Show MARKED IN I N BY R E BENEDICT Chief Inspector U S Forest Service I believe it was the day of or my arrival In Jn a n logging camp In Wyoming my first trip into the irrigated region of the west some eight years cans ago that I 1 was drawn into an argument about the influence of the forests on the climate and water sup ply ph and I have IJ ve been arguing ever since The question appears to be equally as stubborn of settlement as that of the tariff or the age of the world or the precise nature of electricity and like them it will for tor a long lon time offer ties tics for tor argument and conjecture The factors which control the climate are too indefinite too difficult of or measurement and accurate observation to permit of or an explanation which will satisfy all the natural laws involved The Tim more import ant facts and principles have of ot course been observed but the experts still find it impossible to lay down exact Jaws laws of cause and effect or to forecast re in particular cases with any an hope of or accuracy The question is however and that part which relates to the ef feet on the water supply one of vital I importance to the American people and andu u to the west especially owing to the large number of or uses to which water can bo he put In this region and the meagerness of ot the supply as ns compared with that of the eastern cistern states The fact should not be lost sight of that the scientists of or the government prophesy the exhaustion of the coal supply in a IL comparatively short time and that water stater seems to afford the only feasible means of providing power to replace steam Al AI Already r ready ady the great railroad systems are prepaying pre preparing preparing paring paying to electrify their lines and manu all over the country are be becoming becoming becoming coming anxious to install electric plants in the place of steam stam Of Vital Importance Looking at the subject from every side it is plain hat the climate and the water supply of the thc country countr are of vital Ital Im Importance Importance importance to the nation and a collection of the th proven facts in regard to the in fluence of oC them on the forests will probably probably ably be of ot considerable Interest Int rest to the people of Utah and adjoining states I J cannot do better to start with Ith than from one of oC the highest authorities on forestry who prefaces his discussion of forest Influences with this statement The effects of these agencies have been observed and recorded from ancient times Umes down to the present pres nt and hundreds of pages could he filled with the record r cord of instances in which forest vegetation has affected or has been he en believed to have af the climate the rainfall the regu lation of moisture the stability of o the soli soil the healthfulness of countries and m 1 allied matters If quantity of evidence alone alon were tere wanted the case cn case might be considered con considered considered proven or It U appears then that from the earliest times there have been misconceptions in regard to the actual effect of forests and anda a large portion of ot the supposed evidence has been nothing but opinions and the same can be said of o the present Th The proven facts are surprisingly few and can all be set forth shortly under the following headings Effect of Forests on Temperature Observations of the temperature of the tho theair theair air in forests covering a long Ion term of years shows that the whole effect of a complete forest growth is a reduction In the annual temperature of or about 1 de degree degree degree gree greeBy greeBy greeBy By seasons the effect is 15 much more pro pronounced pronounced pronounced the temperature in the forest be ing about the same in the winter 1 degree de degree dere gree re cooler in the spring 2 degrees de rees in the summer and 1 degree In the fall than in f the open Again the comparison of or the course of o the temperature during the day da in the forest and in the open is to a little more mort striking In the summer time at night nl the air all Is Js 2 to 3 1 degrees warmer wanner warmer In the woods In winter only slightly warmer In the hottest part of the day da in summer the woods are as much as 7 degrees cooler and in winter 2 degrees cooler tooler t than in i the tl e open I think this fact hat 1111 been be n appreciated by h every one fo for r it is just about the difference which can p e noticed in a change from the heat in f the tbt business district of the city and the cool ool shade of the trees in the suburbs or o r in Liberty Libert park parkIn In short the forests lower loer the tempera ture of the air during the day and in increase increase increase crease It during the night and the dif ference Is most pronounced In the sum summer summer summer mer time In other words the forests forest s tend to moderate the extremes of ot heat hea t and cold The above aboc figures apply only locally of course cours Attempts have been made to t determine the effect of large lare areas of n f forests and while the trio indications are that tha t ft the moderating effect is considerable there thre are so many man many stronger influences 9 which govern the temperature such aa as attitude altitude air currents presence of large larg lar e sheets of or water