Agriculture Reference
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Figure 3. Peak biomass of exotic and native C
4
grass species grown in a common garden through two
growing seasons. Exotic species, which are denoted by black bars, are KR = King ranch bluestem,
Bothriochloa ischaemum
, PAN = Kleingrass,
Panicum coloratum
, and PASP = Dallisgrass,
Paspalum
dilatatum
. Native species, which are denoted by gray bars, are LB = little bluestem,
Schizachyrium
scoparium
, IND = indian grass,
Sorghastrum nutans
, SO = side-oats grama,
Bouteloua curtipendula
,
SILV = silver bluestem,
Bothriochloa laguroides
, and SPOR = tall dropseed,
Sporobolus asper
. A, B,
and C denotes the varying results that would have been found if species were not replicated and con-
clusions were based on comparisons of single exotic-native species pairs.
conduct the experiment a second time. Thus, we are attempting to determine if
exotics differ from natives, but only at this site. Mean aboveground productiv-
ity (peak biomass) was 813 g/m
2
for exotics and 524 g/m
2
for natives, and this
represents a highly significant difference (F
1,15
= 49.1, P < 0.001). This repre-
sents a 55% increase in growth overall in exotics over natives. There was also
a large amount of variation among species within native-exotic type (F
6,15
= 29.8, P < 0.001). In order to compare our overall results with what would
have been found if we had not replicated species, we back selected several spe-
cies pairs to point out how variable results could have been. A, B and C in
Figure 3 denote single species pairs, which might have been chosen for com-
parison. In scenario A, if these two species were pre-chosen for comparison,
we would have made the correct qualitative generalization (exotic > native),
but would have hugely overestimated the difference, i.e., a 428% increase in
growth in the exotic. If the species pair in scenario B had been used, an incor-
rect generalization would have been reached: that exotic species had a 55%
decrease
in growth compared to the native species due the use of a non-repre-
sentative native species,
Bothriochloa laguroides
. In scenario C, virtually no
difference (3%) would have been found between the exotic and native species.
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