A Systematic Review of Wild Burro Grazing Effects on Mojave
Desert Vegetation, USA
Scott R. Abella
Received: 19 July 2007 / Accepted: 27 February 2008 / Published online: 1 April 2008
Ó Springer Science+Business Media, LLC 2008
Abstract Wild burros (Equus asinus), protected by the
1971 Wild Free-Roaming Horse and Burro Act on some
federal lands but exotic animals many ecologists and
resource mangers view as damaging to native ecosystems,
represent one of the most contentious environmental
management problems in American Southwest arid lands.
This review synthesizes the scattered literature about burro
effects on plant communities of the Mojave Desert, a
center of burro management contentions. I classified 24
documents meeting selection criteria for this review into
five categories of research: (i) diet analyses directly
determining which plant species burros consume, (ii) uti-
lization studies of individual species, (iii) control-impact
comparisons, (iv) exclosure studies, and (v) forage analyses
examining chemical characteristics of forage plants. Ten
diet studies recorded 175 total species that burros con-
sumed. However, these studies and two exclosure studies
suggested that burros preferentially eat graminoid and forb
groups over shrubs. One study in Death Valley National
Park, for example, found that Achnatherum hymenoides
(Indian ricegrass) was 11 times more abundant in burro
diets than expected based on its availability. Utilization
studies revealed that burros also exhibit preferences within
the shrub group. Eighty-three percent of reviewed docu-
ments were produced in a 12-year period, from 1972 to
1983, with the most recent document produced in 1988.
Because burros remain abundant on many federal lands and
grazing may interact with other management concerns
(e.g., desert wildfires fueled by exotic grasses),
rejuvenating grazing research to better understand both
past and present burro effects could help guide revegetation
and grazing management scenarios.
Keywords Exotic species Á Feral ass Á Herbivory Á
Forage Á Plant community Á Rangeland
Introduction
Wild burros (Equus asinus) have been one of the most
contentious environmental management issues in arid lands
of the southwestern United States. Considered native to
arid northeastern Africa and domesticated more than
5000 years ago, burros are believed to have been brought
to the American Southwest in the sixteenth century by
Spanish explorers (McKnight 1958; Carothers and others
1976; Wagner 1983). Owing to their desert hardiness,
burros were deemed excellent pack animals and were used
extensively to assist with mining operations in the 1800s in
the deserts of Arizona, California, Nevada, and neighbor-
ing states (Thomas 1979). Following a decline in mining
and the development of other transportation methods in the
late 1800s, many burros were released or escaped and
became feral (Zarn and others 1977a). With few predators,
burro density increased in the Southwest in the early and
mid-1900s, alarming ecologists and resource managers
who believed that these nonnative animals negatively
affected desert soils, native bighorn sheep (Ovis canadensis
nelsoni), and plant communities (Dixon and Sumner 1939;
Weaver 1973; Sanchez 1974). Resource managers of some
public lands initiated shooting, translocation, and other
control measures in attempts to reduce burro density and
perceived impacts on desert ecosystems (McKnight 1957;
Carothers and others 1976). However, public outcry about
S. R. Abella (&)
Public Lands Institute and School of Life Sciences, University of
Nevada Las Vegas, 4505 S. Maryland Parkway, Las Vegas, NV
89154-2040, USA
e-mail: scott.abella@unlv.edu
123
Environmental Management (2008) 41:809–819
DOI 10.1007/s00267-008-9105-7