Variation in Gas Exchange Characteristics Among Desert Plants
369
Date of first summer rains
40
39
Death Valley, CA
15
10
5
0
C/)
.....
CO
15
Q)
Needles, CA
>.
- 0 10
.....
Q)
.0
5
E
:J
Z
0
15
Nogales, AZ
10
5
o
Fig. 18.6. The frequency distribution of the date of the first summer rains for three sites
differing in the predictability of that summer precipitation. The first summer storm is
defined as the first storm after June 1 that was ~1O mm. Calculations are based on data
from the US Weather Bureau records (NOAA) during the period 1941-1989. The three
figures are arranged in a north-to-south transect from top to bottom
amined autocorrelations of monthly precipitation for different sites throughout the Great Basin, Mojave, and Sonoran Deserts. As in the previous
analysis, he noted a strong autocorrelation for up to 2-3-month periods in
the Mojave and Sonoran Deserts. However, for the Great Basin, Pianka
(1967) found no autocorrelation between months and concluded that precipitation had little predictability from month to month.
18.3.3 Predictability of Temperature
Air temperatures exhibit less variance than precipitation (Fig. 18.7). However, there is a strong tendency for temperatures in the cooler months of the