Chaparral Shrublands: History, Description, and General Information
Water has historically affected populations occupying this region. Water
related activities have been documented since about 200 B.C., when Hohokam
Indians settled the Salt River Valley in central Arizona and constructed
canals to irrigate their fields (Baker
1999b). European settlers in the Phoenix, AZ area in the late 1860s
depended on irrigation water from the Salt River for agriculture. However,
water supplies fluctuated greatly because the river often flooded in the
winter and dried up during the summer. There were no impoundments to store
water for the dry seasons. Therefore, the Salt River Water Users' Association,
the largest irrigation district in Arizona, signed an agreement in 1904
with the United States government under the National Reclamation Act,
to build a dam on the Salt River below the confluence with Tonto Creek.
The Roosevelt Dam, the first
of 6 dams on the Salt and Verde Rivers, was completed in 1911. Watershed
managers in the early 20th century became concerned that erosion on the
adjacent and headwater watersheds of the Salt River would move sediment
into the newly constructed Roosevelt Reservoir, which would decrease its
capacity. Measurements indicated that 12,450 ha-m of coarse granitic sediments
accumulated behind Roosevelt Dam between 1909 and 1925 (Baker
1999b). Because of the concern about these sediment accumulation,
the Summit Plots were established in 1925 by the USDA Forest Service 24
km upstream from Roosevelt Dam to study the effects of vegetation recovery
from livestock grazing (the dominate land use at the time), mechanical
stabilization of disturbed soil, and reseeding on stormflow and sediment
yields from the lower chaparral zone (Rich
The early research on the Summit Plots was expanded to consider the effects
of watershed management practices on all the region's natural resource
products and uses of the forests, woodlands, and shrublands. The influences
of vegetation manipulation on the natural resources from chaparral shrublands
were studied by the USDA Forest Service and its cooperators at Three-Bar, Whitespar, Mingus,
and Battle Flat because
they contained extensive areas of chaparral vegetation commonly found
throughout the Southwest, thoroughly evaluating the effects of vegetative
manipulations on the array of multiple uses from the ecosystems studied.
Results from this research show that vegetation can often be managed to
increase water yields, while still providing timber, forage, wildlife,
and amenity values required by society in some optimal combination. This
finding was not surprising, as many of the vegetation management practices
studied to improve water yield were common in principle and application
to other management programs often implemented to benefit other natural
The chaparral type is restricted almost entirely to the Lower Colorado
River Basin, where it covers about 1.4 million ha, nearly all in Arizona
1979). Unlike the mountain brush in Colorado and Utah, chaparral species
tend to be low-growing shrubs with thick, evergreen leaves well adapted
to heat and drought. The type is common on rugged terrain from 900 to
2,000 m in elevation. Shrub live oak (Q. turbinella) is most abundant,
followed by mountainmahogany. Other common shrubs are manzanita (Arctostaphylos spp.), Emory oak (Q. emoryi), silktassel (Garrya wrightii),
desert ceanothus (Ceanothus greggii), and sugar sumac (Rhus
ovata). Most species sprout prolifically from root crowns after burning
or cutting and are difficult to eradicate.
Chaparral shrublands occur on rough, discontinuous, mountainous, terrain
south of the Mogollon Rim in central Arizona. Average annual precipitation
varies from about 380 mm at the lower limits to over 630 mm at the higher
1979). Approximately 60% of the annual precipitation occurs as rain
or snow between November and April. The summer rains fall in July and
August, which are the wettest months of the year. Annual potential evaporation
rates can approach 900 mm. Water yield varies greatly depending on precipitation,
elevation, and soils. The overall average is 25 mm or more; the lower,
drier sites produce little, while the wettest sites can yield 75 or 100
Plant SpeciesChaparral shrublands occur on rough, discontinuous,
mountainous, terrain south of the Mogollon Rim at elevations ranging from
3,000 to 7,000 ft. Chaparral stands consist of a heterogenous species
mix in many locations, but often only 1 or 2 species dominate. Shrub live
oak (Quercus turbinella) is the most prevalent species, while true
(Cercocarpus montanus) and birchleaf mountain mahogany (C. Betuloides),
Pringle (Arctostaphylospringlei) and pointleaf (A. pungens)
manzanita, yellowleaf (Garrya flavescens), hollyleaf buckthorn
(Rhammus crocea), desert ceanothus (Ceanothus greggii),
and other shrub species are included in the chaparral mixture of shrub
species. Annual and perennial grasses, forbs, and half-shrubs are present,
particularly where the overstory canopy is open or only moderately dense.
PrecipitationAverage annual precipitation varies from about
14 inches at the lower limits of the chaparral shrubland type (3,000 ft)
to 30 inches at the higher elevations (7,000 ft). Approximately 60 % of
the annual precipitation occurs as rain or snow between November and April.
Summer rains occur in July and August, which are the wettest months of
the year. Annual potential evapotranspiration rates can approach 35 inches.
Also see: water yield and potential
Resources and ActivitiesAlthough the recreational value
(hiking, camping, and hunting) of chaparral is lower than that of higher
elevation vegetation types, its close proximity to major population centers
provide it with an advantage. Research studies also have determined that
chaparral areas are major sources of water if vegetation control is exercised.
Chaparral rangelands are often grazed year-long by livestock, because
evergreen plants common to the shrublands provide a continuous forage
supply. A variety of wildlife species are found in chaparral shrublands,
with comparatively high populations often concentrated in fringe areas.
SoilsChaparral soils are typically coarse-textured, deep,
and poorly developed. Granites occur on more than half of the shrublands.
The topography is characterized by mountain ranges dissected by steep-walled
gorges and canyons. Slopes of 60% to 70% are common.
There are currently over 200 images available in the image
database illustrating various aspects and conditions found in chaparral
ecosystems in southwestern United States. These can be accessed
after getting into the database by using the key words chaparral.
Additional key words are available for searching the images in a drop
down list within the database.