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Influence of environmental factors on the growth of the beech
VOL, 3, 203 - 214
CATENA
GIESSEN 1976
INFLUENCE OF ENVIRONMENTAL FACTORS ON THE GROWTH OF THE BEECH
P. W. van der Poel Laboratory of Physical Geography and Soil Science University of Amsterdam, Dapperstraat 115, Amsterdam - Nederland SUMMARY The measurement of growth indices of the beech (Fagus sylvativa) and of environmental conditions at 59 random sampling points were made in two areas of woodland in the Gutland region of Luxemburg (Grengewald and Warschent). Statistical analysis revealed that the main factor responsible for the growth of the beech is the parent material. Beech trees on sandstone are growing significantly better than those on marl. Moreover on sandstone, the beech trees are lowest on places having a thin A1 horizon and/or a high humus content of the AI horizon and/or a southwest exposure.
ZUSAMMENFASSUNG In zwei Waldgebieten des Luxemburger Gutlandes (Grengewald, Warschent) wurden an 59 z u f ~ l l i g ausgew~hlten Standorten Messungen von Zuwachs-lndices der Rotbuche sowie von Umweltfaktoren durchgefUhrt. Eine s t a t i s t i s c h e Analyse ergab, dab das Ausgangsmaterial der wichtigste Faktor fur die Wuchsleistung der Buche i s t . Buchen auf Sandstein wachsen s i g n i f i k a n t besser als auf Mergeln. Auf Sandstein sind die Buchen am niedrigsten an Standorten mit geringm~chtigem AI-Horizont und/oder einem hohen Humusgehalt im A1-Horizont und/oder bei SUdwest-Exposition. 1.
INTRODUCTION
From investigations in Luxemburg carried out in 1972 and 1973 i t appeared that certain relationships existed between the vegetation and various geomorphological variables. These relationships were further studied in 1974, in a plant-ecological investigation. The results of this study are reported here as far as the growth of the beech is concerned. I.i.
The fieldwork area
Measurements were made in 330 ha of woodland, located in the upper reaches of the Ernz Noire catchment in the Gutland region of South Luxemburg. The gently dipping Mesozoic rocks gave rise to a cuesta landscape, which form part of the Paris Basis. The main l i t h o l o g i c a l
units found in this area are (LUCIUS 1948):
Luxemburg sandstone (Lower Lias): a blue-grey sandstone with calcium carbonate as the principal cementing substance. The weathering product of the Luxemburg sandstone is a yellow or grey sand in which deep d e c a l c i f i c a t i o n has taken place due to i t s high permeability. 203
Psilonotenschichten (Lower Lias): dark marls with limestone banks and a heavy, loamy, calcareous weathering material. Rh~t sandstone (Rh~t): a thin sandstone layer with local layers of boulders, uncemented or with s i l i c a as the cementing substance. Steinmer~elkeuper (Middle Keuper): grey, green and red marls, with a grey, tough, calcareous weathering material. The maximum and minimum heights of the Luxemburg sandstone in the fieldwork area are respectively 424 and 348 m. For the marls and Rh~t sandstone these heights are 368 and 334 m. According to K~PPEN, Luxemburg has the cool and moderate maritime Cfb-climate, which has rain in a l l seasons. The meteorological station "Luxembourg-ville" has a mean annual temperature of 8.80 C and a mean annual precipitation of 739.8 mm (LAHR 1964). According to NOIRFALISE (1949), the ecological requirements of beech forest in the Belgian Ardennes comprise a mean annual precipitation of 1200 mm or more, and a mean annual temperature lower than 7.50 C. These conditions are generally not met at heights lower than 450 to 500 m. However, the beech forest on the Luxembourg sandstone are found at much lower heights, under warmer and drier conditions. The reason for this is not clear. The roots of the beech possibly reach the capillary zone of the groundwater, which may have a low temperature (REICHLING 1951). In the fieldwork area, 1/3 of the woodland is coniferous or mixed forest and 2/3 is deciduous forest. Only the l a t t e r is considered in this study. Two areas of deciduous forest can be distinguished: 1. the northeastern section of Grengewald, a beech forest with scattered oaks on the Luxemburg sandstone; and 2. Warschent, an oak-hornbeam forest on the marls and Rh~t sandstone, in which the beech is also an important component (10 to 40 %). 1.2.
Recent history of the forests
Before 1890 the Grengewald was a "middle-high forest" (Mittelwald) in which a large proportion of the trees were cut down every 20 years. Per ha 60 trees of 20 years, 30 of 40 years, 20 of 60 years and 10 of 80 years were l e f t . Since 1890 attempts have been made to restore the beech forest to a "high forest" (Hochwald), in which trees are cut down over a period of about 20 years following a growth period of 100 to 120 years. Almost a l l beech trees in the Grengewald are of the same age (about 100 years), because they are offshoots of trees cut down an the end of the "middle-high forest"-period. The maximum age of the beech is considered to be in the order of 150 to 160 years. In addition to restoration the Grengewald is at present being rejuvenated. The oak-hornbeam Forest on Warschent was the source of wood for the village of Ernster until 1955 - 1960. Beside the oak (Quercus robur, Q. petraea) and hornbeam (Carpinus betulus), the ash (Fraxinus excelsior), wild service tree (Sorbus torminalis), f i e l d maple (Aver campestre) and beech (Fagus sylvatica) are found. The maximum age reached by the beech trees here is 50 - 60 years, due to the wet ground conditions and the swelling and shrinking of the clayey s o i l , which are unfavourable for the growth of the beech. Since 1960 the Warschent forest has been l a r gely l e f t unused. 2.
DESIGNOF THE STUDY
The purpose of this study was to investigate the relationship between the growth of the beech and certain environmental conditions. The most important c r i t e r i a for recording the growth of the beech are the height and diameter (or girth). These variables are not only dependent on environmental conditions, but also on age. When a tree is s t i l l young i t increases in height very quickly, but this rate of increase slows down rapidly just before the tree attains i t s maximum height. The girth of a tree increases by nearly the same amount every year, differences being mainly caused by the prevailing climate conditions. The age of the beeches in the investigated part of Grengewald is about 100 years and on 204
Warschent up to 60 years. These differences might at f i r s t be thought to be too great to enable a meaningful comparison between the two kinds of forest to be made. However, i t has to be kept in mind that in both kinds of forest most beeches have reached or have almost reached t h e i r maximum age and have thereby v i r t u a l l y attained t h e i r maximum height. Sampling sites were randomly selected according to a grid system. The orientation of the grid was randomly chosen and the distance between the grid lines was 200 m. At each of the 46 sampling points the height and girth of the 5 nearest beech trees was measured. At some points on the marls, due to an i n s u f f i c i e n t density of beeches, only two or three height- and girth measurements were made. In no case were trees measured which were situated more than 20 m away from the sampling point since the environmental conditions would probably not remain unchanged over more than this distance. The environmental conditions recorded at the sampling points are shown in Table 1.
