This section is from the book "Tree Planting For Timber And Fuel", by C. B. Mcnaughton.
The scheme itself is one to be highly commended not only for the certain economic advantages, but also for the indirect benefits that the establishment of a large plantation of selected timber trees will ensure.
In the recommendations made by the Committee of Experts specially appointed in January last to inquire into and report on the subject of British Forestry, is seen the following :—
"That the attention of corporations and municipalities be " drawn to the desirability of planting with trees the catchment areas of their water supply."
This recommendation coming from the leading authorities as it does, requires no explanation or endorsement, for its arguments, generally widely known, are irrefutable. The Town Council at Oudtshoorn do not intend at present to plant upon the catchment area of their supply, but rather land available below the intake of their pipe system. The work however, will prove a highly valuable object lesson to the country in as far as it will shew the effect of afforesting a catchment area which serves farms situated below the Town Council property in the same valley—farms which are said to be at present insufficiently supplied with water at certain seasons owing to the town servitude on the main source of supply. The successful establishment of such a plantation should prove of great service in the encouragement of tree-planting on an extensive scale in a district where so much in this direction should be done, and I would strongly recommend that the scheme should be supported in every way by Government both in regard to grants possible under Act 4 of 1876 and to advice and general assistance in the carryings out of the project. Personally my services, with the sanction of Government, will always be readily given when possible. As this report is intended to be only of general assistance in the establishment of a plantation under conditions which are perhaps not altogether similar to those which any practical example in the Colony has experienced, and further as the work must necessarily be left in hands possibly not highly experienced in the introduction and establishment of timber exotics, a few remarks on the general laws which govern such introduction may not be out of place, so before making any special recommendations I have inserted a short resume of such general sylvicultural principles as may be of interest, and a few notes on the forest nursery including seed germination and the handling of transplants.
In the introduction of exotics a main point to be considered is the temperature of the atmosphere during the growing season of the year, indeed a knowledge of the summer mean is almost fundamental. Forest species may be grown far from their natural habitat provided that the local climate is similar to that to which they are naturally accustomed. To some extent differences in aspect and soil locality may compensate for certain differences in climatic conditions.
Such as the introduction on a warm and dry aspect of a species hailing from a somewhat warmer climate, or on a cold aspect and moist locality that which is naturally accustomed to a colder climate. While it is undoubted that species will accommodate themselves to a change of seasons—flowering and fruiting, etc.—when introduced from one hemisphere to another there is abundant proof that no adaptation is possible to a new or differing climate where this difference is in any way marked. The climatic needs of a species are best determined by a comparison of those which obtain where the species is found naturally. Latitude and altitudes furnish a fair but not quite reliable guide for they may be affected by natural phenomena such as the prevalence of sea breezes etc. etc. The blizzards of Florida form an instance of this fact. As a general rule in low lying lands, latitudes frequently limit the habitat of species, subject of course to such modifying influences as aforementioned and in higher country latitude and altitude combined.
From this fact it is no unusual thing to find a species with two habitats—and classed as a mountain species in one place and a plain species in another. At Rust-en-Vrede an instance of this is seen. Above the "intake" at about 2,800 feet above sea level specimens of the Ilex capensis or Wittehout are to be seen, a species found commonly on the lower Knysna forests plateau, where the mean maximum summer temperature probably corresponds.
In introducing an exotic species it should be remembered that the conditions of light and heat are similarly related, and that in proportion to the differences of the natural climatic conditions and the new conditions in which it is attempted to introduce exotics so will be the difference in their light and shade demanding requirements. If brought to a warmer climate their shade bearing capacities are greater and if to a colder their light requirements will be higher.
