LAMBERTO GOLFARI is a member of the Forestry Department, Celulosa Argentina S.A., Buenos Aires.
The behavior of certain exotic pines, mainly in Latin America
LIKE ANY other plants, conifers1 have certain climatic, soil and biotic needs acquired in the course of time in their habitat. Some species, such as Pinus durangensis and P. cooperi, require cold winters and tolerate temperatures as low as - 27º C (-16º F), while others, like P. caribaea and P. hondurensis,2 do not need cold and suffer at temperatures below -4º C (25º F). Some species, such as P. khasya and P. insularis, prefer hot humid summers, and others, P. patula and P. pseudostrobus for instance, like cool, humid summers. Still others, such as P. radiata, need dry cool summers. Some, like P. merkusii, have a long vegetative period and are adapted to short summer days, while others, like P. engelmanni, have a shorter vegetative period and are adapted to longer days. A few, such as P. elliottii and P. taeda, can grow on poorly drained soils but the great majority require good drainage, as is the case with Araucaria angustifolia and Cunninghamia lanceolata; some, like P. cubensis, require highly acid soils, while others, like P. halepensis and P. elliottii densa, grow on neutral or alkaline soils.
1 This group of certain exotic pines in Latin America includes species that, despite their Temperate Zone origin, are planted in tropical uplands, as well as tropical species that, because they require a temperate climate, can be planted in mountain areas.
2 This nomenclature, although incorrect, is preferred in order to distinguish P. caribaea of Cuba from P. hondurensis of Central America, because of their different ecological needs and behavior in plantations.
When a pine or other conifer is being introduced to a new region the success or failure of its take will, consequently, depend on the degree to which local ecological conditions meet its requirements. The interaction of all factors in the environmental complex provides certain stimuli for various species, depending on their particular reactions. Ideally it may happen that in its new environment a species finds optimum conditions, or it may find fairly good conditions as regards certain factors and unfavorable or even absolutely unsatisfactory conditions for others.
Where experimentation is far advanced, the silviculturist can judge the behavior of various conifers from certain indexes: growth rate, habit, especially of the crown; longevity; sensitivity to cold; pest and disease resistance, etc. Using these indexes and placing them against the background of the environmental conditions, it is possible to select the most suitable species for each region and even to choose the best location by evaluating sites for their suitability for tree growing, namely by grading them: best, good, marginal, or unsatisfactory.
In areas where there has not yet been sufficient experimentation, silviculturists can only select those species with the highest probability of successful take by trying to find analogies between the place of origin of such species and the new environment, taking into account the following factors: rainfall and its seasonal distribution; mean temperature, both annual and monthly, as well as temperature extremes; relative humidity; length of wet and dry seasons; light intensity and duration; depth, texture, drainage, slope and reaction of soils; biotic conditions, etc.
When it is impossible to gather sufficient information regarding the habitat of certain species still relatively unknown as are many of the tropical latitudes it may be enough to examine three fundamental, closely related factors, namely: rainfall distribution, mean annual precipitation and temperature pattern.3
3The factors and indexes already adopted by Pavari (1916), Troup (1932), Swain (1938) and Holdridge (1947) in their respective climatic classifications made especially for silvicultural purposes are used here to a certain extent.
Pines and other conifers fall into three major groups as regards rainfall distribution, namely:
1. species requiring rain mostly in the winter and that can stand a summer drought period (Figure 1);
2. species requiring rainfall uniformly distributed throughout the year (Figure 2);
3. species requiring rain mostly in the summer and that can withstand a definitely dry winter (Figure 3).
FIGURE 1. - Monthly mean rainfall for three sites, corresponding to three different species, typical of the Mediterranean or pronounced winter rainfall areas.
FIGURE 2. - Monthly mean rainfall for three sites, corresponding to three different species typical of areas with either a uniform, or an all-the-year-round, rainfall pattern.
FIGURE 3. - Monthly mean rainfall for three sites, corresponding to three different species typical of monsoonal or pronounced summer rainfall areas.
