eives 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
several thousand years ago. Evidence of ephemeral use of resources can be found
throughout the Forest in the form of hunting and gathering artifacts, and temporary
shelters. However, two sections of the Forest contain evidence of permanent settlement
including significant archeological resources such as petroglyphs and pueblos. Euro-American
settlement in the late 1800s brought timber harvesting and domestic livestock to
the region. Since settlement of the region occurred relatively recently, timber
and grazing records are available for the entire duration of Euro-American settlement.
Logging activity touched much of the southwestern portion of the forest, but several
areas were uncut or only lightly affected by logging. Some of the best examples
of ancient ponderosa pine forests remaining in the Southwest occur on the Centennial
The Centennial Forest is designated as a research and teaching laboratory and administered
by the Arizona State Land Department and Northern Arizona University School of Forestry.
Under current management guidelines, considerable flexibility exists to manage lands
to achieve broad research and educational objectives. Since the Centennial Forest
opperates under a single managerial plan, there exists the possibility to create
and study truly landscape level ecological phenomenon.