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Assessment of drought risk in southern and eastern Scotland

How the assessment was made

Forestry Commission Bulletin 124 coverTo assess the potential effect of dry summers on species suitability, information about the interactions between tree species, climate change, sites and soil properties is necessary at a detailed local level. National digital soil data from the Soil Survey of Scotland (SSS) published at a scale of 1:250 000 (Macaulay Institute) is not sufficiently detailed for assessing the impact of climate change on forest soils at a site-level.

Considering that the main climate impacts on forests are likely to result from by drier summers and wetter winters, a primary source of climatic information are the moisture deficit (MD) maps for different UKCIP02 emissions scenarios.

Suitability analyses were made on the basis of changes only in the climatic data, under the assumption that if the climate becomes drier then soils become drier (and vice-versa). The method of coupling moisture deficit (MD) with soil moisture regime (SMR) is integral to the stand-based methodology of Ecological Site Classification (ESC), outlined in Forestry Commission (FC) Bulletin 124 - An Ecological Site Classification for Forestry in Great Britain (Pyatt, Ray, and Fletcher, 2001).

Impact of more frequent dry summers

It is perceived that the climate projections of more frequent dry summers in the east and south of Scotland will reduce the suitability of some species of tree. Dry summers combined with shallow freely draining soils may lead to widespread moisture stress for sensitive species. This may have implications for timber quality and contribute to the increased risk of outbreaks of disease from pests and pathogens. The photographs below show damage to Sitka spruce stems in eastern Scotland following the dry summer of 2003.

  • Photo
    Longitudinal lesions on the stem of Sitka spruce, growing on shallow stony gleyed podzol, in Durris Forest, Aberdeenshire, following the dry summer of 2003.
    (Photo: Bill Rayner, Forest Research)
  • Photo
    Crack exposed after removing bark lesion on Sitka spruce in Durris forest, Aberdeenshire.
    (Photo: Bill Rayner, Forest Research)

Impact of wetter winters

On some types of soil, the projected wetter winters will increase winter water-logging, leading to anaerobic conditions – root respiration stress, and root death. On such sites trees will have shallower root plates, and this will intensify summer moisture stress. These issues are discussed in detail in the downloadable report below.

Cover of final reportImpacts of climate change on forests in Scotland - final report (PDF-1225K)

By Duncan Ray with sections drafted by Dave Wainhouse, Joan Webber and Barry Gardiner.

14th January 2008.

Suitable tree species on forest soils in eastern Scotland

To try and understand the interactions between climate, soil-site type and the impact on tree species suitability, a data- and knowledge-base is being developed for forest soils in the drier south-eastern area of Scotland. The map below shows the region of eastern Scotland considered to be at most risk of drought in the current climate, and at increasing risk of drought in projected future climate scenarios. The map is based on the Met. Office Regional Evaporation Calculation System (MORECS), 40 km squares. Both the MORECS data and the UKCIP02 climate change simulations show a higher risk of drought (2 summer months without rain) in the area bounded by these squares.

Map
Met Office Rainfall and Evaporation Calculation System (MORECS) 40km grid squares in eastern and southern Scotland in which there is an increased risk of summer drought.

The table below provides some information about the main forest soils in each of the MORECS squares (shown numbered in the map above) in which dry summers can increase the risk of drought. For each 40x40km square, attributes of the main forest soils described by the Soil Survey of Scotland (SSS) and the Forestry Commission (FC) Soil Classifications, have been examined to assess the droughtiness of the given soil type within the square. From knowledge of the soil type and drought risk, a list of tree species and native woodland types are recommended as suited to drier summers on each specific soil type.