Table i : ENVIRONMENTAL CONDITIONS meas.+ symbol scale dimension d e f i n i t i o n AS TCOV SCOV HCOV TAO TA1 TCOL DC DR XA1 TXC TXBC TXCOL VALA1 CHRA1
r r r r r r r r r/o o o o o o o
degrees % % % cm cm cm cm cm -
angle of slope % of cover provided by the tree layer % of cover provided by the shrub layer % of cover provided by the herb layer thickness of the AO horizon thickness of the A1 horizon thickness of the c o l l u v i a l layer depth of the C horizon depth of the R horizon (bed rock) texture of the A1 horizon++ texture of the C horizon texture of the B or C horizon texture of the colluvial layer value of the AI horizon (Munzell Color Charts) chroma of the A1 horizon (Munsell Color Charts) PM n parent material POD n degree of podzolisation EXP n d e g r e e s exposition + In the sclae of measurement: n = nominal, o : ordinal and r = ratio s c a l ~ ++ Texture ranks from coarse to fine.
The growth indices determined at each of the sampling points are set out in Table 2. I t is assumed throughout that the product of height and g i r t h is a measure of the content (wood y i e l d ) of the trees, while the quotient of height and g i r t h can be considered as a measure of the average growth v e l o c i t y . In any given wood the l a t t e r index has a high value for young trees and a low value f o r old trees. Table 2: GROWTH INDICES symbol dimension
definition
H1 AH5 PHG1 PHG5 QHG1 QHG5
height of the highest tree average height of a l l trees product of height and g i r t h of the highest tree product of height and g i r t h of a l l trees quotient of height and g i r t h of the highest tree quotient of height and g i r t h of a l l trees
dm dm dm.cm dm.cm dm/cm dm/cm
205
Table 3: MEANSAND STANDARD DEVIATIONS OF THE GROWTH INDICES FOR DIFFERENT LOCATIONS (for explanations of the growth index symbols, see Table 2)
growth indices Location 1. Grengewald Warschent
n
HI
AH5
PHG1
PHG5 QHG1 QHG5
29 mean 3 4 1 . 4 309.0 59461 43839 2.012 2.342 st.dev. 2 3 . 8 3 2 . 8 12245 11368 0.298 0.285 17
mean 2 0 8 . 5 164.7 22196 12710 2.362 2.736 st.dev. 4 4 . 4 3 6 . 2 11714 6372 0.961 0.544
2. Warschent Steinmergelkeuper
9
mean 1 9 5 . 9 157.6 22032 12137 2.376 2.685 st.dev. 4 3 . 2 4 0 . 6 11935 6986 1.172 0.546
Warschent Rh~t-Sandstone
2
mean 1 9 4 . 0 153.4 14044 9694 2.835 2.768 st.dev. 4 8 . 1 4 0 . 7 7 8 6 9 5306 0.260 0.092
Warschent Psilonotenschichten
6
mean 2 3 2 . 3 179.1 28158 14576 2.183 2.802 st.dev. 4 2 . 3 2 8 . 7 11005 6146 0.784 0.676
Warschent - Steinmergel-11 mean 1 9 5 . 5 156.8 18943 11693 2.460 2.700 keuper + Rh~t sandstone st.dev. 4 1 . 6 3 8 . 6 11226 6545 1.068 0.491 3. Grengewald northern exposure
12 mean 3 4 3 . 3 314.6 57301 46496 2.099 2.303 st.dev. 1 6 . 7 3 8 . 0 10688 13885 0.254 0.357
Grengewald southern exposure
17 mean 3 4 0 . 1 305.0 60985 41964 1.951 2.370 st.dev. 2 8 . 2 2 9 . 1 13338 9196 0.319 0.229
Grengewald 5 mean 3 4 2 . 0 231.6 56388 49981 2.105 2.175 north-eastern exposure st.dev. 2 0 . 0 2 7 . 3 10040 11555 0.190 0.226 Grengewald 12 mean 3 5 1 . 3 309.6 63857 42497 1.986 2.424 south-eastern exposure st.dev. 2 4 . 4 3 1 . 6 13390 9830 0.321 0.227 Grengewald 5 mean 3 1 3 . 0 293.8 54093 40683 1.865 2.241 south-western exposure st.dev. 1 5 . 6 2 0 . 3 11597 8345 0.331 0.193 Grengewald 7 mean 3 4 4 . 1 309.6 57953 44007 2.096 2.394 north-western exposure st.dev. 1 5 . 5 4 5 . 6 11875 15720 0.307 0.420 4. Grengewald podzolised soils Grengewald nonpodzolised soils 5. Warschent northern exposure Warschent southern exposure
206
15 mean 3 3 7 . 8 300.7 58044 40811 2.016 2.397 st.dev. 2 5 . 8 3 1 . 7 10813 10490 0.305 0.310 14 mean 3 4 5 . 2 317.8 60979 47084 2.008 2.284 st.dev. 2 1 . 7 3 2 . 7 13865 11744 0.244 0.254 6
mean 2 3 1 . 5 184.8 27305 16080 2.220 2.595 st.dev. 4 2 . 1 3 8 . 3 12650 7000 0.624 0.089
mean 1 9 6 . 0 153.7 19409 10873 2.440 2.813 11 st.dev. 4 2 . 1 3 1 . 4 10739 5470 1.124 0.672
3.
ANALYSISOF RESULTS
The data obtained were analysed in steps according to the following scheme: 1. I f there are no significant differences between the north-eastern section of Grengewald and Warschent in means and variances of their growth indices, a l l 46 samples are considered to be derived from one population. I f this is the case any significant correlations between growth indices and environmental conditions have to be determined within this single population. 2. I f there are significant differences in growth indices between Grengewald and Warschent and samples are therefore derived from more than one population, i t has to be established whether there are two (Grengewald and Warschent) or three populations (Grengewald, Warschent-Psilonotenschichten and Warschent-Steinmergelkeuper + Rh~t sandstone). In this case the following has to be determined: 2a. the existence of significant correlations between growth indices and environmental conditions within each population; 2b. the existence of significant differences in environmantel conditions between the two or three populations. 3.1
Step 1
Walking through these forests the impression was received that the dimensions of the beech are larger in the north-eastern section of Grengewald than on Warschent I f this impression is correct i t must be reflected in the growth indices. Their means and standard deviations are shown in Table 3, part. 1. To test, i f the differences in the means and the variances of the growth indices are significant, the t - t e s t or an adjusted t - t e s t (for the means) and the F-test (for the variances) were used (DIXON and MASSEY 1969). The adjusted t - t e s t was used instead of the t - t e s t for samples with unequal variances. For a l l tests a minimum significance level of 95 %was chosen. These three tests require a normal distribution of the data. The histograms (Fig. I) constructed for each of the growth indices, and the curtosis amd skewness values of the sample distribution show that i t is reasonable to assume that this requirement is met; only QHG1 on Warschent and on the Steinmergelkeuper is an exception. Table 4 part 1 shows that the assumption that the dimensions of the beech in Grengewald d i f f e r signif i c a n t l y from those on Warschent is valid. Table 4: F- AND t-VALUES OF THE GROWTH INDICES FOR STEP 1 AND STEP 2 growth indices steps and samples 1.: cf. Grengewald-Warschent
2.: cf. Steinmergelkeuper + Rh~t sandstonePsilonotenschichten
values F tl t2 df2 F tl
H1
AH5
3.48 1.22 12.9 11.43 22.8 -
PHG1 PHG5 QHG1 QHG5 0.92 0.31 10.37 3.65 9.26 1 1 . 9 0 1.46 2.77 44.0 18.9 2~5~--6
1.04 0.55 0.96 0.89 0.54 1.90 1.73 1.23 1.63 0.89 -0.56 0.36
F = quotient of the variances in the two samples. t l = the value of the t - t e s t for samples with equal variances. t2 = the value of the adjusted t - t e s t for samples with unequal variances, in which df2 are the associated degrees of freedom (df). The underlined values are significant at the 95 % level or above with the required df, the bold ones at the 95 % level or above the required df. 207
108-
~53-
!-
1 2~ 2~ 3'0 3'2 3'4 36 38 40din AVERAGE HEIGHTOF ALL TREES (AH5)
