FIRE

DANGER

RATING

IN ALASKA

by James W. Scott, Fire Control Officer, Anchorage, Alaska, BLM

is roughly equal to one-fifth of the combined area of the other States. In this vast region there are wide differences from place to place in climate, land forms, and soils. About 80 percent of the area of Alaska is public domain under the jurisdiction of the Bureau of Land Management.

One of BLM's many responsibilities in the management of public dmain lands in Alaska is forest protection. There are about 125 million acres of forest and woodland under BLM jurisdiction in Alaska.

The long hours of daylight and light rainfall which characterize the summers of western and interior Alaska, create a serious forest and rangefire season from April through September each year. Forest fires have burned over an estimated

80 percent of Alaska's public domain forest lands during the past 60 years.

The new State and our Nation cannot afford these tremendous losses. From north of the Arctic Circle to the southernmost tip of Alaska's panhandle, everyone is very dependent upon forests and the lands upon which they grow.

An important factor in combating any enemy is being able to determine when that enemy is most likely to strike. In the case of fire this is done by fire-danger rating.

Fire danger may be described as a resultant of the constant and variable factors which influence the inception, spread, control and terminal damage caused by wildfire. Fire-danger rating is a management system which integrates selected factors into qualitative or numerical indices of current protection needs (1). Perhaps it is better described as total-fire danger since it is, to say the least, a comprehensive term and concept.

Foresters working within fire problem areas of the United States were developing so-called firedanger rating methods long before the advent of organized fire control in Alaska. In 1930, H. T. Gisborne set up the first fire-danger meter for the Northern Rocky Mountain States (2). It was adopted for administrative use in 1935.

The weather factors, relative humidity, wind and fuel moisture plus calendar date advance, made up the burning index. The burning index was modified by the amount of lightning and degree of visibility to create the term fire danger. The burning index set the stage in potential; fire danger provided assistance in determining depth of organization preparedness and strength of attack (3).

In 1942, Alaska's fire control organization was a mere infant. Although organizational maturity has not yet been achieved, the need for a system of fire-danger rating in Alaska was recognized at an early date. In 1949, the Bureau of Land Management took the first step in the direction of fire-danger rating in Alaska. At that time an attempt was made to measure current fuel-moisture at widely scattered localities, utilizing a system developed for the Southeastern States. Favorable results were not realized.

To a small organization charged with the monumental responsibility of protecting 225 million acres of heterogeneous vegetation and topography, there was a particular need for an effective firedanger rating system.

Ideally, the fewer elements requiring accurate measurement the better, both from an economic and operational standpoint. Local knowledge of the fixed elements such as fuels, their density, type, and distribution were fairly well established. A weather history dating to 1934 yielded sufficient information to define climatic patterns. Climatic patterns, as well as soils, topography, aspect and risk are not subject to rapid change.

Local interest was focused upon the variables

which exert immediate influence upon the total fire complex, namely air movement and fuel moisture.

The climatic and vegetative similarity between Alaska and the Northern Rocky Mountain States influenced putting to use in Alaska in 1956 methods developed by the Division of Forest Fire Research. This method, known as the Intermountain Fire Danger Rating System, incorporated into a numerical index the four most important and variable elements influencing fire behavior. They are:

1. Severity index

2. Current fuel moisture 3. Relative humidity 4. Wind

Severity index is the term used to define cumulative fuel moisture in numerical terms. Fuel moisture content is defined as the quantity of moisture in fuel expressed as a percentage of its ovendry weight (4).

In 1956, fire weather stations were established at Anchorage, Fairbanks, Homer, Glennallen, McGrath, Fort Yukon, Tanacross and Palmer. Twice daily throughout the fire season, fireweather measurements were taken and rated. It was quickly recognized that the results did not reflect the total fire condition in Alaska. Analysis of normal and current regional climatological data furnished to BLM by the U.S. Weather Bureau in Alaska showed that broad climatic patterns could not be used to indicate burning conditions at any specific time or place. Fuel moisture measurement appeared to be the principal factor in rating fire danger in Alaska.

All fuel moisture measurements had been made by weighing a unit consisting of four 1/2-inch diameter pine dowels with an ovendry weight of 100 grams. The unit was suspended upon wire racks (Continued on page 14)

PORTABLE fire danger rating station. A BLM fire control man checks relative humidity.

Editor's Note: The following remarks were made before the International Union of Geodesy and Geophysics at Helsinki, Finland, August 8, 1960.

HE semiarid rangelands in western United States yield large quantities of suspended sediment to streams, causing serious erosion problems and resulting in reservoir sedimentation and damage to valley bottom lands. This paper deals with the control of erosion on the higher rangelands, near the sources of sediment, and its effectiveness both in reducing the downstream problems and in restoring the range.

Rangelands comprise more than one-half of the total area of 11 western States. These lands have little agricultural value other than for grazing. The arid to semiarid climate which characterizes most of the area, combined with the characteristically immature and commonly rocky soils and unfavorable topography, precludes their use for crops. Most areas that are amenable to irrigation by reason of available water and favorable relief have already been developed.

The same features which make the land fit only for grazing also tend to make it vulnerable to erosion. The low precipitation supports a sparse vegetation that is only partly effective as a protection against erosion. Periods of drought are often interspersed with high intensity rains, which generate short but destructive floods.

