Sitka spruce/ alternative conifer mixtures a review of the British field record

Transcription

1 ICF North Scotland / University of Aberdeen 1 st December 2015 Sitka spruce/ alternative conifer mixtures a review of the British field record Dr. Scott McG. Wilson MICFor, MRICS Chartered Forester and Surveyor Aberdeen, Scotland, UK

2 Aims of presentation Describe work undertaken during rapid review project (2014) looking at the field record of SS/ alternative conifer mixtures. Summarise outcomes from the range of analyses pursued and indicate implications for future potential of mixtures approach. Make some suggestions for enabling research and development requirements.

3 Background to the review project Evidence of increasing interest in the insurance mixtures approach to enhance resilience in upland spruce plantations. Inherent ecological logic from PNW etc. Sparse body of evidence from British field examples Cinderella silviculture. Restricted level of relevant silvicultural research activity since the early 1980 s.

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5 Objectives of the review project Address current interest in the insurance mixtures approach for upland forestry. Draw together the body of field evidence that we have (known to be fairly limited). Produce some initial indications of the potential advantages and disadvantages of the approach, priority companion spp etc. Make suggestions as to the way forward.

6 Methods of the review project Funded by Scottish Forestry Trust. Literature review/ technical discussion. Pre-identification of candidate examples. Field touring and photo-recording. Exploratory desk analyses ESC, GYC etc. Technical reporting. Dissemination.

7 Pre-identification of candidate sites Circular enquires of FC/ NRW districts and private forestry management companies. Discussions and meetings with local staff, forestry agents and head foresters. Interrogation of public domain GIS database of all sub-compartments on the NFE. Problem of incomplete recording on the FC database as to mixture pattern in s/compts.

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9 Pattern of mixtures Main research interest is in intimate, line-row and mosaic/ patch mixtures, not blocky patterns. Sub-compartment database provides very limited information to pre-determine mixture pattern. Air-photos only occasionally very helpful, staff detailed familiarity with beat stands is variable. Necessitates field visiting to determine pattern, but many stands actually turn out to be blocky. Field tour has a relatively low hit rate per mile.

10 Field touring approach Could only be an initial exploratory survey. Focussed on Scotland, Wales, N. of England Mainly NFE, some UPM Tilhill and others. Emphasised SS/NS, SS/DF, SS/GF, SS/WH, SS/NF established between 1950 and Limited coverage of post 1980 mixed regen. Noted SS/RC, SS/JCR, SS/PSF in passing.

11 SS/NS SS/DF SS/WH SS/NF SS/RC SS/GF

12 Field touring - results Examples generally small, sparse and scattered. Some very nice stand examples located. Many very under-thinned, neglected and isolated with risk of progressive depletion if not reserved. Regional patterns of adoption e.g. SS/DF in Moray, SS/WH in Wales and SS/NF in Argyll Pulse of interest after Bulletin 25 (Wood, 1955). Small database of best examples established with basic stand information and photographic record.

13 NS/ SS mixture, Archiestown, Moray

14 DF/ SS mixture, Balnacoul, Moray

15 WH/ SS mixture, St. Gwynno, Wales

16 GF/ SS mixture, Kirkhill, Aberdeen

17 NF/ SS mixture, Penllyn, Wales

18 GF/ SS mixture, Wales

19 RC/ SS mixture, Stromeferry, Highland

20 ESC site co-suitability analysis Suitability of mixture cannot exceed that of its least suitable component species (weakest link in the chain approach)? Companion almost always narrows down the range of suitable sites for mixture as compared to pure Sitka spruce. Strongly so for SS/DF, SS/GF, SS/RC. Weakly so for SS/WH, SS/NF, SS/PSF.

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22 Silvicultural compatibility Assessing risk of over-topping of the companion species before first thinning by comparison of Christie yield model height-curve families. Very few mixture Permanent Sample Plots, so have to assume that single species yield models (Booklet 48) offer rough idea by no means ideal, but little other evidence available for UK stands. Suggests that SS/DF and SS/GF fairly safe but SS/WH and SS/NF carry greater over-top risks. May need to reflect in initial pattern and ratio.

23 GYC mass comparison exercise Uses FC sub-compartment database GYC estimates for mixed-species (inc blocky). Assumes uniform site conditions between components (not micro-site spp selection). Suggests that companion is usually slower than SS on a site by site basis (not for GF) [cf results from FC Bulletin 49 (Aldhous & Low, 1974)]. Yield penalty for a 50/50 mixture over SS might be 5-10% (volume basis, not value).

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25 Indicative conclusions from review SS/DF and SS/GF look promising on the better classes of sites currently used for SS alone. SS/WH and SS/NF may offer options on the poorer classes of upland sites used for SS alone. Need more evidence on SS/RC, SS/PSF, SS/MCP SS/NS may have some role for drought resilience. Concerns over persistence of companion conifers where thinning is impossible/ inadequate SS is the thug species and companions need help.

26 Research and development priorities New long-term silvicultural upland mixtures trials. UK calibrations for GYC in mixtures based on new mixed species Permanent Sample Plots. Modelling of mixed stands (e.g. in MOSES-GB) Defining optimum initial ratios and patterns. More detailed economic comparisons (e.g. greater establishment and tending costs, deer issues v. risk pricing to evaluate enhanced resilience). Market development for WH, GF, NF timbers.

27 Further reading:- For access to technical report of review see: For co-authored summary article see: Scottish Forestry 2015: 69(1): or For access to mini-database of spruce mixture sites identified during the review contact: