Agriculture Reference
In-Depth Information
9
Fire-adaptive Trait Evolution
Until relatively recently the importance of fire and the origin of fire-adaptive traits
have received minimal attention from paleoecologists, and appreciation of this
importance has varied across the different mediterranean-type climate (MTC)
ecosystems. For example, Axelrod ( 1973 ) and Raven & Axelrod ( 1978 ) wrote
extensive treatises on the origins of the California flora, and yet gave little or no
mention to the issue of fire in the evolution of these taxa. Hopper ( 2009 ) suggests
that fire has only been an incidental factor in the evolution of the Western
Australian flora. These investigators have weighed climate and soils far above fire
as an important evolutionary driver in these plant assemblages and have down-
played this component of community assembly (see Fig. 1.4 ).
Axelrod ( 1989 ) even went so far as to suggest fire was irrelevant to the evolution
of California chaparral. Although he acknowledged that fire could have played a
role in the spread of chaparral-like vegetation during the late Tertiary (2-10 Ma),
he insisted that fire had played no significant role in the origin of “adaptive types.”
In his view, “Several lines of evidence suggest that the modern fire-adapted taxa
may not reflect an evolutionary response to fire. The diverse adaptations to fire
probably represent features that originated without the stimulus of fire. . .” Con-
trary to this belief, we suggest there is sufficient reason to accept a fire origin for
many fire-adaptive traits in mediterranean-type vegetation (MTV), and that fire
has been a potential ecosystem process on landscapes far longer than the late
Tertiary (Bowman et al. 2009 ; Pausas & Keeley 2009 ).
Fire History from the Paleozoic
By the beginning of the Paleozoic Era (540 Ma; Fig. 9.1 ) the atmosphere had
sufficient oxygen to carry fire, and ignition sources from lightning, but lacked fuel.
In a sense the world was poised for fire and waiting for plants to emerge onto land,
as the earliest Silurian land plants are associated with charred remains (Glasspool
et al. 2004 ). These authors interpreted this early presence of charred litter and
coprolites as evidence of a low-temperature surface fire. During the past decade
there have been a number of Paleozoic studies reporting fire impacts on vegeta-
tion, and even a suggestion that this was a regular ecosystem process. Despite
the presence of mesic tropical forest elements, these Paleozoic landscapes were
 
 
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