Our National Forests Part 10

_How Forest Fire Funds Are Distributed._ It devolves upon the Forest Supervisor and also the District Forester to apportion the appropriation allotted for fire protection in the most economical and efficient manner. First of all, the money is allotted to the various Forests in proportion to their needs. These needs are measured by the size of the Forest, the value of its resources, the length of the dangerous dry season, the fire liability or the amount of money loss in case of fire, the fire hazard or the degree to which an area is subject to fire danger, the difficulty of prevention and control and many other factors.

These same factors are employed to apportion the Supervisor's allotment of money to the various Ranger districts on his Forest.

Probably the most difficult factors for the Forest Supervisor to appraise on each Ranger district are the fire liability and the fire hazard. Fire liability has to do with the amount of damage a fire could do if it got started. Valuable timber needs protection most of all, and the value of the forest is determined by the kind of trees in it and the density of the stand. Fire hazard is usually expressed in terms of risk.

The Supervisor asks his Ranger if the risk on a certain area in his district is high, low, or medium. Risk depends, of course, largely upon the character and inflammability of the forest cover and the presence of human causes. Dense forests involve greater risk than open, scattering trees; government forests interspersed with private holdings containing much old slash have a high risk factor; and government forests near sawmills, large towns, and along railroad rights-of-way also have high risk factors. All these matters must be considered, in order that each area on each Ranger district gets just enough money for fire protection and not a bit more.

[Ill.u.s.tration: Figure 39. Putting out a ground fire. Even if the fire does not burn the standing timber, it kills the young trees and so weakens the larger ones that they are easily blown over. Wallowa National Forest, Oregon.]

[Ill.u.s.tration: Figure 40. Forest officers ready to leave a tool box for a forest fire in the vicinity. Such tool boxes as these are stationed at convenient places on National Forests ready for any emergency. Arapaho National Forest, Colorado.]

_Forest Fire History._ Very important also in fire protection are the studies which the Forest Service is carrying on, dealing with forest fire history. For many years back, records have been kept on all fires: their causes, area burned over, date of the fire, damage caused, the exact location of each fire, the cost of fighting it, the total number each month and each calendar year, and many other data. More recently records have been kept upon still further details connected with each fire, such as: the time elapsed between the start and the discovery of a fire, between the discovery and the report to the proper official, between the report and the beginning of the actual work of fighting, and the time required to put the fire out. Intensive studies have been made also upon the length and character of the fire season on each Forest, for it is important to know the maximum length, the minimum length and the average length of the fire season. These data show how much extra help must be hired for fire patrol and fire fighting, and during what periods the greatest damage is done, based both on acreage burned over and by the number of fires. Studies of this kind yield positive information on what areas of each Forest are particularly liable to lightning fires, to camp fires, and to incendiary fires. With this knowledge the Forest Supervisor can plan and distribute his men and funds more intelligently; they tell him during what period he can expect the most trouble, and therefore must have the greatest number of fire fighters at his command. It is scientific study like this that is doing more than anything else to solve the fire protection problem in the Western States.

_Relation of Forest Fires to the Weather._ In cooperation with the United States Weather Bureau, the Forest Service studies weather conditions in relation to forest fires. Weather forecasts have been sent to each Forest Supervisor throughout the fire season, informing him of the probable weather conditions. The velocity and duration of the wind, the temperature, the precipitation, and the relative humidity are all factors which greatly affect the inflammability of the forest. Forest Supervisors have been informed in these forecasts of what are known as emergency conditions, that is, an unusual and abnormal combination of weather conditions which make fire danger very great. These conditions may be a high wind, low relative humidity, high temperatures, or a combination of the three. When a Forest Supervisor is informed by the District Forester that emergency conditions are likely to exist during the next ten days or so, he immediately sends an alarm to all his Rangers to be especially watchful.

_Improvements and Equipment for Protection._ After the preliminaries of fire protection finance, forest fire history, and the study of weather and emergency conditions have been worked out, probably the first and most important prerequisite to forest fire protection is a matter already spoken of, namely, the improvements and the equipment.

