North American Tree Rings, Climatic Extremes, and Social Disasters - Dendroclimatology - page 309

Fig. 10.8
Tree-ring-reconstructed
summer PDSI averaged and
mapped for the
'environmental crisis' of the
mid-nineteenth century, when
a pluvial ( a , 1825-1840) was
followed by a 25-year-long
dry period ( b , 1841-1865),
which West ( 1995 ) argues
interacted with overgrazing of
vital riparian corridors by
Native American ponies and
Euroamerican stock animals
to contribute to the
extirpation of bison from the
central High Plains
over the central Great Plains (Fig. 10.8 ) , where an 'environmental crisis' described
by West ( 1995 ) afflicted the Arapaho and Cheyenne Indians and interacted with their
newly adopted horse culture and with the stock animals of Euroamerican overlan-
ders to degrade critical riparian habitat and lead to the extirpation of the bison from
the central High Plains.