Agriculture Reference
In-Depth Information
In more productive habitats where competition for space is more acute, the
variance in inter-fire interval will strongly affect diversity (
Fig. 8.6
). High variance
in fire frequency (e.g. occasional inter-fire intervals
<
5 yrs) may be required to
maintain diversity in the long term. Such an effect has been well described in
eastern high rainfall wet/dry heaths (Keith & Bradstock
1994
; Tozer & Bradstock
2003
; Keith
et al.
2007
). Fire and productivity therefore have interactive and even
interdependent effects on diversity.
Other mechanisms not accounted for by Huston (
2003
) contribute to the
interplay between fire regimes and diversity. Postfire establishment introduces
randomness into plant populations that promotes coexistence. Movements of
seeds after fire on soil surfaces may remix species and favor certain microsites in
a manner that creates space, allowing coexistence of species with differing com-
petitive abilities (Whelan
1986
; Lamont & Groom
1998
; Howell
et al.
2006
;
Lamont
et al.
2007
; Esther
et al.
2008
). Differential drought tolerances among
species may result in alternative recruitment success after different fires, resulting in
fluctuating abundances (Lamont
et al.
2007
). Long-term resilience is enhanced by
wide ranging “storage effects” afforded by persistent seedbanks and regenerative
organs, common across taxa and growth forms. Abundance fluctuates, thereby
preventing dominance by individual species (Lamont
et al.
2007
). Interactions with
other disturbances and drought (e.g. Ross
et al.
2004
) enhance these effects.
Variations in fire regimes that include fire return interval and fire intensity are
also very important. Arguably MTV exhibits greater sensitivity in this regard than
other fire-prone Australian communities (e.g. tropical savanna woodlands, arid
shrublands). Management of the pivotal obligate seeder component of MTV
that underpins this sensitivity may hinge on spatial variability of fire regimes
(Groeneveld
et al.
2002
,
2008
; Bradstock & Kenny
2003
; Bradstock
et al.
2006
;
Parr & Andersen
2006
). Greater emphasis on the interplay between modeling and
empirical studies is required to understand both the pure and applied ramifica-
tions of the spatial game of fire and habitat that species must play to coexist in
high-diversity MTV landscapes. Many aspects of this model likely apply to other
MTC regions as well, although with very different timescales.
Flammability and Diversity
General models postulate a unimodal response of fire activity to moisture and
productivity (
Fig. 8.7
; Huston
2003
; Bond & Keeley
2005
). Such models implicitly
integrate the respective effects of moisture on plant growth and the availability of
fuel to burn. For example, Pausas & Bradstock (
2007
) showed that a range of
MTV communities in southeastern Australia have a negative relationship between
flammability and productivity. Therefore, MTV broadly occupies part of a tail of
the fire, moisture and productivity spectrum (
Fig. 8.7
). How do variations in the
flammable characteristics of MTV communities emerge from the combined influ-
ence of productive potential of habitats and
in situ
fire weather? Do these vari-
ations in these influences lead to high levels of fire regime heterogeneity (landscape