The construction and maintenance of improvements and the possession of suitable equipment is second in importance only to the organization which is to do the actual fire suppression. Roads, trails, telephone lines, fire lines, lookout stations, Ranger stations, tool and food caches, a central supply depot, and many other things are necessary before men can be effective. Each Forest Ranger has use for the following equipment: fire fighting tools, water bags and pails, teams, pack horses, wagons, automobiles, saddle horses, tents, portable telephone lines, riding and packing equipment, and many other special equipment, which must be hired when occasion for its use arises. If a Forest Ranger has not access to this equipment, and few of them have, he has hanging by his telephone a complete list of all the stores, stables, garages, etc., in the neighboring towns and how much equipment each can furnish when called upon.

_Forest Fire Maps and Charts._ Not the least important bit of equipment, by any means, is the fire map or maps. The Forest Supervisor has a fire map of his whole forest in his office and the Forest Ranger has one of his district (sometimes including the neighboring districts, too) hanging in his cabin, usually posted conspicuously, so that it can be referred to any time of the day or night without delay. These maps have upon them all the available information regarding the country which is to be protected. They show physiographic features, such as topography, creeks, springs, meadows, water, swamps, etc.; vegetative features, such as timber, forage, brush, reproduction, planted areas, regenerating areas, slas.h.i.+ngs, etc.; such man-made features as roads, trails, cabins, ranger stations, corrals, pastures, Supervisor's headquarters, sheep camps, cattle camps, ranches, camp sites, railroads, logging railroads and camps, sawmills, power plants, towns, villages, etc.; and special protective features, such as locations of men, tools, equipment, tool and food caches, local help, emergency help, fire lines, fire breaks, lookouts, government and private telephone lines, instruments and switchboards, locations of stores, state Fire Wardens, livery stables, pack trains, garages, stage routes, etc. All these features and data are not put upon one map; usually a series of maps are used or some of the information is put on charts or on the border of the maps. In short all this information is put in such form that it is available at the shortest notice for emergency conditions. It makes little difference how it is recorded, so long as the information is available when needed.

[Ill.u.s.tration: Figure 41. A forest fire on the Wasatch National Forest, Utah. Forest officers trying to stop a forest fire by cutting a fire line. Note the valuable growth of young trees which they are trying to save on the right.]

_Forest Fire Organization._ The forest fire organization, whether it be on the whole National Forest or upon the Ranger district, consists of three agencies: the fire detection agencies, the fire reporting agencies, and the fire fighting agencies. All these must work in absolute harmony without interruption of any kind, to obtain the maximum of efficiency. The detection agencies consist of the lookout men, stationed at high, advantageous points which overlook large areas, and the moving patrolmen, who are a.s.signed to definite beats or territory which cannot be adequately reached by the lookouts. Lookout men live in small cabins on the tops of high mountains, and they watch for fires constantly. In regions which have very few high points and which are not suited to that method of detection, moving patrolmen are employed.

These men move about on foot, on horseback, on railroad speeders, in automobiles, or in any other conveyance adapted to the country they are in.

When the detectors find a fire they report it immediately to the nearest Forest Ranger or the Forest Supervisor. The Forest Ranger in whose district the fire is located is logically the first man to be informed, but telephone connections and other conditions sometimes alter this procedure. Just because a fire is found in, we will say, Ranger district number one, does not necessarily mean that the Forest Ranger of this district is the proper man to be notified. The fire may be at the very outer boundary of his district and may be much more easily accessible to the Forest Ranger in district number two. In any case it is all arranged beforehand just exactly who shall be notified in case of a fire in each and every corner of a National Forest. Each man in the organization has his duties and responsibilities determined for him in advance and he does his part without being prodded or reminded.

The location of a fire in the wild and inaccessible forest regions of the West, which may seem a very simple matter, is determined in a very ingenious manner.

