Impacts of Climate Change and Land Use on the Southwestern United States
Land Use History of North America (LUHNA): The Paleobotanical Record

Figure 3 - Diagram showing fossil packrat midden records with Texas pinyon (Pinus remota, south of the Hueco Mountains near El Paso), and Colorado pinyon (Pinus edulis, north of Hueco Mountains) during radiocarbon time or the last 40,000 years. The tickmarks on each vertical line represent over 350 radiocarbon-dated middens that show the presence or absence of pinyon pines along a 15-degree latitude (ca. 1600 km) transect from Bermejillo, Mexico (Durango Province) to Ft. Collins, Colorado (from left to right). The diagram depicts the local extinction of pinyon populations growing in the Chihuahuan Desert during the last deglaciation (ca. 11,000 radiocarbon years ago) and the sequential migration to higher elevations and more northerly latitudes during the Holocene (the last 11,000 years). Note that Colorado pinyon's distribution in the state of Colorado may be just a few hundred years old and probably is not yet in equilibrium with modern climate. In Colorado and northern New Mexico, this makes it difficult to discriminate the last phases of Holocene migration from historical tree expansion due to fire suppression and overgrazing.
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