- Email: [email protected]
Changes in soil, vegetation and forest yield between 1947 and 1988 in beech and oak sites of southern Sweden
Forest Ecology and Management, 38 (1990) 37-53 Elsevier Science Publishers B.V., Amsterdam
37
Changes in soil, vegetation and forest yield between 1947 and 1988 in beech and oak sites of southern Sweden Ursula Falkengren-Grerup a a n d H a r r y Eriksson b aDepartment of Ecology, Plant Ecology, Lund University, Ostra Vallgatan 14, S-223 61, Sweden bDepartment of Forest Yield Research, Swedish University of Agricultural Sciences, S- 770 73 Garpenberg, Sweden (Accepted 14 September 1989)
ABSTRACT Falkengren-Grerup, U. and Eriksson, H., 1990. Changes in soil, vegetation and forest yield between 1947 and 1988 in beech and oak sites of southern Sweden. For. Ecol. Manage., 38: 37-53. The upper C-horizon was analyzed in 19 beech and oak stands in southern Sweden over a period of 40 years. The results confirmed a study of ten other stands of the same period. The exchangeablebase and metal cations had decreased,on average, in the followingorder: Na > Mn > Zn > Ca, Mg> K and 20-70% was recovered in 1988. ExchangeableA1had doubled. In spite of soil acidification, which according to earlier results should also have occurred in the upper soil horizons, many field-layer species had increased in cover. Among these were several nitrophilous species. However, a few species had decreased in cover, especially in the most-acid pH range. The yield of beech and oak has been measured since 1945. Beech had increased more than expected in both basal area and site index (height) in 1976-85, while oak showed no stable changes in yield. The simultaneous increase of nitrogen deposition and decrease of soil macronutrients leads to the conclusion that the higher availability of N has been of greater influence on the ground flora and yield of beech than the loss of other macronutrients.
INTRODUCTION F o r e s t soils in s o u t h S w e d e n , as in great p a r t s o f c e n t r a l E u r o p e , were acidified at a n a c c e l e r a t i n g rate d u r i n g t h e last decades; p H d e c r e a s e d s u b s t a n tially in the topsoil as well as in the B- a n d C - h o r i z o n s (Hallb~icken a n d T a m m , 1986; F a l k e n g r e n - G r e r u p , 1 9 8 7 ) . N o c h a n g e s were f o u n d in n o r t h S w e d e n ( T a m m a n d Hallb~icken, 1988; G. Jacks, u n p u b l i s h e d data, 1989 ). Also, the e x c h a n g e a b l e base c a t i o n s ( N a , K, Mg, C a ) , w h i c h were s t u d i e d in ten profiles in the s o u t h e r n p r o v i n c e , Sk~ine, were f o u n d to be r e d u c e d c o n s i d e r a b l y o v e r the s t u d i e d 35 y e a r s ( F a l k e n g r e n - G r e r u p et al., 1987 ). T h e altered soil c h e m i s t r y s e e m s to be r e l a t e d to the d e p o s i t i o n g r a d i e n t o f air p o l l u t a n t s o v e r
0378-1127/90/$03.50
© 1990 - - Elsevier Science Publishers B.V.
38
U. FALKENGREN-GRERUP AND H. ERIKSSON
Sweden, and the enhanced soil acidification can therefore mainly be explained by the precipitation of acidifying substances. With increasing soil acidity, vital conditions for several plants change, which can lead to alterations in species composition and abundance. A review of 15-35-year-old studies in deciduous forests in south Sweden showed that many field-layer species were influenced (Falkengren-Grerup, 1986). Several species decreased in cover when the pH in the topsoil approached the lowest tolerable pH, and they disappeared when pH dropped beyond this limit. However, many species had increased in cover in spite of the soil acidification. Besides changes in competition among species, the most plausible explanation for the higher cover was the increased nitrogen deposition. This conclusion was drawn by Tyler (1987a) for the vegetation differences of varying N-deposition in Swedish sites. It has also been shown in European studies that the deposition of nitrogen and acidifying substances has caused the observed vegetation changes (Ballach et al., 1985; Wittig et al., 1985; Biirger, 1986; Tregenza, 1986; Kuhn et al., 1987). The specific causes of the vegetation changes in acidified forest soils are not known. A decrease in pH influences many chemical, and in the long run also the physical, soil properties. The solubility of P decreases, and the potentially toxic metals such as A1, Mn, Zn and Cd increase, while the pool of essential nutrients such as Ca, Mg and K decreases (Berd~n et al., 1987). The mineralization of nitrogen is affected, and might influence the proportion of ammonium and nitrate, which is important for the growth and vitality of several species (Bogner, 1968; Ingestad, 1976; Gutschick, 1981 ). The strong interactions among soil characteristics obstruct the separation of their biological effects. Soil pH and base saturation in beech forests of comparable properties as the studied sites are strongly correlated (Tyler et al., 1987 ). Tree age and cover, management of the forest, climate, and water conditions may vary even over small distances, and the influence on field-layer species is difficult to estimate. The effects on forest yield of increasing amounts of pollutants and acidification in forest soils have been studied during the last decades (e.g. Jonsson and Sundberg, 1972; Tveite and Abrahamsen, 1980; Jonsson and Svensson, 1982; Kramer, 1986; Bj6rkdahl and Eriksson, 1989). Many of the studies are based on survey data and concentrate on the relationships between forest increment and crown decline or differences in soil properties. However, up to now it has been difficult to demonstrate any clear growth changes with increasing amounts of acidifying elements in the precipitation. Studies of the current annual increment of spruce stands in south Sweden rather indicate an increase during the last decades (cf. Bj6rkdahl and Eriksson, 1989). Yield studies in West Germany also demonstrate a higher than expected increment over time for most species (Kenk, personal communication, 1988 ). A prob-