swamps etc that an ac accurate accurate accurate curate deduction cannot be made Temperature of the Soil Since the temperature of the soil must follow that of the air airy the same differ differences differences between temperature the of the sot soil In forests and in the open as were noted note in the air are found The rhe difference in i the winter fe 5 almost inappreciable while whit in summer he she soil soli In the forests forest is from fro I B S to 7 degrees colder than soil in the th e open Also the difference is much great greater er In evergreen forests than in one com composed composed composed posed of trees which shed their leaves This effect of or forests In lowering the tem ter temperature temperature of the soil soli Is important In as a s much as it shortens hortens the season of growth vegetation In forests starting later In th the spring ann and stopping earlier in the fall fat 1 than in the open Effect on Air Moisture On the absolute nb humidity of or the air or the weight of water in a given quan tits of or air forests forest have only a ver very 5 slight If It any effect Their effect on the relative humidity however or the degree deree of saturation i is B pronounced since the air in the forests forest s Is L cooler than in the open and can ab absorb absorb forb a smaller amount of moisture than tha n the warmer air outside the forests With Wit the same absolute humidity cold air will wit 1 be b nearer the point of saturation or the th point at which the moisture of the air will wil t be condensed condense into trio trie water and this thi s tart tact may he be of great Importance in the th effect of the forest on the rainfall of a L region fe n A Along long Ions series of or experiments e proved that tha the relative humidity of the soil soli In for forests eats ests ranged from 3 to 10 degrees de rees higher highe than In the open the difference being bean greatest at high altitudes This last fact every everyone one in the west wes t It 19 aware of for It Is evidenced by b th thease the ease with which clouds form on mountain n ranges as compared with the valleys alleys and an deserts df I The kind kiml of trees which compose the theor th forests or appears to have some effect on n the th relative humidity It being greater In i dense spruce forests than in forests of o hardwood or pine Influence of Forests on Rainfall The Tile widely prevailing opinion that for tor forests forests ests draw the rainfall has perhaps some som slight basis of or fact but generally speak ing the phrase should be reversed The Th rainfall makes the forests The question q Is such an extremely important one i in the economies of or any country countr that nu numerous numerous numerous attempts have been made to de termine by accurate observations and an I measurements the actual effect of o for tor eats ests on the rainfall but there titre are re so many man y more powerful agencies governing the tho th c rainfall that the scientists place little e dependency Y on the data collected even eve n though they the point strongly to a beneficial il ilir 3 effect of or the forests ile Observations In Germany show that the th e rainfall in the forests f rests Is from 1 I to 43 pe per percent percent ir iri r cent moro mope mo than n the open and averages average 16 per cent the effect being i ble at low altitudes but pronounced In f n the higher regions The effect also ap up appears nears pears to tn be he greater from to tn Jan uary than m In the otter other halt flair or of the Inc year ear That this Increase Is due entirely to the forests Is however doubted by b many foresters and in proof of their conten contention contention tion th they y point to the fact that the rain fall In those portions of or the United States were were once forested has not been be 1 appreciably decreased by cutting off the forests They also al o submit for tor compari comparison son the contradictory contradictor evidence of the ef et effect feet teet of or large bodies of water on i 4 FLUEN FLUENCE E OF FORESTS ON CLIMATE AND WATER SUPPLY f r r a a at I t 1 F k S S 4 M rf t J 4 w fre alt xa f t l t r tt s Y t r is 7 c rw yx t f e 1 8 i r rt zif a r t J sr F 6 lyEst s s gyps ds r d e kI c ra t Y 3 Y rp t Jr y r f e Y r s r saS 4 fd na W k til 61 3 f 13 4 it 3 a a 3 a ie Y i 2 Y r aI ri z I f l Y 3 Z gaa s sf r f x b sK II x r c cf I f v 13 i a ar r at Ys E EL C i L 1 r y I k s 1 f Ja I I r I t Ik r a 4 f y T Tw ri w Y b t 4 4 ra S a r rr r k at x ei t I i oar C I wr N S S A Y I rd a t iS a r rS S a Y t i A LitS I 55 S r The large picture shows the path of a The next two pictures show a panorama the In I n Wyoming The scene is typical of the Rocky mountains where most of the water for irrigation comes from The picture at the lower left shows the th e effects of clearing slopes of timber ip ift a region of heavy rainfall Surface soil is washed away to be deposited in inn the valleys At the lower right t Is shown s own a forest floor which which pre prevents pre prevents prevents vents the rapid runoff of water fall tall For Instance the rainfall near the Great Lakes Ickes Is not materially greater r than In regions several hundred miles dis distant distant distant tant and while on the Pacific coast the Puget Fuget Sound region has a rainfall of about Inches southern