaps due to the water regime being unsuitable for most species or the extremely high P concentration in the soil allowing the most competitive species to dominate.

Note: If using or referring to this published study please read and quote the original paper, this can be viewed at: http://www.blackwell-synergy.com/journal.asp?ref=1061-2971