CHANGES IN SOIL, VEGETATION AND YIELD, 1947-1988, IN BEECH AND OAK
39
able explanation of this pattern is that the nitrogen input has had a positive effect and that the available base cations in soil have not yet become deficient. The purpose of this paper is to study changes over 40 years in permanent forest sample plots by chemical analysis of preserved and new soil samples from the C-horizon (pH, exchangeable Na, K, Ca, Mg, Zn, Mn, A1), reanalysis of the cover of field-layer species, and current measurements of forest yield. MATERIAL AND METHODS
Permanent sample plots have been established during the 20th Century by the former Royal College of Forestry in oak and beech stands, mainly to study the effects of different thinning regimes on forest yield (Carbonnier, 1971, 1975). Soil samples were taken from the C-horizon; one portion was used immediately for mechanical analysis, and the other was saved for future study. Four oak (Quercus robur)and 15 beech (Fagussylvatica)plots with soil samples from 1947 to 52 (one from 1971 ) were resampled in 1988. All plots are situated in the provinces of Sk~ne and Halland in southern Sweden. Soils of the four oak plots are clayey (9-27% in the C-horizon) while only two of the beech plots exceed 5% ( 13 and 19%). In most plots the maximum root depth of the trees, visually estimated from the soil profiles, was 50-60 cm, exceptionally 80 cm. Tree age in 1988 was not high for any of the stands; for age classes (years) 50-59, 60-69, 70-79 and 80-89 there were respectively 1, 9, 5 and 0 beech stands and 1, 2, 0 and 1 oak stands. The methods used in 1988 were copied from the original study. Soil samples were taken at the 70-80-cm depth, usually pooled from 4-5 profiles (a single profile in five sample plots) spread over the investigation area of 0.251 ha. The humus layer (0-5 cm) was sampled only in 1988 as a composite sample of five cores ( 192.5 cm 3). The soil was air-dried and the < 2 m m fraction used for chemical analysis. Ten g of air-dried soil was shaken for 2 h with 50 ml distilled water and 0.2M KC1, and pH measured electrometrically in the supernatant liquid. To measure exchangeable cations, 10 g of air-dried soil was extracted with 50 ml 1M acid ammonium acetate, pH 4.8. The filtrates were analyzed for Na, K, Mg, Ca, Mn, Zn and AI by plasma emission spectroscopy (ICP). pH was also measured in the topsoil in samples taken in 1988. The same method as above was used, but with fresh soil. The field-layer vegetation was described in a circle of 2-m radius around the profiles using the Hult-Sernander-Du Rietz scale, which is logarithmic, with the cover degrees 0, 1 ( < 1 / 1 6 ) , 2 ( 1 / 1 6 - 1 / 8 ) , 3 ( 1 / 8 - 1 / 4 ) , 4 ( 1 / 4 1/2) and 5 ( > 1/2). Only one Swedish study of long-term changes in other chemical soil properties than pH has been published (Falkengren-Grerup et al., 1987). This
40
U. FALKENGREN-GRERUP AND H. ERIKSSON
study concerned changes over 35 years in ten profiles from forest, heathland and pasture ecosystems, studied in 1949-50 and 1984-85. The data were recalculated and included in this article for a comparison with the larger number of plots in this study (to be called '35-year-old plots' below). Combined, the results will cover a great range of soils and decrease the possibility of impact of storage of soil, year and m o n t h of sampling, climate, etc. The chemical analyses were the same as above, except that the < 0.6-mm fraction of soil was used and that pH was measured in 1 : 3 soil extract using distilled water or 1M KCI. To evaluate changes in the cover of single species, a large dataset is needed as soil changes are by no means the only causal factors. The 19 studied plots are presented together with 74 plots of deciduous (mainly beech), well-drained forest soils studied over 15-35 years (Falkengren-Grerup, 1986). The permanent sample plots of the beech and oak stands were initially established for yield purposes, with interest focused on the effects of different silvicultural measures, e.g. thinning regime and wood-quality development. Thinnings have been made according to a research program and revisions followed about every 5th year under the supervision of the Dept. of Forest Yield Research, Garpenberg. Stand characteristics such as stem number, mean diameter, mean and dominant height, basal area (cross-section area at breast height of all trees, per ha) and stem volume (volume above stump of all trees, per ha) were recorded at most or all reviews. The observed annual increment is computed as the difference between the basal area at the end of an investigation period before thinning and the basal area after thinning at the earlier review, divided by the number of years between the two measurements. As height determinations of standing trees are more susceptible to measurement errors, the basal-area increment is more discussed in this study. Fluctuations in basal growth-rate between periods are thus more dependent on climatic variation than on measurement errors. Functions for estimating current annual increment are published by Carbonnier for beech ( 1971 ) and oak (1975). These are based on data from the sample plots studied here up to 1967/1971 (beech/oak). Estimated increment is calculated from the following stand characteristics: stand age; mean diameter; mean diameter of the 100 largest trees per ha; dominant height; stem number; and basal area per ha; for oak, we also included site index (dominant height at a total age of 100 years ) and relative content of soil fraction < 0.06 mm. The calculated growth-rate represents increment at average climatic conditions. RESULTS
Soil The pH changes in the C-horizon were largest in soils with the highest orig-
CHANGES IN SOIL, VEGETATION AND YIELD, 1947-1988, IN BEECH AND OAK
pH H20
0.5-
~
0-
o
pH-
-0.5
pH KC!
