INITIAL SPACING OF POPLARS AND WILLOWS GROWN AS ARABLE COPPICE ETSU B/W2/00336/REP Contractor Silviculture & Seeds Research Branch Forestry Commission Research Agency Prepared A Armstrong & C Johns The work described in this report was carried out under contract as part of the New and Renewable Energy Programme, managed by the Energy Technology Support Unit (ETSU) on behalf of the Department of Trade and Industry. The views and judgements expressed in this report are those of the contractor and do not necessarily reflect those of ETSU or the Department of Trade and Industry First published 1997 © Crown copyright 1997 CONTENTS Figures 1 - 8 NOT AVAILABLE ELECTRONICALLY Summary i List of Figures and Tables iii 1.0 INTRODUCTION 1 2.0 EXPERIMENT DESIGN 1 3.0 SITE DETAILS 2 3.1 Wishanger site 2 3.2 Downham Market site 4 4.0 HARVESTING 8 5.0 RESULTS 10 5.1 Wishanger 10 5.2 Downham Market 11 6.0 DISCUSSION 14 7.0 CONCLUSIONS 19 8.0 RECOMMENDATIONS 19 Acknowledgements 21 References 22 Appendix 23 Experiment Plan 24 EXECUTIVE SUMMARY Two clones of poplar and two clones of willow were grown at two sites, on a three year cutting cycle, at six different square spacings, between 0.8 metres and 1.5 metres. The two willow clones 'Bowles hybrid' and Dasyclados' were planted at both sites. The poplar clones Populus interamericana 'Beaupre' and Populus trichocarpa 'Columbia River' were planted at Wishanger in Hampshire. The poplar clones Populus interamericana 'Boelare' and Populus trichocarpa 'Trichobel' were planted at Downham Market in Norfolk. The highest yield of 17.55 oven dry tonnes per hectare (odt/ha/annum) was obtained from 'Bowles hybrid', at the closest spacing, grown on a water meadow adjacent to the River Wey at Wishanger. The highest yield for all clones at both sites was achieved at the closest spacing (in this first rotation). There was a significant linear effect. One of the most interesting observations was that when comparing the gradient of the linear relationship, within species, the gradient was steeper for the higher yielding clone. This was particularly so for the willows. This would suggest that higher yielding clones are more tolerant of crowding, or, that upright Salix viminalis make better use of close space than the more spreading Salix dasyclados. The new Salix viminalis x Salix schwerinnii hybrids should therefore also be responsive to closer spacing. The same effect was observed for the poplars at Wishanger only, but the difference was not as dramatic. There was a suggestion from the highest yielding poplar plots that i optimum yield may still be obtained at the currently recommended spacing of 1.0 metre x 1.0 metre. An initial close spacing ensures rapid canopy closure and maximises yield production by allowing optimal absorption of available radiation, whilst wider spacings in the early establishment phase do not fully utilise available space. An additional benefit to the grower is the rapid suppression of competing weed growth and reduced herbicide usage with cost and environmental benefits. When comparing the yield from 'Bowles hybrid' 1.0 metre spacing with the yield from 0.8 metre spacing at Wishanger it can be seen that the penalty at the end of the three year rotation for opting for the wider spacing would be 146 odt on a 10.0 hectare field. These trials were planted in a square design and the findings may not hold true for rectangular spacings currently being favoured. In a twin row design of alternatively 1.5 metre and 0.75 metre between rows the distance within the row would have to be reduced to 0.59 metre to increase the stocking to an equivalent 0.8 metre square spacing (15,000 stools/hectare). This may result in a competition effect whilst not making maximum use of space and light in the wider (1.5 metre) row spacing. ii LIST OF FIGURES and TABLES Figure 1 Wishanger 5 Layout 3 Figure 2 Downham Market layout and location of poor growth 5 Figure 3 Foliar nutrient and metal levels at Downham Market 6 Figure 4 Foliar nutrient and metal levels at Downham Market 7 Figure 5 Poplar yield against spacing at Wishanger 9 Figure 6 Willow yield against spacing at Wishanger 9 Figure 7 Willow yield against spacing at Downham Market 13 Figure 8 Poplar yield against spacing at Downham Market 13 Table 1 Wishanger 5 Yield 10 Table 2 Downham Market Yield 12 Table 3 Wishanger Block Yield 16 Table 4 Downham Market Block Yield 17 in 1.0 INTRODUCTION This report covers the period January 1992 - April 1997, and summarises the data from the first harvests at the Wishanger and Downham Market sites. Previous Forestry Commission experiments under contract to ETSU for DTI have investigated