Risk/opportunity:(from the Climate Change Risk Assessment for Scotland 2012):
FO1a Forest extent affected by Dothistroma needle blight (DNB)

Narratives: Pests, diseases and invasive species (forestry)

SCCAP theme: Natural environment

SCCAP objectives:
N3: Sustain and enhance the benefits, goods and services that the natural environment provides

Latest figures

13722 ha/ 1661 sub-compartments[1]

(National Forest Estate only)

This represents approximately 15% of the total high forest pine area in the NFE.

Average annual increase of positive DNB sub-compartments of around 1% of total number surveyed (2006-13)

[1] Includes compartments which have been surveyed as positive for DNB either in the latest year or in an earlier year. Data provided by FCS Dec2013.

Trend
At a glance
  • Dothistroma needle blight (DNB) has become the most significant disease affecting coniferous trees in the UK.
  • Climatic changes may optimise conditions for spore dispersal and infection.
  • The majority of DNB infected forestry is in the north and north east of Scotland, with over half of infected pine in the North Highland district.

Forestpests and pathogens can cause extensive and catastrophic damage to productive forestry stocks. Affected woodlands may experience sufficiently severe outbreaks to reduce productivity, timber quality and/or to require changing forest management. The majority of insect pests that currently affect UK forestry are likely to benefit from climate change as a result of increased activity and reduced winter mortality. If climatic conditions influence the success of a pest or pathogen establishing, breeding and spreading, then a change in climatic conditions is likely to influence their prevalence and severity (Moffat et al., 2012). Other effects may be more indirect and result from increased susceptibility to infection due to damage or stress to the trees as a result of storms, drought or temperature extremes.

The fungal disease Dothistroma needle blight (DNB), often referred to as ‘Red Band Needle Blight’, has become the most significant disease affecting coniferous trees in the UK. The fungus affects the needles of the infected tree, which eventually shed. As this continues, year on year, gradually the tree will weaken, significantly reducing timber yields. It can also eventually lead to mortality. Whilst it was first recorded in the UK in the 1950s, it was not known in Scotland until 2002 and has now been identified in Corsican, Lodgepole and Scots pine stands (though primarily a disease of pines, five spruce species, European larch and Douglas fir are also known to host the disease) (Forestry Commission, 2010).

This indicator monitors the abundance of DNB in the Forestry Commission Scotland National Forest Estate (NFE) which holds over 35% of Scotland’s woodland. The indicator is based on DNB surveys which have taken place annually since 2006 to monitor the distribution and spread of the disease. Although the data covers the NFE only, changes in the abundance of DNB in these areas is likely to be indicative of DNB abundance across forestry in Scotland as a whole.

Related indicators:

NB36 Proportion and area of Caledonian pine woodland exposed to Dothistroma needle blight (DNB)

NF7 Proportion and area of pine woodland exposed to Dothistroma needle blight (DNB)

The current extent of pine woodland in the NFE that is known to have been infected with DNB is 13722 ha from 1661 infected sub-compartments (see Figure 1).

The impacts on timber yields are currently most severe on Corsican and Lodgepole pine (particularly those of ‘Inland’ origin), with trees infected by DNB becoming unmarketable over time (Forestry Commission Scotland 2013).

Figure 1 Total pine area (ha) in FCS sub-compartments with positive DNB survey results (2006-2013). Positive status is accumulative and therefore results include data for compartments which have been surveyed as positive for DNB either in the latest year or in an earlier. Data provided by FCS Dec 2013 (2013 data incomplete).

Due to changes in annual surveying effort over this period (most notably a significant increase in area surveyed between 2010-2011), it is important to consider the positive survey results as a proportion of total area surveyed. Figure 2 shows that over this period there has been an average annual increase of positive DNB sub-compartments of around 1% of total number surveyed, with the latest results showing that approximately 10% of all surveyed pine forestry in the NFE is positive for DNB.

 

Figure 2 Proportion (%) of total (accumulative)sub-compartments surveyed which show a positive result for DNB (results for 2013 are incomplete).

