Clark, J., Hemery, G., Russell, K. & Williams, H. (2005) The future of Black Walnut in Britain. Quarterly Journal of Forestry. 99(3): 207-212. THE FUTURE OF BLACK WALNUT IN BRITAIN Black walnut (Juglans nigra) is economically one of the more productive broadleaved timber species in Britain. However, it is also one of the least planted and known about species, with little or no improved material available. Jo Clark, Gabriel Hemery, Karen Russell and Hugh Williams describe the international research programme aimed at addressing these issues. lack walnut (Juglans nigra L.) was provenance and progeny research programme. Bintroduced to Britain from North America in Field trials containing European and US seedlots the early 17th century (Bean, 1981) and was were planted in two establishment phases during widely planted for its valuable timber. It is 2003 and 2004 with the aim of identifying capable of producing high quality timber on a superior black walnut trees as seed trees or those relatively short rotation of about 60 years and is to be cloned for timber production. A clonal in great demand by end-users. During 2001 collection of superior plus trees has been alone, British imports of this timber rose by 51% established at East Malling Research in Kent (Buckley, 2002). Currently, the species is often (Russell and Hemery, 2004). This article disregarded by British foresters because it is seen summarises the background to this work, as a species that is site-demanding, usually of presents some early results and outlines expected poor form and vulnerable to frost. Until now, no outcomes from the long-term research research has effectively addressed these programme. problems in Britain. The Forestry Commission established a series Methods of black walnut provenance experiments Within the programme, provenance is defined as between 1986 and 1987 to test a limited range of a seed collection unit composed of a community material from four provenances (Wisconsin, of potentially interbreeding trees in an area Southern Illinois, Ohio and Vermont) (Kerr, subject to uniform environmental conditions 1993). Insufficient seed was available for testing (adapted from Turnbull and Griffin, 1986). all material across four low-quality British trial Collections made from scattered individual trees sites. Therefore, a new and more comprehensive within a country are termed a population. collection of material, selecting desirable, Progeny refers to half-sib families where the straight-stemmed and lightly-branched trees female parent is known, but the pollen male is suitable to the climatic conditions of the British unknown. Details concerning provenance Isles should encourage renewed interest in the selection and seed collection and handling are species. detailed by Russell and Hemery (2004) and A collaborative research programme was summarised in the Table 1. The distribution of initiated, resulting in the collection of seeds the provenances sampled is illustrated in Figure across black walnut’s native range in the United 1 (ascross Europe) and Figure 2 (across USA). States (McGranahan and Leslie, 1991) and its Seed was collected from between 10 and 25 introduced European range between 2002 and individual trees for each provenance. Trees were 2003 (Mitchell and Wilkinson, 2001). This established over two years: Phase I in 2003 and material is being tested in a long-term combined Phase II in 2004. 207 QUARTERLY JOURNAL OF FORESTRY Figure 1. Distribution of black walnut provenances Figure 2. Distribution of black walnut provenances sampled across Europe. sampled across the USA. Table 1. Summary of provenances and progeny included in both Experimental phases of the provenance and progeny trials. design The main purpose of Collections Planting year Provenances Progeny Populations the field trials is to nnnassess the suitability European of provenances for Austria 2003 2 15 timber production Czech Republic 2003 1 15 under British condi- France 2004 1 * tions, with particular Great Britain 2003 + 2004 * 8 1 emphasis on selec- Italy 2004 * 1 tion for good form, Serbia & Montenegro 2004 * 1 vigour and late flush- Slovak Republic 2003 1 3 ing. The trials will 5431also provide a US resource for genetic Alabama 2004 1 * diversity studies. Illinois 2004 2 * The trees were plant- Indiana 2004 3 * ed out in combined Iowa 2004 1 * provenance/progeny Kentucky 2004 2 * experiments at two Maryland 2004 2 * sites in central and Minnesota 2004 1 * southern England Missouri 2004 1 * (Table 2) during North Carolina 2004 1 * 2003 and 2004 in Ohio 2004 1 * collaboration with Pennsylvania 2004 1 * the National Forest Tennessee 2004 1 * Company and the Wisconsin 2004 3 * Forestry 20 0 Commission. Trees 208 THE FUTURE OF BLACK WALNUT IN BRITAIN Table 2. Site details for the black walnut provenance/progeny trials. Lat/long Soil Soil Type Altitude Rainfall (pH) (m asl) (mm) Lount Wood, The National Forest, 52° 36’ N/1° 25 W 7.0 Heavy 120 600 Derbyshire clay loam Paradise Wood, Northmoor Trust, 51° 38’ N/1° 12’ W 6.2 Sandy 50 570 Oxfordshire to 7.7 clay loam were spaced at 2 x 2m (2500 trees ha-1) and pro- assigned randomly at planting time and tected by 0.75m treeshelters. The use of two recorded. Each replicate contains 49 trees, one sites will permit the assessment of genotype x of which is a British control, planted in spring site interaction. 