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Thursley Common Defra.jpg

Background

Thursley Common is a National Nature Reserve and Site of Special Scientific Interest owned by Natural England. It is a lowland heath habitat located south of Guildford in Surrey. Atmospheric nitrogen deposition is among the top three threats to biodiversity. It is estimated that by 2050 global N deposition will be almost twice as high as at the beginning of the 1990s. 

Initiated in 1989 and running until 1996, the first phase of this experiment investigated the response of heather (Calluna) to nitrogen addition at different concentrations. Nitrogen treatments ceased in 1996 and the experiment entered a post-treatment recovery phase.

Two years later, in 1998, the experiment entered a second phase studying the on-going heather ecosystem recovery under four new ‘management’ treatments - low/high-intensity mowing, and low/high intensity burning.  Management treatments ended in 2006, after which the treatments plots fell out of active use.

Plots are still marked and the site remains available for new research. The site was one of several operating under the UKREATE umbrella project formerly funded by the Department for Environment Food and Rural Affairs (Defra) and the Natural Environment Research Council (NERC). 

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Design and Treatments

Four replicate blocks comprising randomised duplicated control and nitrogen-addition plots (4m x 4m) with management sub-plots (2m x 2m) nested within. Each replicate block was also associated with two ‘extra’ plots - a control and a nitrogen addition plot. Treatments were:

  • control (receiving artificial rain only) (1989-1996)

  • low treatment of ammonium sulphate at 7.7 kg N/hectare/year (1989-1996)

  • high treatment of ammonium sulphate at 15.4 kg N/hectare/year (1989-1996)

  • alternating treatment receiving either the control or the high nitrogen addition in alternate years (1989-1996)

  • low intensity mow (1998-2006)

  • high intensity mow (1998-2006)

  • low temperature (management) burn (1998-2006)

  • high temperature (simulated wildfire) burn (1998-2006)

Calluna vegetation parameters monitored were:

  • shoot growth and chemistry

  • litter production and decomposition

  • shoot sensitivity to frost and insect herbivory (by the heather beetle Lochmaea suturalis)

Results and Conclusions

The initial experiment (1989-1996) revealed that greater than two-thirds of the applied nitrogen accumulated in the litter and soil and led to increased microbial populations and higher rates of conversion of nitrogen to soluble inorganic forms. Results have been key to modelling the impact of nitrogen deposition under varying conditions and have contributed to an improved understanding of the role of management to mitigate the impact of eutrophication. The experiment also led to a revision of the critical loads of nitrogen for lowland dry heaths at the European level.

Post-treatment monitoring of ecosystem recovery revealed that, eight years after nitrogen treatment ceased, its effects were still measurable in terms of reduced resistance of heather to drought, increased canopy height and a persistent increase in soil microbial activity.

Results from the ecosystem restoration monitoring under new ‘management’ treatments revealed that burning intensity affects stored nitrogen removal, but that there is little or no impact on the rate of ecosystem recovery from the effects of earlier nitrogen addition.


Future Use of Thursley Common Plots

The plots at Thursley Common remain accessible and open for new research use with the permission of the land owner Natural England (NE). If you are interested in using this site for new research, please contact James Giles at NE in the first instance.