Temperature-time curves at the soil surface in maquis summer fires

Abstract

Many summer fires in Valencia are enhanced by the abundance of maquis. Nevertheless, fire field studies on the soil temperature–time curves under summer conditions with controlled amount and structure of fuel are scarce. Experimental summer fires were conducted to analyse the influence of the fuel load and the fuel structure on the soil temperature-time profiles.

The increase of fuel load from 2 to 4 kg m^–2 increased the net radiant heat per unit area (5691 to 11263 kJ m^–2), the total duration of heat (190 to 396 min) and the duration of temperatures greater than 100ºC (19.8 to 35.9 min) whereas the peak temperature increased 100ºC (from 416ºC to 516ºC).

Variations of fuel height from 1.5 to 0.75 m and bulk density from 2 to 4 kg m^–3 respectively, increased net radiant heat per unit area, H_p/a (6510 to 10 444 kJ m^–2), t_total (219 to 375 min), and t_>100ºC (9.7 to 36. 1 min) whereas T_max increased 40ºC (446 to 486ºC).

At plot scale, fire intensity and severity will increase with the fuel load. At plant scale, more degradation will occur in the soil patches with higher bulk density, mainly because an increased duration of high temperatures in soil. Fuel amount and structure are then key factors in maquis fires since they will determine the post-fire patchiness of soil conditions and plant recovery.