0.5-
0 . . . .
o
a
B ~ - e,A, _ a oc~/ee~i~. . . . . . . . . .
o B
o
oB
-
o
O
o
°B
B~
-1.0-
B B
-1.5 -
3
o
-0.5 -
O
B
change -1.0 -
-2.0
41
o
I
I
I
4
5 pH 1947-52
6
o
o
o
o
-1.5 -
o
°
I
7
-2.0 3
I
I
I
I
4
5 pH 1947-52
6
7
Fig. 1. p H in 1 9 4 7 - 5 2 a n d t h e c h a n g e u p to 1988 in t h e u p p e r C - h o r i z o n in s t a n d s o f b e e c h ( B ) , o a k ( O ) a n d a y o u n g ( Y ) b e e c h soil s a m p l e d in 1971. I n c l u d e d a r e t e n 3 5 - y e a r - o l d p l o t s ( o ) , s t u d i e d in 1 9 4 9 - 5 0 a n d 1 9 8 4 - 8 5 .
inal pH and when measured in water extract (Fig. 1 ). Many beech stands were already quite acid 40 years ago, and no further changes seemed to occur below a pH of about 4.8/4.2 (H20/KC1, respectively). Several of the 35year-old plots were less acid when first studied. Adding these plots to the resuits confirmed the trend of large decreases from an originally higher pH. The levels of exchangeable base and metal cations studied decreased in most plots (Fig. 2). On average, the relative decrease was in the order: N a > M n > C a > Mg> Z n > K. After adding the 35-year-old plots, the following order was obtained: Na > Mn > Zn > Ca, Mg > K. Except for Zn, the results were consistent, showing two different patterns. For Na, Zn and Mn the relative change was largest at high original amounts; for K, Ca and Mg the decreases were similar independent of the original amounts. As the 35-year-old plots were richer, particularly in Zn, this is the probable cause of the discrepancy in the order of relative decrease among the ions mentioned above. The 35-year-old plots were poorer in Mg but the relative changes did not deviate from the other plots. Exchangeable A1 in the C horizon increased in practically all of the soils, and was on average doubled (Fig. 2). There was a tendency of a larger increase in soils of initially lower content. Most of the 35-year-old plots were richer in A1 in the original study, and the relative increase was therefore smaller. The beech plot originally sampled at a later date ( 1971 ) was quite acid and poor in base and metal cations. This might be the reason for the relatively small changes in the studied properties, but the time-factor probably contributes. The oak forests did not deviate much from the rest of the plots. The high original content of base cations is probably due to the clayey soils.
U. FALKENGREN-GRERUPAND H. ERIKSSON
42
Na
1000 -
K
1000o
100 remainder % 10-
-
I
-
"-v-n~
-
100-
o
B B
a
o o
.- .v - ~
oo°
so
B
B
- °-d,- . . .o . . . . .
%
ab o
10-
0
~kBo°
1
0.1
i
i
1
10
Ca
1000 -
1
0.1
I000
i
I
1
10
Mg
-
o
Oo_B
a 100-
. . . . .B . . B .
remainder
Y B a°-~
_-0-o-
o
R
BB
%
1
0.01
1000
;
#
O
Bo
-
_ o
B
o
oBo
B~
B
B
10-
I
I
I
i
I
10
100
1
0.01
100-
- - - - - - B . B : - 6 - ~ oo - - . . . . . . . . . . O o o o B o
10B
I
I
i
I
0.1
1
10
100
Mn
1000-
Zn
0.001
B
-,~-
o
0.1
1
_ ~
B
-
100remainder % 10-
_
O
B
10-
100-
B .
o o%~
"
.
.
.
.
o
o
[
I
I
0.01
0.1
1
1
0.01
I
I
0.1
I 1947-52
I
10 meq kg "1
A!
.
1000 -
.
BB B
oo a 100-
.
.
.
.
o
.
.
.
.
.
B . .
aa,~ .
.
remainder
0
o aB B o a _ . o _ g. o
--o
o
% 10-
I
10 1947-52
I
100 meq kg "1
Fig. 2. E x c h a n g e a b l e - c a t i o n p o o l s in 1 9 4 7 - 5 2 in the u p p e r C - h o r i z o n a n d the r e m a i n d e r in 1 9 8 4 - 8 8 as a p e r c e n t a g e o f the p o o l s in 1 9 4 7 - 5 2 . T h e b r o k e n line r e p r e s e n t s n o c h a n g e ( 1 0 0 % ) . F u r t h e r e x p l a n a t i o n s as in Fig. I.
