No remarks seem called for with regard to these last experimental results; for the figures speak clearly for themselves, and the reader can see at once what is represented by the different columns from the headings written on them. Such information has a great practical value. For example, generally speaking, if a piece of Oak of 100 years' growth weighs 35 lb. with the bark on it, it will weigh only 31 lb. after the bark is taken off it. Again, it is shown that 1 cubic ft. of Oak, of the age stated, weighs 90 lb. with the bark on, and only 81 lb. with it off, thus giving the weight of bark that may be expected from such timber per cubic foot in the green state. Or again, 27ğ ft. of unseasoned Oak of 100 years, with the bark off, make 1 ton; hence a wood-merchant, in removing such timber, could only take about this number of feet on one cart as a load. Such a consideration proves the great advantages resulting from the conversion of timber on the spot, as it is further shown that after the same timber is manufactured, although still in the green state, no less than from 32 to 36 ft. of it can be conveyed by one horse, as 1 ton weight; and this makes a difference of 7 ft. to the ton on the average in favour of the converted timber. But a still greater difference is obtained by having the timber properly seasoned before it is removed to a distance. This is shown in the two last columns with reference to Oak of 100 years; for in these it is stated that although from 32 to 36 ft. of the converted timber may be taken as a load of 1 ton weight while the wood is unseasoned, yet when it has been seasoned, no less than from 42 to 54 ft. can be taken. These are facts worthy of the notice of all interested in the utilisation of timber, and may be strongly recommended for study. These tables are simply the results of investigations in one particular locality, and can hardly be taken as anything more than mere approximations regarding the weights of the different classes of wood. produced in different parts of Britain. In order to secure sound and reliable general information on such points, foresters generally will have to make similar experiments in all parts of the country, so as to ascertain the weight of the different kinds of timber per cubic foot, the number of feet that go to a ton, both in the round and after conversion, &c. In making such experiments, however, additional data of various kinds might advantageously be noted. For example, in making experiments with regard to the weight of the timber of any particular kind of tree, it would be advantageous to state the character of the land on which it grew, its aspect, whether a hillside or a flat, the elevation above the sea, whether the land has been drained or was naturally dry, the exact age of the tree on which the experiment was made, its dimensions, and whether it grew in a crowded plantation, &c., &c.; for the weight of any given kind of timber is much influenced by the nature of the land on which it grows, by the aspect of the situation, as well as by the absence or presence of much direct sunlight on the stems and branches, and also by the degree of moistness or coldness of the subsoil. To make complete and satisfactory experiments on this very interesting branch of forestry, therefore, all these points should be kept in view by the investigator; and, if possible, the experiments should be made on each kind of timber, at all ages, from 10 years old up to 100 years. The Technical Qualities of Timber1 are dependent on the amount and nature of the woody fibrous tissue or solid woody substance, on the quantity of water contained, and on the quantity and nature of the matter held in solution in the water. The walls of the cellular tissue and the deposits contained by them consist of Cellulose so long as they belong to the cambium of the shrub or tree; but when they pass beyond the sphere of cambial activity, they gradually become thickened by lignified deposits and form Lignin. The former is much more supple and permeable for fluids, whilst the latter is stiff, hard, and less hygroscopic. In some softwoods there is no hard and fast division or line of demarcation between the sapwood or alburnum, and the heartwood or duramen, such as exists among the hardwoods (Oak, Ash, Elm, &c.). The timber of the softwoods is therefore, as a rule, less durable than that of the latter class, in which the heartwood becomes very hard and heavy through gradual and continuous thickening of the cell-walls by means of ligneous deposits. The quantity of water contained in unseasoned wood amounts in general to about 45 per cent. of the total weight; but, of course, it varies according to (1.) The species of tree. (2.) The portion of the tree. (3.) The nature of the soil and situation; and (4.) The time of the year at which the timber is felled. In general the deciduous trees contain much more water than conifers; whilst trees felled in autumn contain least water, and those felled in the early part of summer most. According to Professor R. Hartig's experiments, the following appear to be the times at which the maxima and minima of water are to be found in the trees : 1 For a full and masterly treatment of this subject, the attention of the student is directed to Gayer's Forstbenutzung, of which the eighth edition will immediately appear. The editor hopes shortly to bring out an authorised translation of this work in English, as well as of Gayer's other great masterpiece, his Waldbau or Sylviculture. With regard to differences of colour between the sapwood and the heartwood, Gayer classifies the various species of trees as follows :— I. Heartwood Trees, exhibiting marked differences in colour between the duramen and the alburnum: Oak, Chestnut, Robinia, Ash, Elm, Poplar, Willow, Yew, Juniper, Arborvitae, Scots Pine, Mountain Pine, Weymouth Pine, Cembran Pine, Black Pines, and Larch. II. Intermediate Trees, exhibiting no marked differences in colour, but distinctly