Professor Sir HARRY CHAMPION and N. V. BRASNETT, Imperial Forestry Institute, Oxford
This article is an excerpt from a forthcoming FAO publication, Choice of Tree Species for Planting, prepared by the authors at the request of the Forestry Division. It deals with the factors which should guide the forester in deciding which species to select for planting, or to favor in silvicultural operations in artificially established forests. Among the elements analysed, apart from the actual site conditions themselves, are silvicultural, economic and social factors. The long-term effects as well as the prospects of early results offered by the species favored, must be kept in mind.
A FORESTER faced with the practical problems of choosing what species to plant on a given site, or of selecting sites and species for the production of a particular type of timber, needs a detailed knowledge of the local climates and plant associations of his territory. This will direct him to other areas on which he might be able to draw for additional species. He will, of course, have made himself familiar with all available relevant experience whether published or to be found in the files of the various organizations concerned with natural history, land use, biological, geological, climatological and hydrological research in his country. He will also have studied the topography, soils and vegetation, both natural and artificial, of the tract in question and of other parts of the country having similar conditions.
If he believes that his purpose may be served best by the trial of exotic species, he will obviously first consider making introductions from homoclimes or climatic analogues. He will turn to zones of similar and similarly distributed rainfall and temperatures with similar latitudes and topography, and seek detailed information about the distribution and growth there of useful species, and the types of soil on which they grow.
These zones will be indicated somewhat vaguely on climatological maps of the world, and more detail about them will be available in local regional maps and in tables of climatological data published in the regions. Then the forester can generally turn to a local flora of the region to ascertain what grows there, and often he will be able to follow up the species which arouse his interest in monographs or other papers dealing with them. If he is fortunate, he will find works such as Applied Silviculture in the United States (Westveld, 2nd. ed. 1949) and The Silviculture of Indian Trees (Troup, 1921), which will give him climatic, ecological and silvicultural information about the trees of considerable areas. Records of trials of species in different parts of the world such as are to be found in Exotic Forest Trees in the British Empire (Troup, 1932) will also be useful. If he has reason to think that some members of the genus Eucalyptus might be of value to him, he can turn to the FAO publication Eucalypts for Planting (Métro, 1954) the various reports of the FAO Eucalyptus Study Tour (1952) and others of the 300 or so publications listed in the bibliography of that book, and the Forest Seed Directory (FAO 1956), which lists 118 eucalypt species classified according to their suitability to grow in any of 18-climatic zones. Other Australian trees besides the eucalypts are included in A Reconnaissance of the Forest Trees of Australia from the point of view of their cultivation in South Africa (Robertson, 1926).
There is, of course, nothing new about this. Horticulturists and foresters have for many years looked to countries with climates similar to their own, visited them and brought back seed of species which they thought might make promising additions to their local floras. The only difference now is that very much more information is available, and that reliable seed can be obtained from the zones selected without difficulty or resort to smuggling as was sometimes necessary in the past.
As an example, it may be noted that in 1823 Douglas was sent to North America by the Royal Horticultural Society of London because it was realized that the Pacific Coast region was the home of a particularly rich flora growing in a climate comparable to some parts of the British Isles. This region from Oregon northwards through Washington and British Columbia to southeast Alaska and bounded on the east by the Coastal Ranges contains a far wider range of climate than does Britain, but the temperature regime at the mouth of the Columbia River around latitude 46° N., with an average in summer of 54° F. (13° C.) and an average for the year of 50° F. (11° C.), is similar to that of the English south coast, latitude about 50.5° N.; and Sitka in Alaska, latitude 57° N., closely matches the northwest coast of Scotland. The rainfall on the Pacific coast is of the winter type with midsummer the driest period, whereas in Britain spring is relatively dry. Further north up the coast the proportion of rain falling in the summer is greater, until in southeast Alaska it is close to the 22 percent commonly found in Britain. Inland, the climate becomes rapidly continental and summer temperatures are higher than in England.
