History of Degradation of Southwestern Ponderosa Pine Forests

“We pursued our course westward to San Francisco Mountain. The country at the foot of that mountain (a gradually ascending plain) although somewhat rocky, in places was covered with the finest grama grass, with timber sufficient for fuel, and water in abundance.[It is] well watered with springs, and is by far the most beautiful region I ever remember to have seen in any portion of the world. A vast forest of gigantic pine, intersected frequently by extensive open glades, sprinkled all over with mountain meadows and wide savannahs, filled with the richest grasses, was traveled by our party for many successive days.”┬áThe comments of E.F. Beale in 1857 as he traveled through northern Arizona, as quoted by D. Ashworth in Biography of a Small Mountain (1991).

The northern Arizona forests of the new millenium are significantly changed from the days of Beale. The arrival of Euro-American settlers began the process of changing the landscape. As early as the 1830’s and 1840’s mountain men began trapping wildlife for commercial purposes. Stockmen followed in the late 1860’s, bringing thousands of sheep and cattle to graze the lush grasses. The giant timber of the region was cut for the railroad and human use. Some would say that by the time the railroad was completed through Flagstaff in 1882 the area was settled.

Early Euro-American settlement radically changed the forest before the dawn of the 20th Century. The grizzly bears, wolves and big horn sheep noted by early explorers as present in “great numbers” were severely reduced or gone. The cattle and sheep consumed the grasses, flowers and shrubs that contributed to the plant diversity of the landscape. Removing the largest trees changed the structure of the forest.

One of the most influential changes that occurred to the forest ecosystem was the alteration of the way the forest burned. Research indicates that the ponderosa pine forest evolved with low-intensity fire (fire that moves along the ground through the grasses and not in the canopies of trees) that occurred at regular intervals of approximately 2-12 years. The crown fires witnessed during the fire season of 2000 were rare or nonexistent.

With the removal of grasses to carry low-intensity fire, the forest stopped burning at regular intervals. Around 1919 conditions were right to create a population explosion of pine seedlings. Because fire was removed, this irruption of trees led the forest to become denser than historical records suggest was natural. In many sites, the tree density went from 40 to 60 trees per acre to more than 2,000 per acre.

The early 1900s saw the birth of an aggressive policy of fire suppression. Although intended to protect trees, the action of stopping fires in the early 1900’s has led to the high-risk fire conditions that exist today. In a naturally functioning forest the frequent ground fires would have reduced the number of small seedlings. Without fire large areas of the forest have become choked with dense stands of small trees. The unnatural density of the forest now permits fire to move up into the forest canopy creating crown fires. The result is an increasing size, frequency and severity of unnatural fires in the pine forest. Unfortunately, this means that fires can kill trees over large landscapes, eliminate important wildlife habitat, and pose significant danger to people and forest communities.