Agriculture Reference
In-Depth Information
Santa Barbara, California
Lat/long: 34°30'N, 119°49'W
Elevation: 670 m
Annual precipitation: 650 mm
Annual temperature: 15.1°C
Tehuacan, Puebla
Lat/long: 18°15'N, 97°26'W
Elevation: 2350 m
Annual precipitation: 611 mm
Annual temperature: 17°C
PET
Precip.
Temp.
140
25
140
25
120
120
20
20
100
100
15
15
80
80
60
60
10
10
40
40
5
5
20
20
J
an
Apr
Jul
Oct
J
an
Apr
Jul
Oct
0
0
0
0
Month
Month
C
R
-2
-2
Q,A
-4
Q
-4
G
-6
-6
A
G
S
-8
-8
C
S
-10
-10
Fig. 10.7
Comparison of climate diagrams for (upper left) a MTC California site with
(upper right) a winter drought/summer rain climate in northeastern Mexico. Physiological
responses of analogous functional types of the dominant MTV at both sites show the pattern
of seasonal pre-dawn water potentials in (lower left) California and (lower right) Mexico. (From
Bhaskar
et al.
2007.) R,
Rhus
spp.; Q,
Quercus
spp.; C,
Ceanothus
spp.; A,
Arctostaphylos
in
California and
Comarostaphylos
in Mexico; G,
Garrya
spp.; S,
Salvia
spp.; PET, potential
evapotranspiration.
dictating the portion of the environment experiencing potentially stressful soil
drought conditions. However, within similar plant functional types, those under
summer drought conditions appear to possess many of the same physiological
drought responses as those in winter drought conditions (Bhaskar
et al.
2007
).
This is supported by comparisons of water relationships between present-day
MTC California chaparral and winter drought and summer rain Mexican chapar-
ral where intra-site variations between functional types are greater than inter-site
variations within the same functional type (
Fig. 10.7
). In other words different
functional types have adapted to specific microsite characteristics of soil moisture
availability more so than to synoptic weather patterns. It seems likely that trait
evolution in semi-arid landscapes may follow very similar trajectories regardless of
the seasonality of rainfall. This is not to suggest that the timing of rain is irrelevant
since it can affect the amount of landscape exposed to drought stress (
Fig. 10.1
).
Thus, it may be instructive to think of MTV as being adapted to seasonal
drought stress and the accompanying effects this has on plant traits and in turn
their effect on fuel structure, which is a major determinant of the fire regime. It
may well be that the major distinction between mid-Tertiary landscapes and
Quaternary landscapes in most MTC regions is that in the former case seasonal