iO 1
HEIGHT OF THE HIGHEST TREE (H1)
4 3
7,0 dmxcm PRODUCT OF HEIGHT AND GIRTH OF ALL TREES (PHG5)
310 3'5 4~) 4~3 5~ 5'5 6'O 6'5 7'0 Y5 8~ 8'5 9~ 9~5 PRODUCT OF HEIGHT AND GIRTH OF THE HIGHEST TREE (PHG1)
I
765" 43-
2',5 ' ~ ' 3'.5' ~. ' '~.5dm/cm QUOTIENT OF HEIGHT AND GIRTH OF ALL TREES(QHG5)
QUOTIENT OF HEIGHT AND GIRTH OF THE HIGHEST TREE (QHG1)
LEGEND
~_ .'O%7NES?.E.cUP',"N RH,~,T ANDSTONE
~--l
LUXEMBURG SANDSTONE NORTHEASTERN GRENGEWALD
I
WARSCHENT
Fi 9. 1: Histograms of the growth indices. 3.2
Step 2
On Warschent three kinds of parent materials are found: the Steinmergelkeuper, the Psilonotenschichten and the RhNt sandstone. The Rh~t sandstone occupies only a small aurface area on Warschent and the number of observations on this parent material is too low as to consider the Rh~t sandstone as a separate population. I t was expected that an overlying thin layer of sandstone has a minor influence on the growth of the trees with their deep roots, even i f its influence on the composition of the herb layer is large. Consequently the Rh~t sandstone observations were expected to make the best f i t with the observations of the underlying parent material, the Steinmergelkeuper. This is confirmed by Table 3 part 2, which shows the means and standard deviations of the growth indices on 208
these three parent materials, and by the histograms (Fig. 1). Consequently the samples from these two parent materials have been combined for further analysis. The nature of the wood in Grengewald is rather uniform. On Warschent there is a difference in the nature of the wood on the Psilonotenschichten, where the beech is f a i r l y common and on the Steinmergelkeuper and Rh~t sandstone, where oaks and hornbeams are more abundant. Although the beech trees are higher on the Psilonotenschichten, the differences are not significant as is shown in Table 4 part 2. Consequently, with regard to the growth of the beech there are two separate populations: Grengewald and Warschent. 3.3
Step 2a
In the following step i t was investigated which relationships exist between growth indices and environmental conditions within each population. The following test were used: the Pearson product-moment correlation test for environmental factors measured at a ratio scale (AS, TAO, TA1, TCOV, SCOV, HCOV, TCOL, DC); the Spearman rank correlation test for environmental factors measured at an ordinal scale (TXAI, TXC, TXBC, TXCOL, VALA1, CHP~A1, DR); F- and t-tests for environmental factors measured at a nominal scale (PM, POD, EXP). 3.4
Gren~ewald
The north-eastern section of the Grengewald has a f a i r l y uniform appearance; nevertheless there are differences in the growth of the beech which seem to be related to environmental characteristics like soil texture, angle of slope, exposition and degree of podzolisation. Because the Luxemburg sandstone has a rather homogeneous particle size distribution, differences in texture are small. Nevertheless they are important enough to be expressed in the growth indices. Table 5 part I shows that the quotient of height and girth (QHG5) is higher on places with a heavier texture of the C horizon or the B or C horizon. Between these two environmental factors and the growth indices AH5 and PHG5 indicating average height and product of height and girth, no significant correlations are found. Consequently on places with a heavier texture of the C horizon or the B the height of the trees is somewhat greater while their girth is somewhat smaller. This is also true for steeper slopes. Table 5: SIGNIFICANT CORRELATIONS BETWEEN GROWTH INDICES AND ENVIRONMENTAL
TORD]TTOI~ population
correlated factors
correl. coeff,
n
significance level
test used+
0.4165 i . : Grengewald QHG5-AS QHG5-TA1 -0.3261 PHG5-TAI 0.3579 QHG5-TXC 0.3272 QHG5-TXBC 0.3129 QHG5-VALAI 0.3952 PHG5-VALAI -0.3223
29 29 29 29 29 29 29
98.8 95.8 97.2 95.8 95.0 98.3 95.5
% % % % ties ++ % ties ++ % %
P P P S S S S
2.: Warschent
17 17 17 17 17
97.5 95.6 98.2 95.4 98.8
% % % % %
S S S S S
HA5-TXA1 PHG5-TXA1 HI-TXAI PHGI-TXAI PHGI-VALA1
-0.4846 -0.4282 -0.5146 -0.4229 0.5462
+P = Pearson product-moment c o r r e l a t i o n t e s t , S : Spearman rank c o r r e l a t i o n t e s t . ++ = The actual s i g n i f i c a n c e l e v e l o f these c o r r e l a t i o n s is less because the f a c t o r s TXC and TXBC have t i e d ranks. 209
Table 5 part 1 also shows t h a t on s o i l s with a t h i c k e r and less humic A1 horizon (growth indices TAI en VALAI), the beech trees have l a r g e r g i r t h s . With regard to the e x p o s i t i o n , Table 3 part 3 shows t h a t on SW-exposed s i t e s the growth indices HI, AH5, PHGI and PHG5 have lower values than on s i t e s with a SE-, NE-, or NW-exposition. But only one of these i n d i c e s , the maximum height of the trees (H1) i s s i g n i f i c a n t l y lower on SW-exposed s i t e s , as i s shown in Table 6. This could be explained by assuming t h a t the southern exposed slopes are too dry f o r an optimal growth of the beech, but the r e s u l t s of the measurements on Warschent apparently do not confirm t h i s explanation, al w i l l be seen l a t e r . On podzolised s o i l s , the growth of the beech was expected to be smaller than on non-podzolised s o i l s , which are less acid. Their means and standard deviations are given in Table 3 part 4. The values of the growth factors HI, AH5, PHGI and PHG5 on podzolised s o i l s are indeed lower than on non-podzolised s o i l s , but the differences are not s i g n i f i c a n t . Table 6: T-VALUES OF SOGNIFICANTLY DIFFERENT GROWTH INDICES IN EXPOSITION CLASSES samples HI(SW) - HI(NW) HI(SW) - HI(SE) HI(SW) - HI(NE)
3.5
t-value
significance limits
3.42 3.52 2.56
t99(phi:10) : 3.169 t99(phi=15) = 2.947 t95(phi:8 ) = 2.306
Warschent
The most important parent materials on Warschent are: the Steinmergelkeuper (Km3), the Rh~t sandstone (Ko2) and the Psilonotenschichten ( L i l ) . As has a l ready been shown, the Rh~t sandstone observations make the best f i t with the Steinmergelkeuper observations. Table 5 part 2 shows t h a t on warschent, on places with a heavier t e x t u r e of the AI horizon the growth indices HI, AH5, PHGI and PHG5 have lower values. Consequently the growth of the beech i s less on these places. This i s not surp r i s i n g , because a more clayey s o i l , e s p e c i a l l y when i t occupies the lower parts of an area causes wetter groundconditions. On Warschent t h i s wetness occurs mainly in winter and causes a low oxygen content of the s o i l , which is very unfavourable f o r the roots of the beech. On the more clayey Steinmergelkeuper s o i l s swelling and shrinking of the s o i l i s common and causes e a s i l y damage of the roots of the beech. Accordingly i t could be expected t h a t beech trees would be smaller on the Steinmergelkeuper (including places where i t i s o v e r l a i n by a t h i n l a y e r of Rh~t sandstone) than on the Psilonotenschichten. Table 3 part 2 shows t h a t the beech trees on the Steinmergelkeuper are indeed smaller, but the differences are not s i g n i f i c a n t , as i s shown in Table 4 part 2. Table 5 part 2 also shows t h a t the maximum height of the trees i s greater on places with a less humic AI horizon. The s i g n i f i c a n c e of t h i s r e l a t i o n s h i p is not c l e a r . In contrast with the s o i l s in the Grengewald s o i l s on Warschent are too wet f o r an optimum growth of the beech. Consequently i t should be expected that on Warschent the beech trees were higher on the d r i e r southern exposed s i t e s than on the northern exposed s i t e s . However, as i s shown by the growth indices HI, AH5, PHG1 and PHG5 in Table 3 part 5, the opposite is t r u e , although these d i f f e r e n ces are not s i g n i f i c a n t . I t is possible t h a t on Warschent as well as in the Grengewald the abundance of s u n l i g h t causes the smaller heights of the beech 210
