Agriculture Reference
In-Depth Information
Regional species pool
Climate
Fire
Soil
Functional types
Community assembly
Fig. 1.4
The environmental template in fire-prone landscapes can be thought of as a process in
which the regional species pool is filtered to a subset of functional types. The combination of
climate and geology places bounds on the range of plant traits that control fire regimes and
feedback from fire further affects the pool of available functional types. This climate, fire,
geology interaction acts as a control on community assembly, with the important emergent
property of fuel types and ignition probabilities determining fire regime
.
in fire-prone regions. Reconstructions of plant evolution in MTC floras
(e.g. Raven & Axelrod
1978
; Axelrod
1980
,
1989
; Ackerly
2009
; Hopper
2009
)
have either ignored fire or treated it as an incidental process and not adequately
considered the immense impact of feedback processes between fire and climate or
fire and geology. By excluding fire, studies have derived incomplete, and in some
cases perhaps spurious, conclusions. For example, the recent contention that
resprouting of top-killed Hawaiian trees reflects an adaptation to drought because
it increases along a gradient of increasing aridity (e.g. Busby
et al
.
2010
)is
confounded by the fact that fires in the Hawaiian Islands likewise increase along
this same gradient during El Nin˜ o/Southern Oscillation (ENSO) events (Chu
et al
.
2002
; Weise
et al
.
2010
). Even on these tropical islands, sources of natural ignitions
from lightning (Pessi
et al
.
2004
) have created a fire regime with the potential for
driving the selection of resprouting, particularly since fires need only occur once in
the life span of an individual to select for this trait.
In this topic we eschew the notion that any single factor such as drought or
oligotrophic soils provides a sufficient explanation for ecological patterns on fire-
prone landscapes. Instead we show how syndromes of fire, soils and climate can
act synergistically to shape vegetation, particularly the sclerophyllous woody
plants that dominate MTC, and sometimes far beyond those climatic boundaries.
The interplay of fire, climate and geology is well illustrated by the convergent
patterns of plant traits and fire response in MTC ecosystems. A primary factor
tying these regions together is the intense summer drought, which potentially
contributes to greater predictability of fires. Winter rainfall under mild tempera-
tures plays a major role in determining levels of primary productivity and thus
fuel structure, which is an additional factor tying together MTC ecosystems.
Subtle differences in climates (
Box 1.1
) and not so subtle differences in soils
(
Fig. 1.5
) as well as different phylogeographic histories (see
Chapter 10
) have