_How Fires Are Located._ The lookout man, as well as the Forest Rangers and the Forest Supervisor, is provided with identical maps of the Forest. These maps show most of the important features useful in fire protection work, including also the private lands, all government holdings, and the public land survey. This public land survey has divided the land surface into legal subdivisions known as towns.h.i.+ps, sections, and quarter sections, and it is by these and with reference to these that all features, both natural and artificial, are located. A towns.h.i.+p is usually a square 6 miles on a side, containing 36 sections.

Each section is divided into quarter sections containing 160 acres each, which are further divided (though not by law) into forty-acre squares. The problem, therefore, that confronts the lookout man upon the discovery of a forest fire is to inform the Ranger or other Forest officer where the fire is--that is, in what _section_ it is located, if it cannot be located with reference to some well-known natural feature.

In order to determine in what section or quarter section a fire is located, each lookout point on the Supervisor's and Rangers' fire maps has a transparent circular protractor mounted on it. (A protractor is a device by which angles are marked off; it consists of a circle upon whose arc the degrees from 0 to 360 are indicated, 0 degrees being equivalent to North, 90 to East, 180 to South and 270 to West.) The center of the protractor is the lookout point. A piece of black thread is fastened to the center of each lookout point, so that it can be stretched across the arc of the circle and the degrees read off.

The other end of the thread has fastened to it a thumb tack or similar device, so that when the thread is stretched to read a certain angle, it can be fixed at that angle. The maps of the lookout men are usually fastened or permanently mounted upon a table which is oriented (that is, the top of the map is turned toward the north). The lookout men have sighting devices, usually alidades, which are placed on the map, by means of which they sight at a fire; but the bearing of the fire is read from the angles marked on the edge of the map, which is in reality a large protractor.

By these devices a fire is quickly and accurately located. When the lookout man sees a fire, he gets its bearing from the map by means of the sighting device. He telephones this bearing to the Ranger, or, in many cases, to the Supervisor. Immediately the Supervisor goes to his map, picks up the black thread attached to this lookout point, stretches the string, and, having marked off the bearing, pushes the thumb tack into the map. In the meantime, another lookout, perhaps two more, have sighted the same fire. The black threads from the other lookout points on the Supervisor's map are stretched and fixed in a similar manner. The fire will be found to be at the point where two or more of these black threads intersect. This is only one of the many ways which have been devised to locate forest fires; there are other methods, but all are based upon the same principle.

[Ill.u.s.tration: Figure 42. A forest fire running in dense underbrush on one of the National Forests in Oregon.]

[Ill.u.s.tration: Figure 43. Men in a dense forest with heavy undergrowth clearing away brush to stop the fire as it is running down hill. Crater National Forest, Oregon.]

_The Fire Fighting Organization._ The organization of men who do the actual fire suppression must be an elastic one, adequate to meet the needs of a Ranger district or of a whole National Forest, or, in some cases, of an entire administrative district, comprising as many as 25 to 30 National Forests. The Forest Guards and Forest Rangers are known as the first line of defense in this war against forest fires.

Upon them falls the brunt of the work of fire suppression. The second line is composed of local stockmen, ranchers, and logging and sawmill crews. When these prove insufficient in number, the large villages and towns are called upon, and the last resort is the labor of the cities and the United States Army. Thus, in the case of a very large fire the organization of the Forest Service is modified to cover not only each and every National Forest, but also entire States. In case of a very large fire, every available man from each Forest is sent to take his place in the organization. Expert fire fighters are sent direct to the fire. Other Forest officers are sent to the large towns and villages to act as quartermasters. These men hire fire fighters, entrain them, and fill orders for food, bedding, tools, and other equipment. Other quartermasters at the scene of the fire check s.h.i.+pments of supplies, check the time of fire fighters, approve accounts, hire transportation, and perform similar duties. Special disbursing agents are sent to the scene to pay the men. In short, everything is done to dispatch as quickly as possible the necessary men, food and equipment to the fire, and to do it in accordance with the prearranged plan for such emergencies.

