Assessment of drought risk in southern and eastern Scotland

How the assessment was made

Forestry Commission Bulletin 124 cover To 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.

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)

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 report Impacts 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.

14^th 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 SSS	Equivalent FC soil type(s) and phase(s) associated with SSS soil series	Drought risk	Species and native woodland options for climate change adaptation on the soil type
MORECS Square No.	Percent area of forest	Dominant forest soil series (top 3) described by the SSS		Drought risk	Suitable productive species	Suitable 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
51	7	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.

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