Deep History and Biogeography of La Frontera - Design with the Desert: Conservation and Sustainable Development - page 119

6
Deep Hist ory and Biogeography of La Frontera*
Thomas R. Van Devender
CONTENTS
6.1 Introduction ........................................................................................................................ 121
6.2 Out of the Tropics .............................................................................................................. 122
6.3 Miocene Revolution ........................................................................................................... 122
6.3.1 Mountain Building ................................................................................................ 122
6.3.2 Evolution of the Deserts ........................................................................................ 124
6.3.3 Pliocene Climates ................................................................................................... 125
6.3.4 Historical Biogeography ....................................................................................... 125
6.4 Desert Ice Ages ................................................................................................................... 126
6.4.1 Packrat Curators ..................................................................................................... 126
6.5 Tropical Interglacials ......................................................................................................... 128
6.5.1 El Golfo, Sonora ...................................................................................................... 128
6.5.2 Rancho La Brisca, Sonora ..................................................................................... 128
6.6 Ice Age Mammals and Grassland Dynamics ................................................................ 129
6.6.1 Pleistocene Overkill ............................................................................................... 129
References ..................................................................................................................................... 130
6.1 Introduction
The border between the United States and Mexico traverses some of the most spectacular
and interesting landscapes of the American Southwest, from the Gulf of Mexico dunes and
Tamaulipan thornscrub of the Río Grande Valley, through the Chihuahuan Desert in the
Big Bend Country of Texas and Coahuila, across the desert grasslands of the Continental
Divide of New Mexico and Chihuahua through the “sky island” country of isolated
Madrean mountains and the saguaro-studded Sonoran Desert of Arizona and Sonora, and
the Mediterranean chaparral of California and Baja California to reach the Pacific Ocean
(see Chapter 7). The dramatic vegetation gradients along the border are summarized in
Biotic Communities of the American Southwest—United States and Mexico , 1 the accompanying
vegetat ion map, 2 Webster, 3 and various regional floras. Historic vegetation changes related
to human activities along the border have been the subject of considerable discussion. 4-6
In this chapter, I will discuss various aspects of the fossil record, paleoenvironmental
* Adapted with permission from Van Devender, T., in G. L. Webster and C. J. Bahre, eds., Vegetation and Flora of
La Frontera : Vegetation Change along the United States-Mexican Boundary (Albuquerque, NM: University of New
Mexico Press, 2001), pp. 56-83.
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