1. Lessons from long-term forested catchment studies - potential impacts on streamflow Dr Mark Robinson Centre for Ecology & Hydrology Wallingford Oxfordshire UK Irish Natural Forestry Foundation 5 th Nov 2008 Integrated science for our changing world www.ceh.ac.uk

2. Climate change scenarios Increase in winter rainfall by between 10 and 40% – hence more severe flooding Reduction in summer rainfall by 50% – hence increase in frequency and intensity of droughts Integrated science for our changing world www.ceh.ac.uk

3. WYE Changing climate An increase in precipitation over this period has been observed at other UK upland sites Integrated science for our changing world www.ceh.ac.uk

4. Potential role of forestry: Post 2007 summer flooding- British Ecological Society. The restoration of native deciduous woodland would help to: increase the interception of rainfall by vegetation; increase water infiltration into the soil and groundwater; increase transpiration to the atmosphere; reduce peak flow due to surface runoff. Integrated science for our changing world www.ceh.ac.uk

5. The forest area in Europe grew by 13 million hectares between 1990 and 2005. The potential for land-use management to help mitigate flooding, in an integrated approach to flood risk, in which land-use practices maximize a range of ecosystem services, including flood control. Integrated science for our changing world www.ceh.ac.uk

6. Ireland and UK amongst lowest forest coverage in Europe.

7. Rises in the price of fossil fuels – renewed interest in biofuels – SRF and biodiesel. Recognition of forest as a supplier of Environmental Services, – so that multitude of benefits can be considered in relation to possible water resource costs. Forestry schemes - New policy drivers

8. Traditional view of forest hydrology: Deeper, more absorbent soil: ↓ peak flows, ↑ baseflows Thicker vegetation canopy ↓ peak flows Greater water use ↓ annual yield, ↓ peak flows, (↓ baseflow?) Overall: Even out flows, reduce flooding Integrated science for our changing world www.ceh.ac.uk

9. Is evaporation from broadleaved woodland the same as from grassland ? Intuitively you would expect it to be greater, and there is evidence due to greater observed soil moisture depletions under woodland Integrated science for our changing world www.ceh.ac.uk

10. Clipstone, Nottinghamshire (after Calder et al., 2000) Integrated science for our changing world www.ceh.ac.uk

11. BUT – Black Wood, Hampshire – no difference! (Roberts and Rosier, 2006)

12. Reason for conflicting results: Higher evaporation per unit area of forest from fragmented woodland and along woodland edges than in the middle of an extensive forest

13. Edge effects – greater drying Integrated science for our changing world www.ceh.ac.uk Greater drying of soil due to higher evaporation rates at the better ventilated forest edge

14. Biofuels: Short rotation coppice Integrated science for our changing world www.ceh.ac.uk (Finch, 2008)

15. Planting of broadleaves is increasing in Ireland and Britain but most forests (and over half of current planting) are conifers: Ireland ~85% conifers Britain ~ 70% conifers Integrated science for our changing world www.ceh.ac.uk

16. Conifer forests are: Different to broadleaves – all-year canopy – Often shallow rooted – monoculture, even-aged Complex – management cycle 40+ years – management interventions at different stages Integrated science for our changing world www.ceh.ac.uk

17. Case studies Plynlimon – comparison forest vs. grass Coalburn – time study moorland → forest Detailed surveys of catchment properties soils, geology and forest cover changes. Measurements over decades of streamflow (floods, baseflows, water yield) plus climate, water quality. Integrated science for our changing world www.ceh.ac.uk

18. Plynlimon catchments Severn (70% forest) Wye (grass) Integrated science for our changing world www.ceh.ac.uk

19. Wye Catchment Land area of 10.55km 2 Mainly moorland Diverse land-use –Sheep farming –Rally driving Integrated science for our changing world www.ceh.ac.uk

20. Severn Catchment Land area of 8.67km 2 Two-thirds planted in 1930s-1960s by the Forestry Commission Forest felling and replanting now taking place Integrated science for our changing world www.ceh.ac.uk