2005 at the same time as the Phase II material in a neighbouring trial. Phase I The experimental design combines both Phase II provenance and progeny assessments in a single This phase contained only provenance data. experiment. Progenies are distributed as single- Provenances were distributed in non-contiguous tree plots (only one tree per replicate) within a multiple-tree plots within 12 replicates at randomised complete block design. Where Paradise Wood and 16 replicates at Lount Wood. possible the identity of seedlots with individual Twenty provenances from the States, one French mother trees has been maintained, thereby provenance, one British population (the control), allowing progeny testing. Where this was not and two progenies, one from Italy and the other possible, or where there were insufficient seeds from Serbia and Montenegro were incorporated. from individual trees, these progeny contribute Tree positions were assigned randomly at towards provenance assessment only. Where the planting time and recorded. Table 3 summarises number of trees within a progeny is less than six, the planting details of both phases. these are excluded from any analysis and Given the high value of this untested genetic contribute only at the provenance level. There material, all spare trees were planted within the are 45 progeny included in the trials (Table 1). two guard rows surrounding each trial, and their Provenances were distributed in non- positions mapped. contiguous, multiple-tree plots within 10 During winter 2004, height and survival were replicates across two sites. The number of trees recorded for Phase I and height baseline data for representing a provenance differed for each of Phase II at both sites. the five provenances. Tree positions were Data were analysed with Genstat using plot Table 3. Material planted at each site in number of replicates. No. of Trees per Provenances Families Total no. of Reps Rep per Rep per Rep trees in trial Lount Wood Phase I 10 49 5 49 490 Paradise Wood Phase I 10 49 5 49 490 Lount Wood Phase II 16 80 21 - 1280 Paradise Wood Phase II 12 80 21 - 960 209 QUARTERLY JOURNAL OF FORESTRY Table 4. Summary results for tree growth and survival lost from the 980 planted across both for Phase 1 (P03). sites. Trees only grew 6cm on Lount Paradise Both average across both sites (Table 4), Wood Wood sites although statistical analyses indicated Tree height (2003) significant (p=0.039) genotype x site mean (cm) 50.3 49.8 50.1 interaction for height increment s.e. 1.3 1.5 1.0 (Table 5). There were highly Tree height (2004) significant (p=0.001) differences for mean (cm) 56.5 55.3 55.9 tree height at the end of the first s.e. 0.9 0.9 0.7 growing season (2004) between Height increment provenances (Figure 3). Height (2003-04) increment was greatest for the mean (cm) 6.1 5.6 5.8 Serbian and UK provenances, s.e. 0.5 0.7 0.4 although these remained significantly Survival smaller in height (p<0.05) than the (%) 99.5 99.7 99.6 Croatian and two Austrian no. dead 2 1 3 provenances (Table 6). means. The model of the variance of analysis Conclusions used was: The provenance/progeny trials will be assessed site + replicate within site + site x provenance. for survival, flushing, vigour (height and diameter), form and occurrence of anthracnose. Results Data will be analysed and superior progenies and Germination of seed lots varied considerably individuals will be selected to form the basis of from zero to 60%. Seedlots that germinated the next stage of the improvement programme poorly were resown winter 2004 with the after ten years. It is anticipated that clonal trials intention of establishing a further combined of plus trees and/or of seedling selections will be progeny/provenance trial if sufficient seedlings established in the future, subject to propagation are obtained. techniques being readily available. In addition, it will also be desirable to establish grafted seed Phase 1 orchards comprising the best performing trees. Tree survival one year after establishment It is also hoped that a collaborative research remained excellent at 99.6%, with only 3 trees programme on the genetic diversity of these collections can be initiated with the Hardwood Tree Improvement Table 5. Analysis of variance for first year tree height Regeneration Center (HTIRC), increment between planting in 2003 and 2004 in the Indiana, USA, with the Phase I black walnut provenance trials, based on plot objectives of assessing the extent means.