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Growth intercept as an indicator of site quality for planted and natural stands of Pinus nigra var. pallasiana in Greece
Forest Ecology and Management, 32 (1990) 103-115
103
Elsevier Science Publishers B.V., A m s t e r d a m - - Printed in The Netherlands
G r o w t h I n t e r c e p t as an I n d i c a t o r o f S i t e Q u a l i t y for P l a n t e d a n d N a t u r a l S t a n d s o f Pinus nigra v a r . paUasiana in G r e e c e A. ECONOMOU
Forest Research Institute, Terma Alkmanos, 11528 Athens (Greece) (Accepted 2 May 1989)
ABSTRACT Economou, A., 1990. Growth intercept as an indicator of site quality for planted and natural stands of Pinus nigra vat. paUasiana in Greece. For. Ecol. Manage., 32: 103-115. Five-year intercept was found to be a reliable index in site evaluation of both planted and natural stands of black pine. Use of more than five internodes improves the precision of the site-index prediction equation, while using less than five nodal lengths gives inaccurate results. Five-year intercept starting at a point higher than breast height does not significantly improve site-index prediction.
INTRODUCTION
Growth intercept, which is usually defined as the length of the first few internodes above breast height, offers a direct measurement of site quality and enables early classification of stands too young for classical methods. The growth-intercept method, which was first proposed by Wakeley in 1954 (Wakeley and Marrero, 1958) for species having easily recognisable internodes marking the progress of annual whorls, is particularly useful for short rotations or for site-quality assessment of young or juvenile stands, but serious errors may result for species that are managed on 80-100-year rotations (Carmean, 1975, 1983). The length of the first 3 to 6 internodes above breast height has been used by most investigators as the growth intercept. Other combinations of starting point and number of internodes may also be used when this improves the precision of site-index estimation. Fewer than 3 internodal measurements are usually less precise due to the year-to-year variation in growth (Smith and Ker, 1956). Breast height is usually used as the starting point because height up to this point is often affected by weed competition, stock quality, planting method, 0378-1127/90/$03.50
© 1990 Elsevier Science Publishers B.V.
104
A. ECONOMOU
injuries, surface soil characteristics and degree of natural or artificial protection (Ferree et al., 1958; Day et al., 1960; Brown and Stires, 1981 ). The use of the growth-intercept method has the following advantages: (1) total age and height measurements are not needed, thus errors associated with erratic early height growth or measurement errors of height and age are avoided and fieldwork simplified; (2) site-index curves, which usually do not extend to very young ages ( < 20 years old) or include large errors, are not needed, so the growth intercept is suited for very young stands; and (3) in close stands it is easier to measure growth intercept than total tree height. However, there are several limitations in using the growth-intercept method because it represents a current site index rather than a long-term one, and early growth of a stand does not always accurately reflect later growth. It might not also indicate the true site quality when the growth conditions are affected by temporary fluctuations in factors such as abnormal weather, excesses of nutrients following burning, browsing damage or temporarily favourable seepage. Bull (1931) used a method similar to growth intercept, which employed the years the trees required to grow from 3 to 9 feet (1-3 m) above ground, as well as the number of years to grow other combinations of lengths. He concluded that this method gave unsatisfactory results for site evaluation. Wakeley and Marrero (1958) found the 5-year intercept significantly related to total tree height, and reported that, in similar cases, the growth-intercept method was more accurate in expressing site quality than the total height. Ferree et al. (1958), Day et al. (1960), Adu (1968) and Malcolm (1970) found the 5-year intercept to be a reliable indicator of site for the species examined, while Oliver (1972) stressed that the 4-year intercept gave good results and pointed out that little improvement could be expected by measuring more than 4 internodes. Brown and Stires (1981), who found 3-, 4- and 10-year intercepts significantly related with tree height, concluded that the precision in site-index estimation increased consistently as the number of internodes included increased, and also as the base of the intercept was moved upwards from breast height to the first and second internode above it. Alban (1972, 1979) stressed that measuring 5-year intercept at 8, 10 or 15 feet ( ~ 2.5, 3.0 and 4.6 m) above the ground resulted in a better prediction of 50-year height of red pine than did measuring it at breast height. Beck (1971a, b) noted that the 5-year intercept was more precise than 3-year intercept and as precise as the site index estimated from polymorphic site-index curves, while Papamichos (1973) stated that the 5-year intercept was more sensitive to environmental factors than top height of Sitka spruce, and noticed that measuring it at 2.5 m instead of at breast height resulted in a better site index. Blyth (1974), however, found the 5-year intercept of the same species to be more
GROWTH INTERCEPT AS INDICATOR OF SITE QUALITY FOR PINUS
105
variable than top height and suggested that measurements should begin 3 m from the ground to avoid height variabilityarising from early check. Hatzistathis and Papageorgiou (1976) and Arabatzoglou (1985) found the 5-year intercept to be highly associated with site index of black pine plantations in Greece, while the former also noticed that starting at 2.5 m above ground gave better results. The purpose of the present study was to investigate the precision and effectiveness of the growth-intercept method in estimating site index of planted and natural young stands of black pine in Greece using 3-, 4-, 5-, 6-, 8- and 10year intercepts and more than one startingpoint. '
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Fig. 1. Location of the study areas.
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106
A. ECONOMOU
MATERIALS AND METHODS
Data of the present study were collected from two areas, Arcadia (central Peloponnese) and the Pindos mountain range (central and northern Greece), in plantations and natural stands, respectively (Fig. 1 ). The climate of the two sampling areas is weak meso-Mediterranean with the number of bioclimatically dry days (x) more than 40 and less than 75 (40 < x < 75; Mavrommatis, 1980). The mean annual rainfall for Arcadia forest is 1017.5 mm (Settas, 1975) and the mean monthly temperature 11.9 ° C. For Pindos forest the corresponding values are 1038.5 mm and 10.9°C (MarkouJakovaki et al., 1975). The warmest months are July and August with mean monthly air temperatures of 22~C and 21.5°C, for Arcadia and Pindos, and the wettest month December, with 172 mm and 163 mm rainfall, respectively. The soil parent material in Arcadia forest is metamorphic rock (mica schist and phyllites) and in Pindos forest flysch (sandy and argillaceous) and peridotites. The soils of the former sites are coarse-textured in the A horizon, mainly sandy-loams, but medium-textured in the B and C horizons, sandy-loams to sandy-clay-loams. The soils derived from flysch and peridotites are mediumtextured, sandy-loams to clay-loams. The understory vegetation in Arcadia sites is mainly scrub, while it is herb and grass in Pindos sites. In Arcadia, stands were planted in the 1960s on former heathland. In the Pindos sites, stands were between 25 and 35 years old, growing mainly on previous black-pine stands destroyed by fires. A total of 81 sample plots of 0.01 ha were all located on pure black-pine stands, 39 in plantations and 42 in natural stands, of which 22 were on flysch parent material and 20 on peridotite. Considerable care was taken in plot selection. Plots were restricted to hoTABLE 1
Growth variablesi, with their maxima (max.), minima (rain), means and standard deviations
(sD) No.
