Location and Setting
The Centennial Forest is 19,114 ha of State Trust Land located in northern Arizona.
Approximately half, 9,012 ha, of the Forest is located to the southwest of Flagstaff
in a checkerboard pattern interspersed primarily with the Coconino National Forest.
The second half, 10,102 ha, is located north of Flagstaff, to the west of Wupatki
National Monument in a contiguous block. The Centennial Forest is close to two major
travel routes - Interstate 40, and Highway 89. Portions of the forest are within
a 10 minute drive from Northern Arizona University.
Landforms and Geology
Most of the region encompassed by the Centennial Forest is composed of geologically
young volcanoes and lava flows known as the San Francisco Volcanic Field. Volcanic
activity has shifted from the southwest portion of the Centennial Forest to the
northeast portion over the past six million years. Consequently, volcanic soil parent
materials range from several million years old in the southwest to less than 70,000
years old in the north. The hilly, cratered landscape formed by this volcanism rests
upon an elevated sedimentary plateau that marks the southern boundary of the Colorado
Plateau region. Small outcrops of the plateau's sandstones and limestones occur
throughout the Centennial Forest.
The climate within the Centennial Forest is affected primarily by elevation. In
general, precipitation increases and temperatures decrease along a 600 m elevational
gradient from the northeast (lowest elevation, 1700 m) to the southwest (highest
elevation, 2300 m). However, climate varies significantly from year to year. For
example, the length of the growing season in the Flagstaff area averages 115 days,
but has been as long as 177 days and as short as 73 days. Precipitation follows
a bimodal distribution. Snow is concentrated during the winter months of December
through March. The summer months of July to October receive precipitation from often
heavy monsoon driven thunder storms. The entire northern portion of the Centennial
Forest receives greater than 50% of its precipitation during the summer precipitation
period whereas the southwest portion of the Centennial Forest receives greater than
50% of its precipitation during the winter months. Mean annual precipitation increases
from approximately 28-36 cm in the northern grassland portion of the forest to 60-68
cm in the ponderosa pine forests southwest of Flagstaff.
Geology, geomorphology and climate differences help form a diverse array of vegetation
in the Centennial Forest. Regional forest and grassland vegetation types are well
represented throughout the forest. Vegetation in the northern portion of the Centennial
Forest can be classified into four major terrestrial ecosystems and several minor
ecosystem classes. These ecosystems, described by potential climax vegetation include
approximately 5,000 ha of grasslands (Bouteloua gracilis, Elymus elymoides, Aristida
longiseta, and Agropyron smithii), 5,300 ha of pinyon-juniper (Pinus edulis, Juniperus
monosperma) woodlands, and transition zone forests (J. monosperma-P. ponderosa).
The southwest portion of the forest is dominated by extensive (7,200 ha) Pinus ponderosa
and P. ponderosa-Quercus gambelii forests. Another 425 ha are composed of vegetation
types that include Juniperus deppeana, and Fallugin paradoxa as indicator species.
In addition to forests and grasslands, the Centennial Forest contains over 1,200
ha of wetland-meadow ecosystems. Carex, Poa, Festuca, Agropyron, Allium, and Muhlenbergia
species typify these environments. Minor vegetation types include Quercus turbinella-Arctostaphylos
pungens shrublands which represent a transition zone into upland Sonoran Desert,
and Populus tremuloides-Pseudotsuga menziesii forests which transition into mixed-conifer
vegetation. Throughout the Centennial Forest, transitional zones between these diverse
vegetation types and along elevational gradients are particularly well represented.
Land Use History
Centennial Forest natural resources were first exploited by Native American inhabitants
severa