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Microhabitat availability and seedling recruitment of Lobelia urens: a rare plant species at its geographical limit

Published online by Cambridge University Press:  22 February 2007

J.M. Dinsdale ,
M.P. Dale  and
M. Kent
J.M. Dinsdale
Affiliation:
Department of Biological Sciences, University of Plymouth, Drake's Circus, Plymouth PL4 8AA, UK
M.P. Dale
Affiliation:
Department of Biological Sciences, University of Plymouth, Drake's Circus, Plymouth PL4 8AA, UK
M. Kent*
Affiliation:
Department of Geographical Sciences, University of Plymouth, Drake's Circus, Plymouth PL4 8AA, UK
*
* Correspondence Fax: +44 1752 233054 Email: [email protected]
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Abstract

In Britain, Lobelia urens (L.) (the heath lobelia) occurs in rough grassland, is rare and only found in southern England, where it is at the northern limit of its range. Emergence and survival of L. urens was investigated at six locations in two geographically distinct sites experiencing spring, autumn or no grazing in two consecutive years. Four factors were evaluated qualitatively, as a means of characterizing microhabitats for germination and survival: all permutations of higher plant cover, bryophytes, plant litter and surface depressions. The potential effect of adjacent plants on recruitment was also assessed using the nearest neighbour distance (NND). Grazing created depressions, removed plant litter and increased the proportion of sites with higher plant cover. It also resulted in a more open sward with higher NNDs. None of these changes stimulated recruitment. Instead, small increases in the frequency of some rare or very rare microhabitat types were vital in making grazed rough grassland more suitable for emergence. Reduced litter loads and a greater quantity of moss were two key responses. Overall, survival of L. urens was less than 1% and was particularly favoured by moss and an increase in NNDs. Shading from higher plants, with or without plant litter, decreased emergence, but the precise role of litter was complex and most probably related to its quantity. In an experimental seed bed, only empty depressions favoured emergence. The microhabitat relationships of L. urens were unusually consistent among locations and consecutive years. L. urens requires high soil surface temperatures but also adequate water for large scale recruitment, and such conditions are encouraged by grazing. The particular problems of experimental design and statistical analysis of data from recruitment experiments are also discussed.

Keywords

demographygrazingLobelia urensmicrohabitatrare plant conservation
Type
Research Article
Information
Seed Science Research , Volume 10 , Issue 4 , December 2000 , pp. 471 - 487
Copyright
Copyright © Cambridge University Press 2000

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