Some Characteristics of Heath Fires in North-East Scotland

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Abstract
The course of temperature in fires burnt in the autumn and spring respectively in mature (15 years) and over-mature (25 years) Calluna heath in north-east Scotland was monitored and recorded using thermocouples and a recording potentiometer. Characteristics of the stands, the amount of available fuel, and the weather conditions at time of burning, were noted. Two fires were burnt in the autumn under dry, windy conditions in Calluna about 15 years old. Available fuel was 15900 kg ha-1, of which 93% was burnt. The 1st fire at its maximum intensity (estimated from the heat of combustion, rate of spread, and fuel consumed) produced approximately 7500 gcazl sec-1 cm-1. In the 2nd fire the temperatures (c. 500[degree]) in the crown of the vegetation were high, but the surface temperatures were low (c. 60), and these temperatures were maintained for short periods only (c. 30 sec). Both fires removed all the longer Calluna stems and the regeneration of Calluna after the fire was vigorous. Several fires were burnt in the spring under cool, moist conditions in over-mature heather about 25 years old with 23200 kg ha''l of available fuel. The burns were very Incomplete only 30% of the fuel was consumed and the crown and surface temperatures were low (c. 250[degree] and ambient to 100, respectively) . The ensuing regeneration was poor. The ineffectiveness of the fires burnt in the spring is attributed to stand structure, lower wind speed, high moisture content of the Calluna, and generally wetter conditions associated with the cool damp weather.

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