Whilst it was first recorded in the UK in the 1950s, it was not known in Scotland until 2002 and has now been identified in Corsican, Lodgepole and Scots pine stands (though primarily a disease of pines, five spruce species, European larch and Douglas fir are also known to host the disease) (Forestry Commission, 2010).

There has been a dramatic increase in identified infection since first detected in 2002, with the earliest available survey figures being from 2006 (see Figure 3 for comparison between 2007 and 2013).

Figure 3 Distribution of Dothistroma needle blight in Forestry Commission Scotland National Forest Estate blocks, 2007 and 2013

Analysis for the Climate Change Risk Assessment for the Forestry Sector (Moffat et al 2012) indicated that potentially by the 2020s, between 12% to 25%[1] of pine forest area in the UK may be affected by DNB, with this figure rising to between 49% to 98%[2] in the 2050s and 100%[3] in the 2080s. Projected increases in spring and summer rainfall, along with temperature increases are considered to be the key drivers for determining the prevalence of DNB (Brown and Webber, 2008). Regions with the highest mean summer temperatures, along with those areas with the greatest projected change in temperatures are likely to see the greatest change in the level of risk (Moffat et al 2012). However, the basis of the response functions was associated with high uncertainty and further research is required to provide stronger evidence for future risk.

Limiting the spread and potential impact of DNB on Scottish forestry is being addressed by the FCS Dothistroma Needle Blight Action Plan, which is reviewed annually. As well as increasing awareness, research and detection effort, the action plan also covers preventative measures (e.g. destruction of infected plants in nurseries, buffer zones around Caledonian pinewoods), and the prioritisation of felling infected stock (FCS, 2013). Increasing diversity in the forest stock is also believed to increase overall forest resilience to a wide number of potential risks as well as delaying or reducing the build-up of pests and diseases within a plantation (Brown & Claydon, 2012).

In 2011, the disease was found in Abernethy, an RSPB-owned native pinewood, bringing to the fore the threat to native pinewoods. Many of these areas have until recently had a poor regeneration record, and there is concern that impacts of DNB on young trees could further threaten the age class structure, and hence continuity of these woodland (Forestry Commission 2012). Mature pine in Caledonian pinewoods currently appear to be less susceptible to the disease but there is concern that this could change as there is considerable potential for genetic exchange due to the presence of two mating types, a high number of genotypes of Dothistroma septosporum, and the possible introduction of D. pini, which is responsible for DNB in North-Central America, Russia, Ukraine, France and Hungary (Forestry Commission Scotland 2013).


[1] Estimated range of 11% to 98% for the p10 to p90 probability levels for the medium emissions scenario

[2] Estimated range of 11% to 100% for the p10 probability level low emissions scenario to the p90 probability level high emissions scenario

[3] Estimated range of 12% to 100% for the p10 probability level low emissions scenario to the p90 probability level high emissions scenario

The majority of DNB infected forestry is in the north and north east of Scotland, with over half of infected pine in the North Highland district (see Table 1 and Figure 4a). This distribution largely reflects the distribution of pine in general across Scotland.

Figure 4b highlights that over a third of all forestry surveyed in the North Highland district is now infected with DNB. However, the detected infection proportion  does not show quite such a clear relationship with pine forestry distribution as Figure 4a, with the Scottish Lowlands having a relatively high proportion of infection (16.8%), though this district holds only approximately 2% of the National Forest Estate pine.

Table 1 Changing DNB distribution in FCS Forest Districts (area (ha) of surveyed FCS sub-compartments with positive DNB survey results). Table also provides 2013 figure for total pine area in each district. Positive status is accumulative and therefore results include data for compartments which have been surveyed as positive for DNB either in the latest year or in an earlier. Data provided by FCS Dec 2013, results for 2013 are incomplete.