1. 2. 3. 4. 5. 6. 7. 8.
Variable
5-year intercept 6-year intercept 8-year intercept 10-year intercept 3-year intercept (3-1) 4-year intercept (4-2) 5-year intercept (4-1) Site index 25
1All values in m.
Arcadia sites
Flysch sites
Ma~-
Min.
Mean
SD
Max.
Min.
Mean
SD
2.89 3.61 5.10 6.46 2.30 2.86 3.66 14.88
1.31 1.77 2.63 3.69 1.09 1.72 1.79 9.53
2.21 2.72 3.79 4.94 1.58 2.22 2.69 11.67
0.359 2.51 0.428 3.05 0.547 4.08 0.623 5.29 0.261 1.62 0.279 2.24 0.375 2.83 1 . 2 0 3 13.12
1.51 1.82 2.36 3.16 0.76 1.26 1.58 7.74
1.98 2.40 3.22 4.09 1.23 1.69 2.10 9.91
0.325 0.383 0.509 0.603 0.250 0.284 0.355 1.207
G R O W T H INTERCEPT AS INDICATOR OF SITE QUALITY FOR PINUS
107
mogeneous areas with regard to topography, soil and litter cover, and supported well-developed and stocked, even-aged stands with closed canopies, showing no visible damage from fires, grazing, winds, snow, disease, erosion or destructive cutting. The plots were situated well away from forest margins to avoid their influences. Three dominant and codominant trees with the largest diameter were selected and measured. Since the stands examined were young, the distinction between dominant and codominant trees was very small - almost non-existent. Trees obviously injured were rejected. From each plot the following growth measurements were made: 1. Total height. Heights of the three largest trees were measured with a counting folding pole or with a tape fitted on a folding pole 8 m long. Trees higher than 8 m were measured twice with a Blume-Leiss altimeter and the average recorded. 2. Five, 6-, 8- and lO-year intercepts. These are the internodal distances of the 5th, 6th, 8th and 10th nodes of the same trees measured for the top height, starting with the whorl at or just above breast height. Measurements were done with the same instruments as for total height and the length recorded to the nearest cm. 3. Tree height above breast height. This was derived from the total tree height by subtracting 1.30 m, and was used for estimating site index at 25 years. 4. Age of trees at breast height and base. This was found by counting the whorls from breast height or the tree base up to the tree top (tip). The age found was checked by taking an increment core at breast height and/or tree base. From the age and the tree height above breast height, site index 25 was
Peridotite sites
P i n d o s sites
All sites
Max.
Min.
Mean
SD
Max.
Min.
Mean
SD
Max.
Min.
Mean
SD
2.34 2.82 3.79 4.86 1.60 2.07 2.67 12.26
1.46 1.78 2.26 2.89 0.75 1.11 1.38 6.85
1.82 2.20 2.93 3.70 1.11 1.50 1.89 9.27
0.308 0.361 0.487 0.615 0.226 0.293 0.360 1.332
2.51 3.05 4.08 5.29 1.62 2.24 2.83 13.12
1.46 1.78 2.26 2.89 0.75 1.11 1.38 6.85
1.91 2.30 3.08 3.91 1.17 1.60 2.00 9.61
0.324 0.382 0.514 0.632 0.244 0.300 0.310 1.292
2.89 3.61 5.10 6.46 2.30 2.86 3.66 14.88
1.31 1.77 2.26 2.89 0.75 1.11 1.38 6.85
2.04 2.51 3.42 4.40 1.37 1.90 2.34 10.60
0.378 0.453 0.638 0.811 0.325 0.423 0.508 1.615
Y(1) Y(2) Y(3) Y(4) Y(5) Y(6) Y(7) Y(8)
Flyschsites
Y(1)* Y (2) Y (3) Y(4) Y(5) Y(6) Y(7) Y(8)
1.0000 0.9798 0.9133 0.8752 0.5597 0.5377 0.5706 0.7668
1.0000 0.9703 0.9173 0.8823 0.5484 0.4828 0.6781 0.7011
Arcadia sites (schist, phyllites)
1
1.0000 0.9677 0.9312 0.6968 0.6307 0.6843 0.8281
1.0000 0.9632 0.9254 0.6857 0.5336 0.7644 0.7250
2
Correlation matrices of growth indices
TABLE 2
1.0000 0.9788 0.8486 0.7767 0.8258 0.8643
1.0000 0.9712 0.8361 0.6921 0.8121 0.7721
3
1.0000 0.8551 0.8701 0.8966 0.8560
1.0000 0.8238 0.8143 0.8564 0.8267
4
1.0000 0.8823 0.9393 0.7628
1.0000 0.7881 0.7710 0.6554
5
7
8
1.0000 0.6113
1.0000
1.0000 0.9850 0.7069
1.0000 0.7513
1.0000
Significant value of r at P = 0.05 =0.4427 Significant value of r at P = 0.01 = 0.5368 Significant value of r at P=O.O01 =0.6524
1.0000 0.7403 0.7345
Significant value of r at P = 0.05 = 0.3172 Significant value of r at P = 0.01 = 0.4079 Significant value of r at P = 0.001 = 0.5072
6
c) z o
.>
oo
1.0000 0.9805 0.9022 0.8421 0.8900 0.8674
All sites (schist+flysch+peridotite) Y(1) 1.0000 Y(2) 0.9446 1.0000 Y(3) 0.9067 0.9694 Y(4) 0.8765 0.9309 ¥(5) 0.6848 0.7824 Y(6) 0.6688 0.7140 Y(7) 0.7399 0.8046 Y(8) 0.7558 0.8044
*For Y(1 ) ...... Y(8), see Table 1.
