The Couonino Forest Experiment Station near Flagstbff, Ariz

The largest pine forest on the North American Continent estends from north-central Arizona in a southeasterly direction into southwestern New Mexico, a distance of approsiinately 250 miles The forest occupies an extensive plateau, known as the Colorado Plateau, which has a general elevation of from 6,000 to 8,000 feet above sea level, with numerous peaks the highest of which reaches an altitude of about 13,000 feet. Western yellow pine occupies the level mesas and lower slopes of the plateau from approximately 6,500 to 8,500 feet elevation, forming a belt 10 to 30 miles in width. The timber of this region naturally grows in very open stands, the characteristic mode of occurrence being in sniall groups SO to 300 feet in diameter, separated by openings of about the same size, but frequently there are much larger openings, some of them covering several hundred acres. These larger openings are conimonly known as “parks”. A number of theories have been advanced in esplanation of the origin of the parks of this region. One is, that they were once timbered but have subsequently been denudecl by fires. A more plausible theory in the case of most parks is that they are naturally treeless owing to the presence of conditions unfavorable to tree growth. With a view to determining these conditions, and also the influence of forest cover on reproduction, the Cocoiiino Forest Esperinient station, with the cooperation of the Weather Bureau, began, in 19008, a systematic study of the nieteorological conditions obtaining in one of the larger parks, locally known as Fort Valley, and in the adjoining timber. This park lies about! S miles northwest of Flagstaff, Ariz., on the Coconino National Forest, and is about I + miles in width by 24 miles long, the major diameter extending northeast and southwest. The topography is practically level, and the average elevation approxiinately 7,300 feet above sea level. The soil is mainly a fine alluvial loam underlain at depths ranging from 1 to 3 feet by deposits of volcanic cinders. About one-forth of the land is under cultivation ancl the remainder is covered by a fairly dense growth of a low tufted grass. A motlerately heavy forest of western yellow pine, opened in places by light cuttings, surrounds the park. The timber almost invariably occurs at a slightly higher elevation than the acljacenb park land. In Flaces the timbered area rises from the edge of the park in a very gentle slope, while in other places there is a rather abrupt rise of 25 to 100 feet. Occasionally narrow, slightly elevated tongues of timbered land estend out into the opening a distance of 4 to 4 mile, and in two instances sniall isolated patches of trees occur on slight eminences well out in the park. The park and the surrounding timbered areas present the appearance of a partial basin. From 3 to 3+ miles north and east of the park begin the steep slopes of the San Francisco Mountains which, in a horizontal distance of from 1.9 to 2.5 miles rise from an elevation of 8,500 feet to an elevation of 12,340 feet, or approximately 5,000 feet above the level of the park. Minor peaks in the vicinity are Wing Mountain, about 2 miles northwest. and A-1 Mountain, at the southern edge of the park, with elevations of 5,500 and 8,300 feet, respectively. On the south and west sides the steep timbered slopes rise 200 or 300 feet above the park to a level mesa which here forms the rim of the basin. The climate of this region which is fairly typical of the higher altitudes of Arizona and New Mesico, is characterized by great daily ranges of temperature and very marked seasonal variations in precipitation, atmospheric moisture, and wind movement. Owing to the rapid radiation incident to high altitudes the change of temperature from day to night is very great, occasionally amounting to 80”. The precipitation occurs mainly during the summer and winter months, the former season esteiirling from about July 15 to September 10, and the latter from December to March, inclusive. During the summer rainy season, showers are very frequent ancl the relative humiclity is usually high. During the winter months the precipitation is mainly in the form of snow, which frequently accumulates to a depth of 3 or 4 feet. As a rule but little precipitation occurs from April 1 to Julyl, and tlie wind movement aiicl evaporation during these months are estrrmely high. This period is estremely trying on vegetation, especially forest seedlings which have not become well establisheil. d similar, though unusually much less severe, period of droughtr estencls from about September 10 to December 1. Three meteorological stations were estal)lished on the western side of the Fort Valley park at which daily readings of temperature, precipitation, relative humidity, and wind movement have been made since January 1, 1909. Evaporation readings were also taken at a11 three stations from July 1 to October 31, 1909. Station No. 1 is located in tlie edge of a projecting point of tinil>er on the west side of the park, a t an elevation of 7,261 feet. Tlie station is equipped with masimuni ancl mininiuni thermometers, psychrometer, anemometer, wind vane, recording rain gage, and one evaporating pan. This station is protected by timber on the west ancl northwest, but receives the full force of the wind from other directions, especially the southwest, which is the prevailing wind direction in this region. Station No. 3 is situated in the park 843 feet southeast of station No. 1, at an elevation of 7,317 feet. The instruiiiental equipment consists of niasimum and niinimuni thermometers, psychrometer, anemometer, rain gage, and evaporation pan. Station No. 3 is in a virgin stand of western yellow pine, 1,453 feet! west froni the edge of the park at an elevation of 7,345 feet. The equipment is the same <as at station No. 2. At each of these stations the thermometers are esposed in louvered slielters, 4 feet above ground, and the anemometers are placed S feet above ground. The instruments were placer1 near the grouncl as it was desired to determine the conditions to which seeclliiig growth is esposecl. A t the forest station the soil is a retlclish, loaiiiy clay, inked with large volcanic boulders and the grounrl cover consists of a sparse growth of grasses and other herbs. Practically no leaf litter is found beyond 30 feet from the trees. Tlie instruments are set in an opening 164 feet in diameter and are 66 feet from the nearest trees. All of the instrunieiit stations are sit.uatec1 slightly above the immediate surrounding country in order to secure good atmospheric drainage. The instruments have been read claily between 4 and 5 p. ni. To determine whether or not the temperature conditions observed at stations 1, 3, and 3 were typical of the whole park and the adjacent timber on both sides, three temporary stations were establishecl a t which records were taken from January 25 to Feliruary 20, 1910. One of the stations was near tlie niitltlle of the park, one-half mile east of station No. 2, at an’elevation of 7,346 feet; another was in the park, 725 feet from the timber on the eastern side, elevation 7,364 feet, ancl the third was in a virgin stand of yellow pine 1,617 feet from the eastern edge of the park, at an elevation of 7,330 feet. Temperature records were obtained at these stations by means of thermographs checked by masimuni and minimum thermometers, and indicatecl practically tlie same relation between forest and park teniperatures as was found at the stations on the western side, escept that on the eastern side the claily maximum temperatures were slightly higher in the forest than in the park, while on the western side the reverse was the rule. At these temporary