20 TECHNICAL PROPERTIES OF WOOD. 



timber than the longitudinal growth, and usually culminates 

 later than it, hut continues longer, only terminating \Yitli the 

 death of the tree. 



The quality of the locality, especially depth of soil, is the 

 chief factor determining the amount of height-growth ; the 

 diameter-growth depends also on the amount of light to which 

 the crown of the tree is exposed. 



As regards the absolute dimensions of the trees now produced in 

 forests, it may be said as a general rule for Germany, that owing 

 to short rotations, the large timber formerly available is no 

 longer produced. Trees from 130-150 feet high are becoming 

 rarities, and chest-high diameter measurements of 12-lG inches 

 are the average sizes of timber. Anything over 16 inches in 

 diameter may be styled large timber. In some districts, trees 

 measuring 12-14 inches are already classed as large timber. 



In order to produce fine timber, both as regards length and 

 diameter, trees should be grown in crowded woods until the 

 principal height-growth has been attained, which will be at 

 about the middle age of the tree ; the wood should then be 

 heavily thinned so as to afford room for the crown and roots 

 to develope and thus secure a good diameter-increment, care 

 being taken to keep the soil well covered with undergrowth. 

 Good localities and long rotations should also be selected, and 

 only trees grown which naturally produce large timber. 



(b) Straightness of Stem. — The axis of the stem of a tree may 

 or may not be in one plane, and if in one plane, it may be in a 

 straight line in that plane. In the latter case the stems are 

 straight, the spruce, silver-fir and larch being the straightest 

 trees, ^and after them the Weymouth-pine, alder and sessile 

 oak. When the axis lies in a plane but not in a straight 

 line, the timber is said to be curved, and may be useful in 

 shipbuilding and some other industries. 



Timber, the axis of which is not in a plane, or crooked 

 timber, is of little use except for fuel. 



Density of growth has the greatest influence on straightness 

 of stem. Most broad-leaved species and the Scotch pine which 

 in the open are frequently crooked, when grown in dense woods 

 yield straight timber resembling that of the spruce and silver- 

 fir. Beech, sycamore, sessile oak, ash, and hornbeam, gain 



