TKEES FOR WATER CATCHMENT AREAS 165 



With all these merits, there are difficulties in the 

 cultivation of black Italian poplar as a forest tree in 

 plantations, whether pure or mixed. Like all poplars, it is 

 unable, after the first few years, to bear the slightest shade, 

 the whole crown of foliage requiring full light ; and each 

 stem in consequence needs a large space for its proper 

 development. Mixed with other species in a wood, black 

 Italian poplar ultimately occupies an enormous area, over- 

 topping and injuring the neighbouring trees. It is useless 

 to plant it with other species, unless the latter is to 

 constitute an underwood. It has been suggested to plant 

 poplars 15 to 20 feet apart, and to fill up the intervals 

 with alders ; but the latter would make poor growth in 

 this mixture unless the soil were good and deep. In a 

 pure plantation of black Italian poplar, only the outer trees 

 that are fully exposed to the light make large dimensions, 

 the interior trees remaining small in diameter and of little 

 use as timber. This might be obviated by severe thinnings ; 

 but these would be of no saleable value, and the number of 

 stems left standing would be so reduced as to yield only a 

 moderate volume per acre. Large plantations of poplar are 

 rarely seen in this country, and actual measurements are 

 still rarer. At Benefield, Northamptonshire, 321- acres of 

 strong clay land, practically useless for agriculture, were 

 planted in 1887 with black Italian poplar, 538 to the acre. 

 In 1916 there were 206 trees per acre surviving, which 

 when felled averaged 45 feet of timber length and 24 

 inches girth at breast height, the total volume being 1300 

 cubic feet (quarter -girth measurement) per acre, or an 

 average annual increment of 45 cubic feet per acre. 



Plantations of black Italian poplar contain a much 

 smaller volume of timber than is generally expected ; and 

 in land where any of the vigorous conifers, such as Sitka 

 spruce, Japanese larch, etc., can be grown, cultivation of 

 poplars would be a failure financially. Black Italian poplar 

 should be restricted to situations where it is impossible to 

 establish conifer plantations ; and in such cases the best 

 method is a combination of meadow or pasture with poplars 