trees on southern exposed sites, because the struggle for l i g h t on these places is smaller than on northern sites. 3.6 Step_2b The last step in the analysis consisted of the determination of any other d i f f e r ences apart from those in the parent material which might occur between the populations and may influence the observed differences in the growth of the beech. During this step the F-test and the t - t e s t are not appropriate because the presumptions of these test are not f u l f i l l e d . F i r s t l y , some of the environmental conditions (Table 7) were not normally distributed as is shown by the histograms (Fig. 2). Secondly, in many cases the variances of the different populations are unequal (see standard deviations in Table 7). Consequently, non-parametric stat i s t i c a l tests had to be used. In this case the Kolmogorov-Smirnov two sample test was chosen, which requires the computation of the maximum difference between the cumulative frequencies of the two samples (= D). The X2-value is then computed to determine i f the difference is significant. The D- and X2-values of the environmental conditions are shown in Table 7. Table 7: MEANS, STANDARD DEVIATIONS, D- AND X2-VALUES OF SOMEENVIRONMENTAL CONDITIONS FOR THE DIFFERENT POPULATIONS
populations
n
AS
TAO
TA1 TCOV SCOV HCOV TXAI VALA1CHRA1
Grengewald
29 mean st.dev.
6.00 3.59 6.07 92.52 0.0 5 . 5 9 1.35 6.11 7.45 0.0
28.83 1.24 2.40 2.80 32.55 0.51 0.52 0.61
Warschent
17 mean st.dev.
7.32 2.23 3.53 98.71 37.65 30.77 3.29 3.44 2.29 4 . 0 4 1.48 3.79 2.02 23.99 24.35 0.77 1.21 0.71
c.f. 46 D 0.42 0.54 0.50 0.51 1.00 0.25 0.79 0.50 0.56 Grengewald2 X2 7.56 12.50 10.71 11.15 42.85 2.68 26.74 10.71 13.44 Warschent The underlined values are significant at the 95 % level or above, the bold ones at the 99 % level or above. The c r i t i c a l values of the X2-test with df = 2 are: chi square (95)=5.99, chi square (99)=9.21 Table 7 shows that the Grengewald and Warschent, which have significantly d i f f e r ing growth indices, also d i f f e r significantly in 8 out of 9 environmental conditions. The Grengewald has steeper slopes (AS), a thicker AO horizon (TAO), a thicker (TA1) and more humic A1 horizon (VALA1) with a sandier texture (TXA1), a lower cover percentage of the shrub layer (SCOV) and a higher cover percentage of the tree layer (TCOV). The properties of the parent material exert a strong influence upon the environmental conditions. This influence can be exerted direct or by way of soil formation, biological a c t i v i t i e s and geomorphological processes. Of course these l a t ter factors and the properties of the parent material are also mutual dependent as well as dependent on other factors like climate and human a c t i v i t i e s . 4.
CONCLUSIONS
This study indicates that in the Gutland region of Luxemburg the growth of the beech on sandstone (Grengewald) is significantly better than on marls (Warschent) 211
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,
=
Consequently the main factors responsible for the existing differences in the growth of the beech seem to be related to properties of the parent material. Features like nutrient content, humus percentage, groundwaterlevel and -flow, and pH exert a large influence on the growth of the beech. These features are indeed influenced by properties of the parent material although factors like soil formation, biological activity, topographic characteristics and geomorphological processes are also important. Human interference also has a great influence on the growth processes of the beech. Man has been changing the distribution of beech trees in the woods, in the f i r s t place by bringing into cultivation selected parts of the woods. I t is not supposed that these factors alter the conclusions of this study. On sandstone as well as on marls, all south-exposed sites have the lowest "average height"- and "maximum height"-values, but only in the Grengewald the maximum height of the beech trees on SW-exposed sites is significantly lower than on places with a NW-, NE- or SE-exposition. Moreover in the Grengewald the average height of the beech trees is greater on places with a thicker AI horizon and a lower humus content of the A1 horizon. On Warschent the parent material is less homogeneous, and here a coarser texture of the A1 horizon, which occurs mainly on the Psilonotenschichten, seems to be more favourable to the growth of the beech. As has been mentioned earlier, the age of the beech trees is also important with regard to their heights and girths. The highest beech trees in both forests can be considered as having almost reached their maximum age, which is twice as high in the Grengewald as on Warschent. In the former the product of height and girth of the highest tree (PHGI) is nearly three times the value of this factor in the latter. This indicates that the beech trees in the Grengewald are growing more rapidly than on Warschent. ACKNOWLEDGEMENT The author wishes to thank Dr. R. Faber of the Minist~re des Eaux et For~ts of Luxemburg and Drs. Sj. de Vos for their advising remarks on the design and analysis of this study, and Dr. A.C. Imeson and Prof. Dr. P.D. Jungerius for their c r i t i c a l reading and suggestions for improving the presentation of this manuscript. REFERENCES DIXON, W.J. and MASSEY, F.J. (1969): Introduction to statistical analysis, third ed., McGraw-Hill, Kogakusha, Tokyo, 630 pp. KUPPEN, W. (1923): Die Klimate der Erde; Grundriss der Klimakunde, Walter de Gruyter Co., Berlin, 369 pp. LAHR, E. (1964): Temps et climat au Grand-Duch~ de Luxembourg, Bourg-Bourger, Luxembourg, 289 pp. LUCIUS, M. (1948): Das Gutland, publication Lux. Geol. Dienstes 5, 4P5 pp. MUNSELL (1965): Standard Soil Color Chart (Munsel]-scale), 6th ed., Nippon, Shikisaisha Co Ltd, Tokyo. NOIRFALISE, A. (1949): Premier apercu sur l'etage du h~tre et les types de hBtaies en Haute Ardenne, Centre de recherches ~col. et phytosoc, de Gembloux, communic. 10. 213
REICHLING, L. (1951): Les For~ts du Gr~s de Luxembourg, Bull, Soc. Roy. Bot Belg. 83, 163 - 212.