CHANGES IN SOIL, VEGETATION AND YIELD, 1947-1988, IN BEECH AND OAK
43
Vegetation ~ The changes of cover in the field-layer are given in Table 1 for the 19 beech and oak plots and 74 deciduous forest plots. No direct comparisons of changes in the topsoil and the vegetation were possible for the 19 forest plots as only the C horizon was reanalyzed. However, all 35-year-old plots had reduced pH in the topsoil over the same period (Falkengren-Grerup, 1987), and as the changes in the C horizons in the two studies were similar, it is most probable that pH has decreased - or at least been unchanged - also in the topsoil of the 19 oak and beech plots studied in 1988. The distribution among the cover classes 0-5 is given for plots containing the species at least at one point in time (Table 1 ). Cover class 0 means that a species has disappeared since the previous time or has colonized the following point of time. Three groups appeared when the cover of single species in 194770 and 1984-88 was compared as to whether the number of plots with occurrence of a species: had increased (group 1 ); was unchanged (group 2 ); or had decreased (group 3). Group 1 consists of 12 species. The c o m m o n feature for these species was the increase from zero to higher cover classes, i.e. colonization of plots. Species which had colonized and attained low cover were Lactuca muralis, Dryopterisfilix-mas and Chamaenerion angustifolium. Colonizing or increasing from lower to higher cover classes were Rubus idaeus, Stellaria holostea, S. nemorum, Melica uniflora and, to some degree, Carex sylvatica and Milium effusum. Convallaria majalis, Poa nemoralis and Urtica dioica were present in a larger number of plots in 1984-88, but showed small or irregular changes among the cover classes. Group 2 consists of nine species with small changes in the number of plots where a species occurred. Among these species were the acid-tolerant Deschampsia flexuosa and Maianthemum bifolium, which did not change much in cover over time. A few species were noted for higher cover classes, e.g. Hepatica nobilis, Lamium galeobdolon and Aegopodium podagraria. Oxalis acetosella was more evenly distributed among the cover classes than earlier but the highest cover class was almost unrepresented. Galium odoratum was no longer found in the two highest cover classes; this change was probably the largest among the species. Group 3 consists of five species. Three species of originally low cover had disappeared from a majority of the plots, independent of pH in the topsoil. These species, Dentaria bulbifera, Pulmonaria officinalis and Polygonatum multiflorum are among the least acidophilous species in deciduous forests in south Sweden, usually found in soils with high base saturation. Luzula pilosa ~Nomenclature follows Lid (1974).
44
U. FALKENGREN-GRERUP AND H. ERIKSSON
TABLE 1 Changes in species cover between 1947-70 and 1984-88 in plots where the species at one or both times was represented Time
Group 1. Increased number of plots Carex sylvatica t1 t2 Chamaenerion angustifolium tl t2 Convallaria majalis t1 t2 Dryopteris filix-mas t1 t2 Lactuca muralis t1 t2 Melica uniflora t1 t2 Milium effusum t1 t2 Poa nemoralis t1 t2 Rubus idaeus tl t2 Stellaria holostea t1 t2 Stellaria n e m o r u m t1 t2 Urtica dioica t1 t2 Group 2. U n c h a n g e d n u m b e r of plots Aegopodium podagraria t1 t2 A thyrium filix-femina t1 t2 Deschampsia caespitosa t1 t2 Deschampsia flexuosa t1 t2 Galium odoratum t1 t2 Hepatica nobilis t1 t2 L a m i u m galeobdolon t1 t2 M a i a n t h e m u m bifolium t1 t2 Oxalis acetosella t1 t2
Cover class
0
1
9 2 9 3 6 3 10 3 11 2 14 3 15 5 14 8 23 7 9 3 16 3 9 4
4 8 3 8 6 8 5 12 4 13 13 16 15 18 22 24 17 20 17 12 11 19 8 11
2 3 3 4 4 4 6 6 7 12
12 5 7 6 7 4 14 11 15 20 12 5 43 22 21 17 33 24
1 4 11 7 8 14 10
No. plots in cover class 2
3
1
4
5
2 1 1
1
1
I 5
1 3
4
2
3
2
1 2 10
2
1 1 2
8 3 4
4 1 3 1
2 4
2 6
1 4
2 2
1 1 1 1 7
3
6 4
1 1 0
1
2
4 13 16
1 2 10 10 1 3 7 13
3 5 19
1 5 13
7
2 4 9
5 4 1
6
9 13
15 2
1-5
0-5
4 11 3 9 7 10 5 12 4 13 21 32 15 25 22 28 20 36 18 24 17 30 9 14
13
18 17 7 6 7 7 18 18 42 37 13 12 68 61 22 21 67 71
12 13 15 15 35 30 36 43 27 33 18
20 10 11 24 49 13 72 29 81
45
C H A N G E S IN SOIL, VEGETATION AND YIELD, 1947-1988, IN BEECH AND OAK
Time
Cover class
0
1
No. plots in cover class 2
3
4
5
1-5
0-5 18
G r o u p 3. D e c r e a s e d n u m b e r o f plots
Dentaria bulbifera
t1
1
17
17
t2
13
5
5
Luzula pilosa
tI
7
18
18
25
Mercurialisperennis
t2 tl t2
12 1 11
13 20 4
13 27 17
28
Polygonatum multiflorum
t1
2
9
9
11
t2
8
3
3
t1
2
18
1
19
t2
16
4
1
5
Pulrnonaria officinalis
2 2
2 5
2 3
1 3
21
N u m b e r o f plots is given for the cover classes 0 - 5 ( H u l t - S e r n a n d e r - D u Rietz scale). 10-lami gal + rubu ida stel nea~ ~- mere per + + dea~-'fl¢ aego pod meli uni stel hol + + +
mill eff 1 m
cover change +_0.1 -
c sylvat + c h a ~ ang
+
+
poa nean + hepa nob + +
de.so ca~ +
urti dio
+ lact+m~rryof-m . . . . . .
-4- . . . . . . . . . . . -I- . . . . . . . . . . . . . . . . . . . . . athy f-f + maia bif
+ poly mul
luzu pil + +eonv maj dentbul putm ,+ oIr r,
-1--
oxal ace gall odo + +
-10 --
I 0.1
. . . . . . . .
I 1
. . . . . . . .