The winter rain or Mediterranean-type species, have as a rule two dormant periods, one due to winter cold and the other to summer drought. The active growth of species requiring an even or constant rainfall is usually limited by winter cold. On the other hand, for the monsoon type conifers that prefer summer rains, growth is usually slowed down by drought but not by cold, since in the subtropics or tropics there is little seasonal variation.4
4 Almost all conifers come from regions belonging to one of the three above-mentioned rainfall types, but there are certain exceptions. For example, Araucaria angustifolia, whose main habitat is southern Brazil and the zone bordering Argentina, can also live further north in small mountain patches in São Paulo and Minas Gerais with summer rains and fairly humid winters. Another species, P. pinaster, which usually demands winter rains, has a race adapted to the uniform rainfall in the northwestern most portion of its area in Les Landes, France. Similarly, P. elliottii, a species that usually prefers an even rainfall distribution, has adapted itself to central Florida at the southernmost bounds of its habitat where the rains come in the summer. There are marginal instances with transition climates. Another variation is represented by the species of the Sierra Madre Occidental in Mexico, P. durangensis, P. engelmanni, P. cooperi and P. arizonica, as well as by the conifers of central and southern China, Cunninghamia lanceolata and P. massoniana, whose winter rest period is due to a combination of cold and drought.
In the new habitats to which species are to be introduced, the alignment between climate and vegetative growth in the original habitat of each species must recur as, if there is no such alignment between the periodicity of the plant and the climate, the chances of successful introduction are limited. The obvious signs of ecological incompatibility are: stunted growth; poor habit; bad crown formation; partial desiccation of foliage; too early flowering; dwarfism; poor appearance; susceptibility to disease; and early death, etc.
Some examples may be given. At the pinetum of Placerville, California, located in a typically Mediterranean climate, none of the Mexican or Central American pines from a monsoon climate prospered; those tried out included P. patula, P. hondurensis, P. pseudostrobus,, P. oocarpa, P. montezumae, P. strobus chiapensis, P. durangensis, P. michoacana, P. douglasiana and others. On the other hand, P. parryana, P. muricata and P. contorta var. latifolia, from the northern part of Lower California, the only area of Mexico with a dry summer and rainfall mostly in the winter, that is, a climate similar to that at Placerville, grew satisfactorily.
In central Chile where rains come mainly in winter and the summers are dry, P. radiata has been successfully introduced from the coast of California where the climate is similar. Also, further south near Valdivia, on sites with more rainfall, Pseudotsuga menziesii promises well as it does in the mountainous region along the Argentine border in the provinces of Neuquen, Rio Negro and Chubut. On drier adjoining sites the following flourish: P. ponderosa, P. lambertiana, P. contorta var. latifolia. All these species come from parts of North America where the climate resembles that in the above-mentioned places.
In Minas Gerais, Brazil, at high altitudes with monsoon climate and a short winter drought period, P. radiata grows almost continuously and has long, slender, barely ramified branches, the tips of which are sometimes dry. This abnormality, also observed by Lamprecht (1959) in Venezuela and García Díaz (Wadsworth, 1960) in Colombia, is probably due to the fact that the climate in these areas is not suited to the plants. Another case of climatic incompatibility is the experimental plot of P. elliottii (a species that likes a uniformly distributed rainfall) at Augustine, Belice, in the monsoon rainfall area, with warm dry winters. At the age of six-and-a-half years the specimens were less than 3 meters (10 feet) tall, with irregular branching and hard shoots, sometimes dry at the tips. Since there is no reason to attribute this abnormality to the soil, it is assumed that the species suffers from the drought which lasts from January to May and the absence of the winter conditions to which it is accustomed.
Experiments have shown that species indigenous to winter rainfall areas can be successfully established in similar regions and, to a limited extent, in areas with a uniformly distributed rainfall provided that other ecological conditions are favorable;5 on the other hand they are a complete failure in the monsoon areas (Figure 4).