1.OOOO 0.9830 0.8711 0.8321 0.8637 0.8261
1.0000 0.9742 0.9435 0.7475 0.7154 0.7507 0.7749
Pindos sites (flysch + peridotite) Y(1) 1.0000 Y(2) 0.9814 Y(3) 0.9294 Y(4) 0.8966 Y(5) 0.6285 Y(6) 0.6395 Y(7) 0.6544 Y(8) 0.7170
1.0000 0.9860 0.8795 0.8615 0.8808 0.7651
1.0000 0.9781 0.9509 0.7729 0.7608 0.7837 0.6913
Peridotite sites Y(1) 1.OOO0 Y(2) 0.9807 Y(3) 0.9372 Y(4) 0.9056 ¥(5) 0.6582 Y(6) 0.6895 Y(7) 0.6897 Y(8) 0.6290
1.0000 0.9116 0.9204 0.9365 0.8963
1.0000 0.8789 0.9565 0.9216 0.8238
1.0000 0.8925 0.9243 0.9317 0.7685
1.0000 0.9105 0.9193 0.8353
1.0000 0.9030 0.9499 0.7873
1.0000 0.9184 0.9600 0.z931 1.0000 0.7733
1.0000
1.0000 0.7780
1.0000
1.0000 0.9341 0.8576
1.0000 0.8299
1.OOO0
Significant value of r at P = 0.05 = 0.2189 Significant value of r at P = 0.01 =0.2854 Signficant value Of r at P=O.O01 =0.3603
1.0000 0.9873 0.7516
Significant value of r at P = 0.05 = 0.3044 Significant value of r at P = 0.01 = 0.3931 Significant value of r at P=O.O01 =0.4896
1.0000 0.9874 0.7589
Significant value of r at P = 0.05 =0.4412 Significant value of r at P = 0.01 =0.5563 Significant value of r at P = 0.001 = 0.6920
¢D
r~
0
0
0
N
g
0
Growth intercept (x) variable
5-year intercept 6-year intercept 8-year intercept 10-year intercept 3-year intercept (3-1) 4-year intercept (4-2) 5-year intercept (4-1)
1. 2. 3. 4. 5. 6. 7.
5-year intercept 6-year intercept 8-year intercept 10-year intercept 3-year intercept (3-1) 4-year intercept (4-2) 5-year intercept (4-1)
Peridotite sites
1. 2. 3. 4. 5. 6. 7.
Flysch sites
Arcadia sites 1. 5-year intercept 2. 6-year intercept 3. 8-year intercept 4. 10-year intercept 5. 3-year intercept (3-1) 6. 4-year intercept (4-2) 7. 5-year intercept (4-1)
No.
20.37
17.60 13.97 13.80 12.50 14.29 13.55
y=3.680+2.547x y = 3.160 + 2.091x y = 3.120 + 1.665x y=4.095 +4.677x y = 4.100 + 3.450x y=3.890+2.861x
12.61 9.62 7.75 8.18 12.80 15.32 13.33
27.98 26.10 22.23 17.42 31.40 25.35 34.47
RSS
y = 4.340 + 2.718x
y = 4.260 + 2.850x y = 3.654 + 2.609x y = 3.320 + 2.050x y = 2.898 + 1.715x y---5.381 +3.683x y = 4.840 + 3.001x y=4.530 + 2.556x
y = 6.474 + 2.351x y = 6.118 + 2.041x y = 5.223 + 1.669x y = 3.783 + 1.597x y=6.869+3.027x y = 4.650 + 3.166x y = 6.380 + 1.964x
Site index 25 (y) prediction equation
Site index (y) prediction equations using growth intercept indices (x)
TABLE 3
0.6290 0.6913 0.7651 0.7685 0.7931 0.7589 0.7733
0.7668 0.8281 0.8643 0.8560 0.7628 0.7069 0.7513
0.7011 0.7250 0.7721 0.8267 0.6554 0.7345 0.6113
r
0.3956 0.4779 0.5854 0.5906 0.6290 0.5759 0.5869
0.5880 0.6857 0.7470 0.7327 0.5819 0.4997 0.5645
0.4915 0.5256 0.5960 0.6834 0.4295 0.5395 0.3737
r2
1.035 0.962 0.858 0.852 0.811 0.867 0.856
0.775 0.677 0.607 0.624 0.781 0.854 0.797
0.858 0.829 0.765 0.677 0.909 0.817 0.952
SEE
28.546*** 43.657"** 59.059*** 54.827*** 27.831"** 19.975"** 25.929***
35.772*** 41.012*** 54.625*** 79.879** * 27.865*** 43.336*** 22.078***
11.780"* 16.476"** 25.421"** 25.959*** 30.528*** 24.448*** 28.770***
F
18 18 18 18 18 18 18
20 20 20 20 20 20 20
37 37 37 37 37 37 37
DF (n-2)
0
o
0
C~
5-year intercept 6-year intercept 8-year intercept lO-year intercept 3-year intercept (3-1) 4-year intercept (4-2) 5-year intercept (4-1)
1. 2. 3. 4. 5. 6. 7.
5-year intercept 6-year intercept 8-year intercept lO-year intercept 3-year intercept (3-1) 4-year intercept (4-2) 5-year intercept (4-1)
All sites (schists + flysch + peridotite)
1. 2. 3. 4. 5. 6. 7.
Pindos sites (flysch+peridotite)
y = 3.419 + 2.869x y=3.082+2.197x y = 2.743 + 1.785x y = 4.908 + 4.152x y=4.395+3.271x y = 4.448 + 2.636x
y = 4.019 + 3.229x
y--- 3.573 + 2.62 Ix y----3.218 + 2.079x y = 3.034 + 1.685x y=4.719+4.173x y----4.435 + 3.235x y=4.179+2.717x
y=4.171+2.856x
89.43 73.63 51.64 41.02 63.06 55.19 64.94
33.25 27.35 21.73 22.00 26.02 29.78 27.01
0.7558 0.8044 0.8674 0.8963 0.8353 0.8576 0.8299
0.7170 0.7749 0.8261 0.8238 0.7873 0.7516 0.7780
0.5712 0.6471 0.7524 0.8034 0.6977 0.7355 0.6887
0.5141 0.60O4 0.6824 0.6786 0.6198 0.5649 0.6053
1.057 0.959 0.804 0.716 0.888 0.834 0.901
0.901 0.817 0.744 0.732 0.797 0.852 0.812
105.279"** 144.804"** 240.117"** 322.705*** 182.316"** 219.567"** 174.748"**
42.190"** 60.105"** 85.979*** 84.443*** 65.200*** 51.928"** 61.351"**
79 79 79 79 79 79 79
40 40 40 40 40 40 40
o
0
112
A. ECONOMOU Arcadia sites
Flysch sites
Peridotite sites
Pindas sites
Total sites
0~
0,8
Ev -~ 0.7
~::t
I I
0 u O.f
c_ 8 0.S ilil '.::~ 0.4 5
6
8
10 "3
6
10
Number
$
of
10 3
5
5
81034
tO
1
4
internodes
Fig. 2. Correlation coefficient values of the relationship between site-index 25 and the growthintercept indices.