_Forest Fire Cooperation._ A very important part of the plan of fire protection on the National Forests are the cooperative agreements entered into between the Forest Service and private individuals or companies. Such cooperation may be in the form of building improvements for fire suppression, furnis.h.i.+ng men in case of fire, furnis.h.i.+ng lookouts or patrols, furnis.h.i.+ng equipment, and, in fact, in connection with any of the necessary means for fighting fire. This cooperation has been of mutual benefit. One National Forest may cooperate with one or more neighboring Forests or with sawmills, power plants, logging camps, or railroad companies. Cooperation may also be with a well-organized Forest Protection a.s.sociation, of which there are a large number in the Western States. These cooperative agencies agree to send a large force of their men to fires on the National Forest in their vicinity, and the Forest Service reciprocates by sending men for fires occurring on their lands, which may threaten National Forest timber. Often cooperative agencies enter into agreement to build jointly with the Forest Service certain improvements, such as telephone lines, lookout towers, or trails, which will benefit public fire protection as well as private.

Many sawmills and logging companies who operate on or near the National Forests have agreements with the Service, by which they suspend all operations and send all their help to fires which threaten National Forest timber. All timber sale contracts of the Forest Service provide for cooperative fire protection.

_Fighting Forest Fires._ The most important requirements for successful fire suppression are: quick arrival after discovery, adequate forces of men, proper equipment, thorough organization on the fire line, skill in attacking, and careful, systematic patrol after the fire is thought to be out. All fires, whether large or small, require generals to lead the attacking forces, and the strategy of fire fighting can only be learned after long experience on the fire line. A cool, level-headed man is the greatest necessity in an emergency, for it is as disastrous to get too many men as it is too few. A few men that know how to attack a fire are worth a great deal more than a great many that are inexperienced.

[Ill.u.s.tration: Figure 44. Fire in a Lodgepole pine forest in Colorado.

Arapaho National Forest, Colorado]

[Ill.u.s.tration: Figure 45. A mountain fire in "Chaparral," five hours after it started. Pasadena, California]

There are different kinds of fires, depending upon their size, their intensity, and the nature of the country in which they are burning.

And there are as many different methods of fighting fire as there are kinds of fires. Some fires, such as gra.s.s fires or those burning in the needles and litter in the forest, can be extinguished directly by being smothered or beaten out. For this purpose Rangers sometimes use their saddle blankets, when nothing else is handy, but usually wet gunny sacks, boughs, and tree branches are used. Often, if it is available, sand or dirt is thrown on the fire with a shovel. Surface fires are a little more difficult to extinguish. They are more intense and more swift and consume brush, young growth, and fallen dry trees. These usually cannot be attacked directly, but must be controlled indirectly by the building of a trench or a fire break, or by a system of back firing. Trenches are fire breaks in miniature, usually from one to several feet wide. Fire breaks or fire lines are broad belts from 30 to 50 feet wide, which are cleared of inflammable material, not so much to stop the fire when it reaches this belt as to furnish a safe area from which fire can be fought and, most of all, from which back firing can be started. These lines or belts are usually built along ridges. If a fire starts on the lower slope of a mountain and the wind carries it up the mountain toward the fire line, the only hope of stopping the fire at the top of the ridge at the fire line is to start fires on the top of the ridge, which will burn down the slope and meet the original fire coming up. In rare cases, as, for instance, in the Idaho fires of 1910, the fires get to be so large and swift that all methods of attack prove futile and the only salvation is in natural barriers, such as rivers, or a change of the wind, or rain, to extinguish them.

In all fire fighting work, the plan is to surround the fire (if it cannot be beaten or smothered out) by a trench, fire line, or fire break, and to prevent the fire from spreading. In this kind of work, shovels, spades, mattocks, rakes, and hoes are used to move the soil; saws and axes are used to remove fallen trees from the fire line, and in some cases plows, dynamite, and other implements are employed.