5 In addition to the amount of rainfall and its pattern, and the temperature range, soil conditions are also a decisive factor in establishing a species in an area outside its natural habitat.
A valuable indicator species is P. radiata, indigenous to the Mediterranean type of region with a cool summer. In Conceptión, Chile, where conditions are similar and in some respects even better than its own habitat, this pine grows exceptionally fast, shows excellent habit and is long-lived. It also grows fairly satisfactorily on the south coast of Uruguay and in isolated spots of the southeast coastal belt of Buenos Aires province in Argentina, where the rainfall is uniform and moderate and the summers are cool, and soils are light, deep and well drained. In the north and west, however, in zones with a uniformly distributed rainfall but with hotter and more humid summers, with shallow clayey soils where drainage is slow or faulty, this species is at a disadvantage and grows unevenly, the hole sometimes being excessively branched, forked or crooked (Barret and Garborsky, 1960). Further north conditions gradually become even more unfavorable, inducing slow growth, malformation, and severe Diplodia attack. Unable to survive in Misiones, Argentina, in a subtropical zone with an abundant, uniformly distributed rainfall, P. radiata dies off in a few years. It is found in Sao Paulo, Brazil and in Tucumán, Argentina in the pronounced summer rainfall area. In the latter case environmental factors, in addition to wet summers, are probably the high temperature and unsuitable photo-periodism.
FIGURE: 4. - Graph showing the relation between the rainfall pattern suited to some conifers and the prospects of their successful cultivation in other countries.
Experiments in South Africa corroborated this finding (Poynton, 1957). Attempts made to extend P. radiata plantings from the southwest part of Cape Province, which has a winter rainy season or uniformly distributed rainfall throughout the year, to the northeast - Orange Free State, Natal and Transvaal - with very wet summers, were a failure. Owing to unsuitable environmental conditions the trees were severely attacked by Diplodia and planting had to be abandoned.
Another Mediterranean-type species, P. pinaster, has been successfully introduced into the Uruguayan southern coastal belt which has a uniformly distributed and moderate rainfall. It did not thrive, however, in northern Argentina or in the south of Brazil.
FIGURE 5 Seven-gear-old plantation of Araucaria angustifolia on red soil in a subtropical area with 69 in. annual rainfall uniformly distributed. Broadleaved hygrophytic forest in the background. (Photo, Celulosa Argentina S.A.)
FIGURE 6. - Three-year-old plantation of Araucaria angustifolia on logged-over land, subtropical broadleaved forest at the back. (Photo, Celulosa Argentina S.A.)
FIGURE 7. - Fifteen-year-old plantation of Araucaria angustifolia on red soil in subtropical area with 69 in. annual rainfall uniformly distributed. (Photo Celulosa Argentina S.A.)
Uniform rainfall area conifers
Experience has shown that species indigenous to areas with the rainfall uniformly distributed throughout the year can be successfully established in similar regions and, under certain conditions, also in areas with seasonal rains with the maximum fall in summer, but are seldom adaptable to winter rainfall areas (Figure 4).
Araucaria angustifolia, a South American, mountain-foothill species which requires rain throughout the year and a moderately warm summer, has recently been tried outside its natural range. In areas with the same type and amount of rainfall though with somewhat higher temperatures as in northern Misiones, Argentina, results are excellent. With intermittent rains and dry winters, however, growth is slow (São Paulo) or stunted (Tucumán).
P. elliottii is also being grown successfully in Argentina from the Paraná delta and northern Buenos Aires to Misiones; in the central and northern parts of Uruguay; and in Brazil in northeast Paraná and southwestern São Paulo, all regions where the rainfall is uniformly distributed. By contrast, in the central part of the country and the area north of São Paulo, which has seasonal rains and a pronounced dry winter, growth is slow and irregular and it is unlikely that this species will prove satisfactory under such conditions.
