3.0 SPECIES EXTIRPATED FROM PIMA COUNTY

As many as 13 species are believed to have been extirpated from Pima County (see Table 3). Most of these species no longer exist in Pima County due to the loss of habitat which they depended upon for survival. The Mexican Gray Wolf and Grizzly Bear are exceptions, because they were purposefully extirpated in Pima County through bounty hunting and government trapping programs The Mexican Gray Wolf and Grizzly Bear are the only species in this table which are listed under the Endangered Species Act.

A disproportionate number of species were extirpated through loss of aquatic habitat. In Pima County, several streams have entirely ceased to flow during much of the year, most notably the Santa Cruz River and Rillito Creek. In addition, many other streams and springs have been diverted or developed for human or livestock use in a manner incompatible with the existence of native species.

4.0 VULNERABLE SPECIES IN PIMA COUNTY

Vulnerable species are species that are at risk of becoming extirpated in Pima County if current land use practices continue to persist. This category is divided into the following subcategories:

1. Species at risk in Pima County and for whom habitat in Pima County is crucial for their existence
2. Species at risk in Pima County and/or are generally declining throughout their range
3. Species that are rare in Pima County, but the overall status is unknown
4. Species at risk in Pima County but are not at risk overall.

Information for each species is displayed in Table 4 according to the criteria above. This list provides the focal point for discussions on species to be included within the Sonoran Desert Conservation Plan.

5.0 HABITATS OF CONCERN & TARGET PLANT COMMUNITIES

Table 5 displays a list of habitats of concern and target plant communities for conservation within Pima County. Target environments were determined during interviews. Target plant communities were based on supplemental information provided by the Coalition for the Sonoran Desert Protection Plan with additions made by Pima County staff and the STAT.

Aquatic environments, wetlands and riparian woodlands are considered to be a high priority for conservation planning based on discussions during the interviews. These environments are rapidly disappearing throughout the United States, including Pima County. Diversion of water and desiccation of these environments has caused extirpation of at least five fish species in Pima County. A large number of species listed within this report either live in aquatic or riparian habitats, or utilize them in some way. Primary threats include groundwater pumping, which has reduced water tables needed to sustain these ecosystems, and the establishment of introduced or "invader" species which inhibit growth of native species.

Native grasslands were also mentioned by our experts as being important to protect within Pima County. Grassland communities are rapidly disappearing throughout Pima County due to development pressures and poor land and fire management. Development causes fragmentation throughout these communities which depend on large tracts of undeveloped land to maintain a healthy existence. Introduction of exotics, lack of fire, and other activities (e.g. overstocking livestock) have degraded grasslands and reduced species diversity. One specific grassland type mentioned by our experts as a conservation target is the big galleta grass (Hilaria rigida) association.

Although common in many areas of the Southwest, saltbush communities are another important habitat within Pima County which is gradually disappearing due to development pressures and agriculture. Saltbush (Atriplex polycarpa and A. canescens) occur within valley floors, where silty soils prevail. They provide good cover for small animals such as the shovel-nosed snake, and are a palatable browse for larger animals like the Sonoran Pronghorn.

Some environments contain "indicator species" which identify climates, soil conditions, etc. that are favorable to listed and unlisted species mentioned within this report. Ironwood and Saguaro are two examples of indicator species mentioned in Table 5. Ironwood communities indicate areas that are thermally buffered, providing a suitable climate and habitat for other native species. Saguaro communities indicate areas suitable for cavity nesters such as the Cactus Ferruginous Pygmy-owl and the Gila Woodpecker. Several experts recommended that attention should be focused on these indicator species and communities when determining critical habitat for species listed within the SDCP.

6.0 OTHER SPECIES DISCUSSED

Appendix B contains a list of species which were discussed in the interviews, for which interviewees had little concern regarding their status in Pima County. Most of the species on this list are commonly found in Pima County or are commonly found elsewhere and were never common in Pima County. A majority of these species would benefit under a conservation plan designed for threatened and endangered species (Table 1) or any of the other species listed in Table 4 or Appendices D through F (  D ,  E ,  F   ).

7.0 PEST SPECIES FOUND IN PIMA COUNTY

A list of pest species which occur in Pima County is located in Appendix C. Many of these species are closely associated with humans and human modified environments. Some of them can take over natural environments, creating monocultures which are very harmful to other species. Other species can affect natural processes. For instance, buffel grass, red brome and Lehmann's lovegrass are capable of changing the frequency of fire in the landscape. Nearly all of the pest species are not native to this region.

Changes in species composition are to be expected over the geologic time scale. As climate changes, and land bridges are formed or sundered, the geographic range over which plants and animals will extend or contract in distribution. These changes are occurring now, but they are hard to detect. A recent example may be provided by animals such as javelina and coatimundi, which appear to have extended their ranges northward over the last 100 years (Brown and Davis, 1994). Over the last several thousand years, indigenous human cultures of North America also moved some plants and animals beyond their natural ranges, principally through domestication and cultivation.

Today new species are being introduced at a rate which is much higher than has been typical over geologic time. Rapid, intercontinental commerce allows many species to move beyond their native ranges, in effect connecting environments that have not been linked for to millions of years (Westbrooks and Eplee, 1995). Species from other lands are now a growing threat to native plants and animals in the U.S. (OTA, 1993).