PROTECTION AGAINST TRESPa.s.s, FOREST INSECTS, EROSION AND OTHER AGENCIES

While the protection of the Forest resources from fire is probably the most important phase of forest protection, it is not the only one by any means. The National Forest force also protects the Forest resources from trespa.s.s, from insect damages, and from tree diseases. Also water supply for domestic use, for irrigation, water-power, and navigation must be protected, and the public health must be safeguarded against the pollution of the streams emerging from the Forests. It is also the duty of Forest officers, in cooperation with the state authorities, to protect game, fish, and birds from illegal practices.

_Trespa.s.s._ The Act of June 4, 1897, authorizes the Secretary of Agriculture to make rules and regulations for the occupancy, use and protection of the National Forests, and provides that any violation of such rules and regulations shall be punishable by a fine or imprisonment or both. This and later acts provide for fines or imprisonment for all violations of the regulations governing National Forests. The violation of these regulations const.i.tutes trespa.s.s, and these may be either fire, timber, grazing, occupancy or property trespa.s.s, depending upon the offense. Since the United States has all the civil rights and remedies for trespa.s.s possessed by private individuals, it may bring action to recover damages resulting from trespa.s.s or breach of contract.

Fire trespa.s.s includes the following offenses: setting fire to timber, brush or gra.s.s; building camp fires in dangerous places where they are hard to extinguish; or leaving camp fires without completely extinguis.h.i.+ng them. The various railroads that cross the National Forests are one of the most frequent offenders in that the sparks issuing from the locomotives or the hot ashes dropping from the fire box set fire to National Forest timber. The railroads are required to use every precaution to prevent such fires, but many of them are started, resulting in damage suits by the Government. The damages cover not only the merchantable timber and forage destroyed, but damages are also collected for young, immature growth, which at first thought might seem to have little or no value. But the courts have held that while the young, unmerchantable trees have very little value now, they have a great value as the basis for a future crop of timber. Thus, in the case of the United States versus the Chicago, Burlington and Quincy Railroad, in 1910, for fire trespa.s.s on the Black Hills National Forest, caused by sparks from the locomotives operated by the company, the damages included $17,900 for young growth. Also, in the case of the United States versus the Great Northern Railroad, in 1911, in which suit was brought upon the negligence (causing fires to start) of the defendant company on their right-of-way, which fires subsequently spread to the Blackfeet National Forest, damages included the destruction of a great many immature trees, the value of which was estimated on the basis of their value at maturity discounted to date. It is significant that this case never went to trial; the defendant paid damages and costs without argument.

[Ill.u.s.tration: Figure 46. A few years ago this was a green, luxuriant forest. Picture taken after the great fires of August 20, 1910, on the Coeur d'Alene National Forest near Wallace, Idaho]

Under timber trespa.s.s are included the following acts: the cutting, killing, girdling, or otherwise damaging trees; the cutting of timber under sale contract or permit before it is marked by a Forest officer; the removal of timber before it is scaled, measured, or counted by a Forest officer; and the fraudulent stamping of any timber belonging to the United States with the regulation marking tools or similar device. Under grazing trespa.s.s are included such acts as: grazing stock on National Forest lands without permit; grazing stock on areas which are designated as closed to grazing; driving stock across a National Forest without permit; and refusal to remove stock upon instructions from an authorized Forest officer when an injury is being done to the National Forests by reason of the improper handling of the stock. The use of National Forest land without a permit for any purpose for which special use permits are required const.i.tutes occupancy trespa.s.s. But traveling, temporary camping, hunting, surveying, or prospecting may be carried on without permit, and camp wood and forage for stock used in connection with such activities may be taken free of charge. The unauthorized appropriation, damage, or destruction of property belonging to the United States, which is used in the administration of the National Forests, also const.i.tutes trespa.s.s.

Innocent trespa.s.s is usually settled amicably between the trespa.s.ser and the Supervisor. If the violation of the timber, grazing, or land regulations was due to a misunderstanding and was not of a willful character, a permit is issued and the trespa.s.ser pays for the timber or special use, as under regulation. Fire and property trespa.s.s cases seldom can be construed as innocent, hence in most cases such offenses result in litigation.