estimated from the site-index curves established by Economou (1987). The 3-, 4- and 5-year intercepts were also calculated later in the laboratory by subtracting 5- and 6-year intercepts from 8- and 10-year intercepts. RESULTS AND DISCUSSION
The data were analysed by forest (plantation and natural stands), and by soil parent material, and combined using correlations and regression analyses. The range, mean, and standard deviation of site-index 25 and the intercept indices are given in Table 1. Correlation coefficients of site-index 25 with all growth intercepts for all sets of data examined were strong to very strong and highly significant, varying from 0.6113 to 0.8963 (Table 2). The coefficients of determination, varying from 0.37 to 0.80, show that approximately 40-80% of the site-index variation is associated with variation in growth intercept (Table 3). Figure 2 illustrates the graphical representation of the correlation-coefficient (r) values by set of data and number of internodes measured. The highest correlation coefficient for Arcadia and total data set is that of 10-year intercept, while 8-year intercept has the highest values for the other sets of data. The 5-year intercept with breast height as starting point gives better results for Arcadia and sites on flysch: however, when a starting height of approxi-
GROWTH INTERCEPT AS INDICATOR OF SITE QUALITY FOR PINUS
113
mately 3.30 m above ground is used, it gives better results for peridotite, Pindos and total sites. Taking these findings into account, and the fact that no significant differences were found (P-- 0.05 ) between the correlation coefficients of site index 25 and the 5-year intercept starting at breast height and at 3.30 m, and also the difficulties in measuring this last intercept, it can be concluded that the 5-year intercept with breast height as starting point is a better index for site-quality evaluation. The regression analysis and the analysis of variance (Table 3) showed the slope of the relationship curves to be positive and highly significant ( P < 0.001 ). The predictive value of growth intercepts can be placed in the following decreasing order: 10-, 8-, 6- and 5-year intercepts starting at breast height, followed by those with other starting points. For the latter, no particular order was established because of the observed differences in their values and between the data sets, probably due to year-to-year variations of climatic conditions. Thus, 5 nodes are considered the least number of nodes to be used for black pine's site-quality assessment. The results of the present study revealed the 5-year intercept to be a fairly reliable index for site-quality evaluation of both planted and naturally regenerated stands of black pine, and agree with the results reported by Ferree et al. (1958), Day et al. (1960), Adu (1968), Beck (1971a,b), Papamichos (1973), Blyth ( 1974 ), Hatzistathis and Papageorgiou (1976) and Arabatzoglou ( 1985 ). The use of more than 5 internodes improves the precision of the site-index prediction equations (Table 3) and is in agreement with the results reported by Brown and Stires (1981). The 8-year intercept is considered to be the best growth intercept for the areas studied because it represents a reasonable compromise between ease of measurements and precision in estimating site index. The use of 3-, 4- and 5year intercept starting higher than breast height does not significantly improve the precision of the site-index prediction equation and also presents more difficulties in measuring them. However, Alban (1972, 1979) found a more accurate prediction of red-pine site index, using the 5-year intercept when the base was moved upwards from 8 to 10 and 15 feet above breast height. Brown and Stires (1981) also reported similar results, but Hatzistathis and Papageorgiou (1976), even though suggesting a starting point 2.5 m above ground, noticed that the correlation coefficient was only slightly improved in comparison with that of the 5-year intercept starting at breast height (r--0.88 to r = 0.91, respectively). The growth-intercept approach simplifies the site index of the young stands studied permitting its estimation even for those stands which have grown for only 5-10 years beyond breast height. However, when applying growth-intercept methods on new areas and different species, it would be better to test the precision of results using various numbers of internodes and starting points in addition to breast height.
114
A.ECONOMOU
ACKNOWLEDGEMENTS
I would like to express by gratitude to Dr. P.C. Burnham, Senior Lecturer at Wye College, London University, U.K. and Dr. G. Nakos, Soil Scientist with the Forest Research Institute, Athens, Greece, for their helpful comments made on the manuscript.
REFERENCES
Adu, S.V., 1968. Studies of land capabilityfor Scots pine in Strathdon. Ph.D. Thesis, University of Aberdeen, Aberdeen. Alban, D.H., 1972. An improved growth intercept method for estimating site index of red pine. U S D A For. Serv. North Cent. For. Exp. Stn., Res. Note 80, 7 pp. Alban, D.H., 1979. Estimating sitepotential from the early height growth of red pine in the Lake States. U S D A For. Serv. Res. Pap. NC-166, 7 pp. Arabatzoglou, L., 1985. Examination of the relationship between site index and 5-year height intercept in Pinus nigra plantations. FAO/UNDP/FO:DP/GRE/78/O03 (Greece) Work. Doc. No. 24. Beck, D.E., 1971a. Height-growth patterns and site index of white pine in southern Appalachians. For. Sci., 17: 252-260. Beck, D.e., 1971b. Polymorphic site index curves for white pine in southern Appalachians. USDA For. Serv. Res. Pap. SE-80, 8 pp. Blyth, J.F., 1974. Land capability assessment for forestry in NE Scotland. Ph.D. Thesis, University of Aberdeen, Scotland. Brown, J.H. and Stires, J.L., 1981. Growth intercept methods for predicting site index in white pine plantations. Ohio Agric. Res. Dev. Cent. Circ. 265, 15 pp. Bull, H., 1931. The use of polymorphic curves in determining site quality in young red pine plantation. J. Agric. Res., 43: 1-28. Carmean, W.H., 1975. Forest site quality evaluation in USA. Adv. Agron., 27: 175-269. Carmean, W.H., 1983. Forestry development and reforestation. UNDP/FAO/FO:DP/GRE178/ 003 (Greece) Work. Doc. No. 14. Day, W.M., Bey, C.F. and Rudolf, V.J., 1960. Site index for planted red pine by 5-year growth intercept method. J. For., 58: 198-212. Economou, A., 1987. Site quality evaluation of planted and naturally regenerated black pine (Pinus nigra (Am.) vat. pallasiana (Lamb.)) in Arcadia and central Pindos range (Greece). Ph.D. Thesis, Wye College, University of London, 349 pp. Ferree, M.J., Shearer, T.D. and Stone, C.L. Jr. 1958. A method of evaluating site quality in young red pine plantations. J. For., 56: 328-332. Hatzistathis, A. and Papageorgiou, V., 1976. Estimation of site index on the basis of 5-year height growth on man-made stands of black pine. Arist. Univ. Thessaloniki, Sci. Anna., 19:200-227 (in Greek, with English summary). Malcolm, D.C., 1970. Site factors and tree growth of Sitka spruce. Ph.D. Thesis. University of Edinburgh. Markou-Jakovaki, P., Lioki-Livada H. and Tselepidaki, 1975. Climogram and aridity index of the Greek territory. Univ. of Athens, Laboratory of Climatology, 79 pp. (in Greek with summary in English).
