Fire Hazard Warnings

New Zealand Journal of Agriculture, Volume 91, Issue 4, 15 October 1955, Page 363

Fire Hazard Warnings

"II is a message from the Forest Service.". These now familiar words are often II heard over the air during spring, summer, and autumn, with warnings of fire hazard in various parts of the country. This article by W. F. Wright, Fire Control Officer, New Zealand Forest Service, explains the circumstances which prompt these warnings and emphasises the need for constant care to prevent forest fires.

THE radio messages issued by the Forest Service are usually heard when the national stations are linked for the weather forecast, which most country people tune in to hear. Hence, one can be sure that the greatest number of people hear that there is acute danger of forest fires, say, in the southern lakes districts. Though this may not rivet the attention of listeners in Northland, where it may be raining at the time, they cannot help hearing about it. Two objects are thus achieved: — 1. Southlanders are warned of the fire danger. 2. Northlanders are reminded about the business of fire prevention. These messages are normally heard on the national link for two or three days in succession, and then there may

be silence for a while. This will not mean that the fire danger in Southland has passed. Warnings may still be issued from a local broadcasting station. The national link is used sparingly, for emergency purposes only, in the hope that such warnings will command the attention of all listeners. . Farmers' Use of Fire It is often asked why a Forest Service officer should be better than an experienced farmer in judging when it is safe to burn. It is a matter of approach and special techniques. There are still many farmers who must use fire to some extent. Each has his own special problems with this country’s complex climate and topography. Farmers understandably enough tend to view matters accord-

ing to their special needs, and from the nature of their calling are strongly individualistic in outlook. The farmer must often burn to clear rubbish on rough grazing country or to prepare land for sowing. If he is not allowed to burn when he thinks the conditions are right for him, his programme is sometimes upset and very understandably he is displeased. A forest officer is a member of a service which has. the statutory responsibility to manage the national forests for water and soil conservation, the maintenance of scenic and recreational amenities, and the production of timber. Any form of forest management or preservation would be impossible under New Zealand conditions without the power to control the use of fire within forests and on adjoining lands. A forest officer therefore thinks in terms of fire control and is sure that it is in the national interest that he should do so. The Forest Service also has a responsibility to warn other rural fire authorities when a fire hazard exists in any area.

Happily there is now a much better understanding in most districts between the farmer and forester about fire control, and relations are now generally cordial. It is certainly the policy of the Forest Service that they should be so. However, the farmer as a rule is not now the main problem in fire control. Rapidly expanding urban communities in their contacts with forest and rural areas pose the problems. Fire Hazard Prediction In New Zealand all . rural fires are caused by human action in one way or another. Dry lightning, a major cause of forest fires in many countries, does not occur here. Trees are set on fire, yes, but not forests, because lightning is usually followed by rain here. This being so, a forest officer in discussing fire control can never resist an opportunity for anti-fire publicity. He will always try to influence people to be careful with fire. How is fire hazard predicted in this capricious climate? The story goes back 30 years or more to the United States of America, where there had been a long period of appalling forest fires. The Pesktigo fire in 1871 in Wisconsin, for example, destroyed 1,280,000 acres of forest and burnt 1500 people to death. The forest services of the U.S.A, and Canada put research teams on to looking into the causes of forest fires,, and a number of principles were established for the control of rural fires. This article is concerned only with those relating to weather and fire behaviour and the techniques developed for the prediction or assessment of fire hazard conditions. As any hill country farmer knows, fire rarely behaves in the same way for two days running, even when all the conditions appear to be similar. A sluggish burn one day may be followed the next day by a fire which will bring along a forest officer with a what-do-you-think-you-are-playing-at expression on his face. The data used in fire hazard prediction are: —■ 1. Number of days since ,25in. or ,50in. of rain. 2. Moisture content in forest litter, dead scrub, and bracken. 3. Air humidity. 4. Temperature. 5. Wind force. ' 6. Condition of vegetation in open country. When the air humidity is very low it is the most important factor of all. With very dry air almost any form of forest vegetation will burn. An example of such “blow-up” conditions occurred in 1937, when 4000 acres of virgin rimu-matai-totara forest in the Tongariro National Park locality literally exploded. Rainfall, temperature,

and wind are recorded in the usual way. Air humidity is measured by an instrument called a psychrometer, which is simply a pair of “wet” and “dry” thermometers coupled together. This instrument is revolved in the air and the thermometers are read against a set of tables to find the air humidity. The moisture content of forests is found by specially prepared pieces of wood called indicator sticks. These register changes in the fuels due to the combined effect of temperature, humidity, rainfall, and wind. One stick jin. x jin. represents quick-dry-ing fuels such as bracken, manuka, and dead litter in the open. The second stick 2in. x 2in. simulates the cumulative effect of the same factors on heavier fuels. The sticks are weighed on a scale which registers the moisture present in the fuels as a percentage. These data are then correlated by a set of tables or meter on the slide-rule principle, in which the several factors are given weighted values according to their relative importance in fire behaviour, to give one of nine ratings of fire from 0 to 9, where 9 is extreme danger. Readings from 40 fire-weather stations maintained by the Forest Service

are radioed twice daily to the head office of the Service during the fire season. When the readings from a district give a rating of 6, considerable danger, or higher the Weather Office is asked for a forecast for the district. If this is not reassuring, the familiar “Here is a message from the Forest Service” is heard at the time the national weather forecast is broadcast.

Government-approved Turnip and Swede Seed NEW ZEALAND Government■L ’ approved. turnip and swede seed for distribution this year has, as previously, been made into a single blend for each variety and packed in lib. and 21b. calico bags. With two exceptions the germination of all varieties being distributed in 1955 is over 90 per cent. Germination of the exceptions, N.Z. Grandmaster swede and N.Z. Purple Globe turnip, is 88 per cent, and 87 per cent, respectively. All packages of Governmentapproved turnip and swede seed being distributed to retailers' this year carry the letter A as an identification mark.