Seeds, sprouts and saving water - strategies for surviving
fire
Fires are a normal part of several
ecosystems in many of the warmer parts of the world. However, the ground does
not remain bare for long after the fire because many species are adapted to
living in these fire-prone habitats. In Europe,
this is typified by the regeneration of shrubland in the Mediterranean region,
as described by Saura-Mas and Lloret (Barcelona, Spain, pp. 545-554).
They focused on a region of coastal shrubland in north-east Spain that experiences a sub-humid
Mediterranean climate. The authors note three main strategies for regeneration
after fire: re-sprouters - these are able to re-grow from organs that are
protected from the heat; seeders - these have heat-tolerant seeds that
germinate after fire; and re-sprouter/seeders - these make use of both
mechanisms. The question asked was whether the shrubs that fall into these
three categories show differences in their physiology under normal conditions.
Thirty woody plant species typical of the habitat were classified according to
their regeneration strategy and this was related to plant phylogeny: plants
from the same family were very likely to exhibit the same regeneration
strategy, indicating that some adaptive features go back a long way in the
evolution of these groups. Several indicators of water and nutrient physiology,
such as leaf relative water content (RWC) and leaf dry matter content (LDMC),
were measured from spring through to winter and there were clear correlations
between these indicators and regeneration strategy. Thus, leaf RWC was always
higher in re-sprouters, suggesting a greater ability to reduce water loss and
maintain water content. By contrast, the seeders appear more drought
tolerant. Re-sprouters also had a greater LDMC, attributed to “a more efficient
conservation of nutrients”. Interestingly, the re-sprouter/seeders resembled
the seeders rather than the re-sprouters in respect of both these variables.
The plant community is thus moulded both by climate and by sporadic factors
such as fire.
Professor J. A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