GROWTH INTERCEPT AS INDICATOR OF SITE QUALITY FOR PINUS
115
Mavrommatis, G., 1980. The bioclimate of Greece. Relations of climate and natural vegetation. Bioclimatic maps. For. Res. Inst.Athens, For. Res. No. 63 (in Greek with summary in French). Oliver,W.W., 1972. Height intercept for estimating siteindex in young ponderosa pine plantations and natural stands. U S D A For. Serv. Pac. Southwest. For. Range Exp. Stn. Res. Note 276,4 pp. Papamichos, N., 1973. The evaluation of a physiographic approach in forest capability assessment. Ph.D. Thesis, Univ. of Aberdeen, Scotland. Settas, N., 1975. The Climate of Greece. Kleissiounis,Athens, 446 pp. (in Greek). Smith, J.H.G. and Ker, J.W. 1956. Some problems and approaches in classificationof some site in juvenile stands of Doughs-fir. For. Chron., 32: 417-428. Wakeley, P.C. and Marrero, 1958. Five year intercept as siteindex in southern pine plantation.J. For., 56: 3 3 2 - 3 3 6 .
103
Elsevier Science Publishers B.V., A m s t e r d a m - - Printed in The Netherlands
G r o w t h I n t e r c e p t as an I n d i c a t o r o f S i t e Q u a l i t y for P l a n t e d a n d N a t u r a l S t a n d s o f Pinus nigra v a r . paUasiana in G r e e c e A. ECONOMOU
Forest Research Institute, Terma Alkmanos, 11528 Athens (Greece) (Accepted 2 May 1989)
ABSTRACT Economou, A., 1990. Growth intercept as an indicator of site quality for planted and natural stands of Pinus nigra vat. paUasiana in Greece. For. Ecol. Manage., 32: 103-115. Five-year intercept was found to be a reliable index in site evaluation of both planted and natural stands of black pine. Use of more than five internodes improves the precision of the site-index prediction equation, while using less than five nodal lengths gives inaccurate results. Five-year intercept starting at a point higher than breast height does not significantly improve site-index prediction.
INTRODUCTION
Growth intercept, which is usually defined as the length of the first few internodes above breast height, offers a direct measurement of site quality and enables early classification of stands too young for classical methods. The growth-intercept method, which was first proposed by Wakeley in 1954 (Wakeley and Marrero, 1958) for species having easily recognisable internodes marking the progress of annual whorls, is particularly useful for short rotations or for site-quality assessment of young or juvenile stands, but serious errors may result for species that are managed on 80-100-year rotations (Carmean, 1975, 1983). The length of the first 3 to 6 internodes above breast height has been used by most investigators as the growth intercept. Other combinations of starting point and number of internodes may also be used when this improves the precision of site-index estimation. Fewer than 3 internodal measurements are usually less precise due to the year-to-year variation in growth (Smith and Ker, 1956). Breast height is usually used as the starting point because height up to this point is often affected by weed competition, stock quality, planting method, 0378-1127/90/$03.50
© 1990 Elsevier Science Publishers B.V.
104
A. ECONOMOU
injuries, surface soil characteristics and degree of natural or artificial protection (Ferree et al., 1958; Day et al., 1960; Brown and Stires, 1981 ). The use of the growth-intercept method has the following advantages: (1) total age and height measurements are not needed, thus errors associated with erratic early height growth or measurement errors of height and age are avoided and fieldwork simplified; (2) site-index curves, which usually do not extend to very young ages ( < 20 years old) or include large errors, are not needed, so the growth intercept is suited for very young stands; and (3) in close stands it is easier to measure growth intercept than total tree height. However, there are several limitations in using the growth-intercept method because it represents a current site index rather than a long-term one, and early growth of a stand does not always accurately reflect later growth. It might not also indicate the true site quality when the growth conditions are affected by temporary fluctuations in factors such as abnormal weather, excesses of nutrients following burning, browsing damage or temporarily favourable seepage. Bull (1931) used a method similar to growth intercept, which employed the years the trees required to grow from 3 to 9 feet (1-3 m) above ground, as well as the number of years to grow other combinations of lengths. He concluded that this method gave unsatisfactory results for site evaluation. Wakeley and Marrero (1958) found the 5-year intercept significantly related to total tree height, and reported that, in similar cases, the growth-intercept method was more accurate in expressing site quality than the total height. Ferree et al. (1958), Day et al. (1960), Adu (1968) and Malcolm (1970) found the 5-year intercept to be a reliable indicator of site for the species examined, while Oliver (1972) stressed that the 4-year intercept gave good results and pointed out that little improvement could be expected by measuring more than 4 internodes. Brown and Stires (1981), who found 3-, 4- and 10-year intercepts significantly related with tree height, concluded that the precision in site-index estimation increased consistently as the number of internodes included increased, and also as the base of the intercept was moved upwards from breast height to the first and second internode above it. Alban (1972, 1979) stressed that measuring 5-year intercept at 8, 10 or 15 feet ( ~ 2.5, 3.0 and 4.6 m) above the ground resulted in a better prediction of 50-year height of red pine than did measuring it at breast height. Beck (1971a, b) noted that the 5-year intercept was more precise than 3-year intercept and as precise as the site index estimated from polymorphic site-index curves, while Papamichos (1973) stated that the 5-year intercept was more sensitive to environmental factors than top height of Sitka spruce, and noticed that measuring it at 2.5 m instead of at breast height resulted in a better site index. Blyth (1974), however, found the 5-year intercept of the same species to be more
