270 SYLVICULTURE IN THE TROPICS pt.iv 



possible, fire-lines along the foot of a very steep slope or 

 along bottoms of ravines should be avoided, owing to the 

 difficulty of burning the fire-lines without setting fire 

 to the overhanging mass of vegetation. 



As regards the width to be given to the guide-line, it 

 will depend chiefly on the nature of the vegetation to 

 be fired, on the trace, on the strength of the prevail- 

 ing winds, on whether the trace is cut in the direction of 

 these winds or across them, and also on the composition 

 of the soil and on the gradient. 



It is by no means necessarily the tallest grass that is 

 most readily inflammable. In such grass the flames 

 ascend to a greater height and sparks may be carried 

 farther, but the flames usually progress comparatively 

 slowly among the giant grasses or sedges ; it is the 

 short, wiry, rather sparse grass along the tops of which 

 the fire will run, sometimes with great rapidity. Such 

 grass is often found on sandy soils which, owing to their 

 loose texture, are full of air, and on getting warmed fan 

 the flames to still greater activity. When a fire-line is 

 cut across the direction of the prevailing wind, it may be 

 necessary to make the guide-line to leeward of the trace 

 wider than that to windward of it. In the same way, 

 when the line crosses a steep slope horizontally or 

 obliquely, it may also be advisable to make the upper 

 imide-line broader than the lower. Thus local circum- 

 stances and a knowledge of them must help in deter- 

 mining their width. For ordinary purposes, however, 

 the width of the guide-lines may be taken as more or 

 less equal to the height of the adjoining grass increased 

 by 1 metre (3 ft.). 1 ' 



The width of the trace will also depend on the 

 factors stated above, on the amount of labour avail- 

 able in case of an outbreak of fire, and, in the case of 

 exterior fire-lines, on the nature of the surrounding 

 country. If cultivation, or land bare of vegetation, or 

 green pastures extend right up to the boundary of the 

 forest, the same width of line will not be required as 



1 Fernandez, op. rib. p. -lis. 