214
CATENA
GIESSEN 1976
INFLUENCE OF ENVIRONMENTAL FACTORS ON THE GROWTH OF THE BEECH
P. W. van der Poel Laboratory of Physical Geography and Soil Science University of Amsterdam, Dapperstraat 115, Amsterdam - Nederland SUMMARY The measurement of growth indices of the beech (Fagus sylvativa) and of environmental conditions at 59 random sampling points were made in two areas of woodland in the Gutland region of Luxemburg (Grengewald and Warschent). Statistical analysis revealed that the main factor responsible for the growth of the beech is the parent material. Beech trees on sandstone are growing significantly better than those on marl. Moreover on sandstone, the beech trees are lowest on places having a thin A1 horizon and/or a high humus content of the AI horizon and/or a southwest exposure.
ZUSAMMENFASSUNG In zwei Waldgebieten des Luxemburger Gutlandes (Grengewald, Warschent) wurden an 59 z u f ~ l l i g ausgew~hlten Standorten Messungen von Zuwachs-lndices der Rotbuche sowie von Umweltfaktoren durchgefUhrt. Eine s t a t i s t i s c h e Analyse ergab, dab das Ausgangsmaterial der wichtigste Faktor fur die Wuchsleistung der Buche i s t . Buchen auf Sandstein wachsen s i g n i f i k a n t besser als auf Mergeln. Auf Sandstein sind die Buchen am niedrigsten an Standorten mit geringm~chtigem AI-Horizont und/oder einem hohen Humusgehalt im A1-Horizont und/oder bei SUdwest-Exposition. 1.
INTRODUCTION
From investigations in Luxemburg carried out in 1972 and 1973 i t appeared that certain relationships existed between the vegetation and various geomorphological variables. These relationships were further studied in 1974, in a plant-ecological investigation. The results of this study are reported here as far as the growth of the beech is concerned. I.i.
The fieldwork area
Measurements were made in 330 ha of woodland, located in the upper reaches of the Ernz Noire catchment in the Gutland region of South Luxemburg. The gently dipping Mesozoic rocks gave rise to a cuesta landscape, which form part of the Paris Basis. The main l i t h o l o g i c a l
units found in this area are (LUCIUS 1948):
Luxemburg sandstone (Lower Lias): a blue-grey sandstone with calcium carbonate as the principal cementing substance. The weathering product of the Luxemburg sandstone is a yellow or grey sand in which deep d e c a l c i f i c a t i o n has taken place due to i t s high permeability. 203
Psilonotenschichten (Lower Lias): dark marls with limestone banks and a heavy, loamy, calcareous weathering material. Rh~t sandstone (Rh~t): a thin sandstone layer with local layers of boulders, uncemented or with s i l i c a as the cementing substance. Steinmer~elkeuper (Middle Keuper): grey, green and red marls, with a grey, tough, calcareous weathering material. The maximum and minimum heights of the Luxemburg sandstone in the fieldwork area are respectively 424 and 348 m. For the marls and Rh~t sandstone these heights are 368 and 334 m. According to K~PPEN, Luxemburg has the cool and moderate maritime Cfb-climate, which has rain in a l l seasons. The meteorological station "Luxembourg-ville" has a mean annual temperature of 8.80 C and a mean annual precipitation of 739.8 mm (LAHR 1964). According to NOIRFALISE (1949), the ecological requirements of beech forest in the Belgian Ardennes comprise a mean annual precipitation of 1200 mm or more, and a mean annual temperature lower than 7.50 C. These conditions are generally not met at heights lower than 450 to 500 m. However, the beech forest on the Luxembourg sandstone are found at much lower heights, under warmer and drier conditions. The reason for this is not clear. The roots of the beech possibly reach the capillary zone of the groundwater, which may have a low temperature (REICHLING 1951). In the fieldwork area, 1/3 of the woodland is coniferous or mixed forest and 2/3 is deciduous forest. Only the l a t t e r is considered in this study. Two areas of deciduous forest can be distinguished: 1. the northeastern section of Grengewald, a beech forest with scattered oaks on the Luxemburg sandstone; and 2. Warschent, an oak-hornbeam forest on the marls and Rh~t sandstone, in which the beech is also an important component (10 to 40 %). 1.2.
Recent history of the forests
Before 1890 the Grengewald was a "middle-high forest" (Mittelwald) in which a large proportion of the trees were cut down every 20 years. Per ha 60 trees of 20 years, 30 of 40 years, 20 of 60 years and 10 of 80 years were l e f t . Since 1890 attempts have been made to restore the beech forest to a "high forest" (Hochwald), in which trees are cut down over a period of about 20 years following a growth period of 100 to 120 years. Almost a l l beech trees in the Grengewald are of the same age (about 100 years), because they are offshoots of trees cut down an the end of the "middle-high forest"-period. The maximum age of the beech is considered to be in the order of 150 to 160 years. In addition to restoration the Grengewald is at present being rejuvenated. The oak-hornbeam Forest on Warschent was the source of wood for the village of Ernster until 1955 - 1960. Beside the oak (Quercus robur, Q. petraea) and hornbeam (Carpinus betulus), the ash (Fraxinus excelsior), wild service tree (Sorbus torminalis), f i e l d maple (Aver campestre) and beech (Fagus sylvatica) are found. The maximum age reached by the beech trees here is 50 - 60 years, due to the wet ground conditions and the swelling and shrinking of the clayey s o i l , which are unfavourable for the growth of the beech. Since 1960 the Warschent forest has been l a r gely l e f t unused. 2.
DESIGNOF THE STUDY
The purpose of this study was to investigate the relationship between the growth of the beech and certain environmental conditions. The most important c r i t e r i a for recording the growth of the beech are the height and diameter (or girth). These variables are not only dependent on environmental conditions, but also on age. When a tree is s t i l l young i t increases in height very quickly, but this rate of increase slows down rapidly just before the tree attains i t s maximum height. The girth of a tree increases by nearly the same amount every year, differences being mainly caused by the prevailing climate conditions. The age of the beeches in the investigated part of Grengewald is about 100 years and on 204
Warschent up to 60 years. These differences might at f i r s t be thought to be too great to enable a meaningful comparison between the two kinds of forest to be made. However, i t has to be kept in mind that in both kinds of forest most beeches have reached or have almost reached t h e i r maximum age and have thereby v i r t u a l l y attained t h e i r maximum height. Sampling sites were randomly selected according to a grid system. The orientation of the grid was randomly chosen and the distance between the grid lines was 200 m. At each of the 46 sampling points the height and girth of the 5 nearest beech trees was measured. At some points on the marls, due to an i n s u f f i c i e n t density of beeches, only two or three height- and girth measurements were made. In no case were trees measured which were situated more than 20 m away from the sampling point since the environmental conditions would probably not remain unchanged over more than this distance. The environmental conditions recorded at the sampling points are shown in Table 1.