In South Africa (Poynton, 1057), P. elliottii has been grown successfully in different ecological environments, on the southern coastal belt of Cape Province with rains uniformly distributed throughout the year, in Natal where the rainfall is intermediate between year round and intermittent and in the Transvaal which has periodical rains. The best results are obtained in eastern Transvaal in areas which have an abundant summer rainfall and a mild climate due to the altitude, with a mean temperature of 18º C (65º F) in the hottest month (MTHM) and 10º a (50º F) in the coldest month (MTCM) Here the winter drought is tempered by a cool temperature and mists, which maintain a higher degree of humidity throughout the year.
In Australia (Bednall, 1967; New South Wales Forestry Commission, 1957; Rogers, 1957), P. elliottii; is grown along the east coast from New South Wales, in areas with a uniformly distributed rainfall, up to a point north of Rockhampton midway up the coast of Queensland, which has a summer rainfall. This species is however mostly grown in southern Queensland near Brisbane and shows the highest increment in areas with an abundant rainfall intermediate between uniform and periodical. P. elliottii is not planted in those southern Australian areas which have a Mediterranean climate as there its growth is very slow and much inferior to that of P. radiata.
FIGURE 8. - Sixteen-year-old plantation of Pinus elliottii on alluvial hydromorphic soils of the Rio Paraná Delta (the water table lies close to the surface).
(Photo, Celulosa Argentina S.A.)
FIGURE 9. - One-year-old Pinus elliottii plantation on red sandy soil in the 'cerrado' (savanna) zone. (Photo, Itapetininga, Brazil)
Experiments have shown that the species indigenous to regions of pronounced summer rainfall can be successfully established in similar regions and sometimes also in areas with a uniformly distributed rainfall, though they seldom thrive in winter rainfall areas (Figure 4).
In the central and northern areas of the State of São Paulo which has summer rainfall, the most promising species are: P. hondurensis, P. caribaea, P. insularis in the subtropics at altitudes of from 480 to 700 meters (1,650 to 2,300 feet) above sea level, and Cunninghamia lanceolata, P. patula, Cupressus lusitanica, Cryptomeria japonica in the mild and cold Temperate Zone parts at low mountain altitudes of 700 to 2,000 meters (2,300 to 6,700 feet). All these species are indigenous to monsoon areas. In regions of uniformly distributed but abundant rainfall, such as Misiones, the annual average being 1,700 millimeters (67 inches), P. hondurensis and P. caribaea show great promise and far better growth than P. elliottii and Araucaria angustifolia, although the first species has a great variety of habit not observed to such a marked extent in São Paulo, despite the same seed being used in each case. Presumably this lack of uniformity in shape is due to the absence in Misiones of a dry winter period which occurs both in its natural site and in São Paulo, and is conducive to an almost unbroken growth. The latter trait is a disadvantage in that the winter frosts may damage the newly formed leaves or shoots which do not have time to harden. Further south, in Santa Fe and Buenos Aires provinces, with a moderate, uniformly distributed rainfall between 900 and 1,000 millimeters (36 and 40 inches) a year and a temperate climate, P. hondurensis and P. caribaea are inferior to P. elliottii and by other signs show very poor adaptability to this environment.
Occasionally monsoon conifers can be successfully established in winter rainfall areas as, for example, Cupressus lusitanica in Bussaco, Portugal. It is to be noted, however, that the climate in Bussaco is not Mediterranean but transitional towards uniform, as is evidenced by the short summer dry period. Other favorable conditions are abundant annual rainfall of 1,530 millimeters (60 inches) and temperatures similar to that of the mountain regions of Guatemala and Mexico where this species is indigenous.
FIGURE 10. - Three-year-old Pinus hondurensis on red soil in subtropical area with 69 inches annual rainfall uniformly distributed. (Photo, Celulosa Argentina S.A.)
FIGURE 11. - Thirty-two-year-old plantation of Cunninghamia lanceolata on red soil in a subtropical area with 58 in. annual rainfall, seasonal in type, with dry winter. (Photo Comp Melhoramentos de São Paulo Brazil)
FIGURE 12. - Range of annual mean temperatures, in Centigrade and Fahrenheit, for conifers on their natural sites.
