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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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