MORECS Square No.Percent area of forest Dominant forest soil series (top 3) described by the SSSEquivalent FC soil type(s) and phase(s) associated with SSS soil seriesDrought riskSpecies and native woodland options for climate change adaptation on the soil type
Suitable productive speciesSuitable woodland communities
14 23 Sabhail 4px Medium Scots pine, lodgepole pine, downy birch Downy birch with purple moor grass, native pinewood, willow scrub
Ramscraigs 4bx(g) Medium Scots pine, lodgepole pine Downy birch with purple moor grass, upland birch/oak woodland, native pinewood, juniper woodland
Blanket peat 9, 10, 11, 14 Low Mixture lodgepole pine and Sitka spruce on soil type 9. No suitable woodland for soil type 10 Wet woodland – downy birch with purple moor grass, fen carr, and willow scrub on flushes. No suitable woodland for soil type 10
20 41 Millbuie 3xg Medium Scots pine, lodgepole pine, Corsican pine Upland birch/oak woodland, native pinewood, juniper woodland
Kindeace 3xg Medium Scots pine, lodgepole pine, Corsican pine Upland birch/oak woodland, native pinewood, juniper woodland
Corby 3xs High Scots pine, lodgepole pine Upland birch/oak woodland, native pinewood, juniper woodland
21 38 Basin peat 8, 10 Low Sitka spruce, lodgepole pine. No suitable woodland for soil type 10 Alder wet woodland on soil type 8. No suitable woodland for soil type 10
Strichen 3x High Scots pine, lodgepole pine Upland birch/oak woodland, native pinewood, juniper woodland
Corby 3xs High Scots pine, lodgepole pine Upland birch/oak woodland, native pinewood, juniper woodland
22 17 Durnhill 4zpx Medium Scots pine, lodgepole pine Downy birch with purple moor grass, native pinewood
Strichen 3x High Scots pine, lodgepole pine Upland birch/oak woodland, native pinewood, juniper woodland
Blanket peat 9, 10, 11, 14 Low Mixture of lodgepole pine and Sitka spruce on soil type 9. No suitable woodland for soil type 10 Wet woodland – downy birch with purple moor grass, fen carr and willow scrub on flushes. No suitable woodland for soil type 10
23 7 Strichen 3x High Scots pine, lodgepole pine Upland birch/oak woodland, native pinewood, juniper woodland
Thurso 7 Low Sitka spruce, Norway spruce, silver birch, common alder, pedunculate oak, sycamore, ash Ash, oak or mixed broadleaved woodland
Blanket peat 9, 10, 11, 14 Low Mixture of lodgepole pine and Sitka spruce on soil type 9. No suitable woodland for soil type 10

Wet woodland – downy birch with purple moor grass, fen carr, and willow scrub on flushes. No suitable woodland for soil type 10