I
I
10
20
mean cover % Fig. 3. M e a n cover (%) in 1947-70 a n d its change up to 1984-88. M e a n cover is calculated from the class middle o f the cover classes 0 - 5 for the total n u m b e r of studied plots (n = 93). For species codes see text.
had also disappeared, but not to the same extent. Mercurialis perennis had disappeared from several sites but only those of lower cover classes. The picture is somewhat different when looking at the mean cover of each species in all studied plots, i.e. including plots which lacked the species at
46
U. FALKENGREN-GRERUPAND H. ERIKSSON
both observation times (Fig. 3). As the highest cover classes seldom were reached, and few species occurred in more than one third of the plots, the average cover usually was below 5%. At these low cover figures, changes from or to the highest cover class (class middle 75%) will influence the mean to a great extent. A large proportion of the species had increased in mean cover. Rubus idaeus, Mil. effusum, S. nemorum and Mel. uniflora had a relatively high increase due to colonization of plots but also to high cover in several plots. Other increasing species (Table 1, group 1 ) did not deviate much from species with small changes (group 2) in their average cover. Several of these species also increased over time, e.g. De. flexuosa, while G. odoratum and O. acetosella showed a marked decrease in mean cover. The substantial increase in mean cover ofL. galeobdolon and Mer. perennis was due to the higher cover classes in some plots. The disappearance from several plots will only have a small impact on the average cover.
Forest yield The mean of quotients between the observed and the estimated annual basalarea increment has been plotted against the central point of successive fiveyear periods. There are two curves for the beech plots, one representing all permanent sample plots available for yield studies in southern Sweden, and the other the fraction of plots where soil analysis was performed. The mean
1.2-
J
quotient 1.0 obs/exp
y
Y
0.8-
No. ofobs. Year
12/3 I 1945
26/16
32/22 I 1955
30/lff
30/19
I 1965
31/17
30/16 I 1975
11/16 I 1985
Fig. 4. Average quotient a n d s t a n d a r d error between observed a n d estimated basal-area increm e n t according to the function for beech stands ( C a r b o n n i e r , 1971 ). D a t a from all p e r m a n e n t beech sample plots in southern Sweden (solid) a n d from plots with repeated soil analysis ( d a s h e d ) . The n u m b e r s o f observed plots are given below.
CHANGES IN SOIL, VEGETATION AND YIELD, 1947-1988,1N BEECH AND OAK
47
1.2-
quotient 1.0 obs/exp
0.8-
No. of obs. Year
5
6
13
12
12
13
13
9
I
I
I
I
I
1945
1955
1965
1975
1985
Fig. 5. The average and standard error for quotients between observed and estimated basal area increment for all permanent oak stands in southern Sweden (Carbonnier, 19 75 ). Further explanations as in Fig. 4.
relative
change
0
%
-2--
~ v
~
___
t -4.8 No. of obs. Year
11/3
27/17
38/26
25/16
26/15
30/15
11/5
11/5
I
I
I
I
I
1945
1955
1965
1975
1985
Fig. 6. Relative changes of site index (dominant height at a total stand age of 100 years) for beech stands. Site index for beech according to revisions 1980-87 represents reference level ( z e r o ) . Negative values indicate lower index. Further explanations as in Fig. 4.
quotient for beech (Fig. 4) varied around 1.0 during 1945-75 but increased significantly (t-test) in 1976-85. The results were similar for both curves. The probable cause of the early variations is climatic conditions, but it is unlikely that favourable weather conditions should have existed during two successive periods. As only four oak plots were available for soil analyses, the growth changes over time are given for the total number of permanent oak plots. The quotient for oak (Fig. 5 ) varied irregularly over time and was only just approaching 1.0 after some periods of lower observed than expected increment in basal area. The changes in site index showed that the height in beech plots increased over time (Fig. 6 ), indicating a higher productivity as both height and basal
48
U. FALKENGREN-GRERUP AND H. ERIKSSON 2--
relative change %
No. of obs. Year
4
10
13
14
13
13
13
11
I
I
I
I
I
1945
1955
1965
1975
1985
Fig. 7. Relative changes of site index for all permanent oak stands in southern Sweden. Further explanations as in Figs. 4 and 5.
area had increased more rapidly than expected. Site index of oak stands (Fig. 7 ), on the other hand, varied more and lacked the relatively stable increase with time that beech stands showed. DISCUSSION
In a comparative study of this kind, it is important that no systematic error distorts the results. As all soils were well-drained and groundwater did not reach the sample depth at either point in time, the C horizon can be seen as a relatively stable environment. The effect of annual and seasonal variations were diminished as the original studies were made at different years and seasons, and the repeated studies were made at the same season as in the first study. Differences in cover measures can arise between observers (Kennedy and Addison, 1987; Hermy, 1988 ). As the original studies were made by several persons and the repeated studies only by a few, the latter group must deviate from all earlier observers to create a systematic error. As cover was found to increase as well as decrease, it is probable that cover was not extremely overestimated in either direction. The C horizon was probably relatively unaffected by the direct root release of hydrogen ions for other cations, as only a fraction of the roots reached this level and the main nutrient uptake takes place in the upper soil levels. In spite of this, the changes of the chemical properties in the upper C horizon were quite pronounced. Soil pH over 35 years decreased to different extents in a north/south gradient in Sweden and seemed to approach some kind of steady-state value related to the degree of acid deposition (G. Jacks, unpublished data, 1989). This steady-state pH increased towards the north of Sweden and also towards greater soil depths within a region. The pH value in our study, beyond which
CHANGES IN SOIL, VEGETATION AND YIELD, 1947-1988, IN BEECH AND OAK
49
