8 



Permanent mixed woods have certain advantages over pure woods. 



(a) Whenever the area to be planted is of any considerable extent, and in the 

 hills of Jamaica, even if such area be of small extent, there are many variations 

 of soil and situation ; and in order to utilise the soil in the most economical way, 

 each small spot should be planted with a species which suits it. 



(6) There are comparatively few species of trees that are suitable for pure woods. 

 Many most valuable timber trees are not dense enough in the crown to preserve 

 the soil, and only make fine boles giving large-sized timber when they are planted 

 with others which bear a dense mass of foliage. 



(c) Many species suffer less from injurious influences, such as wind, insects, 

 fungi, if mixed with other species. 



Shallow-rooted species are not so easily thrown by wind if intermixed with deep 

 rooted trees. What Fream says of agricultural crops is applicable also to woods. 

 " Side by side with the excessive, or exclusive, cultivation of one kind of plant, 

 the pests — whether insects or fungi —which prey upon the plant may be expected 

 to become more abundant, for they find their victims literally crowded together, 

 and therefore extremely accessible. " For instance, in Hong Kong the pure woods 

 of Pimis sinensis were threatened with extermination by an insect pest which 

 would not have been so dangerous in a mixed forest ; and as another illustration, 

 the leaf-fungus that destroyed the coffee in Ceylon would probably not have done 

 so much damage if the fields had been in smaller patches separated by woods or 

 shelter belts of tree. 



FORMATION OF MIXED WOODS. 



In forming a mixed wood, the most numerous trees should be shade-bearing, 

 that is, have dense crowns giving ample shade and plenty of fallen leaves, so 

 improving the soil. 



Different species of shade-bearing trees may be grown together, provided they 

 grow at about the same rate; or when the slower-growing species is protected 

 against the quicker growing by giving them a start or by allowing it to form the 

 great majority of the crop and later by lopping or cutting out the other species of 

 trees threatening to suppress it. 



Shade-bearing trees may be mixed with light demanding thinly-foiiaged trees, 

 if the latter are of quicker growth, or are given a start, and are less numerous than 

 the shade-beariDg trees. 



Two are more light- demanding species should not be planted as a mixture with- 

 out shade-bearing trees, as the soil deteriorates ; except in very fertile spots, or in 

 places with such poor soil that nothing else will grow, or when the timber is cut 

 at short intervals, or when one species is used to protect another slow growing 

 species. 



The species are to be mixed by groups or by single trees according to circum- 

 stances. Two shade-bearing species growing at the same rate may be mixed by 

 single trees, unless the soil, etc., varies, suiting one species in one place and another 

 in another. The least numerous species are, as a rule, to be introduced individually, 

 unless the quality of the soil is variable, so that patches here and there specially 

 suit one particular class of tree. 



SYLVICULTURAL SYSTEMS. 



There are several methods of making, renewing, and tending woods which are 

 adopted accoi ding to varying circumstances, whether the forest is intended for large 

 timber and renewed by seedlings, or to be cut at short intervals as coppice, or a 

 combination of both, and whether the new wood is created on a clear cutting or 

 under the shelter of existing trees . 



Where a wood is formed in a clear cutting in high forest, the young trees are 

 all about the same age and height, and as soon as the branches meet they form a 

 continuous leaf canopy overhead so that the sunlight reaches only the upper parts of 

 the crown. This favours the quickest growth in height and formation of clear 

 boles without branches. If the trees are judiciously thinned so that they are 

 encouraged to grow almost to their full height, and then thinned strongly to allow 

 of the full development of their crowns, they will ultimately increase in diameter, 

 and form long clean boles of considerable thickness, — the best condition for timber. 



Sometimes instead of making a clear cutting, some of the old trees are left to 

 shelter the seedlings which either spring naturally from the seeds that have 

 dropped from the mother trees, or have been transplanted from nursery beds, or 