31 22 Countesswells 3x High Scots pine, lodgepole pine Upland birch/oak woodland, native pinewood, juniper woodland
Foudland 3 Medium European larch, Scots pine, sessile oak, silver birch, sycamore Upland oak woodland
Charr 4zpx Medium Scots pine, lodgepole pine Upland birch/oak woodland, native pinewood
32 8 Countesswells 3x High Scots pine, lodgepole pine Upland birch/oak woodland, native pinewood, juniper woodland
Tarves 1 Medium European larch, Scots pine, sessile oak, silver birch, sycamore, Douglas fir Oak and birch woodland
Corby 3xs High Scots pine, lodgepole pine Upland birch/oak woodland, native pinewood, juniper woodland
38 22 Countesswells 3x High Scots pine, lodgepole pine Upland birch/oak woodland, native pinewood, juniper woodland
Tarves 1 Medium European larch, Scots pine, sessile oak, silver birch, sycamore, Douglas fir Oak and birch woodland
Charr 4zpx Medium Scots pine, lodgepole pine Downy birch with purple moor grass, native pinewood
39 22 Countesswells 3x High Scots pine, lodgepole pine Upland birch/oak woodland, native pinewood, juniper woodland
Strichen 3x High Scots pine, lodgepole pine Upland birch/oak woodland, native pinewood, juniper woodland
Dess 3xg Medium Scots pine, lodgepole pine Upland birch/oak woodland, native pinewood, juniper woodland
44 17 Strichen 3x High Scots pine, lodgepole pine Upland birch/oak woodland, native pinewood, juniper woodland
Balrownie 1g Low European larch, Scots pine, sessile oak, silver birch, sycamore, Douglas fir Oak and mixed broadleaved woodland
Sourhope 1d Medium Sessile oak, silver birch, sycamore, Douglas fir, European larch Oak and birch woodland
45 10 Balrownie 1g Low European larch, Scots pine, sessile oak, silver birch, sycamore, Douglas fir Oak and mixed broadleaved woodland
Forfar 3g Low Scots pine, European larch, Corsican pine, pedunculate oak, sycamore Upland birch/oak woodland, native pinewood, juniper woodland
Lour 7 Low Sitka spruce, Norway spruce, silver birch, common alder, pedunculate oak, sycamore, ash Ash, oak or mixed broadleaved woodland
50 14 Sourhope 1d High Sessile oak, silver birch, sycamore, Douglas fir, European larch Oak and birch woodland
Winton 7b Low Sessile oak, downy birch, beech, sycamore, European larch, Corsican pine, Scots pine, Sitka spruce Oak woodland
Basin peat 8, 10 Low Sitka spruce, lodgepole pine. No suitable woodland for soil type 10 Alder wet woodland on soil type 8. No suitable woodland for soil type 10
51 7 Fraserburgh 12b High Scots pine, Corsican pine Birch and scrub
Allanhill 3 High Scots pine, Corsican pine, European larch, silver birch Birch woodland, Juniper woodland
57 12 Linhope 1 Medium Sitka spruce, European larch, Scots pine, sessile oak, silver birch, sycamore, Douglas fir Oak and birch woodland
Dod 4p Low Sitka spruce, Scots pine, lodgepole pine, downy birch Downy birch wet woodland
Basin peat 8, 10 Low Sitka spruce, lodgepole pine. No suitable woodland for soil type 10 Alder wet woodland on soil type 8. No suitable woodland for soil type 10
58 9 Linhope 1 Medium Sitka spruce, European larch, Scots pine, sessile oak, silver birch, sycamore, Douglas fir Oak and birch woodland
Minchmoor 3 Medium Scots pine, sessile oak, birch, Corsican pine, European larch Birch woods, oak woodland, juniper woodland
Blanket peat 9, 10, 11, 14 Low Mixture of lodgepole pine and Sitka spruce on soil type 9. No suitable woodland for soil type 10 Wet woodland – downy birch with purple moor grass, fen carr, and willow scrub on flushes. No suitable woodland for soil type 10
59 6 Linhope 1 Medium Sitka spruce, European larch, Scots pine, sessile oak, silver birch, sycamore, Douglas fir Oak and birch woodland
Hardlee 6 Low Lodgepole pine, Sitka spruce lodgepole pine and birch in mixture Downy birch wet woodland
Aberdona 7b Low Sitka spruce, Scots pine, pedunculate oak, European larch, downy birch, Mixtures of Sitka spruce and lodgepole pine and birch Oak woodland, birch woodland
65 30 Carter 6p Low Lodgepole pine, Sitka spruce lodgepole pine and birch in mixture Downy birch wet woodland
Blanket peat 9, 10, 11, 14 Low Mixture of lodgepole pine and Sitka spruce on soil type 9. No suitable woodland for soil type 10 Wet woodland – downy birch with purple moor grass, fen carr, and willow scrub on flushes. No suitable woodland for soil type 10
Ettrick 7 Low Sitka spruce, Norway spruce, silver birch, common alder, pedunculate oak, sycamore, ash Ash, oak or mixed broadleaved woodland
66 5 Sourhope 1d High Oak, silver birch, sycamore, Douglas fir, European larch Oak and birch woodland

See Forestry Commission (FC) Bulletin 124 - An Ecological Site Classification for Forestry in Great Britain - for an explanatory key for the equivalent FC soil type(s) and phase(s) associated with the SSS soil series.