Deep History and Biogeography of La Frontera - Design with the Desert: Conservation and Sustainable Development - page 128

middens record the survival of woodland plants in desert lowlands for several thousand
years in the early Holocene after the megafaunal extinction and before the formation of
desert grassland in the northern Chihuahuan Desert. 39 It is clear that the large herbivore
faunas of La Frontera wereare dramatically reduced compared to previous interglacials. 57
The ecological impacts of these missing herbivores on Holocene biotic communities were
probably substantial.
A 12,000 year old stratified vertebrate fauna from Howell's Ridge Cave in the Little
Hatchet Mountains of southwestern New Mexico (12 miles north of the international
boundary) 60 helps place the historical increase in shrubs in desert grasslands in New
Mexico in perspective. Bones of an extinct horse were found in the lower Wisconsin levels
close to a California condor bone radiocarbon dated to 13,460 year B.P. 61 A pinyon-juniper-
oak woodland was probably on the ridge in the late Wisconsin.
Thousands of bones and teeth of small vertebrates were carried to the ridge by owls and
hawks, and deposited in the cave in regurgitated pellets, providing faunal samples from
all nearby habitats. Percentages of the minimum numbers of individuals of species with
specific habitat requirements allowed environmental changes through time to be inferred.
Tiger salamander and Colorado chub bones, and teeth of voles in the deposit suggest that
the playa contained perennial water more often from 12,000 to 4,000 years ago, and again
at about 3,000 and 1,000 years ago.
Declines in typical grassland animals and increases of typical desert species such as
Couch's spadefoot toad and round-tailed horned lizard about 3900, 2500, and 990 years ago
reflect shift to habitats with more exposed soil—increases of shrubs in the desert grassland
similar to that recorded in the last century.
References
1. Brown, D. E., Biotic communities of the American Southwest—United States and Mexico,
Desert Plants 4: 1-342, 1982.
2. Brown, D. E. and C. H. Lowe, Biotic Communities of the Southwest (Fort Collins, CO: U. S.
Department of Agriculture, Forest Service, General Technical Report RM-78 (map), Rocky
Mountain Forest and Range Experimental Station, 1980).
3. Webster, G. L., A reconnaissance of the vegetation and flora of La Frontera, in G. L. Webster and
C. J. Bahre, eds., Vegetation and Flora of La Frontera: Historic Vegetation Change along the United
States/Mexico Boundary (Albuquerque, NM, University of New Mexico Press, 2001), pp. 6-38.
4. Bahre, C. J., A Legacy of Change: Historic Human Impacts on the Vegetation of the Arizona Borderlands
(Tucson, AZ: University of Arizona Press, 1991).
5. Bahre, C. J., Human impacts on the grasslands of southeastern Arizona, in M. P. McClaran
and T. R. Van Devender, eds., The Desert Grassland (Tucson, AZ: University of Arizona Press,
1995).
6. Bahre, C. J. and C. F. Hutchinson, Historic vegetation change along the United States-Mexico
boundary west of the Río Grande, in G. L. Webster and C. J. Bahre, eds., Vegetation and Flora of La
Frontera: Historic Vegetation Change along the United States/Mexico Boundary (Albuquerque, NM,
University of New Mexico Press, 2001), pp. 67-83.
7. Wolfe, J. A., Paleogene floras from the Gulf of Alaska Region (U.S. Geological Survey
Professional Paper No. 997, 1977).
8. Wolfe, J. A., An interpretation of Alaskan Tertiary floras, in A. Graham, ed., Floristics and
Paleofloristics of Asia and Eastern North America (Amsterdam, the Netherlands: Elsevier, 1972),
pp. 201-233.