Fans of the flames—following the fire
The role of fire as an ecological factor was brought
home to me when I was walking on a late summer day in the ‘high country’ of
Yosemite National Park in California when I could see plumes of smoke rising in
several different places, some of them very remote. Adaptation to fire has been
investigated by Dolors Verdaguer and
Fernando Ojeda of Girona and Cadiz, Spain (pp. 593–599), in the
very diverse genus Erica in a
fire-prone heathland ecosystem in South Africa. The genus exhibits
two main methods of regeneration after fire. Some species are ‘resprouters’,
regrowing from buds on a lignotuber, a woody swelling at the stem base. Starch
deposits in the roots are an energy source for the sprouting buds. Others
species are seeders, repopulating fire-cleared zones by germination of
previously dormant seeds. Seeders do not lay down extensive starch stores in
their roots. The contrast is therefore between bud banks and seed banks.
Interestingly, there are species that exhibit both strategies, exemplified by E. calycina and E. coccinea. The seeder and resprouter lifestyles occur in
separate lineages and are inherited from one generation to the next. The
authors had previously shown that starch deposition in roots is confined to the
resprouter lineages. In the present work they show that there are clear
differences in axillary bud formation and activity in the cotyledonary region
and in the first two nodes. Resprouters have active buds from which the
lignotuber is thought to grow; seeder lineages possess only rudimentary and/or
atrophied buds in this region. The authors argue that the possession of
atrophied buds is an indication that functional buds (i.e. the resprouter
lifestyle) represent the ancestral state. They carry on to
suggest that the seeder lifestyle is an adaptation that allows the
exploitation of more diverse habitats and the evolution of many endemic
species.
Professor J. A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
