Productivity of Closely-spaced Young Poplar on Agricultural Soils in Britain |
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Authors: | CANNELL M G R |
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Institution: | Institute of Terrestrial Ecology Bush Estate, Midlothian, Scotland |
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Abstract: | Recent ideas on silage and fuelforestry call for more information on the total harvestablewoody dry matter produced by hardwoods grown at very close spacingsin fertile soils and coppiced every few years. Yields of oven-driedstems and branches (S and B) are presented here for Populustrichocarpa Torr. and Gray, clone Fritzi Pauley.Plantings in Bedfordshire at 21 600 trees ha1 had a meanannual increment (M.A.I.SB) of 5.2 t ha1 y1 overfive years, and plantings in the Cambridgeshire fens at 1480trees ha1 produced 4.8 t ha1 y1 over sixyears. Fan-shaped spacing experiments, established in Midlothianby inserting cuttings through black polythene into nursery soilwith added fertilizers, gave 4.6 t ha1 y1 at theend of the first year and about 7 t ha1 y1 oneyear after coppicing, but only with over 250 000 stems ha1producing closed canopies with leaf area indices of about 4.Similar spacing experiments planted without fertilizer on farmlandin Gloucestershire, Suffolk, Argyll and Midlothian gave averageM.A.I.SB values of 6.57.0 t ha1 y1 afterthree years with over 25 000 trees ha1 and similar valuesafter five years with over 10 000 trees ha1. Peak currentannual increments (C.A.I.SB) averaged 1012 t ha1y1. The maximum M.A.I.SB, attained in Gloucestershire,was 10.0 t ha1 y1 at age 5 with over 20 000 treesha1, with maximum C.A.I.SB values of about 14 t ha1y1 at age 4; M.A.I.SB values of about 11.5 t ha1y1 were anticipated at this site by age 68. Equivalentstem volumes are given. As expected, trees subjected to competitionaccumulated greater proportions of their woody biomass in stemsrather than branches. Biomass yields of fully-stocked young hardwood stands are independentof planting density. In Britain, M.A.I.SB values of 68t ha1 y1 can be obtained over 1 or 25 years byplanting 250 000 or 2000 trees ha1, using vigorous Populusspp, Salix spp or Nothofagus procera on good sites. Advantages and problems of silage forestry arediscussed, and it is considered that hardwood fuel coppicescould not meet more than about 2% of national energy needs. The reciprocals of individual tree weights were linearly relatedto planting density. |
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