California has only twenty inches Reasons for these differences can be advanced adan d but the fact remains that stronger agencies asen les than local variations in temperature and humidity govern goern the rainfall ll of ot ofa a region I J r It may be of or Interest to know that in ina Ina ina a dense forest only about 77 71 per cent of the precipitation reaches the ground the remainder being beir intercepted by the crowns of or the trees andis either cither evaporated or trickles down the tree and is so lost to measurement Effect of Forests on Evaporation Owing to the lower temperature the greater humidity and the protection from fro froL L 4 t t alt all the evaporation in forests is about 40 per cent less than In the open While the amount am of ot difference varies with the kind of forest and the species of field crops it has been beep proven that even een a dense dens forest absorbs less moisture from the soil for plant growth than any an ano of o the field crops It is also estimated that in regions where the precipitation is In the form of ofrain ofrain rain In rather than snow twice as much c t water sinks Into the he ground in forested land than in the open Altogether then after deducting the tilt amount intercepted in the crowns of the trees the soil In forests receives and holds for the use of vegetation or 01 for feeding springs and streams ms a very much larger proportion of the total precipitation than doe does the soil soli of the open countries The effect of or the forests in this re respect resPect respect I is ls much greater in regions subject 1 I I I 1 to heavy he vy rainstorms than In the moun mountain mountain tain tam districts of ot the west where over half haIr the precipitation is In the form torm of ot snow which collects during the cold months and melts more or less gradually during the spring and early summer It is this difference in the conditions in the east and the Rocky Rock mountains which has brought about the rather acri acrimonious debate between the stockmen and the government officials In regard to the actual effect of or the protection of the for tor forests forests ests here and the restriction of or grazing The stockmen stockman claim that the snowdrifts from the principal sources sources of the summer water supply and advance the theory that if it all the forests were cleared off so that drifts could form the water sup supply ply ph pl y would be increased This is of course entirely a matter of conjecture My Sip I own can opinion is in favor of or forest protection for tor their action Is almost identical with that of irrigated ted areas Measurements show that in regions where crops require sooty heavy hea Irrigation irr atlon about 20 0 per cent of the water applied to the land returns to the streams in seepage se page Wasatch valley valle near Heber Hebern In n this state Is a case casa in point During some months of the year rear all of or the flow of the Provo river is diverted above aboe He Heber Heber Heher ber her vet yet there is always a good stream of water w ter at the lower end of the val vaI vaIle lev le The timbered areas above aboe an alti altitude altitude tude rude tu de of to feet are a e saturated with the water from the melting snow up to the middle of June or the first of fort July Tul and I cannot annot c but believe ethey they fur furnish furnish nish Wish a larger amount of at t heat water case to the the streams than would be the case if f the lands were open If the latter condition d obtained there would undoubtedly be more mored drifts but the snow would muse melt several a weeks weeks earlier and mu mua much h more quickly and anda a smaller proportion of the water would enter the ground The loss through evaporation evaporation evaporation oration would also be much greater Protection of the Soil Soli I In mountain regions which are subject to heavy rainfalls the beneficial effects of a forest cover corer in preventing erosion cannot be questioned Anyone Anone who is s ac acquainted acquainted acquainted with the Appalachian n moun tins of the east or r the mountain ranges of southern Colorado New Ne Mexico and Ari Arl Arizona Arizona zona has observed the scored hillsides from which the th timber Umber has been cleared or the vegetation removed by b overgrazing and noticed the deep gullies or or which have been formed farmed since the settle settIe settlement settlement ment of or the country countr This subject again Is one which Is dependent on local oval condi conditions conditions ti ons and an attempt to lay down precise laws in regard to the effect of forest pro protection protection protection or grazing would be futile 1 would like to say sa here that in my opinion the irrigation interests are arc making man claims as to the effect of or grazing on an th the summer flow of or water which are not noi t wholly holly w sustained by b the facts Of the th bat bad d effects of over grazing there can be no n 0 question but I believe von very ver strongly that the t most of the mountain ranges of or the west which constitute the sources of ot the water supply s for irrigation can be grazed bj by byboth b both cattle and sheep In such a way that the the water supply will not be materially affected In other words the increase j in the supply of ot water which would |