the effect of initial spacing on yield over two and four year rotations. The results (Tabbush, 1993 and Armstrong, 1996) have suggested that a spacing of 1.0 metre results in higher yields than that for a 2.0 metre spacing over both two and four year rotations. The difference in yield from Populus interamericana 'Beaupre' and 'Boelare' compared with Populus trichocarpa 'Trichobel' is less pronounced at 2.0 metre spacing than at 1.0 metre spacing. The results from Nelder plots were examined by Tabbush (1993) and Armstrong (1996). Tabbush found that both in the first four year rotation and the second four year 2 rotation Populus interamericana 'RAP' had optimum yield at 1.42 m /stool (1.2 m equivalent square spacing). Armstrong found that in the first four year rotation of Populus interamericana 'Beaupre' optimum yield occurred at 1.38 m2/stool (1.18 m equivalent square spacing). The first four year rotation of Populus interamericana 'Boelare' produced optimum 2 yield at 0.62 m /stool (0.78 m equivalent square spacing) although there was little difference 22 in yield between 0.62 m /stool and 1.37 m /stool (0.78 m and 1.17 m equivalent square spacing). These similar findings were not observed for Populus trichocarpa 'Trichobel' 2 which achieved optimum yield at 3.02 m/stool (1.74 m equivalent square spacing). The Nelder design is limited, and the findings needed to be confirmed in experiments with plots of square spacing. 2.0 EXPERIMENT DESIGN At two sites, two different clones of two species (poplar and willow) were tested at six different spacings on a three year rotation in a randomised block design with four replicates. Each species was treated separately. Square spacings of 0.8 m, 1.0 m, 1.15 m, 1.3 m, 1.4 m and 1.5 m were tested. Plot size was 7 x 7 trees to include a 1 row buffer surround giving a 1 5 x 5 assessment plot (25 stools). Plots were planted either side of a central base line (Figure 2). Wishanger site: For poplar: 2 clones (Populus interamericana 'Beaupre' and Populus trichocarpa 'Columbia River') x 6 spacings = 12 treatments x 4 randomised blocks = 48 plots For willow: 2 clones (Salix caprea x cinerea x viminalis 'Dasyclados' and Salix viminalis 'Bowles hybrid') x 6 spacings = 12 treatments x 4 randomised blocks = 48 plots Downham Market site: For poplar: 2 clones (Populus interamericana 'Boelare' and Populus trichocarpa 'Trichobel' x 6 spacings = 12 treatments x 4 randomised blocks = 48 plots For willow: 2 clones (Salix cap x cin x vim 'Dasyclados' and Salix viminalis 'Bowles hybrid') x 6 spacings = 12 treatments x 4 randomised blocks = 48 plots Data were analyzed by analysis of variance (ANOVA) using GENSTAT 5 (Genstat 5 Committee, 1987) 3.0 SITE DETAILS 3.1 Wishanger site Both species were planted adjacent to the river Wey at Wishanger estate in north Hampshire in April 1992 (Figure 1). Two distinct site types were identified. The willow were planted on Figure 1 - Wishanger plot layout NOT AVAILABLE ELECTRONICALLY 2 a water meadow on an alluvial soil whilst the poplars were planted on ex-arable land on Lower Greensand Folkestone beds, Shirrell Heath 1. association. Within these areas there were still differences in the soils. The willows were blocked such that block 1 closest to the poplars was on an interface between the alluvial soil and the greensand. Blocks 2 and 3 were on the better alluvial soil and block 4 was on heavier land with seasonal water logging. Blocks 1 and 2 of the poplar experiment were more sheltered than blocks 3 and 4 which were exposed to cold easterly winds. Block 3 and in particular block 4 were more stony than blocks 2 and 3. The site lies at 60 masl with an annual rainfall of 705 mm. Previous land use was cereal production. The site was kept weed free by repeated applications of contact and residual herbicides, prior to and after stumping back in January 1993. First year survival was excellent: 'Beaupre' - 97%, 'Bowles hybrid' - 97%, 'Columbia River' - 95% and 'Dasyclados' - 95%. 3.2 Downham Market site Both species were planted on what appeared to be a very homogenous site that had been under continuous arable production. The willows were planted to the south of the site and poplars to the north (Figure 2). The soil is Downham association resting on ferruginous Lower Greensand. The site lies at 15 masl, with an annual rainfall of 630 mm. Previous land use had been cereal production. The site was kept weed free by repeated applications of contact and residual herbicides, prior to and after stumping back in January 1994. Survival was excellent for all clones (>99%). In the first year abnormal growth was observed in one block of poplars.