A Note on Shade Tolerance and Vegetative Propagation of Woodland Species

E. Salisbury
1976 Proceedings of the Royal Society of London. Biological Sciences  
Evidence is provided to show th at, for many 'shade to leran t' species vegetative modes of increase may compensate for meagre seed-prodnction which may be imposed by the habitat conditions. Two features, affecting seed production especially, characterize the deciduous woodland habitat, namely the diminished light intensity during the ' shade phase ' and the high humus content of the surface layers with the resulting high n u tri tional status and moisture content. Late-flowering species may in
more » ... ring species may in consequence fruit sparsely. Thus Chamaenerium angustifolium may shed all its flower buds in the diminished illumination, or fail to produce them, bu t its rapid vegetative spread provides compensation with respect to local occurrence and this feature, it m ust be noted, characterizes many other shade-tolerant species, as for example Aegopodium podagraria, Oircaea lutetiana and Galeobdolon luteum. Lithospermum purpureocoeruleum may fruit freely under slight shade bu t flourishes under con siderable shade where its prostrate shoots may attain an average of 50 cm. machia nummularia spreads almost exclusively by its runners and only produces any appreciable amount of seed in hot summers where the shade is slight. One section of the genus Veronica presents an interesting series of closely allied species showing reproduction and h abitat relations. Veronica officinalis is typically an open-habitat plant, with small seeds (0.09 mg) and its vegetative spread is slow. V. chamaedrys, which is slightly shade-tolerant, also has small seeds (0.02-0.15 mg) bu t a marked vegetative spread. Measurements of a random sample of radial increments from one locality yielded an average of 8.6 cm and from another 9 cm. The observed maximum was 21.5 cm. The very shade-tolerant Veronica montana not only has appreciably heavier seeds (0.5 mg) b u t produces prostrate shoots th at, for instance, on a specimen growing with bu t slight competition, were six in number varying in length from 30 to over 60 cm. Dentaria bulbifera, which often grows in very shaded calcareous woodlands, exhibits, annual increments of the rhizome commonly between 3 and 10 cm in length. Its seeds have an average mass of 1.9 mg but quite frequently, except in better lighted areas, reproduction is by bulbils th a t in p art or wholly replace the flowers. The latter is true also of Ficaria verna and the very shade-tolerant and local Gagea lutea the seeds of which normally vary between 2 and 3 mg. Many other shade-tolerant species could be cited from our own flora which exhibit a marked capacity for vegetative increase, such as Stachys sylvatica (a [ 257 ]
doi:10.1098/rspb.1976.0012 fatcat:guclqaxo3ndqpnstzufk4v3yqq