35
Similar greenhouse competition studies were done between P. glandulosa and C 4
grasses from these former C 4 arid and semiarid grasslands (Van Auken and Bush
1987 , 1988 , 1989 , 1990 , 1997 ; Bush and Van Auken 1991 , 1995 ). When one
P. glandulosa plant was grown separately with Schizachyrium scoparium little bluestem or Bouteloua curtipendula side oats grama in greenhouse additive experiments, in low nutrient soil, dry mass or growth of the woody plant was dependent
on the grass density of both grass species. The presence of one grass plant reduced
the aboveground dry mass of the P. glandulosa plants by 46 or 84 %, depending on
the species it was grown with, and belowground dry mass by 67 or 69 % (Fig. 6.3
for S. scoparium ) (Van Auken and Bush 1988 ; Bush and Van Auken 1989 ). At the
highest grass density tested, 97 S. scoparium plants per pot, P. glandulosa total dry
mass was approximately 4 % of the control (no grass present, Fig. 6.3 ). However,
there were no Prosopis mortalities. Prosopis glandulosa was suppressed by 96 % at
the high grass density but not killed.
An interspecifi c (de Wit) greenhouse competition experiment (Harper 1977 ) with
and without addition of nutrients was completed with P. glandulosa and B. curtipendula at a density of six plants per pot. Proportions of the two species were 6:0, 4:2,
3:3, 2:4, and 0:6, respectively. The results were the same at both nutrient levels; the
grass was always the better competitor (Fig. 6.4 ) (Van Auken and Bush 1988 , 1989 ;
Bush and Van Auken 1989 ). Relative yields per plant for all proportions of P. glandulosa and B. curtipendula were signifi cantly different from the relative yield for
the plant without a competitor. Relative yield totals for B. curtipendula without the
addition of nutrients in mixture were 80–92 % depending on the proportion of plants
and 95–98 % with nutrients added but depending on the proportion of plants present. The percent yield for P. glandulosa was 8–20 % without added nutrients, and it
Fig. 6.2 Aboveground dry mass of Vachellia is presented. Dry mass was measured with or without
competition and herbivory between Vachellia farnesiana a C 3 woody plant and Cynodon dactylon
a C 4 grass. In the right panel, no nutrients were added, and in the left panel , nutrients were added.
The target species ( Vachellia ) was not clipped or clipped. In addition, the target species ( Vachellia )
was grown in three competition treatments, ALONE or with the grass competitor that was either
clipped (GRASS CLIPPED) or not clipped (GRASS NOT CLIPPED), note the x -axis (modifi ed
from Van Auken 1994 )
0
1
2
3
4
5
6
7
8
9
10
ALONE
GRASS
CLIPPED
GRASS NOT
CLIPPED
ABOVEGROUND DRY MASS
GROWTH CONDITION
NO CLIPPING
CLIPPING
N+
0
1
2
3
4
5
6
7
8
9
10
ALONE
GRASS
CLIPPED
GRASS NOT
CLIPPED
ABOVEGROUND DRY MASS
GROWTH CONDITION
NO CLIPPING
CLIPPING
N6 Competition
Similar greenhouse competition studies were done between P. glandulosa and C 4
grasses from these former C 4 arid and semiarid grasslands (Van Auken and Bush
1987 , 1988 , 1989 , 1990 , 1997 ; Bush and Van Auken 1991 , 1995 ). When one
P. glandulosa plant was grown separately with Schizachyrium scoparium little bluestem or Bouteloua curtipendula side oats grama in greenhouse additive experiments, in low nutrient soil, dry mass or growth of the woody plant was dependent
on the grass density of both grass species. The presence of one grass plant reduced
the aboveground dry mass of the P. glandulosa plants by 46 or 84 %, depending on
the species it was grown with, and belowground dry mass by 67 or 69 % (Fig. 6.3
for S. scoparium ) (Van Auken and Bush 1988 ; Bush and Van Auken 1989 ). At the
highest grass density tested, 97 S. scoparium plants per pot, P. glandulosa total dry
mass was approximately 4 % of the control (no grass present, Fig. 6.3 ). However,
there were no Prosopis mortalities. Prosopis glandulosa was suppressed by 96 % at
the high grass density but not killed.
An interspecifi c (de Wit) greenhouse competition experiment (Harper 1977 ) with
and without addition of nutrients was completed with P. glandulosa and B. curtipendula at a density of six plants per pot. Proportions of the two species were 6:0, 4:2,
3:3, 2:4, and 0:6, respectively. The results were the same at both nutrient levels; the
grass was always the better competitor (Fig. 6.4 ) (Van Auken and Bush 1988 , 1989 ;
Bush and Van Auken 1989 ). Relative yields per plant for all proportions of P. glandulosa and B. curtipendula were signifi cantly different from the relative yield for
the plant without a competitor. Relative yield totals for B. curtipendula without the
addition of nutrients in mixture were 80–92 % depending on the proportion of plants
and 95–98 % with nutrients added but depending on the proportion of plants present. The percent yield for P. glandulosa was 8–20 % without added nutrients, and it
Fig. 6.2 Aboveground dry mass of Vachellia is presented. Dry mass was measured with or without
competition and herbivory between Vachellia farnesiana a C 3 woody plant and Cynodon dactylon
a C 4 grass. In the right panel, no nutrients were added, and in the left panel , nutrients were added.
The target species ( Vachellia ) was not clipped or clipped. In addition, the target species ( Vachellia )
was grown in three competition treatments, ALONE or with the grass competitor that was either
clipped (GRASS CLIPPED) or not clipped (GRASS NOT CLIPPED), note the x -axis (modifi ed
from Van Auken 1994 )
0
1
2
3
4
5
6
7
8
9
10
ALONE
GRASS
CLIPPED
GRASS NOT
CLIPPED
ABOVEGROUND DRY MASS
GROWTH CONDITION
NO CLIPPING
CLIPPING
N+
0
1
2
3
4
5
6
7
8
9
10
ALONE
GRASS
CLIPPED
GRASS NOT
CLIPPED
ABOVEGROUND DRY MASS
GROWTH CONDITION
NO CLIPPING
CLIPPING
N6 Competition