Geologic, Hydrologic, and Urban Hazards for Design in Desert Environments - Design with the Desert: Conservation and Sustainable Development - page 118

of the southwestern desert region discussed in Chapter 6 by Thomas provides us with
a window into the past to gain a better understanding of the ancient communities that
once inhabited the region. The difference in desert seasonality of rainfall explains, in part,
the structure of plant communities as outlined in Chapter 7 by Ward Brady, adaptations
of desert plants as outlined in Chapter 8 by Mark Dimmitt, and animals as discussed in
Chapter 9 by Mark Sullivan et al.
Unique plant communities can be found in the desert bioregion. Vegetation zonation is
found with increase of elevation on isolated mountain ranges and has been termed “the
sky islands” discussed in Chapters 7 and 10. These habitats are biological islands, because
of the geographic separation of small mountain ranges in the warm part of the basin and
range geological province. With increasing altitude, the general weather associated with
the blocks of mountains becomes cooler, with increased rainfall compared to the sur-
rounding warm deserts. The sky islands are the areas where Merriam's biotic zones were
developed and can be easily seen. In the sky islands, desert shrublands or desert grass-
lands give way to “evergreen” oak and juniper woodland, and at the highest elevations to
coniferous forest dominated primarily by pine trees.
This part on the living desert establishes the biological and ecological foundation for
humans living in arid landscapes of the southwestern part of the North American conti-
nent. Through the knowledge of desert ecology, persons may design a lifestyle in a fashion
that is more sustainable in a region with limits in natural resources, like water. Knowing
about the vegetative and animal history of the region provides an appreciation for cur-
rent ecosystems making up this part of North America. Historical knowledge also helps
people adapt to changes that are inevitable in the ecological context. Current vegetation
zones or types are reflections of the past and point to the future. In addition, animals of all
kinds inhabit the vegetated ecological communities, and the chapter dealing with animals
begins to show the human interaction with desert ecosystems. The wildlife chapter points
out anthropogenic changes including some public policies established to help provide for
the continuation of animal species on the landscapes.
Humans have effected major changes in desert ecosystems and accordingly have dis-
turbed or “wounded” the habitats available to plants and animals. These wounds are dis-
cussed in Chapter 10 by Dave Foreman, as are objectives to help recovery of native species.
Humans have changed the southwestern landscapes by acts of commission and omis-
sion. Acts of commission include modifying the hydrologic cycle by reservoir construc-
tion, placing transportation corridors across the bioregion, mining mineral and energy
resources, poorly controlling grazing by livestock, and allowing urban areas to sprawl
across the land. Acts of human omission that have negatively impacted southwestern
landscapes include the suppression of wildfires and introduction of some invasive species.
Two chapters deal with this subject: Chapter 11 by Stephen Pyne entitled “Built to Burn”
begins the discussion of fire and managing its effect on the landscape, and Chapter 12 on
ecological restoration by William Wallace Covington deals, in part, with the lack of natural
fires, discusses forest restoration, and shows how humans can change ecological trajecto-
ries by the use of land management tools. This part provides readers a window into the
ecological concepts that can lead to sustainable habitation of the semiarid and arid regions
of southwestern North America.