GROWTH INTERCEPT AS INDICATOR OF SITE QUALITY FOR PINUS
105
variable than top height and suggested that measurements should begin 3 m from the ground to avoid height variabilityarising from early check. Hatzistathis and Papageorgiou (1976) and Arabatzoglou (1985) found the 5-year intercept to be highly associated with site index of black pine plantations in Greece, while the former also noticed that starting at 2.5 m above ground gave better results. The purpose of the present study was to investigate the precision and effectiveness of the growth-intercept method in estimating site index of planted and natural young stands of black pine in Greece using 3-, 4-, 5-, 6-, 8- and 10year intercepts and more than one startingpoint. '
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106
A. ECONOMOU
MATERIALS AND METHODS
Data of the present study were collected from two areas, Arcadia (central Peloponnese) and the Pindos mountain range (central and northern Greece), in plantations and natural stands, respectively (Fig. 1 ). The climate of the two sampling areas is weak meso-Mediterranean with the number of bioclimatically dry days (x) more than 40 and less than 75 (40 < x < 75; Mavrommatis, 1980). The mean annual rainfall for Arcadia forest is 1017.5 mm (Settas, 1975) and the mean monthly temperature 11.9 ° C. For Pindos forest the corresponding values are 1038.5 mm and 10.9°C (MarkouJakovaki et al., 1975). The warmest months are July and August with mean monthly air temperatures of 22~C and 21.5°C, for Arcadia and Pindos, and the wettest month December, with 172 mm and 163 mm rainfall, respectively. The soil parent material in Arcadia forest is metamorphic rock (mica schist and phyllites) and in Pindos forest flysch (sandy and argillaceous) and peridotites. The soils of the former sites are coarse-textured in the A horizon, mainly sandy-loams, but medium-textured in the B and C horizons, sandy-loams to sandy-clay-loams. The soils derived from flysch and peridotites are mediumtextured, sandy-loams to clay-loams. The understory vegetation in Arcadia sites is mainly scrub, while it is herb and grass in Pindos sites. In Arcadia, stands were planted in the 1960s on former heathland. In the Pindos sites, stands were between 25 and 35 years old, growing mainly on previous black-pine stands destroyed by fires. A total of 81 sample plots of 0.01 ha were all located on pure black-pine stands, 39 in plantations and 42 in natural stands, of which 22 were on flysch parent material and 20 on peridotite. Considerable care was taken in plot selection. Plots were restricted to hoTABLE 1
Growth variablesi, with their maxima (max.), minima (rain), means and standard deviations
(sD) No.
1. 2. 3. 4. 5. 6. 7. 8.
Variable
5-year intercept 6-year intercept 8-year intercept 10-year intercept 3-year intercept (3-1) 4-year intercept (4-2) 5-year intercept (4-1) Site index 25
1All values in m.
Arcadia sites
Flysch sites
Ma~-
Min.
Mean
SD
Max.
Min.
Mean
SD
2.89 3.61 5.10 6.46 2.30 2.86 3.66 14.88
1.31 1.77 2.63 3.69 1.09 1.72 1.79 9.53
2.21 2.72 3.79 4.94 1.58 2.22 2.69 11.67
0.359 2.51 0.428 3.05 0.547 4.08 0.623 5.29 0.261 1.62 0.279 2.24 0.375 2.83 1 . 2 0 3 13.12
1.51 1.82 2.36 3.16 0.76 1.26 1.58 7.74
1.98 2.40 3.22 4.09 1.23 1.69 2.10 9.91
0.325 0.383 0.509 0.603 0.250 0.284 0.355 1.207
G R O W T H INTERCEPT AS INDICATOR OF SITE QUALITY FOR PINUS
107
mogeneous areas with regard to topography, soil and litter cover, and supported well-developed and stocked, even-aged stands with closed canopies, showing no visible damage from fires, grazing, winds, snow, disease, erosion or destructive cutting. The plots were situated well away from forest margins to avoid their influences. Three dominant and codominant trees with the largest diameter were selected and measured. Since the stands examined were young, the distinction between dominant and codominant trees was very small - almost non-existent. Trees obviously injured were rejected. From each plot the following growth measurements were made: 1. Total height. Heights of the three largest trees were measured with a counting folding pole or with a tape fitted on a folding pole 8 m long. Trees higher than 8 m were measured twice with a Blume-Leiss altimeter and the average recorded. 2. Five, 6-, 8- and lO-year intercepts. These are the internodal distances of the 5th, 6th, 8th and 10th nodes of the same trees measured for the top height, starting with the whorl at or just above breast height. Measurements were done with the same instruments as for total height and the length recorded to the nearest cm. 3. Tree height above breast height. This was derived from the total tree height by subtracting 1.30 m, and was used for estimating site index at 25 years. 4. Age of trees at breast height and base. This was found by counting the whorls from breast height or the tree base up to the tree top (tip). The age found was checked by taking an increment core at breast height and/or tree base. From the age and the tree height above breast height, site index 25 was
Peridotite sites
P i n d o s sites
All sites
Max.
Min.
Mean
SD
Max.
Min.
Mean
SD
Max.
Min.