2013 total pine area (ha)*

DNB infected pine area (ha)

2006

2007

2008

2009

2010

2011

2012

2013

West Argyll

2964

0

0

2

5

46

50

107

168

Tay

10101

66

87

155

155

184

365

795

844

Moray & Aberdeenshire

16443

68

141

315

366

740

983

1090

1339

North Highland

23119

0

155

162

569

715

7715

8230

8365

Inverness, Ross & Skye

20156

0

98

111

434

984

1258

1588

1873

Lochaber

4634

0

0

14

14

87

124

225

247

Cowal & Trossachs

2628

0

0

0

129

154

213

274

291

Scottish Lowlands

1774

0

0

0

0

0

26

196

298

Galloway

5870

0

0

0

8

28

89

92

198

Dumfries & Borders

1914

0

0

0

0

3

48

83

97

* Total area of high forest pine (positive and negative for DNB)

Figure 4 Comparison of extent of pine woodland containing DNB in Forestry Commission districts: a) Total pine area (ha) in FCS sub-compartments with positive DNB survey results (2006-13); b) Proportion (%) of total pine area surveyed with positive DNB survey results (2006-13)

Whilst reasons for the increase in the disease are presently unclear, there is some evidence to suggest that increased rainfall in spring and summer coupled with a trend towards warmer springs is optimising conditions for spore dispersal and infection (Brown and Webber, 2008).

The increase in geographic extent and intensity of the disease across the whole of Britain is probably due to a combination of factors including an increase in favourable climatic conditions, as well as availability of suitable hosts, a genetically diverse fungal population, and movement of the pathogen through the plant trade.

The survey methodology targets priority areas, and survey effort has varied considerably over the period (Figure 5). There was a significant increase in 2011 in the amount of forestry included in the annual survey, with 2012 also maintaining this extent (NB the data presented here for 2013 does not represent the full data for the year).

Figure 5 Annual DNB survey extent (number of sub-compartments surveyed) in the National Forest Estate forestry districts 2006-13.

  • Data covers FCS National Forest Estate only, however, changes in the abundance of DNB in this forestry is likely to be indicative of DNB abundance across Scotland.
  • Survey effort has varied considerably over the period.
  • The survey methodology targets priority areas, therefore positive results should not be seen as a random subset of the National Forest Estate.
  • Positive survey results are applied to the whole sub-compartment, though detection may only have been at the edge of a sub-compartment.
  • Positive status has been assumed to remain for a compartment for all subsequent years. Additional analysis could begin to establish re-surveying effort and what change is detected in these areas, though it is potentially difficult to infer complete change in a sub-compartment due to the issues with survey methodology mentioned above.

Brown, A. & Claydon, H. (2012) Dothistroma (red band) needle blight in Scotland. Forestry Journal2/12. Available online at: http://www.forestryjournal.co.uk/newsitefiles/2012/0212Web/DNB.pdf

Brown, A. & Webber, J. (2008) Red band needle blight of conifers in Great Britain. Research Note FCRN002. Forestry Commission, Edinburgh.

Forest Research (2013) Status of Dothistroma needle blight in Britain. Available online at: http://www.forestry.gov.uk/

Forestry Commission (2010) Red band needle blight in Scottish tree nurseries. Available online at: http://www.forestry.gov.uk/

Forestry Commission (2012). Dothistroma Needle Blight GB Strategy. Available online at: http://www.forestry.gov.uk/

Forestry Commission Scotland (2013). Dothistroma needle blight action plan– Scotland (2013/14). Available online at: http://www.forestry.gov.uk/

Moffat, A.J., Morison, J.I.L., Nicoll, B., & Bain, V. (2012) Climate Change Risk Assessment for the Forestry Sector. DEFRA, available online at: http://www.defra.gov.uk/environment/climate/government/

Forestry Commission Scotland- Ben Griffin, Glenn Wilson for provision of FCS data and reviewing; Colin Edwards for review and advice.

Forest Research- Anna Brown, Kate Beauchamp for advice regarding indicator development.

Contains, or is based on, information supplied by the Forestry Commission. © Crown copyright and database right 2014. All rights reserved. Ordnance Survey Licence number 100021242.