The trees of the region important to forestry in Britain and parts of western Europe have been found to be Sitka spruce, Douglas fir, Pinus contorta Dougl., Abies grandis Indl., Tsuga heterophylla Sarg. and Thuya plicata Don. All penetrate into climates of much lower winter temperature than are found in Britain, and Douglas fir and the Abies than those of Britain, in particular grow best in warmer summer temperatures averaging 52° to 56° F. (11.1°-13.3°C.) though there is no reason to suppose that they are limited by summer temperature (Wood, 1955). In their native habitat, neither Douglas fir nor Sitka spruce appear to form part of climax forest communities, but are pioneer species giving way to Tsuga, Thuya and Abies. Sitka spruce thrives at low elevations in the British Columbian region with mean annual temperatures varying from 44° to 49° F. (6.7°- 9.4°C.), summer mean of 55° to 68°F. (12.8°-20°C.), winter mean of 30° to 38° F. (1.1°-3.3° C.) and a rainfall of 40 inches (1,020 mm.) a year upwards, conditions which can easily be matched in Britain.
It is now possible to buy from government forest departments and from merchants seed certified as collected from known climatic and elevational zones in this region as from several other regions of the world. The Forest Seed Directory mentioned above contains the forms of agreed international certificates of origin and quality, and the sources from which a large number of species can be obtained. One firm divides its collection area on the Pacific coast from Alaska to California into 25 climatic regions, subdivided into 127 zones, each of which is further split up into 500 foot (150 m.) elevation bands. It provides tables which give the temperatures (average annual, average summer, absolute maximum and absolute minimum), precipitation (annual and summer), and the number of frost-free days in the year, for the most representative weather station in each zone.
Another country which was drawn on early for plantation species was Australia. In 1843, several species of eucalypt were tried in the Nilgiri Hills of India, and later Eucalyptus globulus Labill. solved a serious fuel shortage there. In 1870, Acacia mollissima Willd. was introduced into Natal and eastern Transvaal in South Africa and by 1952 a great tanbark industry depending on some 640,000 acres (259,000 ha.) of black wattle plantations had been built up. In 1876, Eucalyptus saligna Sm. was first planted for railway fuel in South Africa, and now there are some 200,000 acres (80,000 ha.) of it in eastern and northern Transvaal and on the Zululand coast. Early in the present century, the Companhia Paulista de Estradas de Ferro, the State railway of Saõ Paulo, Brazil, imported 143 species of eucalypts and now has some 30,000 acres (12,000 ha.) of plantations, mainly of E. camaldulensis Dahn., E. citriodora Hook and E. saligna. The Mediterranean countries, Spain, Portugal, France, Italy and Greece, have all found E. globulus and E. camaldulensis valuable additions to their plantation species. In California, 80 percent of the considerable eucalypt plantations are of E. globulus, and 15 percent of E. camaldulensis. Peru, Chile and Uruguay all make considerable use of E. globulus, while in Turkey, Cyprus, Palestine, Jordan, Tripolitania and Morocco the most popular eucalypt is E. Camaldulensis. Many other species are found to be suitable to particular parts of these and many other countries.
It is, therefore, worth considering the climate and vegetation of the Australian continent. Australia has a central desert zone covering nearly 40 percent of its whole area, and the rest can be divided very roughly into three main climatic zones:
1. A tropical northern zone of summer rainfall, north of about 20° S. on the west coast and about 14° S. on the east coast. The mean annual rainfall varies from about 20 inches (510 mm.) in the south of the zone to 60) inches (1,525 mm.) and more on the north and east coasts, with some areas receiving 120 inches (3,050 mm.). The mean annual temperature is in the neighborhood of 80° F. (26.4° C.), the interior being warmer than the coastal areas and the west coast warmer than the east.2. A zone of moderate winter rainfall and dry summers in the southern parts of South Australia, Western Australia, the greater part of Victoria, and the south of New South Wales. Mean annual rainfall varies from about 10 inches (250 mm.) to about 30 inches (760 mm.) with isolated areas of up to 40 inches (1,020 mm.) on the south coast. Summer temperatures are around 70° F. (21.1° C.) and winter temperatures around 35° F. (1.7° C.)
