Agriculture Reference
In-Depth Information
Landscape
position
Soil
texture
Soil
nutrients
Precipitation
Avilable
Soil
moisture
Primary
production
Plant
structure
Temperature
Available
fuel
Seasonal
distribution
(ppt/temp)
Fire combustion
and propagation
Ignitions
Fig. 10.5
A conceptual model relating direct and indirect interactions between fire activity and
available fuels, including the influence of plant structure, primary production and available soil
moisture. Equally important in determining soil moisture are proximal site factors as well as
regional climate
.
age (Hopper
2009
). However, on fire-prone landscapes (see
Fig. 1.3
), climate and
geology interact to affect soil moisture stress and this has direct effects on plant
flammability as well as indirect feedback effects of fire on the evolution of plant
traits.
In some ways the selective factors driving the origin of taxa, as well as specific
traits that affect fire response, are a function of the scale at which the problem is
viewed. It is common to think of seasonal climatic parameters as the most
critical, but of course from the plant's perspective it is much more proximal factors
(
Fig. 10.5
) that are most important. For example, seasonal patterns of primary
production are directly affected by the water deficit or difference between poten-
tial evapotranspiration and available water (Stephenson
1990
). Water deficit, or
available soil moisture, is controlled by both precipitation inputs and by evapora-
tive demand of the atmosphere. In MTCs drought occurs in the summer when
high temperatures exacerbate soil-drought deficits by increasing evaporative
demand. However, soil texture, soil depth and topographic drainage patterns
are other factors, beyond the seasonal timing of drought, that contribute to soil
moisture deficits. As an illustration, southwestern North American chaparral
under bimodal rainfall conditions in Arizona may have summer water deficits