no further decreases occurred, was 4.8 (H20) in the C horizon, which conformed to the values in the Swedish gradient. Factors such as differences in forest growth, climate and soil formation are also positively correlated with the pattern of acid deposition. These factors have a more long-term effect and have smaller effect on the observed changes during the investigation period. There was a smaller decrease in pH (KC1) than in pH (n20), which partly is due to the fact that pH is a logarithmic measurement of hydrogen ions and that pH (KC1) gives a lower pH-value. The difference between the two pH measurements has become smaller in these C-horizon samples. This was also characteristic for acid mineral soils in beech forests in Sk~ne (Tyler, 1987b ). The small change in pH (KC1) in the relatively acid soils in that study is a consequence of the changes from silicate/cation buffering to aluminium buffering (Ulrich, 1981 ). The more acid the soil, the more will base cations be replaced by aluminium rather than by hydrogen ions. Our study also showed a considerable increase in exchangeable A1. The exchangeable-cation pools of the C horizon were reduced over time in the following order: Na > Mn > Zn > Ca, Mg > K. Sodium is weakly adsorbed by clay minerals and therefore susceptile to leaching, while K ions have a much higher affinity for clay minerals, particularly 2: 1. Accordingly, a larger negative budget is often found for Na than for K in Soil water of acid forests in south Sweden (Bergkvist, 1987 ). On average, the remainder of exchangeable Na was 20%, Mn and Zn 30-50% and Ca, Mg and K 50-70% after 3540 years. As about the same figures were found also in more upper soil layers (Falkengren-Grerup et al., 1987 ), the removal of these elements must partly be an incorporation in the biomass and partly a leaching to deeper horizons, perhaps to surface waters or even to groundwater. The study of changes in the field-layer species was complemented by adding 74 plots from deciduous forests studied in 1984-85 (Falkengren-Grerup, 1986) to the 19 permanent sample plots studied in 1988. The data support each other for all species except Deschampsiaflexuosa. The increase in cover in the acidified soils has become too small to be significant. In all plots taken together, more species increased in cover and occurrence than decreased. The increasing species, however, conceal the fact that some species tended to decrease in cover in the most-acid soils. Some decreasing species also responded more strongly on the more-acid soils. Light is an important factor for the field-layer, especially in the dark beech forests. An altered management causing a more-open stand could therefore result in a moreabundant vegetation. However, the thinning regime for the permanent sampiing plots causes only a short lighter period as the degree of tree cover is regained after about two years (Svensson et al., 1987 ). By adding an element that has been scarce in forest ecosystems, increased growth might be expected if competition or other nutrients are not restricting. The nitrogen content in precipitation has more than doubled since 1955
50
U. FALKENGREN-GRERUP AND H. ERIKSSON
(Anonymous, 1986) and the total deposition to forest ecosystems is about 15-20 kg h a - 1 (Westling, 1989). This increase ought to promote nitrophilous species, and higher covers were also found for, e.g. Rubus idaeus, Stellaria nemorum, Chamaenerion angustifolium and Aegopodium podagraria. Another feature that might be advantageous for a species in a changing environment is longevity of the individual. The long-lived Hepatica nobilis (Inghe and Tamm, 1985 ), that usually occurs on less-acid soils, was found to increase where already established but did not colonize new plots. However, other relatively long-lived species with nutrient reserves and translocation in the rhizomes decreased in the most-acid soils (Mercurialis perennis), or over the entire pH-range ( Dentaria bulbifera, Pulmonaria officinalis, Polygonatum
multiflorum ). In spite of soil acidification, acid-tolerant species did not increase distinctly. Deschampsia flexuosa, Maianthemum bifolium and Luzula pilosa showed small changes and the quite tolerant Oxalis acetosella rather decreased. This is probably not due to increased light competition with other species, as the vegetation in the acid soils seldom covers the whole ground and has been relatively unchanged over the period (Falkengren-Grerup, 1986). The competition could rather be for nutrients in the rhizosphere, including tree roots. There might also be a response to an antagonism between A1 and Ca, Mg, P or to an increase of toxic elements, e.g. A1 or Mn, although D. flexuosa is known to be tolerant (Rorison, 1985, 1986). The increase of yield in the beech stands during the last ten years is contradictory to the demonstrated decreases of the nutrient pools. Whether the increase in yield will be persistent or not cannot be extrapolated from this material. The oak plots did not show any trend in growth changes. Unfortunately, the small number of oak soils which could be chemically analyzed does not illustrate the influence of the different soil chemical properties. As to the physical soil properties of the different soils, the permanent sample plots of beech had on average 28% and the oak plots 42% of particles < 0.06 mm. The differences in soil properties between the oak and beech stands are probable causes for the different growth patterns for the two species during the last decades. Most of the beech plots were relatively young at the time of the first soil sampling. The biomass of the beech plots has increased dramatically, which can be examplified from an average beech plot in the province of Halland (T54: 1-4, Carbonnier 1971 ). The stem volume in 1951 was 43 m 3 ha -~, in 1988 180 m 3 ha-1, and removed in thinnings was 181 m 3 ha-~. The increment in stem volume during the whole period was thus 318 m 3 h a - ~. An approximative conversion to biomass for the whole stand including bole, branches, twigs, leaves, stump and roots indicate a biomass increase including the removed stemwood of 250 t ha -~. The incorporation of base cations into the biomass most certainly affects the exchangeable amounts in the top-
CHANGES IN SOIL, VEGETATION AND YIELD, 1947-1988, IN BEECH AND OAK
51
soil, but might also to some degree affect the C horizon, as many studies demonstrate considerable amounts of roots in this horizon (e.g. Vyskot, 1976; NSrgaard Nielsen, 1988 ), although the studied plots showed a shallower root depth. Unfortunately, the lack of soil samples from the A and B horizons makes it impossible to present a total budget of the studied chemical elements. The yield increase of beech stands in 1976-87 is most probably not caused by favourable weather conditions. A common method to correct observed values of stand increment is to use the so-called annual ring indices. Such indices are presented for spruce but not for beech in south Sweden. The mean index for 1974-85 was 101 for spruce (Persson, 1986), which indicates normal weather. During the period 1910-1984 it has not at any time occurred that the mean annual ring indices for two successive periods both have exceeded the average value very much. Fertilization experiments with nitrogen offer another explanation of the increased yield in beech stands. Experiments in spruce stands in south Sweden gave increased wood production even on relatively fertile sites (Fahlroth, 1970). The growth increase in the beech stands may therefore be interpreted as a fertilization effect caused by the increased nitrogen deposition. This effect seems still to overwhelm the effects of the decrease of cations in the soil. The important question now is, how long will the fertilization effect exist and when will the indicated imbalances in nutrient supply influence the stand increment? Given the present state of knowledge it is difficult to give a sound answer to this question. ACKNOWLEDGEMENTS
The chemical analysis of soil and the repeated description of ground vegetation was financed by the World Wide Fund for Nature. We thank G. Tyler for comments on the manuscript, K. Olsson for field assistance, E. Sj/SstdSm for laboratory work and K. Karlsson for computer help.
