PSAT Reading Practice Test 10
Questions 1-9 refer to the following information.
This passage is adapted from E. Gene Towne and Joseph M. Craine, "Ecological Consequences of Shifting the Timing of Burning Tallgrass Prairie."© 2014 by E. Gene Towne and Joseph M. Craine. A forb is an herbaceous flowering plant.
Periodic burning is required for the maintenance
of tallgrass prairie. The responses of prairie vegetation
to fire, however, can vary widely depending upon
when the fires occur. Management and conservation
05objectives such as biomass production, livestock
performance, wildlife habitat, and control of specific
plant species, often influence when grasslands are
burned. In some prairie regions, timing of seasonal
burns have been used to manipulate the balance of C3
10and C4 species, control woody species, stimulate grass
flowering, and alter the proportion of plant functional
groups. Most grassland fire research, however, has
focused on either burn frequency or comparing
growing season burns with dormant season burns,
15and there are few studies that differentiate effects
from seasonal burning within the dormant season.
In the Kansas Flint Hills, when prairies are burned is
an important management issue, but the ecological
consequences of burning at different times are poorly
20understood.
The Flint Hills are one of the last remaining
regions supporting extensive native tallgrass prairie
in North America and frequent burning is integral
to its preservation and economic utilization. Since
25the early 1970's, recommendations have been to burn
Kansas Flint Hills grasslands annually in late spring,
typically once the dominant grasses have emerged
1.25–5 cm above the soil surface. Although frequent
late-spring burning has maintained the Flint Hills
30grassland, the resultant smoke plumes from en masse
burning often leads to air quality issues in nearby
cities. Concentrated smoke from grass fires produces
airborne particulates, volatile organic compounds,
and nitrogen oxides that facilitate tropospheric ozone
35production. Burning in late spring also generates more
ozone than burning in winter or early spring due to the
higher air temperatures and insolation.
If the Flint Hills tallgrass prairie, its economic
utilization, and high air quality are all to be
40maintained, a good understanding of the consequences
of burning at different times of the year is necessary.
Burning earlier in spring has been regarded as
undesirable because it putatively reduces total biomass
production, increases cool-season [grasses] and
45undesirable forbs, is ineffective in controlling woody
species, and lowers monthly weight gains of steers
compared to burning in late spring. Consequently,
burning exclusively in late spring has become
ingrained in the cultural practices of grassland
50management in the Flint Hills, and local ranchers often
burn in unison when weather conditions are favorable.
Despite long-standing recommendations that
tallgrass prairie be burned only in late spring, the data
supporting this policy is equivocal. Total biomass
55production was lower in plots burned in early spring
than plots burned in late spring, but the weights
included grasses, forbs, and shrubs. It was not known
if [grass] biomass was reduced by early-spring burning
or if the differences were a site effect rather than a
60treatment effect. Burning in early spring also shifted
community composition in a perceived negative
pattern because it favored cool-season grasses and
forbs. This shift in community composition, however,
may actually be desirable because many cool-season
65grasses have higher production and nutritional quality
than warm-season grasses at certain times of the year,
and many forb species are beneficial to the diet of
grazers. Burning in late spring has been considered
the most effective time to control invasive shrubs,
70but Symphoricarpos orbiculatus was the only woody
species that declined with repeated late spring burning.
Finally, average weight gain of steers was lower in an
unburned pasture than in burned pastures, but there
was no significant difference in monthly weight gain
75among cattle grazing in early-, mid-, or late-spring
burned pastures.
The historical studies that formed the foundation
for time of burning recommendations in tallgrass
prairie are inconclusive because none had
80experimental replications and most were spatially
limited to small plots. All of these studies were
interpreted as suggesting that shifting the time
of burning by only a few weeks would negatively
influence the plant community. A more recent large-
85scale replicated study that compared the effects of
annual burning in autumn, winter, and late spring
found that the timing of burning had no significant
effect on grass production and no reductions in the
composition of desirable warm-season grasses.
Changes in Upland and Lowland Grass (a) and Forb (b) Productivity Over Time for Autumn-, Winter-, and Spring-Burned Watersheds