Physical features of the land likewise tend to favor rapid eroding. Hilly terrains with thin rockly soils usually support an ineffective vegetative cover and so are eroded easily. Even flat valley lands with deep alluvial soils often have a poor vegetative cover, owing to insufficient moisture, and are thus vulnerable to certain types of erosion, particularly gully cutting.

Gullying combined with other types of erosion is causing serious problems in most western streams. The filling with sediment of the mainstem reservoirs, such as those located on the Colorado River and Rio Grande, is not expected for many generations, because of their very large stor

age capacities. However, smaller reservoirs located on minor streams and tributaries are being filled at a rapid, and in some cases an alarming, rate. This applies particularly to stock ponds and small irrigation and conservation reservoirs.

As an example, consider a group of 17 retarding reservoirs constructed for flood control and erosion abatement in the 23-square-mile drainage area of Cornfield Wash in north central New Mexico. Studies show that these reservoirs lost 39 percent of their capacity in the first 5 years of operation, 1951-55. The drainage area for the reservoirs ranges from 0.1 to 7.1 square miles and the initial storage capacity averaged 35.5 acre-feet per square mile of drainage area. The reduction in capacity resulting from sediment deposition has seriously impaired the usefulness of the reservoirs for their designed function. The example may be somewhat extreme, but in the main it is typical of other lo calities in the Southwest.

In recent years deposition of sediment in the major stream valleys has added to the seriousness of another problem, namely, the consumption and waste of water by phreatophytes, particularly salt cedar (Tamarix gallica) and related types. The deposits of sediment along streambanks and on the adjacent floodplains provide what appears to be the ideal environment for phreatophyte growth. The high water table common to these localities, combined with the natural fertility of the freshly laid sediments, stimulates very rapid growth of the plants.

Studies made in the Safford Valley of Arizona show that salt cedar will use up to 9 feet of water per year with the water table 4 feet below ground level, and 7 feet per year with the water level 7 to 8 feet below ground level. This loss is approximately five times greater than natural evaporation from bare ground would have been with the water table at the same distance from the surface, and it is probably two to three times greater than would have been required to raise crops of small grain or grass. As the phreatophytes have no commercial value, the difference between the

water they consume and the natural loss, or the water that might have been used for raising crops, is a complete waste.

Recognizing the continually expanding problem of damage related directly to excessive erosion, corrective conservation measures of varied kinds and types have been attempted during the past 25 years, with varying degrees of success. The measures are divided into two general classifications: (1) those dealing with the land; and (2) those dealing with water or runoff.

Land treatment includes such measures as reduction and regulation of grazing, reseeding, brush removal, contour furrowing, ripping, pitting, and other similar practices designed primarily either to slow down the runoff or to increase permeability by puncturing the soil mantle.

Although each of these measures has some effect on water yield, a more positive control of runoff is obtained through use of structures. These may vary in size and cost from the relatively large dams designed primarily for flood control, but occasionally operated in connection with waterspreading operations, to the simple gully plugs used in an effort to control and heal small gullied channels.

Other conservation structures used mainly for the control of water are the various types of water spreaders designed to intercept runoff and distribute it evenly across the surface, thus affording greater opportunity for infiltration and the growth of vegetation. The waterspreaders were constructed of a variety of materials including

earth, loose rock, hand-placed rock, concrete, slash, loose brush, brush ties with wire, and even dense plantings of cactus and low shrubs in the form of hedges.

Among the land-treatment practices, control of grazing was early recognized as essential if success of other conservation measures were to be achieved. Such control became possible with establishment of grazing districts and assignment of grazing allotments to individual users. Under these conditions the user was willing to support regulation and reduction in the number of livestock, since in doing so any improvement of the range accrued to his benefit and he did not run the risk of losing it to a less conservation-minded competitor as he did under open-range conditions. As a result there was a reduction in the total amount of grazing between 1937 and 1955 of about 25 percent.

The effects of grazing reductions and other nonstructural land-treatment measures are difficult to define or evaluate. It is practically impossible to isolate the effect of any one measure. It is to be expected that where various types of treatment have been accompanied by grazing reduction, any resulting improvement would represent the combined effect of all measures.

As an example of this condition, changes in the Colorado River basin can be cited. Beginning about 1942 there has been a gradual reduction in the ratio of suspended sediment discharge to annual runoff as indicated by double-mass diagrams (Continued on page 16)

The study showed that with photographs taken from a height of 10,000 feet, errors in measuring were less than 2 feet per mile.

Other new survey concepts and techniques are being pressed into service to speed up the Alaska survey program. These include helicopters and electronic distance-measuring devices. To carry out its expanded program, BLM increased its Alaska sur

vey staff from less than 50 to 72

men in the last 2 years.

The survey program was put into high gear so BLM could act on applications filed by the State under the 103-million-acre Statehood land grant. The Statehood Act requires that selected land be surveyed.

HUNTERS

A total of nearly 12 million hunters in 46 States purchased one or more licenses to hunt during 1959. This is a decline of 2.2 percent from the number of

hunters in the sa ing 1958.

Hunters in 50 about $58 millio licenses, stamps, mits required by game departmen pursue and kill ga tures for 1959 exc 1958 by about $4

HIGHEST EARTH Trinity Dam, a m the Central Valle Project in northe has reached its ul structural height, highest earthfill world.

The dam will storage reservoir River.

Trinity Dam co their large fleets o equipment, have placement of 33 yards of earth a working for a 31 since April 1957.