Table 1 gives the mean annual rainfall for the various conifer habitats. When conifers are introduced into another sits they should have the same amount of rain as. or more than. the natural site. For instance, P. radiata has the highest increment, both in Chile and New Zealand, in areas with an annual rainfall of 1,100 to 1,700 millimeters (43 to 67 inches), that is, much higher than in its natural site.
Sometimes a species will grow in regions where rainfall is less, though in this case the smaller amount of rain is offset by the coastal or mountain mists, a cooler average temperature or by a deeper soil. For example, P. elliottii is grown in Queensland (Rogers, 1957), usually in fairly low-lying areas where the annual rainfall varies between 1,300 and 1,550 millimeters (51 and 61 inches), as in the natural site. In Passchendaele, in the same State, however, where it is grown at an altitude of 3,000 feet (900 meters), the annual rainfall is barely 850 millimeters (34 inches); in this case the low rainfall is offset by the cooler temperature due to the altitude.
In regions which Bet less rain compared with the natural site and where the other conditions are not favorable, it is doubtful whether conifers will be successful. The species in this State are frequently stunted, with conical habit and excessive branching, and are more susceptible to disease.
TABLE 1 - CLIMATIC DATA FOR SOME CONIFER HABITATS
The values which best indicate the thermal requirements of each species, and which can be used as equivalents, are the mean temperatures for the year, for the coldest and the hottest months, and the absolute minimum (Table 1). Figure 5 shows, in degrees Centigrade and Fahrenheit, the range of mean annual temperatures suitable for some conifers within their habitats. Obviously species with a wide geographical range, such as P. taeda, P. pseudostrobus and P. merkusii, have a wider temperature range in line with different latitudes and altitudes.6 By contrast, species restricted to specific sites, such as P. caribaea and P. radiata, have a limited temperature range, though such species do adapt themselves to wider limits, as they can be grown successfully in somewhat colder or hotter regions provided the differences in temperature are not excessive. For example, Araucaria angustifolia is accustomed in its original habitat to an annual mean temperature of 10º C a (50º F) to 18º C (64.5º F), but can he grown successfully in Misiones outside its natural range in areas with a temperature of 20º C (68º F); on the other hand, there is little likelihood of establishing P. patula owing to its very different temperature requirements.
6As has been shown experimentally by Wakeley (1944) for P. taeda in the United States, and by Rycroft and Wicht (1947) for P. pinaster in South Africa, it is highly probable that other widely distributed species are formed by different geographical races or ecotypes with a different rate of growth. The choice of the most suitable species for each region is another problem which will have to be solved through experimentation.
Other important temperature values are the mean temperature of the coldest month (MTCM) and the mean temperature of the hottest month (MTHM), that Swain (1938) uses for his climatic index.
Taking these values as a basis, present-day experience shows that hot-summer species can be successfully transferred to regions with a cooler summer, although it is less likely that a cool-summer conifer can be established in hot-summer areas. For instance, Pinus elliottii is indigenous to a region where the mean temperature of the hottest month is between 26º C and 28º C (79º and 82.5º F), but it can be successfully grown in regions where the mean temperature of the hottest month is only 19º C (66º F) as in Graskop, East Transvaal; on the other hand, P. patula, a species of cool areas where the MTHM is between 12.6º C and 16º C (54º and 61º F), cannot thrive on the lower coast of Zululand with hot summers and a mean temperature in January of 24º C to 25.5º C (75º to 77º F). The same species grows poorly in Gourie, on the central highlands of Jamaica (Lamb et al., 1960), where the mean summer temperature is between 20º C and 23º C (68º and 73º F).
Another point to be taken into account is the difference in extremes of seasonal temperatures. P. massoniana and P. elliottii are indigenous to areas with fairly cold winters and hot summers, the difference between the mean temperature of the coldest month and that of the hottest month being 28º C (60º F) for the first species and 18º C (32º F) for the second. Neither species was successful in the Federation of Malaya or in the Fiji Islands (Barnard and Beveridge, 1957; Cottle, 1967) under a humid tropical climate with a mean monthly temperature range below 5º C (41º F), possibly owing to the absence of the winter conditions to which they are accustomed, Tropical species like P. hondurensis and P. caribaea might possibly be more suitable for these areas.
