A.D. Miller
A.D. Miller is a silviculturist engaged in British bilateral assistance work in Ecuador.
The author compares the rates of growth of Pinus radiata in various parts of Ecuador at different altitudes and on different soils. The effects of altitude are examined in particular. Different thinning plots at one location are compared and observations are made concerning soils and pathology. Some economic factors affecting the growth of P. radiata in Ecuador are presented.
Pinus radiata has been planted extensively in Australia, New Zealand, South Africa and Chile, but there is little published information on its growth in these countries. Beekhuis (1966) and Lewis (1954) both publish some sample plot data but are more concerned with generalized tables and alignment charts which, though excellent for estimating volumes and other data about a particular stand, give little idea of what may be considered normal. The FAO study on Pinus radiata (1960) gives considerable data on height growth and some on volume, but the two are not always related. The United Kingdom forest management tables (1971) do not include P. radiata, but recommend that the tables for P. nigra var. maritima should apply; these, however, indicate relationships between height-age-volume production which are very different from those for P. radiata in Ecuador and in the southern hemisphere generally.
P. radiata has not been planted widely in Ecuador, nor are there any extensive plantations of this species more than a few years old, but there are enough small plantations of various ages and on a sufficiently broad range of sites to give a good general indication of its performance. The first recorded trial plot of this species in Ecuador was set out at Cotopaxi in 1925 at an altitude of 3 550 metres. Unfortunately, no growth measurements were taken; the plot was neglected and is now very understocked, but the height and girth of remaining trees generally support conclusions and forecasts made from other and younger plantations.
In 1954 and 1959 small plantations were made at Hacienda El Refugio at 3 510 and 3 620 metres respectively. Also in 1959, a few hectares were planted at Achapichu at 3 180 metres (where a permanent sample plot was set out in 1973), and at Cotopaxi at 3 550 metres, the latter plantation being divided up into plots of different thinning grades in 1968. At Conocoto, at an altitude of 2 550 metres, a plot was set out in 1955 that is now valueless except for measurements of individual trees, but in 1963 a permanent sample plot was established at the same place and has been the subject of repeated measurements. In 1965 a small plantation was made at Hacienda Tortorillas, near Palmira, in a low-rainfall area; following grazing and other damage, volume measurements are not possible there, but height measurements are of interest and are discussed below.
Thus, on the basis of the very limited data available, it seems best to compare the growth of P. radiata in Ecuador with that in other countries. The height growth in the 1963 sample plot at Conocoto equals the best published data from anywhere in the world, and the nearby 1955 trees indicate that these results will probably be maintained. At the other end of the scale, a 1963 plantation at Cotopaxi has a height growth rate slower than that indicated in any published data known to the writer.
1. MEAN ANNUAL INCREMENT OF PINUS RADIATA BY AGE
Comparison of volume production by P. radiata in different countries is complicated by the fact that published data are not always strictly comparable. Some tables include bark and some do not; some include thinning volumes and some do not; and the top diameter limits to which measurements are made also vary. The curves shown in Figure 1 give, in some cases approximately, representative data for total production over bark to a top diameter of 9 cm. There is variation between different countries in the way in which volume production is related to the mean height growth of a stand, and also in the length of rotation at which the maximum mean annual increment is reached (Table 2). It is not clear to what extent these differences in volume production are due to understocking in the stands, and co what extent local conditions produce significantly different form factors in the trees.
P. radiata has been planted on a considerable range of sites in Ecuador, and the variations in height between sites are significant. The sites all lie in the Sierra mountains at altitudes between 2 500 and 3 600 metres above sea level. The soils have a generic similarity in that they are all derived from successive layers of volcanic ash on which vegetation has developed, leaving layers of soil with high organic content separated by layers of wholly inorganic pumice, but the depth of the various layers varies considerably from place to place.
In texture the soils are generally sandy or silty and are well drained except where compacted or cemented layers occur locally. In regions of high rainfall (over 1 000 mm per year), incipient iron pans have been noted. The parent material is of great depth, and penetration by tree roots is generally, good.
TABLE 1.-P. RADIATA IN ECUADOR: DISTRIBUTION AND AGE
|
Location |
Year of planting |
|
Cotopaxi |
1925 |
|
Cotopaxi |
1959 |
|
El Refugio, Chaupi |
1954 |
|
El Refugio, Chaupi |
1959 |
|
Achapichu |
1959 |
|
Conocoto |
1955 |
|
Conocoto |
1963 |
|
Tortorillas-Palmira |
1965 |
For forest soils the pH values are rather high, generally between 6.0 and 7.0; the nitrogen content of the soils is generally adequate at 15 and 40 ppm; the potash content varies from adequate to high, at 30 to 150 ppm; the phosphate content is invariably low, between 1 and 6 ppm throughout the profile, though it is occasionally concentrated in the surface 1-cm layer to the extent of 9 to 12 ppm. Rainfall varies from low (450 mm per year) to high (2000 mm per year).