Mean
SD
2.34 2.82 3.79 4.86 1.60 2.07 2.67 12.26
1.46 1.78 2.26 2.89 0.75 1.11 1.38 6.85
1.82 2.20 2.93 3.70 1.11 1.50 1.89 9.27
0.308 0.361 0.487 0.615 0.226 0.293 0.360 1.332
2.51 3.05 4.08 5.29 1.62 2.24 2.83 13.12
1.46 1.78 2.26 2.89 0.75 1.11 1.38 6.85
1.91 2.30 3.08 3.91 1.17 1.60 2.00 9.61
0.324 0.382 0.514 0.632 0.244 0.300 0.310 1.292
2.89 3.61 5.10 6.46 2.30 2.86 3.66 14.88
1.31 1.77 2.26 2.89 0.75 1.11 1.38 6.85
2.04 2.51 3.42 4.40 1.37 1.90 2.34 10.60
0.378 0.453 0.638 0.811 0.325 0.423 0.508 1.615
Y(1) Y(2) Y(3) Y(4) Y(5) Y(6) Y(7) Y(8)
Flyschsites
Y(1)* Y (2) Y (3) Y(4) Y(5) Y(6) Y(7) Y(8)
1.0000 0.9798 0.9133 0.8752 0.5597 0.5377 0.5706 0.7668
1.0000 0.9703 0.9173 0.8823 0.5484 0.4828 0.6781 0.7011
Arcadia sites (schist, phyllites)
1
1.0000 0.9677 0.9312 0.6968 0.6307 0.6843 0.8281
1.0000 0.9632 0.9254 0.6857 0.5336 0.7644 0.7250
2
Correlation matrices of growth indices
TABLE 2
1.0000 0.9788 0.8486 0.7767 0.8258 0.8643
1.0000 0.9712 0.8361 0.6921 0.8121 0.7721
3
1.0000 0.8551 0.8701 0.8966 0.8560
1.0000 0.8238 0.8143 0.8564 0.8267
4
1.0000 0.8823 0.9393 0.7628
1.0000 0.7881 0.7710 0.6554
5
7
8
1.0000 0.6113
1.0000
1.0000 0.9850 0.7069
1.0000 0.7513
1.0000
Significant value of r at P = 0.05 =0.4427 Significant value of r at P = 0.01 = 0.5368 Significant value of r at P=O.O01 =0.6524
1.0000 0.7403 0.7345
Significant value of r at P = 0.05 = 0.3172 Significant value of r at P = 0.01 = 0.4079 Significant value of r at P = 0.001 = 0.5072
6
c) z o
.>
oo
1.0000 0.9805 0.9022 0.8421 0.8900 0.8674
All sites (schist+flysch+peridotite) Y(1) 1.0000 Y(2) 0.9446 1.0000 Y(3) 0.9067 0.9694 Y(4) 0.8765 0.9309 ¥(5) 0.6848 0.7824 Y(6) 0.6688 0.7140 Y(7) 0.7399 0.8046 Y(8) 0.7558 0.8044
*For Y(1 ) ...... Y(8), see Table 1.
1.OOOO 0.9830 0.8711 0.8321 0.8637 0.8261
1.0000 0.9742 0.9435 0.7475 0.7154 0.7507 0.7749
Pindos sites (flysch + peridotite) Y(1) 1.0000 Y(2) 0.9814 Y(3) 0.9294 Y(4) 0.8966 Y(5) 0.6285 Y(6) 0.6395 Y(7) 0.6544 Y(8) 0.7170
1.0000 0.9860 0.8795 0.8615 0.8808 0.7651
1.0000 0.9781 0.9509 0.7729 0.7608 0.7837 0.6913
Peridotite sites Y(1) 1.OOO0 Y(2) 0.9807 Y(3) 0.9372 Y(4) 0.9056 ¥(5) 0.6582 Y(6) 0.6895 Y(7) 0.6897 Y(8) 0.6290
1.0000 0.9116 0.9204 0.9365 0.8963
1.0000 0.8789 0.9565 0.9216 0.8238
1.0000 0.8925 0.9243 0.9317 0.7685
1.0000 0.9105 0.9193 0.8353
1.0000 0.9030 0.9499 0.7873
1.0000 0.9184 0.9600 0.z931 1.0000 0.7733
1.0000
1.0000 0.7780
1.0000
1.0000 0.9341 0.8576
1.0000 0.8299
1.OOO0
Significant value of r at P = 0.05 = 0.2189 Significant value of r at P = 0.01 =0.2854 Signficant value Of r at P=O.O01 =0.3603
1.0000 0.9873 0.7516
Significant value of r at P = 0.05 = 0.3044 Significant value of r at P = 0.01 = 0.3931 Significant value of r at P=O.O01 =0.4896
1.0000 0.9874 0.7589
Significant value of r at P = 0.05 =0.4412 Significant value of r at P = 0.01 =0.5563 Significant value of r at P = 0.001 = 0.6920
¢D
r~
0
0
0
N
g
0
Growth intercept (x) variable
5-year intercept 6-year intercept 8-year intercept 10-year intercept 3-year intercept (3-1) 4-year intercept (4-2) 5-year intercept (4-1)
1. 2. 3. 4. 5. 6. 7.
5-year intercept 6-year intercept 8-year intercept 10-year intercept 3-year intercept (3-1) 4-year intercept (4-2) 5-year intercept (4-1)
Peridotite sites
1. 2. 3. 4. 5. 6. 7.
Flysch sites
Arcadia sites 1. 5-year intercept 2. 6-year intercept 3. 8-year intercept 4. 10-year intercept 5. 3-year intercept (3-1) 6. 4-year intercept (4-2) 7. 5-year intercept (4-1)
No.
20.37
17.60 13.97 13.80 12.50 14.29 13.55
y=3.680+2.547x y = 3.160 + 2.091x y = 3.120 + 1.665x y=4.095 +4.677x y = 4.100 + 3.450x y=3.890+2.861x
12.61 9.62 7.75 8.18 12.80 15.32 13.33
27.98 26.10 22.23 17.42 31.40 25.35 34.47
RSS
y = 4.340 + 2.718x
y = 4.260 + 2.850x y = 3.654 + 2.609x y = 3.320 + 2.050x y = 2.898 + 1.715x y---5.381 +3.683x y = 4.840 + 3.001x y=4.530 + 2.556x
y = 6.474 + 2.351x y = 6.118 + 2.041x y = 5.223 + 1.669x y = 3.783 + 1.597x y=6.869+3.027x y = 4.650 + 3.166x y = 6.380 + 1.964x
Site index 25 (y) prediction equation
Site index (y) prediction equations using growth intercept indices (x)
TABLE 3
0.6290 0.6913 0.7651 0.7685 0.7931 0.7589 0.7733
0.7668 0.8281 0.8643 0.8560 0.7628 0.7069 0.7513
0.7011 0.7250 0.7721 0.8267 0.6554 0.7345 0.6113
r
0.3956 0.4779 0.5854 0.5906 0.6290 0.5759 0.5869
0.5880 0.6857 0.7470 0.7327 0.5819 0.4997 0.5645
0.4915 0.5256 0.5960 0.6834 0.4295 0.5395 0.3737
r2
1.035 0.962 0.858 0.852 0.811 0.867 0.856
0.775 0.677 0.607 0.624 0.781 0.854 0.797
0.858 0.829 0.765 0.677 0.909 0.817 0.952
SEE
28.546*** 43.657"** 59.059*** 54.827*** 27.831"** 19.975"** 25.929***
35.772*** 41.012*** 54.625*** 79.879** * 27.865*** 43.336*** 22.078***
11.780"* 16.476"** 25.421"** 25.959*** 30.528*** 24.448*** 28.770***
F
18 18 18 18 18 18 18
20 20 20 20 20 20 20
37 37 37 37 37 37 37
DF (n-2)
0
o
0
C~
5-year intercept 6-year intercept 8-year intercept lO-year intercept 3-year intercept (3-1) 4-year intercept (4-2) 5-year intercept (4-1)
1. 2. 3. 4. 5. 6. 7.
