C.—3

3. Fire Districts. The area subject to forest-fire-district legislation was increased during the year by 80,000 acres, bringing the total area so protected up to 3,203,558 acres. During the year consideration was given to several proposals to increase this area in a wholesale manner by the issue of " blanket " proclamations over very large areas of unsettled or sparsely settled countryside. The proposals were finally rejected, because the essence of effective fire-district protection is intensive administration. Proclamation of fire-district restrictions in remote country where no patrolman could penetrate except at irregular intervals, and where no protective force could be assembled to deal with the occasional fire which does occur, would have the effect of making the law a dead-letter : and it has been deemed preferable to confine proclamations to areas where there is reasonable chance of enforcement of the preventive provisions. Plate No. 16 is a reproduction of a map of the fire districts near Rotorua and Taupo, and is published to direct the attention of the public to their obligations in that locality. 4. Fire-control. Up to the present time it has been customary for forest officers to rely wholly on their local experience in deciding whether or not danger from fire is likely to arise. As an index of inflammability in the forest the feel of moss and other types of fuel has commonly been used, but, owing to the rapidity with which conditions have recently been shown to change from relatively safe to very unsafe, it has been necessary to develop a more scientific approach to the determination of relative fire hazard. While ordinary meteorological equipment is of considerable use in this connection, it has been found necessary to supplement the usual rain-gauge and wet and dry bulb thermometers with specially-designed psychrometers and moisture-content-indicator scales, the purpose of which is to measure directly the moisture content of various types of forest fuel by simple weighings of specially prepared " fire sticks " representative of each type of fuel. Equipment for twenty stations has been secured and is now in course of erection. Plate No. 18 shows a louvred shelter within its fenced enclosure which also protects the rain-gauge and the " fire sticks " resting on wires several inches off the ground. In the interior of the louvred shelter the special psychrometer with its wet and dry bulb thermometers and the small hand-driven fan for drawing air across the bulbs may be seen at the right hand side. At the left side is mounted a moisture-content-indicator scale on which the " fire sticks " are periodically weighed, while in the centre may be seen a hygrograph recording graphically wet and dry bulb thermometer readings. Factors conducive to fire hazard are : — (a) Absence of rain—measured by rain-gauge. (b) Low relative humidity—figures obtained from tables using the dry-bulb temperature and the " depression of the wet bulb " induced by a draught of air over the bulb. The thermometers on their mount may be whirled, as in the wall-mounting psychrometer, or the requisite air-current may be produced by a fan, as previously described. (c) Warm temperatures —recorded by the dry-bulb thermometer of the psychrometer. (d) Wind —the Beaufort scale estimates may be supplemented by anemometer readings. Evaporation and rate of fire-spread increase with the wind velocity. (e) Fuel inflammability—a product of the foregoing interrelated conditions. The wood of which the " fire sticks " are made becomes wet during rain, dries out slowly under calm warm conditions, but very much faster with wind, and follows closely the variations in the relative humidity of the atmosphere. It represents as nearly as possible the scrub, fern, and dry timber in which outbreaks of fire commence. Readings of relative humidity taken thrice daily generally indicate the approach of dangerous conditions, the " fire sticks " recording their cumulative effect. The

3—C. 3.

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