3. A zone of more uniformly distributed rainfall on the east coast and the southeastern part of the continent with annual rainfall generally between 20 inches (510 mm.) and 60 inches (1,526 mm.). This zone includes the mountains of New South Wales, and there and on the east coast the rainfall is from 40 to 60 inches (1,020-1,526 mm.) a year, with isolated areas of 120 inches (3,050 mm.) on the coast of northern Queensland, where the summer is the wetter season. In the south (Victoria), there is a tendency towards a maximum rainfall in winter. In New South Wales, the even distribution is more noticeable, though in the north and on the east coast more rain falls in summer, and on the south coast more in winter. There are very considerable variations in temperature regimes within the zone, because of the topography.
De Beuzville (1943) considered that the whole of the east coast of Australia has a climate predominantly similar to that of Argentine, Brazil and Mexico and certain parts of South Africa, and also, in its wetter parts, in Madagascar. The north coast and its hinterland has a climate similar to those of parts of Madagascar, India and Mozambique. On the west coast and inland from it there are stations with climates similar to some found in South Africa, Algeria, Sudan, Mexico and Arizona. The climate in the south southwest is more like that of California and South Africa, and in small areas like that of Spain. The Australian Alps and the Dividing Range have cool slopes where the climate approximates to that of France and Italy. The dry center of Australia has a climate similar to that of Egypt, Arizona, Israel and parts of the Californian desert. Robertson (1926) found that, while coastal temperatures, latitude for latitude, were very similar in Australia and South Africa, the interior of Australia was warmer than that of South Africa because of the greater elevation of the latter.
The forest formations of Australia may be roughly divided into Rain Forest (tropical, sub-tropical, and temperate), Moist Sclerophyllous Forest, pry Sclerophyllous Forest, and Open Woodland, all of which merge into each other.
The rain forests occur only in isolated relict patches. In the tropical zone their flora is Malayan without predominant species, and the natural succession is very confused. From the Hastings River, about 30° S., in New South Wales to the north of Queensland, Araucaria cunninghammii Ait is found on the coast and up to 100 miles (160 km.) inland with an annual rainfall of 50 to 70 inches (1,270-1,780 mm.), falling mainly in summer. Araucaria bidwillii Hock. and Agathis robusta are found in southeast Queensland in areas with 50-60 inches (1,270-1,525 mm.) summer rain, with summer temperatures of 75° to 85° F. (24°-29° C.) and winter temperatures of 50° to 60° F. (10°-16° C.). What are apparently secondary forest formation after fires include Tristania conferta R. Br. and Syncarpia laurifolia Ten. mixed with eucalypts such as Eucalyptus saligna.
The sclerophyllous formations are mainly composed of eucalypts and acacias. Closed stands of Eucalyptus are not usually found where the rainfall is less than 30 inches (760 mm.) a year, below which limit open and scrubby vegetation occurs. Many of the eucalypt species are confined to particular zones of rainfall amount and distribution, but some are very adaptable. One of the most widely distributed is E. camaldulensis which Boosman (1950) states can put up with 5 to 10 inches (130-250 mm.) of rain a year, is often found in zones of 22 to 28 inches (560-710 mm.), and exceptionally with 40 to 45 inches (1,020-1,140 mm.) though 35 inches (890 mm.) is regarded as its normal maximum. Actually its range is determined more by soil moisture conditions than by precipitation and it is characteristic of alluvial flats, often along river banks where water is available by inundation or percolation. It likes warmth and extends into some of the hottest parts of the Northern Territory. It is not found in the highlands of New South Wales in which State de Beuzville (1943) gives a mean temperature of the coldest month of 46° F. (7.8° C.) as the lower thermal limit of its range. It must be remembered that the form, as well as the stand density, of eucalypt species growing in areas of their minimum rainfall is very different from what it is under optimum rainfall.
