38
native grasslands would be high as would be mortality and populations or potential
populations of woody plants would be reduced or maintained relatively low. The
previous comments concern aboveground woody plant herbivory, but there is no
information available concerning belowground herbivory and its potential effects on
woody plant growth, survival, or mortality.
Soil depth is another important environmental factor for dry mass production and
growth of some arid land woody legumes like P. glandulosa (Bush and Van Auken
1991 ) which does have very deep roots (Van Auken 2000 ). When P. glandulosa was
grown alone in 180 cm deep pots (10 cm diameter PVC pipes), P. glandulosa dry
mass was 4.25 times greater compared to growth in 30 cm deep pots (Fig. 6.6 ). But,
soil depth was not the only critical factor examined. The results of soil depth and
relative time of planting were examined simultaneously in the experiment.
The woody legume was planted early (before the grass as in a gap), at the same
time as the grass or after the grass. Results of the two-way ANOVA for aboveground, belowground, and total dry mass for P. glandulosa and both experimental
factors (soil depth and planting combination) and their interaction were signifi cant
( P < 0.0003 for all). When grown in competition with Bouteloua curtipendula , pot
depth (30, 90, or 180 cm) and the time of planting of P. glandulosa compared to the
grass were both important (Fig. 6.6 ). When P. glandulosa was planted with the C 4
grass, but 60 days before the grass was planted ( P. glandulosa planted early),
P. glandulosa dry mass was reduced by approximately 50 % (compared to alone),
but it was reduced less in the 180 cm deep pots. If P. glandulosa and the grass were
planted at the same time, growth of the woody plant was further reduced compared
to growth alone, but growth was still greater in the deeper pots. When P. glandulosa
and the grass were planted together, but the woody plant was planted after the grass,
the dry mass or growth of the woody plant was reduced to 3 % of dry mass when
Fig. 6.6 Figure represents total dry mass (aboveground plus belowground) of P. glandulosa grown
alone or with a C 4 grass Bouteloua curtipendula . Both P. glandulosa and the grass were planted in
180 cm, 90 cm, or 30 cm deep, 10 cm diameter PVC pipes ( pots ). Prosopis glandulosa was planted
alone or with the grass, but planted 60 days before the grass was planted (early), at the same time
as the grass, or 60 days after the grass was planted (late) (modifi ed from Bush and Van Auken 1991 )
6 Competition
native grasslands would be high as would be mortality and populations or potential
populations of woody plants would be reduced or maintained relatively low. The
previous comments concern aboveground woody plant herbivory, but there is no
information available concerning belowground herbivory and its potential effects on
woody plant growth, survival, or mortality.
Soil depth is another important environmental factor for dry mass production and
growth of some arid land woody legumes like P. glandulosa (Bush and Van Auken
1991 ) which does have very deep roots (Van Auken 2000 ). When P. glandulosa was
grown alone in 180 cm deep pots (10 cm diameter PVC pipes), P. glandulosa dry
mass was 4.25 times greater compared to growth in 30 cm deep pots (Fig. 6.6 ). But,
soil depth was not the only critical factor examined. The results of soil depth and
relative time of planting were examined simultaneously in the experiment.
The woody legume was planted early (before the grass as in a gap), at the same
time as the grass or after the grass. Results of the two-way ANOVA for aboveground, belowground, and total dry mass for P. glandulosa and both experimental
factors (soil depth and planting combination) and their interaction were signifi cant
( P < 0.0003 for all). When grown in competition with Bouteloua curtipendula , pot
depth (30, 90, or 180 cm) and the time of planting of P. glandulosa compared to the
grass were both important (Fig. 6.6 ). When P. glandulosa was planted with the C 4
grass, but 60 days before the grass was planted ( P. glandulosa planted early),
P. glandulosa dry mass was reduced by approximately 50 % (compared to alone),
but it was reduced less in the 180 cm deep pots. If P. glandulosa and the grass were
planted at the same time, growth of the woody plant was further reduced compared
to growth alone, but growth was still greater in the deeper pots. When P. glandulosa
and the grass were planted together, but the woody plant was planted after the grass,
the dry mass or growth of the woody plant was reduced to 3 % of dry mass when
Fig. 6.6 Figure represents total dry mass (aboveground plus belowground) of P. glandulosa grown
alone or with a C 4 grass Bouteloua curtipendula . Both P. glandulosa and the grass were planted in
180 cm, 90 cm, or 30 cm deep, 10 cm diameter PVC pipes ( pots ). Prosopis glandulosa was planted
alone or with the grass, but planted 60 days before the grass was planted (early), at the same time
as the grass, or 60 days after the grass was planted (late) (modifi ed from Bush and Van Auken 1991 )
6 Competition