Scientific Descriptions

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.

Climate

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.

Vegetation

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 Forest.

Management

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.