Moist sclerophyllous forest is found mainly in the southeastern coastal strip of New South Wales and Victoria, and in the southwest corner of Western Australia, in the zones of either winter or fairly uniform rainfall. In Western Australia, Eucalyptus diversi-color F. v. M. is found in stands of a type approaching temperate rainforest in a climate of 40 to 60 inches (1,020-1,525 mm.) mean annual rainfall and mean annual temperatures of 62° to 65° F. (16.7°-18.6° C.) In Victoria and New South Wales, Eucalyptus globulus grows in the higher and cooler sites with 35 to 65 inches (890-1,650 mm.) of rain and mean annual temperatures of 44° to 49° F. (6.7°-9.4° C.) sometimes mixed with Acacia melanoxylon R. Br. and with an understorey of Acacia mollissima Wild. or A. dealbata Link. In the wetter range of these sites in Victoria, stands of Eucalyptus regnas F. v. M. are found.
Eucatyptus gomphocephala A. Dc. with an undergrowth of Acacia cyanophylla Lindl. is found growing on calcareous sands in the southwest of Western Australia in an annual rainfall of 30 to 40 inches (760-1,020 mm.) mainly in winter, with an annual mean temperature of 60° to 64° F. (15.6°-17.8° C.) and a summer temperature of 67° to 72° F. (19.4°-22.2° C.). There are either no frosts or only occasional light ones in places. Both species have proved valuable in the afforestation of coastal sand in South Africa, and more recently have shown considerable promise when used in combination on calcareous sand dunes in Morocco (FAO, 1954)
In the dry sclerophyllous forests there is a very great variety of eucalypt species, not many of which attain timber dimensions in the lower rainfall areas. In New South Wales and Queensland, Eucalypts crebra F. v. M. grows with a rainfall of 20 to 26 inches (510-660 mm.) a year mainly in summer in areas of high temperature, often mixed with Callitris glauca R. Br. Eucalypts sideroxylon A. Cunn. is found in poor sites in New South Wales, Victoria and Queensland with about 20 inches (510 mm.) of rain a year. There are also species which are characteristic of moister forests but nevertheless can grow with as little as 22 to 25 inches (560-635 mm.) a year, such as Eucalypts marginata Sm. in Western Australia, and E. oblique l'Herit. in South Australia, Victoria and New South Wales. Where there is moisture enough to permit of under this is often Acacia pycnantha or A. mollissima in the east, and A. cyanophylla or A. cyclops Cunn. in the west.
These formations merge into open woodland, particularly in western Queensland and New South Wales. Eucalypts salmonophloia F. v. M. grow in Western Australia in the zone of 9 to 12 inches (220-305 mm.) of rain, mainly from June to September. 'Mallee' formations consisting of a great variety of small, often bush-like, eucalypts attaining up to 20 feet (6 m.) in height with stems of 3 to 6 inches (7.6-15.2 cm.) in diameter, cover considerable areas of low rainfall.
South Africa is a good example of a country with inadequate natural forests and slow-growing indigenous species. The need to supplement the natural flora was recognized early. Conifers and hardwoods were imported from northern Europe from 1665, but did not thrive. Later some Mediterranean species, notably Pinus pinea L., which became naturalized in the Cape Peninsula, and Pinus pinaster Sol., which has been widely planted and does best in the zone with winter or all-the-year-round rainfall, were introduced. By the middle of the nineteenth century P. radiata had been brought from California and had proved to be very adaptable in climates similar to those favored by P. pinaster, though more particular about soil. Later in the century, P. longifolia Roxb. was introduced from the outer ranges of the Himalayas in India and proved useful in the cool and warm temperate summer rainfall areas.