Soil variations do not seem to lead to significant variations in the rate of height of P. radiata though, as noted below, they may have very important effects on the health of the crops. Evidence of the effect of rainfall is scanty because most of the plantations lie in regions of adequate or high rainfall, although the 1965 plantation at Tortorillas receives an average of a little less than 500 mm per year and the height growth of the crop appears to have been depressed by seasonal drought effects.
By far the most important site characteristic affecting the rate of growth of P. radiata in Ecuador is altitude, and a striking correlation is found there. If values of the height of various crops on humid sites at age 15 years are plotted against the altitude above sea level at which each plantation is growing, all the points lie on a single line. There are insufficient data for sites below 2 500 metres, but the inference is that growth would reach a maximum on humid well-drained soils at about 2 200 metres, and that below this altitude the rate of growth would fall off as the climate became too hot for P. radiata There are no data for sites above 3 600 metres, but the writer's impression is that above this altitude height growth would fall sharply and that P. radiata would not survive above about 4 000 metres.
Data are available from only one "dry" site, Tortorillas, and here the probable height at 15 years lies significantly below that expected for a site at the same elevation on a humid site. The other main factors at Tortorillas - exposure and soils - are strictly comparable with the humid sites, and the writer therefore believes that the reduced rate of growth is due to the lower rainfall in that area. With the loss of height growth amounting to about 3 metres at age 15 years, growth on a dry site appears to correspond with that on a humid site 200 metres higher.
Special note should be taken of areas where healthy growth was apparently checked, in plantations established in 1963 at Cotopaxi, at altitudes between 3 500 and 3 600 metres. In one such area, the height at 10 years is 4 metres, while in another not far away the height at 10 years is 2.25 metres. The reasons for this are not clear: the factors of rainfall, soil analysis, and exposure all indicate that at 10 years of age the mean height of these crops should have been 6 to 7 metres. There is no record of the provenance of these crops, and a partial answer may lie there, but one has the strong impression that there is more to be learned about the factors governing the growth rate of P. radiata when it is near its upper limit of altitude.
TABLE 2. - A COMPARISON OF THE MEAN ANNUAL INCREMENT OF P. RADIATA
|
Country |
Height at 20 year |
Rotation of maximum MAI |
Maximum MAI |
|
Metres |
Years |
m³/ha/year¹ |
|
|
Ecuador |
24 |
21 (?) |
32 |
|
New Zealand II |
24 |
30 |
28 |
|
Australia III |
24 |
25 |
26 |
¹ Measured over bark, including thinnings to a top diameter of 9 cm.
The pathology of P. radiata in Ecuador has been little studied in spite of the fact that many stands are alarmingly unhealthy. The principal symptoms observed were:
- Yellowing of needle tips.
- Distortion and death of leading and side shoots.
- Drooping and eventually actual severance of side branches.
- Lesions and weakness of main stem, leading to breakage.
- Instability or wind throw after the age of about 10 years.
In addition, there have been defoliating attacks by unidentified geometric larvae, with effects varying from mild to severe. As mentioned previously, the phosphate content of the soils is very low, and this may well have the primary effect of weakening the crops and making them susceptible to attacks by insects and fungi. In some sites the phosphate content of the surface layers of the soils is much above that of the lower layers; in these places rooting is very superficial, and this fact apparently contributes to instability or wind throw after the age of about 10 years. Further, the particular manner of distortion and die back of leading and side shoots is strikingly similar to that attributed to boron deficiency (Stone and Will, 1965; Frith, 1972). It therefore appears likely that the primary cause of the observed pathological conditions lies in soil deficiencies, and experiments have been set out to test the effect of adding boron and phosphate to the soils.
It must be mentioned, however, that microscopic mites, which could be a source of primary damage, have been observed in distorted shoots taken from Cotopaxi, and that the branch drooping and falling is associated with a fungal attack in the timber at the point where the branch joins the main stem, although it is not known whether this attack is primary or secondary.
A curious feature of these various conditions is that although ill health of one sort or another is widespread, and more than half the trees in a crop may be affected, timber production continues at the rates shown in the graphs. Certainly some trees become badly distorted, and forking is common, but the total volume per hectare appears little changed. The marketable volume may prove to be another matter, and the results of adding fertilizer may have a critical importance in maintaining proper stem form and hence the market value of the trees.