REFERENCES
Anonymous, 1986. Sura och frrsurade vatten (Acid and acidified waters). National Swedish Environmental Protection Board, Solna, 180 pp. Ballach, H-J., Greven, H. and Wittig, R., 1985. Biomonitoring in Waldgebieten NordrheinWestfalens. Staub Reinhalt. Luft, 45: 567-573. Berdrn, M., Nilsson, S.I., Rosrn, K. and Tyler, G., 1987. Soil acidification. Extent, causes and consequences. Swed. Environ. Prot. Board, Solna, Rep. 3292: 1-164. Bergkvist, B., 1987. Soil solution chemistry and metal budgets of spruce forest ecosystems in s. Sweden. Water Air Soil Pollut., 33:131-154. Bjrrkdahl, G. and Eriksson, H., 1989. Effects of forest decline on increment in Norway spruce
52
U. FALKENGREN-GRERUP AND H. ERIKSSON
(Picea abies (L.) Karst) in southern Sweden. In: K. Bjor and B. Halvorsen (Editors), Air Pollution as Stress Factor in Nordic Forests. Medd. Norsk Inst. Skogforsk., 42: 19-36. Bogner, W., 1968. Experimentelle Priifung von Waldbodenpflanzen aufihre Anspriiche and die Form der Stickstoffern~ihrung. Mitt. Ver. Forstl. Standortsk. Forstpflanzenz., 18:115-124. BiJrger, R., 1986. Ver~inderungen der Bodenvegetation als Indikator ftir m/Sgliche landschafts/3kologische Folgen des Waldsterbens. Projekt europ~iisches Forschungszentrum ftir Massnahmen zur Luftreinhaltung. KFK-PEF-Berichte, 4: 375-384. Carbonnier, C., 1971. Bokens produktion i s6dra Sverige (Yield of beech in southern Sweden). Stud. For. Suec., 91: 1-89. Carbonnier, C., 1975. Produktionen i kulturbest/tnd av ek i s/Sdra Sverige (Yield of oak plantations in southern Sweden). Stud. For. Suec., 125: 1-89. Fahlroth, S., 1970. Gran p~i god bonitet - analys av ett g6dslingsf6rs6k (Spruce on a fertile site --analysis of a fertilization experiment). F6reningen Skogstr~idsf6r~idling, Inst. f. Skogsf6rb~ittring, ~,rsbok, pp. 76-86. Falkengren-Grerup, U., 1986. Soil acidification and vegetation changes in deciduous forest in southern Sweden. Oecologia, 70: 339-347. Falkengren-Grerup, U., 1987. Long-term changes in pH of forest soils in southern Sweden. Environ. Pollut., 43: 79-90. Falkengren-Grerup, U., Linnermark, N. and Tyler, G., 1987. Changes in acidity and cation pools of south Swedish soils between 1949 and 1985. Chemosphere, 16: 2239-2248. Gutschick, V.P., 1981. Evolved Strategies and Vegetation Processes. Wiley, Chichester. Hallb~icken, L. and Tamm, C.O., 1986. Changes in soil acidity from 1927 to 1982-1984 in a forest area of south-west Sweden. Scand. J. For. Res., 1:219-232. Hermy, M., 1988. Accuracy of visual cover assessments in predicting standing crop and environmental correlation in deciduous forests. Vegetatio, 75:57-64. Ingestad, T., 1976. Nitrogen and cation nutrition of three ecologically different plants. Physiol. Plant., 38: 29-34. lnghe, O. and Tamm, C.O., 1985. Survival and flowering of perennial herbs. IV. The behaviour of Hepatica nobilis and Sanicula europaea on permanent plots during 1943-1981. Oikos, 45: 400-420. Jonsson, B. and Sundberg, R., 1972. Has the acidification by atmospheric pollution caused a growth reduction in Swedish forests? R. Coll. For., Dep. For. Yield Res. Rep. Uppsat., 20: 9-14. Jonsson, B. and Svensson, L-G., 1982. A study of the effects of air pollution on forest yield. Swed. Univ. Agric. Sci., Sect. For. Mensur. Manage. Rep., 9: 9-43. Kennedy, K.A. and Addison, P.A., 1987. Some considerations for the use of visual estimates of plant cover in biomonitoring. J. Ecol., 75:151-157. Kramer, H., 1986. Relation between crown parameters and volume increment of Picea abies stands damaged by environmental pollution. Scand. J. For. Res., 1:251-269. Kuhm N., Amiet, R. and Hufschmid, N., 1987. Vedindernngen in der Waldvegetation der Schweiz infolge N~ihrstoffanreicherungen aus der Atmosph~ire. Allg. Forst JagdZtg., 158: 7784. Lid, J., 19741 Norsk og Svensk Flora. Det Norske Samlaget, Oslo. Linnermark, N., 1960. Podsol och brunjord (Podsols and brown soils) I-II. Summary in English. Publ. Inst. Mineral. Paleontol. Quart. Geol., Univ. Lund, Sweden, 75: 1-233. N/Srgaard Nielsen, C.C., 1988. EinfliJsse von Plantzenabstand und Sturmzahlhaltung auf Wurzelforme, Wurzelbiomass, Verankerung sowie auf die Biomasseverteilung im Hinblick auf die Sturmfestigkeit bei Fichte. Thesis, Univ. G/Sttingen, Part 2, pp. 19-26. Persson, O., 1986. The Atvidaberg thinning experiment. Swed. Univ. Agric. Sci., Dep. For. Yield Res. Rep., 18: 12-16.