A great step forward was made about 1905 when Hutchins decided that Mexico, a plateau country like the Transvaal, lying in approximately similar latitudes, having a summer rainfall and a rich flora, should be a promising source of exotics. He tried a number of species including Pinus patula Seem. of which there is now a bigger acreage in South Africa that that of any other softwood, particularly, of course, in the summer rainfall areas. Hutchins also recommended P. caribaea Morelet from the southern United States of America for the sub-tropical zone, and it has shown exceptionally vigorous growth in both the temperate and sub-tropical zones with winter or all-the-year-round rainfall. It is being planted on a large scale for paper pulp in Zululand. By 1947, some nervousness was felt about the dangers of disease in large pure blocks of these two species and an officer was sent to America to study the pines in their natural habitats and to find additional species if possible (Loock, 1950). He was particularly interested in Pinus pseudostrobus Lind. which had originally been tried under the name of P. teocote Schl. v Cham. with success, but the seed of which could not be obtained. He was able to collect 350 pounds (159 kg.) of seed in Mexico. He was also impressed by Pinus hondurensia Loock in British Honduras, only lately distinguished from P. caribaea. This illustrates the importance of botanical identification and of securing seed of the most suitable species and varieties for use in particular localities. Where reliable local agencies for the supply of seed do not exist it may be necessary to go and collect exactly what is wanted.
These conifers and others from California, Central America, India, the Mediterranean region, and Mexico now cover more than 600,000 acres (243,000 ha.) of South Africa, alongside some 640,000 acres (259,000 ha.) of acacias and 450,000 acres (186,000 ha.) of eucalypts from Australia, an example of what can be done by selection and trial of species from climates similar to those in which they are required to grow.
Reference is made earlier, in the study of which this article is an exerpt, to the agro-climatic analogues established at the American Institute of Crop Ecology by Nuttonson (1937-53). Up to the latter year analogues had been established between North America and Ukraine, Poland, Czechoslovakia, Yugoslavia, Greece Albania, China, Germany, Finland Sweden, Norway, Siberia, Japan, and the Ryukyu Islands. Each of these studies gives a general and comparative geography of the country covered and a brief account of its climate. There is also a varying amount of information about the natural resources of the country, its soils, major plant species, land-use, agricultural and forestry practices, etc. Relief maps show the location of the meteorological stations within the country studied and the regions of any North American climatic counterparts found. Charts give full meterological data for each station and for the counterparts.
The purpose of this series of studies is "to formulate an agronomic and horticultural approach to ecology and to promote research along the lines of crop ecology as it affects plant adaptation, plant introduction, and the exchange of varietal plant material among the various agricultural areas of the worlds". Its value is not, however, confined to agriculturists. For instance, the paper on Japan (1951) points out:
"Over one half of the total land area of the country is covered with luxuriant forests of a great diversify of broadleaved and coniferous species and of dense undergrowth. These forests are found largely in the mountainous regions, as more than three-fourths of the country's land consists of rough and rugged mountains and hills topographically unsuitable for cultivation of farm crops."
The climate of Japan is largely determined by the prevalence of the monsoons. There is an abundance of precipitation throughout the year with a predominantly summer-maximum distribution pattern, high relative humidity, and high summer temperatures, except in the higher latitudes and altitudes. Nuttonson mapped and described eight climatic regions, two of which he subdivided into three and two districts respectively, and provided graphs of average monthly temperatures, monthly rainfall, and frostless seasons from 16 weather stations. Unfortunately, because the study is mainly concerned with agriculture, not a great deal of information is given about the climates in the mountain forests, where the trees of greatest interest to other countries grow. Data for two high level stations in central Honshu are:
|
Latitude |
Elevation |
Mean annual rainfall |
Mean annual temperature |
Mean Jan. temperature |
Mean August temperature |
|||||
|
ft. |
m. |
inch. |
mm. |
F. |
C. |
F. |
C. |
F. |
C. |
|
|
35° 28' |
3 687 |
1 124 |
73.9 |
1 877 |
45.3° |
7.4° |
24.8° |
4 0° |
66.0° |
18.9° |
|
36° 25' |
4 514 |
1 376 |
92.1 |
2 339 |
41.7° |
5.4° |
19.9° |
6.7 |
64.0° |
17.8° |
These figures are quoted because they are probably typical of the natural habitat of two of the most important conifers, Cryptomeria japonica Den. and Chamaecyparis obtusa Sieb. About one-third of the total forest area of Japan consists of plantations and they are being extended at a rate of about 720,000 acres (292,000 ha.) a year. In the best sites in the moister inter-mountain valleys and on the lower slopes Cryptomeria is planted, on the middle and upper slopes Chamaecyparis, and on the ridges from about 6,000 to 7,000 feet (1,830-2,130 m.) elevation, Pinus densiflora Sieb. According to Turner (1937), Larix leptolepia Murr. is the species most used for planting in Hokkaido. It is also native to the volcanic mountain soils between altitudes of 4,000 and 6,000 feet (1,2201,830 m.) elevation.