In 1968 experimental thinning plots were set out in plantations of P. radiata at Cotopaxi dating from 1959 and 1960. These trees were measured by the Ecuadorian Forest Service in 1968 and 1969 and a British team measured the 1959 plots in December 1972. The 1971 projections of what the growth would be in 1972 turned out to be optimistic.
These are the only comparative thinning plots for P. radiata in Ecuador, and their establishment reflects much credit on the División de Capacitación e Investigación of the Ecuadorian Forest Service. Unfortunately, the smallness of the area available, and the considerable degree of variation in the original crops, have lessened the value of the results. In the 1959 plots there are four repetitions of four treatments in random block design, the measured plots being 10 x 10 metres in size with no surrounds. The original planting spacing had been approximately 2 x 2 metres, but by 1968 the actual stocking varied from 1 800 to 2 150 per hectare. The heaviest thinning was applied to the lightly stocked plots, while the most heavily stocked plots were kept as controls. There was also a variation of about 30 percent in the total standing volumes in the original plots. The treatments and measurements to date are shown in Table 3. It will be seen that treatments 1, 2 and 3 involved a thinning at age 9 years, while treatment 4 was the unthinned control. In the writer's view the short time since the thinning and the small differences between treatments 1, 2 and 3 make it best, at this stage, to consider these three as being effectively the same, i.e., as having no significant statistical differences between them; accordingly, the means of these three are also shown in Table 3.
It will be noticed that in treatments 1 and 2 a number of trees were lost between the ages 10 and 13.3 years without any record of their volume. The loss amounts to about 56 trees per hectare in the column of mean values, and probably amounts to a total volume of about 5 cubic metres, This correction is shown in the values of current annual increment (CAI) and mean annual increment (MAI) in Table 3. Table 3 shows three observations for the mean annual increment and two for the current annual increment for each of the two effective treatments, i.e., thinned and unthinned. These are shown as graphs in Figure 3, and the MAI curves have been extended to show the possible points of intersection of the CAI curves with the MAI curves at their peaks.
TABLE 3. - P. RADIATA IN ECUADOR: RESULTS OF THINNING PLANTATIONS
|
|
Treatment 1 |
Treatment 2 |
Treatment 3 |
Mean of treatments 1, 2, 3 |
Treatment 4 | ||||||||||
|
Age (years) |
9 |
10 |
13.3 |
9 |
10 |
13.3 |
9 |
10 |
13.3 |
9 |
10 |
13.3 |
9 |
10 |
13.3 |
|
Trees per hectare |
1 825 |
1 325 |
1 170 |
2 050 |
1 425 |
1 400 |
1 925 |
1 500 |
1 500 |
1 933 |
1 413 |
1 357 |
2 125 |
2 125 |
2 120 |
|
Basal area (m²/ha) |
13.2 |
15.9 |
32.8 |
17.2 |
19.0 |
38.7 |
13.2 |
17.7 |
34.3 |
14.5 |
17.5 |
35.3 |
16.7 |
23.2 |
44.3 |
|
Mean height metres |
5.9 |
7.1 |
10.1 |
6.8 |
7.7 |
9.8 |
6.2 |
7.5 |
11.2 |
6.3 |
7.4 |
10.4 |
6.3 |
7.2 |
10.6 |
|
Standing volume after thinning (m³/ha) |
32.8 |
58.9 |
129 |
44.8 |
76.1 |
144 |
39.2 |
71.3 |
146 |
38.9 |
68.8 |
140 |
56.9 |
98.2 |
175 |
|
Thinning volume (m³/ha) |
9.7 |
- |
- |
15.3 |
- |
- |
4.4 |
- |
- |
9.8 |
- |
- |
- |
- |
- |
|
Total volume including thinnings (m³/ha) |
42.5 |
68.6 |
138.7 |
60.1 |
91.4 |
159.3 |
43.6 |
75.7 |
150.4 |
48.7 |
78.6 |
149.8 |
56.9 |
98.2 |
175 |
|
Periodic increment (m³/ha) |
- |
26.1 |
70.1 |
- |
31.3 |
67.9 |
- |
32.1 |
74.7 |
- |
29.9 |
71.2 |
- |
41.3 |
76.8 |
|
Current annual increment |
- |
26.1 |
21.2 |
- |
31.3 |
20.5 |
- |
32.1 |
22.6 |
- |
29.9 |
21.6 |
- |
41.3 |
23.2 |
|
Mean annual increment |
4.7 |
6.9 |
10.4 |
6.8 |
9.1 |
12.0 |
4.8 |
7.6 |
11.3 |
5.4 |
7.9 |
11.2 |
6.3 |
9.8 |
13.2 |
3. EXPERIMENTAL PLOTS OF PINUS RADIATA AT COTOPAXI, ECUADOR
The very sharp fall in current annual increments between ages 10 and 13 years will be noted, together with the implication of an early peak in the mean annual increment curves at ages 15 to 18 years. Of course, in many ways these data are not satisfactory: the thinning plots are too small and have no surrounds, and the time over which measurements have been taken is, as yet, too short. Nevertheless they indicate a real trend, and in the writer's view this serious loss of current increment is due to the present ill health of the crops, and is probably quite typical of P. radiata in Ecuador at altitudes of about 3 500 metres. It seems probable that this condition could have been improved by the earlier addition of phosphate and trace elements to the soil, but the extent of such response and also the extent to which the increase in timber production would justify the cost of fertilizer will have to await the results of current investigations.
