Watercourse Buffers With Specific Wildflower Mixtures or Altered Vegetation for Specific Outcomes
November 17th, 2021Key Concepts
Here the properties of the grass buffer as a surface runoff filter strip are enhanced by including a variety of 'designer' vegetation to satisfy specific goals. A common example is sowing a mixture of native wild flower seed from a conservation mix. The measure considered here is of specific grasses and herbs (to make the measure distinct to a wooded buffer) that have habitat improvement for plants and associated animals. For example, there may be associated effects for beneficial insects such as pollinators and those predating crop pests. But also 'designer' vegetation may include stiff-stemmed grasses for better erosion control, or nutrient-mining vegetation that can contribute to green manures, or human food crops such as berries and high value specialist hay e.g. for horses.
Summary of Evidence on Functions
Wildflower buffers can benefit vegetation diversity to benefit invertebrates. But they are unlikely to promote increased numbers of rare plant species. Fencing out livestock from narrow riparian buffers can increase structural diversity of vegetation but has been found to reduce number of plant species and favour competitive weeds, so some form of grazing or cutting is beneficial.
Technical Evidence References
Cole et al. (2020) Managing riparian buffer strips to optimise ecosystem services: A review. Agric. Ecosyst. Environ. 296, doi: org/10.1016/j.agee.2020.106891
Blake et al. (2012) Enhancement of buffer strips can improve provision of multiple ecosystem services. Outlooks on Pest Management, doi:10.1564/23dec05
Stockan & Cole 2014. Impact of riparian buffer strips on the ecological structure of ground beetle populations. RPC RB 2014/07; Cole & Stockan 2015. The role of riparian buffer strips in the conservation of insect pollinators. RPC RB 2015/12.;
Rasmussen et al. 2011. Buffer strip width and agricultural pesticide contamination in Danish lowland streams : Implications for stream and riparian management. Ecological Engineering 37, 1990–1997
Cole et al (2012), Riparian field margins: can they enhance the functional structure of ground beetle (Coleoptera: Carabidae) assemblages in intensively managed grassland landscapes? Journal of Applied Ecology, 49: 1384–1395. doi: 10.1111/j.1365-2664.2012.02200.x
Stockan et al (2014), Effects of riparian buffer strips on ground beetles (Coleoptera, Carabidae) within an agricultural landscape. Insect Conservation and Diversity, 7: 172–184. doi: 10.1111/icad.12043
Main Countries Where This Is Practiced
U.S., across Europe
Challenges and Limitations, Including Site-specific Factors, Planning Requirements and Particular Suitability to Farming System
Establishment of wild flowers can be tricky amongst grasses that outcompete them for light and other resources, necessitating ground preparation such as herbicide or physical cultivation. Any vegetation manmagement should be timed after periods of flowering. The best habitat diversity amongst vegetation can be gained form buffers having areas of both wetter and freer draining soils. In some countries lack of regulation of wildflower seeds, leading to uncertified provenance, presents issues. This situation in Ireland, for example, leads to current best advice being to allow natural vegetation to regenerate, as opposed to planting with seeds of unknown provenance. Wildflower management is eligible for cross-compliance payments.
Ability to Modify It For Site Requirements
Seed mixes may be varied for differing required outcomes and according to local natural communities according to soil and climate conditions.
Critical Factors in Establishment and Ongoing Management
Many of the points of management can be drawn from general wildflower field margin guidance. However, for riparian contexts important aspects are: that cultivation is not allowed within 2 metres of the banks so a streamside grass border or a natural established flower band must be used, herbicides and grazing as vegetation management has special rules close to waters. Specialist wildflower seed mixes are available off-the-shelf for different climatic regions and goals. For example, in existing 6 m grass margins for stewardship schemes there is already a recommended grass/wildflower sowing mix. Often competing vegetation must be mechanically removed to allow flowering plants to establish. For this topping to 6-10 cm in the first years can be good and maybe graminicde can be carefully used. Grazing in late autumn may be beneficial if allowed (e.g. sheep would be less impact). Sow from Mar to Sept when soil is moist and warm, by broadcasting onto fine seedbed and rolling. The functionality for FIO retention in grassland requires a fenced buffer and this brings management issues for providing off-stream animal watering. Special survey and planning may be required if diverse or mosaic vegetation on different soil moisture regimes is to be established, or trees and herbaceous mixtures.
Guidance and Other Resources
Game & Wildlife Conservation Trust has guidance on seed mixes, sowing and what species at https://www.gwct.org.uk/farming/advice/habitat-issues/wildflower-mixtures/:
Comprehensive leaflet on field margins and hedgerow management at https://www.agricology.co.uk/sites/default/files/Field%20margins%2C%20hedgerows%2C%20woodland%20and%20scrub.pdf;