This file was created by scanning the printed publication. Errors identified by the software have been corrected; however, some errors may remain. MEASUREMENTS OF THE EFFECTS OF FOREST COVER UPON THE CONSERVATION OF SNOW WATERS. BY W. R. M^rrOON. The large treeless.openings or "parks"in the westernyellow pine forestsof the southwest,which form a well known characteristic,afford an excellentopportunityfor a comparativestudy of the effectof a forestcanopyuponlocal snowconditions. During the late winter and springof •9o9, the writer had an exceptionallyfavorableopportunityfor observingthe progressof snowfall and subsequent melting in a virgin standof westernyellow pine near the baseof the San Franciscopeakson the Coconino National Forest in northern Arizona. The observations include the measurement of each successive snowfall,and the total depth of snow at intervalsof sevendays under two entirely different forest conditions,namely,in a virgin standof mature timber and on an adjacenttreelesspark, covering au area of severalsquaremiles. The observations were taken during the period from February 26 to April 25, at an altitude of approximately7,5oofeet. On March zz, the averagedepth of the snowfall from a two days' storm was 4.0 inchesin the park, as comparedwith 5.0 inchesin the forest, a differenceof 25 per cent. in favor of the forest. A snowfallon March 23 measured•o.8 per cent. deeperin the forest. Thesemay be takenas fair examplesof the difference under the two conditions. As an explanation,it seemsprobable that the sweepof wind acrossthe park carriesalong a certainexcessamountor load of snow from the snow gauge,which under the quieteratmospheric conditionsprevailingin the forestis ordinarily deposited a phenomenoncorrespondingin many respects to the well known laws governingthe depositionof silt by water currents. Over a forested area broken by parks the maximum depositionoccursat the margin of the parks, the normal deposition in the forest body, and the minimum over the parks and larger openings. Contraryto the usuallyacceptedfact, during the early spring, 246 ForestryQuarterly. meltingcommences earlierand progresses more rapidlyin the forestthan in the opentreelessareas. This is due to differencein radiation. Recordstakenin bothsituations showa muchhigher averagetemperaturein the forest,due to the fact that the night temperatures are from 5 to t5 degreeswarmerthanin the adjacent parks. Early in Marchit wasnotedthat the soilbeneaththesnow in the forestgenerallycontainedno frost and consistedof soft mud. The originof the.soil is from decomposing "malpais,"a basalticlava bed. At this time, however,a thick ice layer had formedbeneaththe snowin the openpark and was constantly thickening,dueto thelow dailyminimumtemperatures.By April t, the ice layer had reacheda thicknessof 3 to 6 inches,and it is safe to say that during the month of March a relativelysmall amount of water from the surface melting reached the soil throughoutthe park. On March •7, the averagedepthof snowin the forestwas • •-5 inches,and of snow and ice in the park •9.5 inches,with water equivalentsof 5.2 and 9.4 inches,respectively.The figuresare significant,when it is recalled that the measurementsshow considerablyless snowfall in the park than in the forest. The disproportionof the ratio causedby the high water contentin the park will be noted. The distribution of snowwasuniformin the smooth,openpark, while in the forestthe groundsurfacewasexposedin manyplaces and snow banks from 2 to 4 feet deep occurred in the natural openingsand lanes betweentree groups. The depth for the forestwas obtainedby averagingmeasurements taken at ten snow stationsspacedabout 5ø feet apart on a due north and south line. A similarline of stationswasestablished andusedin obtainingthe park measurements. The surfacerun-offin the two situations is interesting fromthe standpointof water conservation. By April •, bodiesof water overlying the ice sheet had collectedin the depressionsin the park, and a good-sizedstreamwas flowing at the outlet. No perceptiblesurfacerun-off from the forest (over the locality under consideration)occurredduring March. The days of April •, 2 and 3 were unusuallywarm analquiet, and resultedin the only run-off from the forest during the entire spring. The amount was insignificantcomparedto the total water contentof the snow mass. It is well to state, incidentally, that the writer made dailv Effects o[ Forest Upon Snow Waters. 247 trips betweenthe two measuringstations,which afforded an opportunityfor notingthe conditions. A spell of warm weather occurred during the first half of April. By April 8, the depthhad decreasedto an averageof 8.5 inchesin the park (6.5 inchesof snowand 2.o inchesof ice), and 3.8 inchesin the forest. In the followingfive days,o.f high temperatureand strongsouthwestwinds,practicallyall of this snow and ice disappearedfrom the park, accompanied, it is needlessto state, by an excessiverun-off which continuedfor a few days after the period. On April •5, no snowexistedin the park, while throughoutthe forest there remained considerablesnow distributedin banksand ridgesover the north slopesand level surfacesas well. Photographsshownon the frontispiecegive a good idea of the appearanceon this date of the measuringstationsin the park and forest, and the remainingsnow,banksof snow, on northerlyslopesin the mature timber. In the timber throughout this regionthere remainedon April 25 a considerable quantityof snowin shelteredsituationsfavorablefor late melting,while the last trace of snowhad disappearedfrom the park by April •2. The progressof accumulation and later meltingof snowin the two comparativesituationsmay be summarizedas follows: (•.) The total snowfallin the forest is somewhatmore than over the openparks, due chieflyto acceleratedwind velocityover the parks,resultingin a lighter depositionof snow,a casesimilar to the depositionof silt in streamcourses. (2.) Due to protectionaffordedby the forestcoveragainstextremesof cold resultingin a higher averagetemperature,the processof meltingduringthe springcommences considerably earlier in the forest than in the adjacentopenpark. (3.) The low minimumdaily temperatures in the park account for the formation of a thick layer of ice at the base of the snow duringthe earlyspring. This in turn servesto retainthe moisture above the soil. (4.) During the month of March, the park remainedalmost entirely coveredwith a deepand quite uniœormlayer of sno,wand ice, while in the forest the snow cover was much broken along rockledgesand bankedhigh in the naturaltree avenues,and the total amount of snow and water content above the soil surface was decidedlylessper unit of area in the forestthan in the park. 248 Forestry Quarterly. The conditionstronglysuggestedan apparentadvantageof a treelessover a forestedarea in conservingthe winter snowfall and storinga supplyof moisturefor distributionin the late spring when most needed. (5.)_With risingspringtemperatures and absence in the park of protectionagainstextremesof heat, a point is reached--the usual"warm spell"--whenthe layer of snowand ice in the park "breaksup" very rapidly and the water goesoff with a rush, resultingin a very small undergroundstorage,and the further consequence of a rapid drying or bakingof the soil. (6.) In the forest,dueto the high efficiencyof the tree canopy in modifying surface temperatures,and of the forest cover in checkingthe velocityof the winds which at this seasonof the year are strongand from the southwest, and blowwith the regularity of the "trades,"the progressof meltingproceeds moreuniformly and is prolongedinto late spring or early summerwith a minimum lossof water by surfacerun-off and evaporationand a relativelyhigh storagein the forestsoil.