Table i : ENVIRONMENTAL CONDITIONS meas.+ symbol scale dimension d e f i n i t i o n AS TCOV SCOV HCOV TAO TA1 TCOL DC DR XA1 TXC TXBC TXCOL VALA1 CHRA1
r r r r r r r r r/o o o o o o o
degrees % % % cm cm cm cm cm -
angle of slope % of cover provided by the tree layer % of cover provided by the shrub layer % of cover provided by the herb layer thickness of the AO horizon thickness of the A1 horizon thickness of the c o l l u v i a l layer depth of the C horizon depth of the R horizon (bed rock) texture of the A1 horizon++ texture of the C horizon texture of the B or C horizon texture of the colluvial layer value of the AI horizon (Munzell Color Charts) chroma of the A1 horizon (Munsell Color Charts) PM n parent material POD n degree of podzolisation EXP n d e g r e e s exposition + In the sclae of measurement: n = nominal, o : ordinal and r = ratio s c a l ~ ++ Texture ranks from coarse to fine.
The growth indices determined at each of the sampling points are set out in Table 2. I t is assumed throughout that the product of height and g i r t h is a measure of the content (wood y i e l d ) of the trees, while the quotient of height and g i r t h can be considered as a measure of the average growth v e l o c i t y . In any given wood the l a t t e r index has a high value for young trees and a low value f o r old trees. Table 2: GROWTH INDICES symbol dimension
definition
H1 AH5 PHG1 PHG5 QHG1 QHG5
height of the highest tree average height of a l l trees product of height and g i r t h of the highest tree product of height and g i r t h of a l l trees quotient of height and g i r t h of the highest tree quotient of height and g i r t h of a l l trees
dm dm dm.cm dm.cm dm/cm dm/cm
205
Table 3: MEANSAND STANDARD DEVIATIONS OF THE GROWTH INDICES FOR DIFFERENT LOCATIONS (for explanations of the growth index symbols, see Table 2)
growth indices Location 1. Grengewald Warschent
n
HI
AH5
PHG1
PHG5 QHG1 QHG5
29 mean 3 4 1 . 4 309.0 59461 43839 2.012 2.342 st.dev. 2 3 . 8 3 2 . 8 12245 11368 0.298 0.285 17
mean 2 0 8 . 5 164.7 22196 12710 2.362 2.736 st.dev. 4 4 . 4 3 6 . 2 11714 6372 0.961 0.544
2. Warschent Steinmergelkeuper
9
mean 1 9 5 . 9 157.6 22032 12137 2.376 2.685 st.dev. 4 3 . 2 4 0 . 6 11935 6986 1.172 0.546
Warschent Rh~t-Sandstone
2
mean 1 9 4 . 0 153.4 14044 9694 2.835 2.768 st.dev. 4 8 . 1 4 0 . 7 7 8 6 9 5306 0.260 0.092
Warschent Psilonotenschichten
6
mean 2 3 2 . 3 179.1 28158 14576 2.183 2.802 st.dev. 4 2 . 3 2 8 . 7 11005 6146 0.784 0.676
Warschent - Steinmergel-11 mean 1 9 5 . 5 156.8 18943 11693 2.460 2.700 keuper + Rh~t sandstone st.dev. 4 1 . 6 3 8 . 6 11226 6545 1.068 0.491 3. Grengewald northern exposure
12 mean 3 4 3 . 3 314.6 57301 46496 2.099 2.303 st.dev. 1 6 . 7 3 8 . 0 10688 13885 0.254 0.357
Grengewald southern exposure
17 mean 3 4 0 . 1 305.0 60985 41964 1.951 2.370 st.dev. 2 8 . 2 2 9 . 1 13338 9196 0.319 0.229
Grengewald 5 mean 3 4 2 . 0 231.6 56388 49981 2.105 2.175 north-eastern exposure st.dev. 2 0 . 0 2 7 . 3 10040 11555 0.190 0.226 Grengewald 12 mean 3 5 1 . 3 309.6 63857 42497 1.986 2.424 south-eastern exposure st.dev. 2 4 . 4 3 1 . 6 13390 9830 0.321 0.227 Grengewald 5 mean 3 1 3 . 0 293.8 54093 40683 1.865 2.241 south-western exposure st.dev. 1 5 . 6 2 0 . 3 11597 8345 0.331 0.193 Grengewald 7 mean 3 4 4 . 1 309.6 57953 44007 2.096 2.394 north-western exposure st.dev. 1 5 . 5 4 5 . 6 11875 15720 0.307 0.420 4. Grengewald podzolised soils Grengewald nonpodzolised soils 5. Warschent northern exposure Warschent southern exposure
206
15 mean 3 3 7 . 8 300.7 58044 40811 2.016 2.397 st.dev. 2 5 . 8 3 1 . 7 10813 10490 0.305 0.310 14 mean 3 4 5 . 2 317.8 60979 47084 2.008 2.284 st.dev. 2 1 . 7 3 2 . 7 13865 11744 0.244 0.254 6
mean 2 3 1 . 5 184.8 27305 16080 2.220 2.595 st.dev. 4 2 . 1 3 8 . 3 12650 7000 0.624 0.089
mean 1 9 6 . 0 153.7 19409 10873 2.440 2.813 11 st.dev. 4 2 . 1 3 1 . 4 10739 5470 1.124 0.672
3.
ANALYSISOF RESULTS
The data obtained were analysed in steps according to the following scheme: 1. I f there are no significant differences between the north-eastern section of Grengewald and Warschent in means and variances of their growth indices, a l l 46 samples are considered to be derived from one population. I f this is the case any significant correlations between growth indices and environmental conditions have to be determined within this single population. 2. I f there are significant differences in growth indices between Grengewald and Warschent and samples are therefore derived from more than one population, i t has to be established whether there are two (Grengewald and Warschent) or three populations (Grengewald, Warschent-Psilonotenschichten and Warschent-Steinmergelkeuper + Rh~t sandstone). In this case the following has to be determined: 2a. the existence of significant correlations between growth indices and environmental conditions within each population; 2b. the existence of significant differences in environmantel conditions between the two or three populations. 3.1
Step 1
Walking through these forests the impression was received that the dimensions of the beech are larger in the north-eastern section of Grengewald than on Warschent I f this impression is correct i t must be reflected in the growth indices. Their means and standard deviations are shown in Table 3, part. 1. To test, i f the differences in the means and the variances of the growth indices are significant, the t - t e s t or an adjusted t - t e s t (for the means) and the F-test (for the variances) were used (DIXON and MASSEY 1969). The adjusted t - t e s t was used instead of the t - t e s t for samples with unequal variances. For a l l tests a minimum significance level of 95 %was chosen. These three tests require a normal distribution of the data. The histograms (Fig. I) constructed for each of the growth indices, and the curtosis amd skewness values of the sample distribution show that i t is reasonable to assume that this requirement is met; only QHG1 on Warschent and on the Steinmergelkeuper is an exception. Table 4 part 1 shows that the assumption that the dimensions of the beech in Grengewald d i f f e r signif i c a n t l y from those on Warschent is valid. Table 4: F- AND t-VALUES OF THE GROWTH INDICES FOR STEP 1 AND STEP 2 growth indices steps and samples 1.: cf. Grengewald-Warschent
2.: cf. Steinmergelkeuper + Rh~t sandstonePsilonotenschichten
values F tl t2 df2 F tl
H1
AH5
3.48 1.22 12.9 11.43 22.8 -
PHG1 PHG5 QHG1 QHG5 0.92 0.31 10.37 3.65 9.26 1 1 . 9 0 1.46 2.77 44.0 18.9 2~5~--6
1.04 0.55 0.96 0.89 0.54 1.90 1.73 1.23 1.63 0.89 -0.56 0.36
F = quotient of the variances in the two samples. t l = the value of the t - t e s t for samples with equal variances. t2 = the value of the adjusted t - t e s t for samples with unequal variances, in which df2 are the associated degrees of freedom (df). The underlined values are significant at the 95 % level or above with the required df, the bold ones at the 95 % level or above the required df. 207
108-
~53-
!-
1 2~ 2~ 3'0 3'2 3'4 36 38 40din AVERAGE HEIGHTOF ALL TREES (AH5)
