Agriculture Reference
In-Depth Information
Table 8.2 Mechanisms responsible for transitions from rainforest to sclerophyll vegetation during the Tertiary
in Australia
Mechanism
Response
Changing fire weather, ignition
and climate
Fire has a non-linear response to moisture/climate (Bond & Keeley
2005
; Pausas & Bradstock
2007
). Given the likely domain of
Tertiary climate, increasing dryness caused an increase in fire
activity.
Habitat transformation under
a drying climate
Drying created new, more open habitats exploited by sclerophyll
species with superior drought tolerance and competitive ability
to exploit space. Fire reinforced the transition to sclerophyll
vegetation through nutrient losses and additive effects of
changing climate on fertility. An ongoing increase in amount
of core and facultative habitat available for sclerophyll species
resulted.
Influence of life history and
resilience traits
Sclerophyll species have traits that enhance persistence and
exploitation of large gaps created by fire, and rapid replenishment
of regeneration capacity. Rainforest species lack these traits. If
sclerophyll vegetation is more resilient to relatively frequent
disturbance, then fire would play a role in maintaining the grip of
sclerophyll vegetation on newly available habitat.
Influence of flammability
If sclerophyll vegetation is more flammable (ignitable and sustainable
combustion) than rainforest, then under altered circumstances
(see above), an increase in the amount of fire may result. This
may not only reinforce acquisition of habitat (see above), but
also result in further attrition of rainforest at its margins,
promoting further sclerophyll expansion.
Given the antiquity of key families, MTV, with its high diversity of woody
plants and pronounced sensitivity to variations in fire return interval, can be
regarded as an
old fire world
. It displaced vegetation where fire may have been
less prevalent and important as an ecological driver - a world largely of very
limited fire. This notion implies domination by a suite of vegetation types and
emergent fire regimes, which result via mechanisms driven by particular climatic
settings. MTV dominates habitat provided by poor soils in interaction with
moderate rainfall and decadal-scale fire recurrence, dictated by fire weather/
ignition syndromes characteristic of a temperate climate. Accordingly, differing
settings of climate may alter these respective mechanisms and tilt the balance to
suit dominance by other fire regimes, habitats and plant functional types, as
shown by the contemporary interplay between MTV and rainforest in southern
Australia.
MTV transcends a broad sweep of the non-linear relationship between fire
regimes and available moisture. Given the position of MTV, both an increase
and decrease in fire frequency may occur in response to declining moisture.
Arguably, the potential for contemporary temperate rainforest, and its antece-
dents, to predominate lies at the extreme left of this relationship (
Fig. 8.7
).