differing with regard to the quantity of water respectively contained: Spruce, Silver Fir, Beech. III. Sapwood Trees, in which there is no duramen differing from the alburnum either in colour or in the quantity of water contained: Birch, Lime, Alder, Maple and Sycamore, Hornbeam, Aspen. The general proportion which exists between the respective amounts of timber, branchwood, and brushwood in woodland crops varies according to (1.) The species of tree. (2.) The density of the crop. (3.) The age of the crop; and (4.) The nature of the soil and situation. Among the broad-leaved trees the most regular stems are formed by Alder, Oak (especially the sessile Oak), and Ash, then by Birch and Aspen; but the Conifers generally, and more particularly the shade-bearing genera, Spruce and Silver Fir, surpass even the light-demanding broad-leaved trees in their tendency towards the formation of a good bole. As a general rule, the greater the density of crop, the larger will be the proportion of timber, and the smaller the relative proportion of branchwood and brushwood. Hence crops grown rationally in high timber forest must produce a larger proportion of long logs than is obtainable from standards or coppice. In young woods the proportion of timber is of course small; but as the crops approach maturity the percentage of branchwood and brushwood decreases in woods that are managed on true sylvicultural principles, so that, in general, in crops of most species of trees which have been subjected to rational treatment, the percentage of timber contained in the stem amounts to from 80 to 90 per cent. of the total yield of wood. And as regards the nature of the soil and situation, the percentage of timber contained in the stems of the trees forming the crop is more or less directly proportional to the quality of the land. The percentages of the different classes of wood yielded at an advanced age by the various kinds of high-timber forest-crops, of normal density, and growing on favourable soils and situations, is as follows (Gayer, op. cit., p. 17): The percentages yielded by standards in copse is, according to Lauprecht, as follows: : These figures must of course be taken as mere approximations, subject to subsequent corrections before they can be applied to British forestry. With regard to the straightness of the stems, the various species of trees exhibit characteristic differences. The straightest boles are formed by Spruce and Silver Fir, and in a secondary degree by Scots Pine, Weymouth Pine, Alder, and sessile Oak. But, as is self-evident, the density of any given crop exerts a very decided influence on this particular matter with regard to most species of trees. Hence Scots Pine, Beech, Maple and Sycamore, Oak, Ash, and Hornbeam all gain in this respect by being grown in such density of canopy as does not absolutely interfere with the performance of their normal vegetative activity in assimilation and in the production of woody-fibrous tissue; whilst, at the same time, the freedom of the bole from branches and knots is directly dependent on the density of canopy that is maintained in any given crop. The importance of these two considerations can hardly be over-estimated with regard to the technical value of the timber for general purposes, which usually determines its financial or market value. The relative proportion of the top end of the bole, as compared with the butt end, is practically one of the other essential points that fix the selling-price of timber; hence whatever sylvicultural measures can be adopted to raise the form-factor of the stems forming the growing-crop must be worthy of the most careful attention of the forester, as well as the general method of stimulating the increment on timber crops approaching maturity by means of partial clearance and underplanting, when once they have completed their main growth in height after being maintained in normal density of canopy throughout all their previous stages of development.1 The investigations of Sachs and R. Hartig have shown that there is no marked difference between the specific weight of the woody tissue of the chief species of wood, but that it is about 1.56, no matter whether the tests be conducted on Oak, Beech, Birch, Spruce, or Pine, or whether the woody tissue be taken from the sapwood or the heart. But, so far as the actual quantity of woody-fibrous tissue per unit of volume is concerned, the various species of trees show great differences, as broad-leaved trees contain in this respect from 25 to 30 per cent. more ligneous matter than conifers. The energy of growth of the trees, however, on which the amount of ligneous matter deposited essentially depends, is itself dependent on many factors connected with the soil and situation, and the amount of light and warmth available for the individual stem. The following table, taken from Gayer (op. cit., p. 27), may be convenient for a comparison of the average specific gravity of the wood of broad-leaved trees with that previously given for the coniferous species of timber (see vol. i. chap. iii. p. 331) and with Rait's data given in Table I. on p. 263 of this volume: : After seasoning, therefore, the following classification of woods may conveniently be made as to their weight for purposes of conveyance and utilisation: Very heavy (sp. gr. 0·75 or above): Turkey Oak, Yew, Pedunculate Oak, Ash, and Heavy (sp. gr. 0·70 to 0.75): Sessile Oak, Hornbeam, Robinia, Pear-tree, (Teak), Beech. Very light (sp. gr. under 0.55): Alder, Willow, Scots Pine, Aspen, Black Pines, Poplar With regard to hardness, Nördlinger classifies the different kinds of timber as follows: Hard: Robinia, Maple and Sycamore, Hornbeam, Wild Cherry, Yew, Pedunculate Oak. Soft: Spruce, Silver Fir, Horse-Chestnut, Alder, Birch, Hazel, Juniper, Larch, Black Very soft: Weymouth Pine, all Poplars, most Willows, and Lime. 1 A detailed account of this operation will be found in the editor's Studies in Forestry, 1894, chap. x. |