iO 1
HEIGHT OF THE HIGHEST TREE (H1)
4 3
7,0 dmxcm PRODUCT OF HEIGHT AND GIRTH OF ALL TREES (PHG5)
310 3'5 4~) 4~3 5~ 5'5 6'O 6'5 7'0 Y5 8~ 8'5 9~ 9~5 PRODUCT OF HEIGHT AND GIRTH OF THE HIGHEST TREE (PHG1)
I
765" 43-
2',5 ' ~ ' 3'.5' ~. ' '~.5dm/cm QUOTIENT OF HEIGHT AND GIRTH OF ALL TREES(QHG5)
QUOTIENT OF HEIGHT AND GIRTH OF THE HIGHEST TREE (QHG1)
LEGEND
~_ .'O%7NES?.E.cUP',"N RH,~,T ANDSTONE
~--l
LUXEMBURG SANDSTONE NORTHEASTERN GRENGEWALD
I
WARSCHENT
Fi 9. 1: Histograms of the growth indices. 3.2
Step 2
On Warschent three kinds of parent materials are found: the Steinmergelkeuper, the Psilonotenschichten and the RhNt sandstone. The Rh~t sandstone occupies only a small aurface area on Warschent and the number of observations on this parent material is too low as to consider the Rh~t sandstone as a separate population. I t was expected that an overlying thin layer of sandstone has a minor influence on the growth of the trees with their deep roots, even i f its influence on the composition of the herb layer is large. Consequently the Rh~t sandstone observations were expected to make the best f i t with the observations of the underlying parent material, the Steinmergelkeuper. This is confirmed by Table 3 part 2, which shows the means and standard deviations of the growth indices on 208
these three parent materials, and by the histograms (Fig. 1). Consequently the samples from these two parent materials have been combined for further analysis. The nature of the wood in Grengewald is rather uniform. On Warschent there is a difference in the nature of the wood on the Psilonotenschichten, where the beech is f a i r l y common and on the Steinmergelkeuper and Rh~t sandstone, where oaks and hornbeams are more abundant. Although the beech trees are higher on the Psilonotenschichten, the differences are not significant as is shown in Table 4 part 2. Consequently, with regard to the growth of the beech there are two separate populations: Grengewald and Warschent. 3.3
Step 2a
In the following step i t was investigated which relationships exist between growth indices and environmental conditions within each population. The following test were used: the Pearson product-moment correlation test for environmental factors measured at a ratio scale (AS, TAO, TA1, TCOV, SCOV, HCOV, TCOL, DC); the Spearman rank correlation test for environmental factors measured at an ordinal scale (TXAI, TXC, TXBC, TXCOL, VALA1, CHP~A1, DR); F- and t-tests for environmental factors measured at a nominal scale (PM, POD, EXP). 3.4
Gren~ewald
The north-eastern section of the Grengewald has a f a i r l y uniform appearance; nevertheless there are differences in the growth of the beech which seem to be related to environmental characteristics like soil texture, angle of slope, exposition and degree of podzolisation. Because the Luxemburg sandstone has a rather homogeneous particle size distribution, differences in texture are small. Nevertheless they are important enough to be expressed in the growth indices. Table 5 part I shows that the quotient of height and girth (QHG5) is higher on places with a heavier texture of the C horizon or the B or C horizon. Between these two environmental factors and the growth indices AH5 and PHG5 indicating average height and product of height and girth, no significant correlations are found. Consequently on places with a heavier texture of the C horizon or the B the height of the trees is somewhat greater while their girth is somewhat smaller. This is also true for steeper slopes. Table 5: SIGNIFICANT CORRELATIONS BETWEEN GROWTH INDICES AND ENVIRONMENTAL
TORD]TTOI~ population
correlated factors
correl. coeff,
n
significance level
test used+
0.4165 i . : Grengewald QHG5-AS QHG5-TA1 -0.3261 PHG5-TAI 0.3579 QHG5-TXC 0.3272 QHG5-TXBC 0.3129 QHG5-VALAI 0.3952 PHG5-VALAI -0.3223
29 29 29 29 29 29 29
98.8 95.8 97.2 95.8 95.0 98.3 95.5
% % % % ties ++ % ties ++ % %
P P P S S S S
2.: Warschent
17 17 17 17 17
97.5 95.6 98.2 95.4 98.8
% % % % %
S S S S S
HA5-TXA1 PHG5-TXA1 HI-TXAI PHGI-TXAI PHGI-VALA1
-0.4846 -0.4282 -0.5146 -0.4229 0.5462
+P = Pearson product-moment c o r r e l a t i o n t e s t , S : Spearman rank c o r r e l a t i o n t e s t . ++ = The actual s i g n i f i c a n c e l e v e l o f these c o r r e l a t i o n s is less because the f a c t o r s TXC and TXBC have t i e d ranks. 209
Table 5 part 1 also shows t h a t on s o i l s with a t h i c k e r and less humic A1 horizon (growth indices TAI en VALAI), the beech trees have l a r g e r g i r t h s . With regard to the e x p o s i t i o n , Table 3 part 3 shows t h a t on SW-exposed s i t e s the growth indices HI, AH5, PHGI and PHG5 have lower values than on s i t e s with a SE-, NE-, or NW-exposition. But only one of these i n d i c e s , the maximum height of the trees (H1) i s s i g n i f i c a n t l y lower on SW-exposed s i t e s , as i s shown in Table 6. This could be explained by assuming t h a t the southern exposed slopes are too dry f o r an optimal growth of the beech, but the r e s u l t s of the measurements on Warschent apparently do not confirm t h i s explanation, al w i l l be seen l a t e r . On podzolised s o i l s , the growth of the beech was expected to be smaller than on non-podzolised s o i l s , which are less acid. Their means and standard deviations are given in Table 3 part 4. The values of the growth factors HI, AH5, PHGI and PHG5 on podzolised s o i l s are indeed lower than on non-podzolised s o i l s , but the differences are not s i g n i f i c a n t . Table 6: T-VALUES OF SOGNIFICANTLY DIFFERENT GROWTH INDICES IN EXPOSITION CLASSES samples HI(SW) - HI(NW) HI(SW) - HI(SE) HI(SW) - HI(NE)
3.5
t-value
significance limits
3.42 3.52 2.56
t99(phi:10) : 3.169 t99(phi=15) = 2.947 t95(phi:8 ) = 2.306
Warschent
The most important parent materials on Warschent are: the Steinmergelkeuper (Km3), the Rh~t sandstone (Ko2) and the Psilonotenschichten ( L i l ) . As has a l ready been shown, the Rh~t sandstone observations make the best f i t with the Steinmergelkeuper observations. Table 5 part 2 shows t h a t on warschent, on places with a heavier t e x t u r e of the AI horizon the growth indices HI, AH5, PHGI and PHG5 have lower values. Consequently the growth of the beech i s less on these places. This i s not surp r i s i n g , because a more clayey s o i l , e s p e c i a l l y when i t occupies the lower parts of an area causes wetter groundconditions. On Warschent t h i s wetness occurs mainly in winter and causes a low oxygen content of the s o i l , which is very unfavourable f o r the roots of the beech. On the more clayey Steinmergelkeuper s o i l s swelling and shrinking of the s o i l i s common and causes e a s i l y damage of the roots of the beech. Accordingly i t could be expected t h a t beech trees would be smaller on the Steinmergelkeuper (including places where i t i s o v e r l a i n by a t h i n l a y e r of Rh~t sandstone) than on the Psilonotenschichten. Table 3 part 2 shows t h a t the beech trees on the Steinmergelkeuper are indeed smaller, but the differences are not s i g n i f i c a n t , as i s shown in Table 4 part 2. Table 5 part 2 also shows t h a t the maximum height of the trees i s greater on places with a less humic AI horizon. The s i g n i f i c a n c e of t h i s r e l a t i o n s h i p is not c l e a r . In contrast with the s o i l s in the Grengewald s o i l s on Warschent are too wet f o r an optimum growth of the beech. Consequently i t should be expected that on Warschent the beech trees were higher on the d r i e r southern exposed s i t e s than on the northern exposed s i t e s . However, as i s shown by the growth indices HI, AH5, PHG1 and PHG5 in Table 3 part 5, the opposite is t r u e , although these d i f f e r e n ces are not s i g n i f i c a n t . I t is possible t h a t on Warschent as well as in the Grengewald the abundance of s u n l i g h t causes the smaller heights of the beech 210