The other point of critical interest shown by this experiment is that the unthinned plots produced 16.7 percent more timber than the thinned plots (i.e., 175 m³/ha compared with 150 m³/ha at age 13.3 years), but this fact is due at least partly to the better stocking in the unthinned plots at the time that the experiment was set out, and partly to the fact that insufficient time has elapsed for the thinned plots to respond adequately, in view of their present lack of vigour. Nevertheless, these figures support the view that P. radiata plantations grown on short rotations for pulp should not be thinned.
Insufficient data are available for a thorough assessment of the economics of P. radiata in Ecuador, but certain broad trends may be discerned.
First is the supreme importance of altitude above sea level. Assuming that growth in yield classes below 10 is likely to be unprofitable, this means that on the greater part of the Páramo sites an altitude of 3 600 metres should be the upper limit. Possibly other species may replace P. radiata at higher elevations. Conversely, the great improvement in growth at slightly lower altitudes (e.g., yield class 20 at about 3 400 metres and yield class 30 at 3 100 metres), demonstrates the importance of planting on lower ground wherever it is available.
Secondly, the question of planting spacing is especially important on short rotations as envisaged in Ecuador. An example will illustrate the point.
Let it be assumed that a certain site planted at 2 x 2 metres will show a mean annual increment of 14 cubic metres per hectare per year on a rotation of 15 years: there will be 2500 trees per hectare of which, say, 2 000 will survive and the total volume production will be 14 x 15 metres, or 210 cubic metres. Hence the mean volume per tree will be 0.105 cubic metre. If, however, the same site were planted at a spacing of 3 x 3 metres, or 1 110 per hectare, of which, say, 1 000 per hectare survive, there would probably be a loss of production of about 15 percent compared with that at 2 x 2 metres. That is, the 1 000 trees at wider spacing would produce about 180 cubic metres per hectare and the mean volume per tree would be 0.180. It is much cheaper per cubic metre to handle these larger trees, and the lower costs of harvesting, combined with the reduced costs of planting at wider spacing, tend to make wider spacing more profitable in spite of the loss in production per hectare. Of course, conditions vary from place to place, and the optimum spacing should be worked out for each site in the light of probable costs and future income.
Calculations by Frith (1972) suggest a third broad trend, that P. radiata plantations growing at 3 500 metres altitude will yield a financial return of about 10 percent, allowing for deductions of 30 percent of total volume because of bark and unsaleable timber. If costs change, the calculations will, of course, need to be revised, but for the time being they are encouraging.
BEEKHUIS, J. 1966. Prediction of yield and increment in Pinus radiata stands in New Zealand. Wellington, New Zealand Forest Service, Forest Research Institute. Technical Paper No. 49.
FAO. 1960. Pinus radiata, by C.W. Scott. Rome. FAO Forestry and Forest Products Studies No. 14.
FRITH, A.C. 1972. Plan modelo para el manejo de plantaciones de pino en las provincial de Cotopaxi y Pichincha. Rome, FAO. FAO-SF/ECU71/22/FO. (Working document)
LEWIS, E.R. 1954. Yield of unthinned Pinus radiata in New Zealand. Wellington, Forest Research Institute. New Zealand Forestry Research Notes, 1(10).
STONE, ILL. & WILL, G.M. 1965. Boron deficiency in Pinus radiata and P. pinaster. Forest Science 11: 425-433.
TOLLENAAR, HUIB. 1970. Boron deficiency in pine plantations in central Chile. Mérida Venezuela, Instituto Forestal Latino-Americano. Boletín Nos. 33-34.
UNITED KINGDOM. FORESTRY COMMISSION. 1971. Forest management tables (metric). London, HMSO. Forestry Commission Booklet No. 34.
