1. MACHAIR VULNERABILITY AND LANDSCAPE RESILIENCE IN SOUTH UIST AND BENBECULA Elizabeth J Young XCECHR Postgraduate Symposium 30 th June 2011

2. The Machair Sandy grassland vegetation Calcareous shell sand Low-angle plain extending from coastal dunes to peat land transition History of grazing, cultivation and artificial drainage Fig 1. Map of the Uists and Benbecula with areas of machair marked in red

3. Orientation Field Visit: 01-06 May 2011 Identification of main threats to machair stability: Storms Agriculture Climate change Identification of areas of the machair which appear to be vulnerable or resilient to these pressures

4. Storms Erosion of machair soil by storm waves Deposition of storm debris across arable land Saline flooding of low- lying machair plain Fig. 2. Severe erosion of machair front from January 2005 storm, Stoneybridge, South Uist.

5. Climate Change PredictionsPossible Effects ~5% less Summer precipitation  lower soil water content leading to higher water repellence and increased erodability Higher Winter precipitation  increase in area and duration of water logged soil, tillage delayed until water table has fallen ~1°C warmer Winters  increase in length of growing season More frequent storms  marine flooding of low-lying machair, increased coastal erosion, greater deposition of sand on machair Higher wind speeds  increased erosion of bare soil after ploughing

6. Agriculture - Grazing Grazing is crucial to maintain machair biodiversity But livestock can contribute to coastal erosion where they have access to the beach Cattle grazing is linked to high biodiversity, and may increase dune stability The area of machair used for grazing is increasing relative to arable land

7. Agriculture - Arable Fig. 3. Sandy machair soil is susceptible to wind erosion on fields adjacent to the coast. Fig. 4. Hay ‘stooking’ is labour intensive, but is subsidised as the rare corncrake nests in the stooks.

8. Field Sites - Stoneybridge Fig. 5. Coastal defences at Stoneybridge.

9. Field Sites – Pollacher & Cille Pheadair Fig. 6. Large fields ploughed up to dune edge at Cille Pheadair. Coastal defence boulders at Pollacher transported several metres by January 2005 storm waves Extensive artificial drainage network at Cille Pheadair to alleviate winter flooding

10. Field sites – South Ford area Fig. 9. Map of South Uist and Benbecula Fig. 7. Storm breach on Gualan Island. Fig. 8. Traditional narrow fields at Borve, Benbecula.

11. Assessing Vulnerability and Resilience I Storms Survey the effects of winter storm damage on sites with different degrees of coastal protection (hard and soft coastal defences; presence or absence of dune cordon; hard/soft coast) Use aerial photographs and historical maps to quantify changes in coastal geomorphology, establishing areas which are vulnerable to erosion

12. Assessing Vulnerability and Resilience II Wind erosion Likely to increase due to: predicted increase in wind speed Less precipitation in Summer  drier soils Fig. 10. Aggregate stability of machair sand in water.

13. Assessing Vulnerability and Resilience III Climate Change How resilient is the machair soil to changes in precipitation, temperature and wind speed? How do different agricultural methods affect the resilience of machair soil to changes in climate, e.g. artificial vs. kelp fertiliser, deep vs. shallow ploughing? What affects will a change in climate have on agriculture, e.g. growing season, crops grown?