The view from a small corner of Anglesey...
Contact Harvest Your Rain Home



The hydrological consensus at Newborough (so far. July 2009)

The Countryside Council for Wales (CCW) claim that the forest is having an adverse impact upon water levels in the warren, and for this reason, parts of the forest should be removed. What constitutes a significant impact on the warren and how this compares to other hydrological factors such as: "…digging of drainage ditches north of the rock ridge, successional development of vegetation and soils leading to increased evapotranspiration, morphological change, past changes in stage state of the small lake in the Warren and the possible effects of nutrient enrichment (Stratford et. al., 2009) " is uncertain.

Long term the "…humid dune slack system at Newborough is drying out (Stratford et. al., 2009)". The initial assumption was that the forest was responsible for wide scale lowering of the water table observed anecdotally (Jennings, 1990; Betson et. al., 2002), and this assertion was supported by the conclusions of an earlier debate (Kirby et. al., 1991) about the adverse effects of upland conifer forests on river flows and water supplies in Mid Wales. However, recent research has found this earlier conclusion is largely incorrect. The situation is more complex, and changes as the forest matures (Marc and Robinson, 2007).

"Much of the variation of the water levels at Newborough can be explained by decadal- and seasonal-scale patterns of rainfall (Robins et. al., 2009)" and water level records, show that few of the dune slacks had water levels which would have qualified as humid slack at the time the SAC was designated (Robins et. al., 2009; Stratford et. al. 2006, 2007, 2009). From 2004, rainfall has been above average, and humid conditions have returned to some parts of the forest and to the warren, including slacks next to the forest.

Although there has been some felling and thinning of the forest, the return to more humid slack conditions at Newborough is dependant upon the rainfall pattern, and parts of this pattern include periods of dry slack conditions. The desire to increase further the area of humid slack should be seen as aspirational and assessed alongside the natural rainfall pattern. It is unlikely to be achieved by large scale felling (Robins et. al. 2009; Stratford et. al., 2007, 2009).

Although the forest is not responsible for the long term drying of the warren, the forest does lower water tables below the forest, whilst water levels recover quickly moving into the warren (Taylor and Low, 2008; Hollingham, 2008). The annual differences, however, are negligible, because the lowering of the water table under the forest also results in a reduction in drainage under the forest (Hollingham, 2008). The greatest difference in water levels between forest and warren will be most evident under a large area of rapidly growing forest (Marc and Robinson, 2007).

In conclusion, the forest is not responsible for the long term drying out of the warren and "it is unlikely that removal of the trees would reverse this trend" (Stratford et. al., 2009)". However, the forest has some effect on the water levels underneath it; therefore the forest should be pulled back around 50-100m from the warren as a precaution to prevent any impact on the neighbouring warren.

This could be used as an opportunity to measure the effects of the forest, as recommended by the Centre of Ecology and Hydrology (CEH) hydrological review team (Stratford et. al., 2006, 2007). To assess the effects of tree age and thinning, parts of the forest should be felled and allowed to regenerate. Forestry Commission Wales should use the results to evaluate the effects of stocking rates and thinning regimes on water levels along the warren forest boundary; whilst CCW should use the results along with other research into the other significant hydrological factors present at Newborough, in formulating their management plans.

 


References

Betson M, Connell M & Bristow C. (2002). Groundwater modelling of Newborough Warren: A report for the Countryside Council for Wales , Volume 5, Hydrogeology, The Impact of Forestry on Coastal Geomorphology at Newborough Warren/Ynys Llanddwyn NNR, SSSI, pSAC.

Hollingham, M.H. (Dec 2008). The relative effects of a Pinus plantation on the hydrology of an Atlantic dune system. (Newborough Warren case study). http://www.thedotenvironment.com/Newbro.htm

Jennings, T. A. H. (1990) The changing hydrology of the Newborough Dune System due to afforestation. M.Sc. dissertation, University of North Wales, Bangor, September 1990.

Kirby, C., Newson M & Gilman K (eds.) (1991) Plynlimon research: the first two decades - IH Report 109. Institute of Hydrology Wallingford. UK .

Marc, V. and Robinson, M. (2007) Long term water balance (1972-2004) of upland forestry and grassland at Plynlimon, mid-Wales. Hydro. Earth Syst. Sci. 11 (1) 22-60.

Robins, N., Stratford, C. and Jones, M.L.M. (2009) Case study: Newborough Warren and Aberffraw, North Wales. Site description and management issues, Report to the Environment Agency: Ecohydrological guidelines for dune slacks, 2009 (draft).

Stratford C., Hughes A., Roberts J., Robins N. (2006) Review of Hydrological Reports for Newborough Warren NNR, Anglesey . CEH, Wallingford.

Stratford C., Ratcliffe J., Hughes A., Roberts J., and Robins N. (2007) Complex interaction between shallow groundwater and changing woodland, surface water, grazing and other influences in partly wooded duneland in Anglesey, Wales. Paper presented at XXXV International Association of Hydrogeologists, Ground water and Ecosystems; Lisbon.

Stratford C., Robins N., and Hollingham M. (2009). An assessment of the interactions between hydrology, land use and climate change at two coastal dune systems in Wales, UK. Paper presented at the 2nd Multidisciplianary Conference on Hydrology and Ecology. Vienna 20-23 April 2009.

Taylor A and Low, R. (2009) Unpublished research for CCW. Mentioned in Comments from Peter Jones, Peatland Ecologist / Hydrologist: Appropriate Assessment screening for the Newborough Forest Design Plan; comments from TSG and MFSG. TSG FDP response December 2008 final draft.

 

Back

Copyright © Martin Hollingham