Stressors: Threats to
Biodiversity
During autumn 1997, thirty-three of the field scientists
responded to the portion of our written questionnaire which
asked them to rank from assessments based on their own field
experiences – the ten most significant threats to the
biodiversity of the Sonoran region. As Table 2 demonstrates,
a total of 17 threats were pre-selected for evaluation, but
the field scientists were welcome to propose others on their
own. By far, the stresses which most concerned the scientists
surveyed were the following:
1. Urbanization's aggravation of habitat conversion and fragmentation;
2. The high rate of in-migration of newcomers to reside, work
and recreate in the region, and their contribution to population
growth and resource consumption;
3. Surface water impoundment and diversion from places where
native vegetation and wildlife have access to it;
4. Inappropriate grazing of vegetation by livestock, especially
when combined with conversion of plant cover to exotic pasture
grasses; and
5. Aquifer mining and salinization, the drop in water table,
and their long-term effects on riparian vegetation and wildlife.
The kind of ranking summarized in Table
2 is a subjective means of assessing the severity of various
stresses which work at different scales and for different
durations. We argue that this "subjectivity" is
of positive value in this case; the average duration of fieldwork
by the scientists surveyed is far longer than most individual
published studies of most federally-employed land managers'
tenure in one landscape. Their views are essential to this
overview because there are few statistical summaries which
document with equal precision on both sides of the international
border the stresses, pressures and threats affecting all habitats
found within the region. While Table 2 highlights these scientists'
ranking of a pre-categorized set of stresses or threats, the
following discussions are more broadly defined, covering additional
statistical data and commentary on regional trends. Whenever
possible, we have included demographic or resource use data
from both sides of the border at the most comparable scale
we could find. The following texts address each stressor in
a sequence different from the ranking in Table 2. However,
we will remind readers of other rankings of threats from various
reports pertinent to the region, for example, Nabhan et al.
(1991)'s ranking of threats to native plants in the U.S./Mexico
borderlands, and Rick Knight's. (pers. comm.) assessment of
endangered species notices in the Federal Register. We will
also include any relevant commentaries which the field scientists
offered in regard to how these threats are actually affecting
the region's biodiversity.
From:
Nabhan, Gary Paul and Andrew R. Holdsworth. 1998. State
of the Sonoran Desert Biome: Uniqueness, Biodiversity, Threats
and the Adequacy of Protection in the Sonoran Bioregion.
p.34-36. Tucson, Ariz.: The Wildlands Project.
Sources
Rick Knight's. (pers. comm.)
Nabhan et al. (1991)
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