29
Prosopis glandulosa seedlings (small plants or juveniles) are found in open
disturbed areas or open grassland early in succession, but they do not seem to be
present below the canopy as the community develops probably because of low light
levels below the canopy (Fig. 5.5 ) (Bush and Van Auken 1987 ; Archer et al. 1988 ).
In time the P. glandulosa plants that are the focus of these patches or clusters in
woodlands or savannas would die and disappear as in succession (Archer et al. 1988 ;
Archer 1994 ). Prosopis glandulosa would not be able to replace itself in woodland
% LIGHT LEVELS
POSITION
0
20
40
60
100
80
120
OPEN
EDGE
MID
TREE BASE
ABOVE VEG
SURFACE
Fig. 5.4 Percent light levels both above and below surface herbaceous vegetation in the open
grassland or gaps ( left ), at the Prosopis glandulosa canopy edge, at the canopy midpoint, and at the
base of the P. glandulosa tree ( right ). The mean light level in the open above the herbaceous
vegetation was 1,858 ± 139 μmol m
−2 s
−1 (Bush and Van Auken 1987 )
Fig. 5.5 Mean dry mass of Prosopis glandulosa grown at fi ve light levels from <1.0 μM/m
2
/s to
885 μM/m
2 /s in a Patrick series clay-loam soil with added nutrients. Dry mass of Prosopis
glandulosa was linearly related to light levels ( r = 0.99, P < 0.001) (modifi ed from Bush and Van
Auken 1987 )
5 Factors that Determine Growth Rates