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Individual study: Survival and growth of birch Betula and willow Salix spp. clones on restored opencast coal sites in the UK

Published source details

Good J.E.G., Williams T.G. & Moss D. (1985) Survival and growth of selected clones of birch and willow on restored opencast coal sites. Journal of Applied Ecology, 22, 995-1008

Summary

Experiments were undertaken to assess survival and growth of selected clones of silver birch Betula pendula, downy birch B.pubescens, goat willow Salix caprea and grey willow S.cinerea that were propagated from saplings or cuttings taken from a variety of UK spoil heaps. These were trialed, along with unselected controls, with and without fertilizers, on six restored opencast coal sites throughout Britain.

Field trial sites: Six sites were chosen to represent a range of planting situations on opencast coal sites throughout Britain. These were: in Scotland (Whaupknowe 'B'), Northumberland (Radar North), Yorkshire (Haigh), North Wales (Ty Cerrig) and South Wales (Empire, Tir-y-Gôf). Site and soil characteristics were assessed.

Sapling clones: Starting in 1972, clones of birch and willow were propagated from saplings or cuttings taken from a range of sites, mostly colliery spoil heaps. They were selected by three criteria:

i) only trees known to have originated by natural seeding onto the site were used.

ii) individuals growing in seemingly favourable situations were rejected.

iii) amenity features (form, bark colour, in birch; freedom of flowering and sex of flowers, in willow), were subjectively considered, so that, as far as possible, clones later
proven to be tolerant might also be visually attractive.

Propagation and maintenance of clones: Softwood cuttings, obtained initially from plants growing on spoil, but subsequently from young, vegetatively-derived containerized plants, were rooted and grown using standard techniques. The bareroot stock was planted with spade or mattock, no additions of fertilizer or other ameliorants were made at planting time. The Ty Cerrig and Empire sites were planted in 1976, Haigh and Radar North in 1977, and those at Whaupknowe 'B' and Tir-y-Gôf in 1978.

Experimental design: A conventional randomized block, split-split plot design, with species allocated to plots, fertilizers to sub-plots and clones to sub-subplots, was used. A specially prepared fertilizer (5:22, N:P) of urea nitrogen and a mixture of superphosphate and slow-release ground rock phosphate, was applied at rates equivalent to 20 kg/ha N + 88 kg/ha P or 60 kg/ha N + 264 kg/ha P. Annual applications were made in May, starting in the May after planting and finishing in May 1982. The plots were hand weeded in May and November each year. During November the length of the leading (longest) shoot of each plant was measured. From November 1981 onwards, the spread of each plant at its widest point was also recorded.

Results of the trials were highly variable. Some clones achieved consistently higher survival than unselected controls over the range of sites. Others achieved higher survival at some sites but not on others.

Willows generally had higher shoot growth than birches, particularly on sites with more fertile soils where topsoil had been replaced as a restoration measure. Growth of unselected birch, and especially willow, equalled or exceeded that of most of the selected clones at most sites.

Clones varied considerably in growth form, but site greatly influenced form. This may be important to take into account if revegetation schemes wish to combine the advantages of height growth with those of low, litter-trapping growth profiles.

Annual applications of fertilizer had no effect on tree survival. Significant growth responses to fertilizer were few and limited to three of the less fertile sites. In general, unselected controls gave greater responses, particularly to higher levels of fertilizer, than selected clones.

Conclusions: These studies have shown that some selected clones of birch and willow, obtained from nutrient deficient colliery spoil and other waste materials, consistently survive better than unselected controls when planted on a range of restored opencast coal sites. However, growth of unselected clones equaled or exceeded that of most of the selected clones at most sites. The use of a combination of relatively upright growing clones with more prostrate ones, could visually enhance plantings, whilst helping to conserve and enhance build-up of soil organic matter and the retention of nutrients. However, growth form of individual clones varied considerably with site, and their likely form on individual sites is difficult to predict.


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