|
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." The 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.
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