Topsoil may be removed, stored and subsequently used in rehabilitation efforts aimed at vegetating old opencast mine sites. In this study, the effect of age and depth on survival of viable seeds in stored topsoil from opencast coal workings at Erin (OS grid ref: SK 440735), Derbyshire (central England) were investigated.
Samples were taken from two topsoil stores (3 months and 4 years old) on 12 November 1985. Three horizontal cores (4 cm diameter x 30 cm long; auger inserted into a vertical horizon exposed by mechanical digger) were taken at each of three depths (surface, 1 m and 2 m) from each store and transported to the laboratory. Core triplicates were mixed and divided, one half stored in black polythene bags in a cold room at 6°C for eight weeks (stratification treatment). The remainder was sieved into plastic seed pans, watered and cultivated in an incubation cabinet and greenhouse for 200 days (similarly stratified samples). Pans were examined weekly, seedlings removed, counted and identified; samples were then stirred to bring light-requiring seeds to the surface.
The viable seed populations (numbers/m²) were estimated.
At least 21 (common) herb species were represented, plus several grasses. Of the herbs, 17 were present in the younger spoil and 10 in the old. Comparison of total seedling emergence suggests a slight but significant reduction due to stratification. However, eight species occurred only in the stratified samples while one (stinging nettle Urtica dioica) only appeared in non-stratified samples. Pre-chilling therefore probably results in a more complete viable seed flora representation.
There were significant effects of age and depth on total seed numbers. Total numbers of seedlings emerging from samples at each of the three depths in the two soil stores (approx. numbers/m² in brackets) was:
Young: 0 m - 117 (3,250); 1 m - 179 (4,972); 2 m - 54 (1,700)
Old: 0 m - 130 (3,611); 1 m - 10 (277); 2 m - 22 (611)
For purposes of restoration, soil in the 3 month old store contained significantly more viable seed at depths of 1 and 2 m (similar at 0 m depth) and species diversity was higher.
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