Landscape History - Mountains and Plains: The Ecology of Wyoming Landscapes - page 23

is often mentioned during discussions about causes of
present-day global warming (see chapters 3 and 18). 46

Big Pryor East Pryor

Centuries and Decades Ago

in addition to the study of pollen and plant fragments,
scientists from various disciplines have learned about
landscape change by studying tree rings, soil profiles,
anthropological data, and old journals and photo-
graphs. What do such records reveal about the past few
centuries?
First, tree-ring studies have documented ongoing
climate change (fig. 2.11), including droughts during
800-1300 ad that were far more severe than any since
that time. tree-ring data collected by Steve Gray and his
associates at the University of Wyoming indicate that
these extended droughts lasted 75 years or more and
were long enough to cause changes in soil profiles.47 47 Soil
characteristics suggesting drought are associated with
fewer American indian artifacts, perhaps because the
number of bison was lower at such times. Since about
1300 ad , Wyoming has experienced a relatively moist,
cool climate. Paleoecologists refer to the 300-year period
from about 1550 to 1850 as the Little ice Age—a period
when a 2°F cooling of mean annual temperature was
apparently enough to cause further vegetation and soil
changes at the boundary between grasslands and big
sagebrush-dominated shrublands. 48 Grasslands were
more widespread during relatively warm, dry periods,
because sagebrush is less drought tolerant (see chapter 7).
compared to changes during the eras and epochs
of the more distant past, Wyoming landscapes have
changed relatively little during the past few centuries.
American indians surely influenced the landscape,
but the details are not well documented for most of
the area. 49 We can infer that they used small trees for
building lodges, and that they started fires from time
to time—some burning over large areas. the adoption
of the horse in the 1700s greatly increased hunting
efficiency. that and human-ignited fires probably had
the most pronounced effect on western ecosystems. 50
Also, some 65,000 emigrants passed through Wyoming
in 1850 alone, some bound for california to search for
gold, others headed to oregon territory for land and
other opportunities. 51 Military forts were built along
the way. Some travelers decided to live in Wyoming

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Relative abundance (percent)
Macrofossils (solid bars), pollen (open bars)

Fig. 2.10. Abundance of plant fragments from two species of
juniper at different times during the past 10,000 years, based
on data from woodrat middens at two foothill locations on
the north side of the Bighorn Basin. the length of the solid
horizontal bars indicates the proportion of all plant fragments
that originated from a single species, which reflects the abun-
dance of each species in the surrounding area. the open bars
indicate the relative abundance (percent) of juniper pollen
(not distinguishable by species). 14 c yr B.P. = years before pres-
ent as determined by carbon-14 dating. Adapted from Lyford
et al. (2002).

lake. Moreover, the treeline was probably 300 feet
higher than it is today, suggesting that the climate was
warmer at that time than it is today. this may have
persisted until about 3,000 years ago. Since then, the
alpine lake has been cooler and surrounded by a mosaic
of subalpine meadow and tundra with scattered white-
bark pine, as is typical of the transition from subalpine
forest to tundra in this region. Dense forests persisted
only at mid-elevations, as they do today. Lodgepole
pine became abundant during the past 3,000 years. 45
Such studies indicate that the climate has changed
dramatically during the past 10,000 years, a fact that