Resistance to cold is another factor to be taken into consideration, since it may limit or prevent the cultivation of a species in a specific area. Table 1 shows the minimum temperatures for different habitats. A point to be noted is that, unlike eucalypts, which, in the countries into which they are introduced, are just as sensitive to cold as in their natural range. conifers are usually more adaptable. P. hondurensis and P. caribaea, for instance, in Misiones, Argentina, withstand temperatures as low as 4º C (25º F), lower than that of their natural site where the minimum of 5º C (41º F) is seldom reached. The cold resistance of each species is subject to various factors such as altitude and exposure of the site, frost, fog, soil moisture and the prevailing winds. It also depends on the compatibility of the species with the environment of the site where it is growing. For example, in Tanganyika (Parry and Willian, 1957) on the Elton plateau at 2,700 meters (9,000 feet), P. patula is just as hardy to cold as it is in its normal habitat and will stand a temperature as low as 10º C (12º F), while in Misiones it is damaged by cold at 5º C (23º F).
FIGURE 13. - Similarity of climatic conditions, on the basis of the mean temperatures of the hottest and coldest months, on the natural site of Pinus radiata in California and in regions where this species has been successfully established: northern New Zealand, southern central Chile, southern Australia, Tasmania and northern Spain. Each locality is represented by two circles, one black corresponding to the MTHM, and the other white indicating the MTCM.
The climatic requirements and tolerances of certain conifers have been outlined in relation to the environmental conditions of their natural habitat and of the sites into which they have been introduced, with results varying from excellent to complete failure.
The successful introduction of a species depends essentially on the degree of similarity of climate in the natural site to that of the new sites. Basic data in determining this similarity are: seasonal rainfall distribution; amount of annual rainfall; mean temperatures of the coldest and hottest months and the absolute minima. Conifers can be divided into three groups, according to the rainfall pattern of their natural sites, corresponding to winter rainfall, uniformly distributed rainfall and summer rainfall areas. It is to be noted that each group, owing to its specific origin, is incompatible to some extent with the other groups as regards rainfall area.
A comparison of such climatic features provides good basis for ascertaining whether a species is likely to succeed in a specific area. For example, the ideal climatic conditions for the following species are:
annual rainfall: between 1,100 and 1,700 millimeters (43 and 67 inches), predominating in the coldest half of the year;
mean temperature of the coldest month: 7º to 11º C (45º to 52º F);
mean temperature of the hottest month: 16.5º to 18.5º C (62º to 65º F);
absolute minimum temperature: if possible not below 7º C (19º F).
rainfall: between 1,250 and 2,175 millimeters (50 and 87 inches) distributed uniformly throughout the year;
no dry season;
mean temperature of the coldest month: between 8º and 14º C (46º and 57º F);
mean temperature of the hottest month: 18º to 24º C (64º to 74º F);
absolute minimum temperature: not below 12º C (17º F).
rainfall: between 1,000 and 3,500 millimeters (40 and 140 inches) mostly in the hottest six months;
mean temperature of the coolest month: 16º to 25º C (61º to 77º F);
mean temperature of the hottest month: 22.5º to 27.5º C (72º to 82º F);
absolute minimum temperature: not below 8º C (17º F).
With fuller information at hand it will be possible to specify for each species and its ecotypes, if any, the optimum climates and also the limits within which their use as forest species is advisable.
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FORTHCOMING FAO MEETINGS IN 1963
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Stockholm, Sweden, 23-30 August
Fifth Conference on Wood Technology
Madison, Wisc., U.S.A., 16-27 September
European Forestry Commission
Geneva, Switzerland, 30 September - 5 October
ECE Timber Committee
Geneva, Switzerland, 7-11 October
FAO Conference - Forest" Committee
Rome, Italy, 31 October - 15 November