Coconino National ForestMay 1999

Ponderosa Pine Forest at Flagstaff

Ponderosa Pine Forests

Prior to Euro-American settlement, periodic low-intensity wildfires swept through the area, creating greater variability in tree sizes and ages than observed today. Because of these frequent fires, establishment of seedlings was infrequent. Native grasses were plentiful and herds of deer, antelope, bighorn sheep and elk traveled between water sources. Water sources included a few springs, ephemeral drainages and marshy bogs. Pioneer settlement began in the 1880s, bringing large herds of cattle and sheep. This extensive grazing reduced the grass and grass litter on the forest floor necessary to support the frequent low-intensity fires.

Historically, the forest around Flagstaff consisted of generally open stands of uneven-aged pines with a large quantity of grasses on the forest floor. Light surface fires occurred on an interval of two to seven years. These fires consumed forest floor organic material, burned much of the young tree reproduction and promoted the growth of dense grasses. Catastrophic crown fires were very rare. This original forest has been subjected to major ecological disturbances from grazing, logging, and fire suppression.

Harvesting of the region's timber resources as firewood and building materials also began with pioneer settlement in the 1880s. Large commercial logging operations were established and an extensive railroad system and road network was created. People began suppressing fires to protect their farms, ranches and buildings. Water sources (tanks) for livestock were constructed, changing the use patterns of wild and domestic grazing animals. The Coconino National Forest was created in 1908 to address concerns that arose because of increased settlement.

Although many early descriptions of the ponderosa pine forest called attention to the park-like stands, there are also descriptions that refer to dense cover. An accurate picture of the pre-settlement ponderosa pine forest would most likely describe a mosaic of open, grassy savanna with clumps of large, yellow-bark ponderosa pine. Scattered about were a few dense patches and narrow strings of dense trees, especially in canyons and on north-facing slopes. These patches would have provided needed cover for various wildlife species, such as wild turkey, but also the conditions for mistletoe and bark beetles to persist and even flourish locally.

Today's vegetation has been shaped by past climatic conditions and human activity. Climatic conditions in 1919, combined with logging, grazing and the suppression of wildfires, created a good seedbed and pine regeneration conditions. This resulted in large areas of similarly aged trees.

The exception to these conditions is in the cinder hills area, where cinder soils support scattered ponderosa pine trees with very little grass in the understory. Individual or small groups of trees probably burned frequently, but fire acreage was small due to the lack of ground-level vegetation.

How Do Dense Forest Conditions Affect Plant and Animal Diversity?

Grasses, forbs and shrubs: When a dense canopy of trees shades the ground, grasses and shrubs are less likely to grow. Where grasses abounded in the past, trees now dominate. The overwhelming majority of the plant biological diversity in Southwestern forests is in the understory community with over 600 understory species versus about 10-15 tree species in the overstory. This diversity of plants in turn comprises the essential habitat for many species of native fungi, soil microorganisms, arthropods, mammals and birds.

Tree size and age: There are relatively few very young or very old ponderosa pine trees. In addition, trees have not grown to their potential because of competition. For example, an 80-year-old tree might be 14-16 inches in diameter or it could be as small as five inches in diameter if grown in very dense conditions.

Types of trees: In mixed conifer forests there has been a decrease in ponderosa pine, limber pine and aspen over time because infrequent fires have allowed these forests to become dominated by Douglas-fir and white fir. There has been a decline in the amount of aspen because of lack of fire to create new aspen stands and because elk and livestock eat new sprouts.

Wildlife: Wildlife are adapted to different types of habitat. Thus, a decrease in a specific type of tree has an effect on the wildlife species that have adapted to that type of habitat. Overall wildlife use of different sizes and ages of ponderosa pine trees is evenly distributed with slightly higher use among very old trees and dense canopies. Large, homogenous areas of dense young ponderosa pine provide low-quality habitat for wildlife.

Species adapted to large prairies or parks have declined. Ranching, farming and later urban development have occurred in most of the area's open parks. There are fewer pronghorn antelope here than historically. The black-footed ferret, an endangered species, was a historic resident and was extirpated from Arizona in the 1950s due to poisoning and loss of habitat.

Below is a list of the threatened, endangered and other endangered species in the Flagstaff area. The historic presence of these species is unknown; however, it is assumed that they did exist in the days of frequent low-intensity fires.

  • Bald eagle (Threatened): 200-400 individuals winter in the Flagstaff area each year, and recently summer use has been observed in several locations. Habitat for bald eagles is around lakes and riparian communities, where they feed on fish and waterfowl. Bald eagles are popular for wildlife viewing.

  • Mexican spotted owls (Threatened): Approximately 25 pairs are known to live within the Flagstaff area. Habitat is predominantly in canyons and on steep slopes in mixed conifer. Some owl areas are at high risk of being lost to catastrophic wildfire. Some owl areas are currently impacted by high levels of recreation use.

  • Northern goshawk (Sensitive): Eighteen northern goshawk areas exist within the project area. However, many parts of the project area have not been surveyed, so more may exist. Road and trail use is currently very high within important breeding locations and there are concerns for reproductive success.

  • Peregrine falcons (Endangered): Several peregrine sites are located within the Flagstaff area, primarily associated with rocky cliffs. Primary threats are disturbance from recreational use of the cliff and cliff areas.

Unusual and unique plant communities exist within the Flagstaff area. Arizona leatherflower (Clematis hirsutissima var. arizonica) is associated with dense stands of ponderosa pine on limestone soils. Hedeoma diffusum, another rare plant, is found on knolls and rocky outcrops in limestone areas. These rare plant communities serve as important biological niches and contribute to the ecosystem.

How Do Dense Forest Conditions Affect Watershed Health?

Watersheds are a reflection of geology, climate and current and past land uses. Watersheds capture precipitation in the form of rain and snow. In response to heavy rain or melting snow, water flows freely as streamflow. Much of the precipitation that is not lost to evaporation and plant transpiration seeps through the soil and recharges groundwater formations, or occasionally rises to the surface as spring flow.

Healthy watersheds contain a balance of grass, forbs, shrubs and trees. Grasses and their litter effectively protect the soil from wind and water erosion while using relatively little moisture compared to the deeper-rooted trees and shrubs. While trees and shrubs provide shade, protection against severe weather and habitat for animals, their roots tend to draw more water from the soil and from greater depths than grasses.

Flagstaff area watersheds are somewhat less healthy than they could be because they contain an imbalance of grass, forbs, shrubs and trees, with trees dominating. Although needles, litter and duff protect the soil surface, the dominance of woody vegetation tends to use more of the soil's moisture. The result of dense forest conditions is likely a decreased capacity to provide usable water by increasing interception and transpiration and decreasing streamflow and groundwater recharge.

Overcrowded forest conditions also significantly reduce the abundance of grasses necessary for foraging animals. The few natural moist and dry meadows that exist within the Flagstaff area receive heavy use from wildlife and livestock as well as recreational use by people. These meadows are generally in poor condition due to compaction, inadequate litter, inadequate soil organic matter and a dominance of exotic/noxious plant species.

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