Details - CALS Networking Lab - University of Arizona

Semi-desert Grassland
Semi-desert grasslands (Desert Grassland; Fig
2.4) occur in some middle elevation areas of the
district, primarily along the northern boundary of
and in a few areas of Tanque Verde Ridge. The
community is composed of perennial short- and
mid-grass species, with most areas invaded by
velvet mesquite (Prosopis velutina Woot.).
Oak Savannah
The oak savannah community (Open Oak
Woodland; Fig 2.4) is found at higher elevations
than the semi-desert grassland community and
lower elevations than the pine-oak woodland, and
it contains elements of both communities. It is
ecologically similar to the chaparral communities
of central Arizona. In this community there are
dense stands of manzanita (Arctostaphylos spp.)
and oak (Quercus spp.), with a variety of annual
and perennial grasses.
Pine-oak Forest and Woodland
Pine-oak forest and woodland (sometimes
referred to as Madrean evergreen woodland;
Fig. 2.4) is ubiquitous at mid-elevations
throughout the Apache Highlands (Bailey
1998, McPherson 1993). Madrean evergreen
woodland is characterized by evergreen oaks
with thick sclerophyllous leaves, such as emory
oak (Quercus emoryi Torr.), Arizona white oak
(Quercus arizonica Sarg.), and Mexican blue oak
(Quercus oblongifolia Torr.). Mexican pinyon
pine (Pinus cembroides Zucc.) and alligator
juniper (Juniperus deppeana Steud.) are the
common gymnosperms. Understory grasses are
usually abundant. At the higher elevations and in
drainages, there is also ponderosa pine.
Coniferous Forest
Dominated by gymnosperms such as pines
(Pinus spp.), and firs (Abies spp.), coniferous
forests (Pine and Montane Fir Forests; Fig 2.4)
represent the cold-hardiest biotic community
in the district. In these communities in the
district, ponderosa pine (Pinus ponderosa P. &C.
Lawson) and Douglas fir (Pseudotsuga menziesii
[Mirbel] Franco) dominate, with some temperate
deciduous plants intermixing, primarily on
the north-facing slopes: Gambel oak (Quercus
gambelii Nutt.), quaking aspen (Populus
tremuloides Michx.), and maples (Acer spp.) and
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boxelder (Acer spp.). Conifer forests are fireadapted
ecosystems, with natural low-intensity
fires occurring every 6 to 15 years (Baisan and
Swetnam 1990, Dimmitt 2000).
Natural Resource Management Issues
Adjacent Land Development
Increasing housing development along the
western and southern boundaries has become
the most pressing natural resource issue for the
district. Sandwiched between both districts
of the park, the greater Tucson metropolitan
area is one of the fastest growing in the United
States. The area currently has an estimated
population of 800,000, a 44% increase over the
last two decades (PAG 2005). The increase
in human residents brings with it a variety of
natural resource-related problems including
harassment and predation of native species by
feral animals, increased traffic leading to altered
animal movement patterns and mortality, the
spread of non-native species, illegal collections
of animals, vandalism, increased water demands,
air pollution from vehicle emissions, and visual
intrusions to the natural landscape (Briggs et al.
1996). Throughout this document we highlight
some of these impacts as they pertain to each
taxonomic group.
Of immediate concern for park
managers is the depletion of groundwater and
its effects on the ecologically valuable Rincon
Creek, in particular (Baird et al. 2000). There
are numerous single-family and large-scale
housing units being constructed (or planned)
directly adjacent to the district, including the
proposed Rocking K Ranch development,
which anticipates 9,000 residents and has been
granted a permit by the Arizona Department of
Water Resources to withdraw 4,400 acre feet per
year from the underlying aquifer (Mott 199 ).
Rincon Creek has the most well-developed
stretch of southwestern deciduous riparian forest
in the district, which will likely be impacted
by drawdown of the aquifer. Groundwater
drawdown at Tanque Verde Wash has already
affected the riparian community there (Mott
199 ).