trees on southern exposed sites, because the struggle for l i g h t on these places is smaller than on northern sites. 3.6 Step_2b The last step in the analysis consisted of the determination of any other d i f f e r ences apart from those in the parent material which might occur between the populations and may influence the observed differences in the growth of the beech. During this step the F-test and the t - t e s t are not appropriate because the presumptions of these test are not f u l f i l l e d . F i r s t l y , some of the environmental conditions (Table 7) were not normally distributed as is shown by the histograms (Fig. 2). Secondly, in many cases the variances of the different populations are unequal (see standard deviations in Table 7). Consequently, non-parametric stat i s t i c a l tests had to be used. In this case the Kolmogorov-Smirnov two sample test was chosen, which requires the computation of the maximum difference between the cumulative frequencies of the two samples (= D). The X2-value is then computed to determine i f the difference is significant. The D- and X2-values of the environmental conditions are shown in Table 7. Table 7: MEANS, STANDARD DEVIATIONS, D- AND X2-VALUES OF SOMEENVIRONMENTAL CONDITIONS FOR THE DIFFERENT POPULATIONS
populations
n
AS
TAO
TA1 TCOV SCOV HCOV TXAI VALA1CHRA1
Grengewald
29 mean st.dev.
6.00 3.59 6.07 92.52 0.0 5 . 5 9 1.35 6.11 7.45 0.0
28.83 1.24 2.40 2.80 32.55 0.51 0.52 0.61
Warschent
17 mean st.dev.
7.32 2.23 3.53 98.71 37.65 30.77 3.29 3.44 2.29 4 . 0 4 1.48 3.79 2.02 23.99 24.35 0.77 1.21 0.71
c.f. 46 D 0.42 0.54 0.50 0.51 1.00 0.25 0.79 0.50 0.56 Grengewald2 X2 7.56 12.50 10.71 11.15 42.85 2.68 26.74 10.71 13.44 Warschent The underlined values are significant at the 95 % level or above, the bold ones at the 99 % level or above. The c r i t i c a l values of the X2-test with df = 2 are: chi square (95)=5.99, chi square (99)=9.21 Table 7 shows that the Grengewald and Warschent, which have significantly d i f f e r ing growth indices, also d i f f e r significantly in 8 out of 9 environmental conditions. The Grengewald has steeper slopes (AS), a thicker AO horizon (TAO), a thicker (TA1) and more humic A1 horizon (VALA1) with a sandier texture (TXA1), a lower cover percentage of the shrub layer (SCOV) and a higher cover percentage of the tree layer (TCOV). The properties of the parent material exert a strong influence upon the environmental conditions. This influence can be exerted direct or by way of soil formation, biological a c t i v i t i e s and geomorphological processes. Of course these l a t ter factors and the properties of the parent material are also mutual dependent as well as dependent on other factors like climate and human a c t i v i t i e s . 4.
CONCLUSIONS
This study indicates that in the Gutland region of Luxemburg the growth of the beech on sandstone (Grengewald) is significantly better than on marls (Warschent) 211
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Consequently the main factors responsible for the existing differences in the growth of the beech seem to be related to properties of the parent material. Features like nutrient content, humus percentage, groundwaterlevel and -flow, and pH exert a large influence on the growth of the beech. These features are indeed influenced by properties of the parent material although factors like soil formation, biological activity, topographic characteristics and geomorphological processes are also important. Human interference also has a great influence on the growth processes of the beech. Man has been changing the distribution of beech trees in the woods, in the f i r s t place by bringing into cultivation selected parts of the woods. I t is not supposed that these factors alter the conclusions of this study. On sandstone as well as on marls, all south-exposed sites have the lowest "average height"- and "maximum height"-values, but only in the Grengewald the maximum height of the beech trees on SW-exposed sites is significantly lower than on places with a NW-, NE- or SE-exposition. Moreover in the Grengewald the average height of the beech trees is greater on places with a thicker AI horizon and a lower humus content of the A1 horizon. On Warschent the parent material is less homogeneous, and here a coarser texture of the A1 horizon, which occurs mainly on the Psilonotenschichten, seems to be more favourable to the growth of the beech. As has been mentioned earlier, the age of the beech trees is also important with regard to their heights and girths. The highest beech trees in both forests can be considered as having almost reached their maximum age, which is twice as high in the Grengewald as on Warschent. In the former the product of height and girth of the highest tree (PHGI) is nearly three times the value of this factor in the latter. This indicates that the beech trees in the Grengewald are growing more rapidly than on Warschent. ACKNOWLEDGEMENT The author wishes to thank Dr. R. Faber of the Minist~re des Eaux et For~ts of Luxemburg and Drs. Sj. de Vos for their advising remarks on the design and analysis of this study, and Dr. A.C. Imeson and Prof. Dr. P.D. Jungerius for their c r i t i c a l reading and suggestions for improving the presentation of this manuscript. REFERENCES DIXON, W.J. and MASSEY, F.J. (1969): Introduction to statistical analysis, third ed., McGraw-Hill, Kogakusha, Tokyo, 630 pp. KUPPEN, W. (1923): Die Klimate der Erde; Grundriss der Klimakunde, Walter de Gruyter Co., Berlin, 369 pp. LAHR, E. (1964): Temps et climat au Grand-Duch~ de Luxembourg, Bourg-Bourger, Luxembourg, 289 pp. LUCIUS, M. (1948): Das Gutland, publication Lux. Geol. Dienstes 5, 4P5 pp. MUNSELL (1965): Standard Soil Color Chart (Munsel]-scale), 6th ed., Nippon, Shikisaisha Co Ltd, Tokyo. NOIRFALISE, A. (1949): Premier apercu sur l'etage du h~tre et les types de hBtaies en Haute Ardenne, Centre de recherches ~col. et phytosoc, de Gembloux, communic. 10. 213
REICHLING, L. (1951): Les For~ts du Gr~s de Luxembourg, Bull, Soc. Roy. Bot Belg. 83, 163 - 212.
214