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The relative effects of a Pinus plantation on the hydrology of an Atlantic dune system.


(Newborough Warren case study)




The annual hydrological effects of an established Pinus forest on coastal sand dune system were quantified using water level records from 1989-1996 and 2006-2008. Previous research at Newborough based on records from 1989-1996 indicated that the forest may lower the water levels and induce vegetation changes in the adjacent warren. Yet winter flooding was observed in 2005-2008, and between Aug 1996 and Aug 2008 water levels have risen on average 0.7m in the Forest and 0.4m in the Warren .


The annual change in storage for the Forest, Warren or the Border areas calculated from the 1989-1996 and 2006-2008 water level records (annual mean: Forest = -16 mm, Border = 21mm, Warren = -25mm). The annual change in Forest storage was 55% and the Border 90% of Warren Storage). Drainage estimates were calculated using the water balance equation. For a given Warren drainage, the change in Forest storage was 10mm lower, while the change in Border storage was up to 15mm lower. For a given effective precipitation, drainage from the forest is 1.4%, and the Border 0.3% of effective precipitation lower than the warren.


Increases in evapotranspiration from the Forest are small and insignificant compared to effective precipitation and drainage, and are compensated for by a decrease in drainage. Removing parts of the Forest to increase water levels on the Warren , will be effective where the trees are removed, but will have little impact on the annual hydrological balance of the Warren .




The sand dune system at Newborough, Anglesey, was part afforested in 1947. There are concerns that the forest reduces the amount of winter flooding in the warren which is an SSSI.

Annual water balances for 19951996 and 2007-2008 were calculated for the Forest, Border and Warren from meteorological data and 26 dip well records. The change in storage was assumed to be 37% of water level movement, and drainage the remainder of precipitation less actual evapotranspiration and change in storage.

The water balance equation is

 Q= EP- ?S

Where: Q = Drainage (estimated)

  • ? S = Change in Storage (Previous Aug water level Aug water level x 0.37)
  • EP = Effective Precipitation  = P- AEt


  • P = Rainfall (RAF Valley)
  • AEt = Actual Evapotranspiration (MORECS data)


Copyright © Martin Hollingham