Nuttonson divided the natural forests into three climatic types, each of which descends in general to lower altitudes in the northern latitudes and ascends in the southern. This classification agrees fairly closely with one drawn up in 1922 which is quoted by Ohmasa (1956).
1. Evergreen hardwood forest, which contains some deciduous hardwood trees and some conifers. It lies mainly south of latitude 36° N. and covers Kyushu from sea level up to about 2,800 feet (850 m.) elevation, Shikoku to 2,450 feet (750 m.) and southern Honshu to about 1,800 feet (550 m.). The mean annual air temperature is 55°-70° F. (13°-21° C.) and there is a well-distributed rainfall with a summer maximum. The more important species are Quercus gilva, other Quercus spp. and Cinnamomum camphora. Pinus thunbergii Parl. is found on the sea coast.
2. Deciduous hardwood forest, which includes mixtures and pure stands of economically important conifers, is found to the north of the evergreen hardwood forest and at elevations above it, reaching latitude 43.5° N. at sea level in the middle portion of Hokkaido. The formation covers the highest elevations found in Kyushu, but only land up to 6,500 feet (2,000 m.) elevation in Shikoku, to 3,600 feet (1,100 m.) in northern Honshu, and to 1,500 feet (450 m.) in southern Hokkaido. The annual mean air temperature of the zone is from 43°-55° F. (6°-13° C.) Valuable hardwoods include Fagus crenata, Quercus crispula, Aesculus turbidata and Zelkova serrata. The principal conifers are Cryptomeria japonica Den. Chamaecyparis spp., Larix kaempferi Lamb. and Pinus densiflora Sieb.
3. Coniferous forest covers the colder northern and more elevated tracts. It does not occur in Kyushu, and in Shikoku only in the small area above 6,500 feet (2,000 m.) elevation. In central Honshu, it is found between about 6,000 and 8,900 feet (1,800-2,700 m.) In southern Hokkaido, the formation covers most of the land above 1,000 feet (305 m.) elevation, and north of latitude 43.5° N. descends to sea level. The annual mean air temperature is 43° F. (6° C.) and below. Picea jezoensis Sieb. and Abies sachalinensis Mas. are the principal conifers, and are sometimes mixed with Quercus crispula Tilia japonica, Betula tauschii, etc. Abies veitchii Lindl. occurs in the colder parts of the zone.
High relative humidity is a feature of most of Japan, and, while similar thermal conditions to those found in different parts of its wide range of latitudes can be found in North America, it is not so easy to match the distribution of rainfall. However, some homoclimes have been found in the Maritime Provinces of Canada, and many in the northern, central and southern regions of the eastern United States.
Nuttonson, 1947, 1951, has pointed out that in many parts of North America the relatively severe winters compared with Japan do not permit the formulation of year-round thermal analogues in a number of areas in which temperatures in the growing season (April-September) should make possible the harvesting of spring planted crops, and many spring-crop analogues are suggested. Similarly there are winter-crop analogues based on October to April temperatures. This points the difference between agriculture and forestry, in which crops are on the ground throughout the year and year-round temperatures are of more importance.
