ungrazed plot with control (grazed) plot to the left
APPLYING NITROGEN TREATMENTS TO AN UNGRAZED PLOT
view down fenceline of rabbit-grazed plot
view down fenceline of ungrazed plot
water-table monitoring at a control plot
Background
The Newborough Warren sand dune system is located in the south-west corner of Anglesey in North Wales, on a National Nature Reserve (NNR) managed by Natural Resources Wales. The public-access site is also a Special Area of Conservation (SAC).
Established in 2003, the Newborough Warren nitrogen addition and grazing experiment was set up to answer two key questions:
• How does excess nitrogen from atmospheric deposition affect species-rich sand dune grassland?
• How does management, in the form of grazing, moderate that response?
At the time it was set up, there were (and still are) very few experiments looking at interactions between management and nitrogen deposition, and no other nitrogen manipulation studies in sand dunes in the UK. Nitrogen treatments stopped in 2011 but the grazing exclosures and control plots are still maintained and monitored. This provides an ideal resource to look at recovery from nitrogen deposition, and continued interactions with grazing.
Experimental Design & Treatments
The nitrogen treatments are highly realistic, with additions of 0 (control), +7.5 and +15 kg N/hectare/year, on top of a background deposition level of around 10 kg N/hectare/year. There is one nitrogen + phosphorus plot (15 kg N/hectare/year + 10 kg P). Nitrogen plots are 2 x 2m, with nitrogen applied monthly at realistic solute concentrations using a watering can (image at left). The control plots received an equivalent volume of water, applied in the same way.
The grazing exclosures are approximately 10 x 10 m (see images left). There are three treatments: ungrazed (excluding rabbits and livestock), rabbit grazed (excluding livestock) and grazed (unfenced plots, grazed by ponies, cattle and rabbits).
Overall there are three replicate blocks of grazing treatment, with nitrogen plots nested within grazing plots.
Key Results
Results show that nitrogen is taken up and stored in the vegetation, particularly the moss layer, but has not yet had an effect on plant composition (Plassmann et al, 2009). This may because plant growth is limited by other nutrients. The site seems to be nitrogen-phosphorus co-limited (Ford et al, 2016).
Dynamic modelling approaches suggest that changes to vegetation will occur in the future (Jones et al, 2013), but that grazing is a key mechanism for improving habitat suitability even if it does not remove much nitrogen from the system (Jones et al, 2017).
Early in the experiment, the rabbit-grazed plots resembled the fully grazed plots. Three years later, after an outbreak of myxomatosis suppressed the local rabbit population, the sward structure became closer to the ungrazed plots.
Further Information
Newborough Warren has a long history of scientific research dating back to the 1950s with work by Derek Ranwell, one of the pioneers of UK dune ecology. More recent work led by the UK Centre for Ecology and Hydrology (UKCEH) includes the following long-term monitoring data:
· Dune chronosequence study on dry dune habitats (0 - 170 years)
· Eco-hydrological monitoring and analysis, with over 85 dipwells and adjacent botanical quadrats
· Restoration monitoring (plants, soils and hydrology), and analysis of large-scale restoration techniques
For more information, read about the additional experiments at Newborough Warren (PDF).
Podcast
Listen to a podcast interview with Principal Investigator Laurence Jones.
grazing welsh ponies on control plot adjacent to grazing exclosure in replicate block 1