_Forest Insects._ Protection against forest insects is carried out in cooperation with the Bureau of Entomology of the Department of Agriculture.

An essential part of good forest protection is the work of locating and reporting evidences of insect depredations. There are scores of insects which are constantly working in the forests, either injuring or killing live trees or attacking the wood of trees after they have been killed.

Weevils kill young shoots on trees and destroy tree seeds; bark beetles and timber beetles infest the bark, girdle the tree and destroy the wood; and various borers and timber worms attack seasoned and unseasoned forest products and destroy the wood in the forest after it has been cut down and sawed into lumber. The greatest annual loss by insects is caused not so much by conspicuous local outbreaks as in the sustained annual loss of scattered merchantable trees. Local infestations often kill a large percentage of trees on an area, but these outbreaks are easily seen; the scattered infestations that kill a tree or two here and there over large forest areas are not so noticeable, but, taken all together, add up to a startling total.

The task of locating and reporting insect infestations falls upon the Forest Ranger and other field men of the Forest Service. Since the Rangers are practically the only cla.s.s of Forest officers that visit all parts of a National Forest during each field season, the Supervisor relies mostly on them to report upon insect infestations. In riding to and from his work, while on fire patrol, while going for mail and supplies, while attending to the timber, grazing and other business of his district, the Ranger does a good deal of traveling and covers practically every part of his district. These are good opportunities to watch for fresh outbreaks of insects, and the wide-awake, progressive Ranger never misses such chances. If he sees reddish-brown ma.s.ses of pitch and sawdust on the bark of a tree he immediately recognizes it as the work of insects. Or perhaps he may see a pine or a spruce tree with all its needles turned yellow. He knows then that this tree was girdled by bark beetles very recently, probably during the previous summer. A tree whose needles had turned red would indicate to him that the infestation was more than a year old, since trees attacked in the spring of one year usually do not show the results until the following summer. These two stages are known by the trained entomologist as the "yellow-top" and the "red-top" stages respectively. The latter is followed by the "black-top" stage. In this stage, insect infested trees stand out very conspicuously as leafless, gray or black snags, and they tell the story of the work of bark beetles that happened years ago.

[Ill.u.s.tration: Figure 47. The first evidence of insect attack are the reddish brown pitch tubes on the bark. Lodgepole pine infested by the mountain pine beetle. La.s.sen National Forest, California. Photo by the author.]

[Ill.u.s.tration: Figure 48. The last stage of an insect-attacked tree. The tree is dead and the dry bark is falling off. La.s.sen National Forest, California. Photo by the author.]

Probably the first external evidence of the attack of a bark beetle upon living trees with normal green foliage, is the presence of pitch tubes upon the outer bark. These are small, reddish-brown (later becoming grayish-white) ma.s.ses of pitch and sawdust, which exude from the small cylindrical entrance made by the adult beetle where it bores through the bark to begin its egg tunnel. Each tube represents the entrance of one or more of these beetles. But we must follow these egg tunnels further, to learn how the actual damage is done to the tree. As soon as the bark beetle has made its entrance through the bark, it starts to work up through the live bark and cambium of the tree, forming a tunnel but little larger than the diameter of the beetle, which is known as the egg gallery, These egg galleries vary in shape from straight to winding, and in length from ten to forty inches. As a rule, male and female beetles work together in one gallery, and the eggs are deposited along the sides of the gallery, often in little pockets. When the tunneling and egg-laying process of the adult beetles is completed, their activity ceases, and they are usually found dead at the upper end of their galleries. The larvae hatch and begin their work by burrowing across the cambium at right angles to the egg galleries. The complete girdling of the cambium layer is not accomplished until the larvae have completed their work, and the numerous larval galleries, by joining one another, form a complete gallery around the cambium of the tree, thus cutting off the food supply which is made in the leaves of the tree, from the lower portion of the tree, namely the roots. Since the roots cannot live without nourishment, the tree dies. As soon as the larvae have completed their development they pupate. Later they develop into adult beetles.