Another very important factor to be considered in all afforesting questions is the degree of air moisture, more especially in the growing months of the year. In North America it has been determined that where the tension of water vapour averages less than 0.50 during the four growing months forests practically cease. Oaks and 2—3 leaved pines fear least, it is said, the neighbourhood of the dry zone, while firs, spruces, cypresses and 5 leaved pines are found only when approaching the moist zones (Mohr) . Where the atmosphere is very dry or subject to sudden variations broad leaf species are to be preferred for experimental forest work and then 2—3 leaved pines The moister the atmosphere, the easier becomes forest culture, both in regeneration and subsequent treatment, and especially is this so during the growing season. Indeed if the mean rainfall for the four growing months, falls below 2 inches and even if the contained air moisture remains always above 50 per cent, true forests disappear unless perhaps where the winter rains are exceptionally heavy or where in the neighbourhood of bodies of water there is a good subsoil percolation. With age the drought resisting capacity of trees increases and mature trees are capable of withstanding often prolonged periods of very dry weather without suffering much harm.
With regard to soil requirements, most trees, in their most suitable climatic situation, are to a great extent polyphagous or in other words if in introducing exotics very suitable climatic conditions are obtainable, the soil of almost any mineral formation will suffice, provided always that its physical properties are suitable. It will suffice for successful growth but not for the best quality of produce, a fact which is well instanced in the Jarrah. forests of West Australia, where the quality of the timber varies with the geological formation on which it is found. Of course to this general rule there are notable exceptions, such as sweet Chestnut, Cluster Pine, etc, where success depends—other conditions being suitable—on the presence or absence of lime both species being calciphobo us. In Oudtshoorn the calciphobic properties of the Chestnut is instanced by the prevalence of dry rot and often by the death of trees before middle age in soils with a lime percentage approaching 4. (This condition may also be caused by excess of moisture).
Adaptation to climate is however the main consideration when the introduction of plant material is intended and probably there is no climate where human life is possible that is impossible for plant life in some form and, within narrower limits, for trees.
In certain extremes there can necessarily be no expectation of the eventual production of trees of high economic value, but arboriculture, with its attendant climatic amelioration, is nearly always possible within certain latitudes.
In agriculture it is a more than evident fact that the rapid progress of any new country is based, not on possible development of the natural or endemic species but rather on the discovery that its climatic and soil conditions are specially suitable to the culture of some introduced or exotic plant or plants of great usefulness to the human race. In Oudtshoorn is this axiom most evident: its present prosperity rests mainly on the tobacco, the vine and the lucerne—exotic plants which flourish under the climatic and other conditions obtaining.
In afforesting, the principle is to a great extent true as well, though the conditions are naturally more limited. In a country with a rich forest flora much can be done once a thorough sylvicultural knowledge of the different species is acquired in addition to a fair understanding of their economic possibilities. Few countries however possess so wealthy a flora as to include species to cover all practical requirements, and naturally the successful introduction of an exotic supplying the natural deficiency is economically successful in proportion to its want. North America for instance possesses a wonderfully rich forest flora but has nothing which it can offer as a substitute for the cork oak, and in view of the large wine industry in parts of the country the establishment of this tree has become a matter of considerable economic importance.
In a country like South Africa, with a limited forest flora comprising principally slow growing hard woods confined naturally to certain small areas, it is undoubted that economic afforestation will depend on the proper selection and introduction of useful quick-growing exotics suited to the varying climatic and other conditions which obtain. Cultivation of the indigenous species can only prove profitable under very limited conditions. Generally speaking the vast eucalypt family furnishes a wide range for selection of quick growing and fairly valuable woods. Professor Charles Naudin gives concisely the main conditions for a successful growth of the species. He says:— "The first condition of success in the culture of the Eucalyptus is a climate appropriate to their nature: that is to say, for a great majority or the species, warm summers, a moderate amount of rain, a certain atmospheric dryness, plenty of sunlight and very temperate winters." These conditions can be found in many parts of South Africa. To Australasia, parts of Asia, Southern Europe, Northern Africa and parts of the United States of America we look for other trees suitable to local conditions. Many have already proved themselves suitable and others have been found unsuccessful, but where the climatic conditions are sufficiently known to admit of comparison the chances of failure should be much minimized.