DROUGHT. 517 



clearings, as in the latter case dew and rain have more access 

 to the soil. When once a planTiation has closed in, so as to 

 cover the soil completely, the chief danger from drought is 

 over; but occasionally spruce poles have been killed by 

 prolonged drought, 



(c) Locality. — In plains and hilly lands, the danger from 

 drought is greater than in mountains where the most 

 extensive forests are found, as then damper air, more 

 frequent precipitations and raoister soil prevail. Eegions 

 over 1,500—1,800 feet altitude have little to fear from drought. 

 Small flat hills and narrow ridges suffer most of all. 



As regards aspect, the southern and south-western slopes 

 suffer most from drought, and the northern slopes least of 

 all. Ill very narrow valleys which have been cleared of 

 trees, or are scantily wooded, the reflection of the heat from 

 side to side greatly increases its eflects, and rows of houses 

 have the same eft'ect on street-avenues. 



As regards soils, woods growing on calcareous soils, and 

 especially on stony superficial soils above calcareous rocks, 

 sufler most from heat ; then those on stiff clays, whilst sandy 

 soils are more favourable as regards drought, especially when 

 the grains of sand are fine ; woods on sandy loams and loams 

 stand drought best of all. This is due to the following 

 causes : poor shallow calcareous soil is not retentive of 

 moisture, while the porous rock beneath it drains away water 

 rapidly from the surface ; marls and clays become hard when 

 exposed t5 heat and crack in all directions ; coarse sands 

 suffer more than fine sands on account of the greater capil- 

 larity of the latter, which attracts water from below ; loams 

 readily al^sorb rain, dew and snow-water, and retain moisture 

 in the subsoil, and can, therefore, easily replace the loss of 

 the surface-water. 



{d) Soil-covering. — Weeds, and especially a dense tall growth 

 of grass, increase the dangers of drought, filling the soil with 

 their roots and absorbing and transpiring its moisture, which 

 would otherwise be available for the woody plants growing in 

 or above the grass. A light covering of isolated shrubs, on the 

 contrary, may prove beneficial by shading the valuable species. 



Leaves and moss and the humus resultinji ivoni tiieir 