These adult beetles issue forth in swarms the following spring, to attack new trees.

The control of insect pests is a difficult matter. On areas where insect depredations are conspicuous and are liable to spread to nearby valuable timber, control measures are undertaken in cooperation with experts from the Bureau of Entomology. In these control projects, crews of men fell the infested trees, strip the bark from them, and burn the bark (usually at a time of the year when the young broods of beetles are still in the bark, namely, fall or winter). Trap trees are sometimes resorted to.

In this method, trees are girdled with an ax and thereby weakened to such a degree that beetles are attracted to it. After such a tree has become thoroughly infested in this manner, it is cut down and burned. In the case of a large, conspicuous infestation, an insect reconnoissance is made, in order to obtain an estimate of the percentage of trees that have been killed by insects. When it is possible, the timber is immediately sold. For example, on the La.s.sen National Forest, the writer several years ago made such an estimate of an infestation caused by the mountain pine beetle, covering over 100,000 acres. The reconnoissance showed that about 35 per cent. of the trees above 12 inches in diameter had been killed. The killed timber was subsequently utilized for telephone and telegraph poles.

There are many administrative measures which are practiced on the National Forests, which aim to prevent insect infestation. The prevention and suppression of forest fires, which form infection courts for insects, is probably the most important one. In all timber sales, old dead snags and slas.h.i.+ng, which are breeding places for insects, are disposed of. Through free use and timber sales, insect-killed timber is disposed of and the loss due to insects is reduced to a minimum, besides in many cases destroying the young insect broods.

_Tree Diseases._ In almost every administrative district there is a Consulting Pathologist, connected with the Bureau of Plant Pathology of the Department of Agriculture, who has charge of all work dealing with the eradication of tree diseases.

A tree disease is really any condition that interferes with the normal functioning of the tree, be this condition caused by fungi, mistletoe, fumes, smoke, frost, sunscald, drought or excess of water in the soil.

Parasitic fungi and mistletoes cause most of the tree diseases. Leaf diseases, by killing a greater part of the foliage, destroy the very organs in which food for the growing tissues is prepared. Diseases of the bark intercept the flow of food coming down in the bark from the leaves. Diseases of the sapwood cut off the water supply, which is pumped upward from the roots. Those that attack the roots also affect the water supply of the tree. Diseases of flowers and seeds destroy the faculty of reproduction.

Certain parasites are able to enter the youngest parts of trees, twigs and leaves directly, but the majority of the fungi causing decay of the wood can get into the interior of the living tree only by way of a pin knot or wound. For this reason, every wound caused by lightning, by fire, by man, or by animals, const.i.tutes a menace to infection. Many coniferous trees cover their wounds by an aseptic coat of pitch, which is very effective in preventing the germination and growth of fungus spores. But the less resinous conifers and the hardwood trees do not cover their wounds very effectively; large wounds are not covered at all. Upon exposure by a wound, the sapwood just underneath the bark dies, dries out, and checks. Spores of parasitic fungi enter the cracks, germinate and infect the heartwood. The spores of a heartwood-inhabiting fungus cannot germinate and thrive unless they fall upon the heartwood of the tree. In this way certain diseases of the heartwood, which result in rot or decay, can very frequently be traced directly to fire scars, lightning scars, spike tops, broken limbs or branches, and other mechanical destruction caused by lightning, fire, storms, cloudbursts, or heavy snowfall.

Fire as a cause of wounds is responsible for more cases of heartrot than all other injuries taken together. For this reason the protection of forests from fire is the most important preventive measure that can be taken to eradicate tree diseases. In fact, the best way of controlling diseases is by preventing them, and the Forest officers are endeavoring to eliminate any danger to the health of the forest, to prevent the injury of the trees, and to establish healthy conditions for their growth. This is forest hygiene, and it bears the same relation to the trees and forests as personal hygiene and community sanitation do to persons and communities.