5-year intercept 6-year intercept 8-year intercept lO-year intercept 3-year intercept (3-1) 4-year intercept (4-2) 5-year intercept (4-1)
All sites (schists + flysch + peridotite)
1. 2. 3. 4. 5. 6. 7.
Pindos sites (flysch+peridotite)
y = 3.419 + 2.869x y=3.082+2.197x y = 2.743 + 1.785x y = 4.908 + 4.152x y=4.395+3.271x y = 4.448 + 2.636x
y = 4.019 + 3.229x
y--- 3.573 + 2.62 Ix y----3.218 + 2.079x y = 3.034 + 1.685x y=4.719+4.173x y----4.435 + 3.235x y=4.179+2.717x
y=4.171+2.856x
89.43 73.63 51.64 41.02 63.06 55.19 64.94
33.25 27.35 21.73 22.00 26.02 29.78 27.01
0.7558 0.8044 0.8674 0.8963 0.8353 0.8576 0.8299
0.7170 0.7749 0.8261 0.8238 0.7873 0.7516 0.7780
0.5712 0.6471 0.7524 0.8034 0.6977 0.7355 0.6887
0.5141 0.60O4 0.6824 0.6786 0.6198 0.5649 0.6053
1.057 0.959 0.804 0.716 0.888 0.834 0.901
0.901 0.817 0.744 0.732 0.797 0.852 0.812
105.279"** 144.804"** 240.117"** 322.705*** 182.316"** 219.567"** 174.748"**
42.190"** 60.105"** 85.979*** 84.443*** 65.200*** 51.928"** 61.351"**
79 79 79 79 79 79 79
40 40 40 40 40 40 40
o
0
112
A. ECONOMOU Arcadia sites
Flysch sites
Peridotite sites
Pindas sites
Total sites
0~
0,8
Ev -~ 0.7
~::t
I I
0 u O.f
c_ 8 0.S ilil '.::~ 0.4 5
6
8
10 "3
6
10
Number
$
of
10 3
5
5
81034
tO
1
4
internodes
Fig. 2. Correlation coefficient values of the relationship between site-index 25 and the growthintercept indices.
estimated from the site-index curves established by Economou (1987). The 3-, 4- and 5-year intercepts were also calculated later in the laboratory by subtracting 5- and 6-year intercepts from 8- and 10-year intercepts. RESULTS AND DISCUSSION
The data were analysed by forest (plantation and natural stands), and by soil parent material, and combined using correlations and regression analyses. The range, mean, and standard deviation of site-index 25 and the intercept indices are given in Table 1. Correlation coefficients of site-index 25 with all growth intercepts for all sets of data examined were strong to very strong and highly significant, varying from 0.6113 to 0.8963 (Table 2). The coefficients of determination, varying from 0.37 to 0.80, show that approximately 40-80% of the site-index variation is associated with variation in growth intercept (Table 3). Figure 2 illustrates the graphical representation of the correlation-coefficient (r) values by set of data and number of internodes measured. The highest correlation coefficient for Arcadia and total data set is that of 10-year intercept, while 8-year intercept has the highest values for the other sets of data. The 5-year intercept with breast height as starting point gives better results for Arcadia and sites on flysch: however, when a starting height of approxi-
GROWTH INTERCEPT AS INDICATOR OF SITE QUALITY FOR PINUS
113
mately 3.30 m above ground is used, it gives better results for peridotite, Pindos and total sites. Taking these findings into account, and the fact that no significant differences were found (P-- 0.05 ) between the correlation coefficients of site index 25 and the 5-year intercept starting at breast height and at 3.30 m, and also the difficulties in measuring this last intercept, it can be concluded that the 5-year intercept with breast height as starting point is a better index for site-quality evaluation. The regression analysis and the analysis of variance (Table 3) showed the slope of the relationship curves to be positive and highly significant ( P < 0.001 ). The predictive value of growth intercepts can be placed in the following decreasing order: 10-, 8-, 6- and 5-year intercepts starting at breast height, followed by those with other starting points. For the latter, no particular order was established because of the observed differences in their values and between the data sets, probably due to year-to-year variations of climatic conditions. Thus, 5 nodes are considered the least number of nodes to be used for black pine's site-quality assessment. The results of the present study revealed the 5-year intercept to be a fairly reliable index for site-quality evaluation of both planted and naturally regenerated stands of black pine, and agree with the results reported by Ferree et al. (1958), Day et al. (1960), Adu (1968), Beck (1971a,b), Papamichos (1973), Blyth ( 1974 ), Hatzistathis and Papageorgiou (1976) and Arabatzoglou ( 1985 ). The use of more than 5 internodes improves the precision of the site-index prediction equations (Table 3) and is in agreement with the results reported by Brown and Stires (1981). The 8-year intercept is considered to be the best growth intercept for the areas studied because it represents a reasonable compromise between ease of measurements and precision in estimating site index. The use of 3-, 4- and 5year intercept starting higher than breast height does not significantly improve the precision of the site-index prediction equation and also presents more difficulties in measuring them. However, Alban (1972, 1979) found a more accurate prediction of red-pine site index, using the 5-year intercept when the base was moved upwards from 8 to 10 and 15 feet above breast height. Brown and Stires (1981) also reported similar results, but Hatzistathis and Papageorgiou (1976), even though suggesting a starting point 2.5 m above ground, noticed that the correlation coefficient was only slightly improved in comparison with that of the 5-year intercept starting at breast height (r--0.88 to r = 0.91, respectively). The growth-intercept approach simplifies the site index of the young stands studied permitting its estimation even for those stands which have grown for only 5-10 years beyond breast height. However, when applying growth-intercept methods on new areas and different species, it would be better to test the precision of results using various numbers of internodes and starting points in addition to breast height.
114
A.ECONOMOU
ACKNOWLEDGEMENTS
I would like to express by gratitude to Dr. P.C. Burnham, Senior Lecturer at Wye College, London University, U.K. and Dr. G. Nakos, Soil Scientist with the Forest Research Institute, Athens, Greece, for their helpful comments made on the manuscript.
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