21. Spatial Data Spatial data included in GIS –Catchment boundaries –Streams (main, minor and artificial) –Contours and spot heights –Vegetation maps –Forestry planting maps –Soil map –Solid geology (Bell, 2005) Integrated science for our changing world www.ceh.ac.uk

22. Changing structure of Hafren forest – from uniform age to multi-aged Integrated science for our changing world www.ceh.ac.uk

23. Greater water use of conifers over plantation cycle Additional water use of the forested Severn catchment compared to the grassland Wye. Integrated science for our changing world www.ceh.ac.uk

24. Flooding Forestry in UK is less effective in reducing peak flows than is popularly claimed – but this depends on silvicultural practices (how the forest is felled, and if it is a plantation, then whether afforestation includes site drainage) BUT Uncertainty remains to what extent afforestation (without intrusive site preparation) will affect flood response. Integrated science for our changing world www.ceh.ac.uk

25. Flood frequency curves Integrated science for our changing world www.ceh.ac.uk

26. Peak flows (4mm h -1 ≈ 1m 3 km -2 ) Integrated science for our changing world www.ceh.ac.uk

27. Annual 95%-ile exceedance flows before and after felling in Severn basin Forests and low flows Integrated science for our changing world www.ceh.ac.uk

28. Summary – Plynlimon felling Integrated science for our changing world www.ceh.ac.uk

29. Coalburn - Britain’s longest running research catchment Aim: to follow the hydrological effects of a whole plantation forest cycle Moorland calibration 1967 - 1971 Drained and afforested 1972 - 1973 Canopy closure 1995 - 2000 Felling anticipated ~ 2010 Second rotation forest ~ 2012 Integrated science for our changing world www.ceh.ac.uk

30. Raingauge Flow gauge Automatic Weather Station KEY Kielder Reservoir N. Tyne COALBURN Lyne Irthing CARLISLE 0.5 km0 Major unplanted areas SOLWAY FIRTH 10 km Winter Hill Wilcocks 1 Longmoss A B A, B Interception sites 310 300 310 300 290 Contours m Soil series boundary Forest Location and main physical characteristics Part of Kielder Forest Peaty soils Area 1.5 km² Precipitation ~1200 mm / yr.

31. Catchment changes: Forestry drainage 1972 Aerial photo

32. Forest growth across the catchment Aerial photos 1983 1989 Growth has been variable across the catchment: Sitka spruce Yield Classes 9 to 15

33. Integrated science for our changing world www.ceh.ac.uk

36. Felling Integrated science for our changing world www.ceh.ac.uk

37. Impact of felling on peak flows Integrated science for our changing world www.ceh.ac.uk

38. Effects of clearfelling lodgepole pine on flood peaks in a blanket peat catchment at Burrishoole, Co. Mayo Estimated response to a 1-hour pulse of 1 mm of net rainfall Integrated science for our changing world www.ceh.ac.uk

39. Managed plantation forest – changes over the cycle

40. Forest plantation cycle - changing impacts Cultivation and planting – species, coupe size, cultivation method, landscape, buffer zones. Peak and low flows, sediment ↑ Thinning – to provide an ‘extra’ crop, unsuitable where prone to windblow. May be selective or systematic. Water yield ↑?↓ Growth – yield class and top height All flows ↓ Fertiliser – perhaps 3 times per crop Water quality Felling – age, machinery, coupe size Flows ↑ mean & extremes Restocking – natural or replanting, original drainage system may satisfactory, revise species selection and landscape design. Flows, water quality.

41. Hydrological issues Water Resources: Annual water yield - depends upon scale and forest age structure Baseflows reduced by forests Flooding: - Limited effect reducing peak flows – but depends on silvicultural practices (i.e. if afforestation includes drainage, how the forest is felled …..)

42. Guidance available elsewhere The Forestry Commission issued Forest & Water Guidelines to protect watercourses from the impact of forestry operations Limit felling coupes Minimum riparian zones corridor width Forestry management is subject to wide consultation through forest design plans.