CHANGES IN SOIL, VEGETATION AND YIELD, 1947-1988, IN BEECH AND OAK
53
Rorison, I.H., 1985. Nitrogen source and the tolerance ofDeschampsiaflexuosa, Holcus lanatus and Bromus erectus to aluminium during seedling growth. J. Ecol., 73: 83-90. Rorison, I.H., 1986. The response of plants to acid soils. Experentia, 42: 357-362. Svensson, J., Bjerk6n, J., M/Lrtensson, B-L. and Einarsson, E., 1987. Kronslutenhet och dessf6r~indring i gallrade bokbest~nd (crown density and its change in thinned beech stands ). Swedish University of Agricultural Science, Dept. Forest Yield Research (stencil), 13 pp. Tamm, C.O. and Hallb~icken, L., 1988. Changes in soil acidity from the 1920s to the 1980s in two forest areas with different acid deposition. Ambio, 17:56-61. Tregenza, N.J.C., 1986. Acidification effects on the flora of Cornwall. Cornwall Trust for Nature Conservation, Cornw. Conserv. Rev. Rep., 1: 1-21. Tveite, B. and Abrahamsen, G., 1980. Effects of artificial acid rain on the growth and nutrient status of trees. In: T.C. Hutchinson and M. Havas (Editors), Effects of Acid Precipitation on Terrestrial Ecosystems. Plenum, New York, pp. 305-318. Tyler, G., 1987a. Probable effects of soil acidification and nitrogen deposition on the floristic composition of oak (Quercus robur L. ) forest. Flora Jena, 179:165-170. Tyler, G., 1987b. Acidification and chemical properties of Fagus sylvatica L. forest soils. Scand. J. For. Res., 2:263-271. Tyler, G., Berggren, D., Bergkvist, B., Falkengren-Grerup, U., Folkeson, L. and Riihling, A., 1987. Soil acidification and metal solubility in forests of southern Sweden. In: T.C. Hutchinson and K.M. Meema (Editors), Effects of Atmospheric Pollutants on Forests, Wetlands and Agricultural Ecosystems. NATO ASI Series, Vol. G 16, Springer, Berlin, pp. 347-359. Ulrich, B., 1981. Okologische Gruppierung von B6den nach ihrem chemischen Bodenzustand. Z. Pflanzenern~ihr. Bodenkd., 144: 289-305. Vyskot, M., 1976. Tree story biomass in lowland forests in south Moravia. Rocnik, 86-sesit 10: 57-74. Westling, O., 1989. Nedfall av luftf6roreningar i Sk/me. (Deposition of atmospheric pollutants ) Swed. Environ. Res. Inst., Rep., 1-14. Wittig, R., Ballach, H.J. and Brandt, C.J., 1985. Increase of number of acid indicators in the herb layer of the millet grass-beech forest of the Westphalian Bight. Angew. Bot., 59:219232.
37
Changes in soil, vegetation and forest yield between 1947 and 1988 in beech and oak sites of southern Sweden Ursula Falkengren-Grerup a a n d H a r r y Eriksson b aDepartment of Ecology, Plant Ecology, Lund University, Ostra Vallgatan 14, S-223 61, Sweden bDepartment of Forest Yield Research, Swedish University of Agricultural Sciences, S- 770 73 Garpenberg, Sweden (Accepted 14 September 1989)
ABSTRACT Falkengren-Grerup, U. and Eriksson, H., 1990. Changes in soil, vegetation and forest yield between 1947 and 1988 in beech and oak sites of southern Sweden. For. Ecol. Manage., 38: 37-53. The upper C-horizon was analyzed in 19 beech and oak stands in southern Sweden over a period of 40 years. The results confirmed a study of ten other stands of the same period. The exchangeablebase and metal cations had decreased,on average, in the followingorder: Na > Mn > Zn > Ca, Mg> K and 20-70% was recovered in 1988. ExchangeableA1had doubled. In spite of soil acidification, which according to earlier results should also have occurred in the upper soil horizons, many field-layer species had increased in cover. Among these were several nitrophilous species. However, a few species had decreased in cover, especially in the most-acid pH range. The yield of beech and oak has been measured since 1945. Beech had increased more than expected in both basal area and site index (height) in 1976-85, while oak showed no stable changes in yield. The simultaneous increase of nitrogen deposition and decrease of soil macronutrients leads to the conclusion that the higher availability of N has been of greater influence on the ground flora and yield of beech than the loss of other macronutrients.
INTRODUCTION F o r e s t soils in s o u t h S w e d e n , as in great p a r t s o f c e n t r a l E u r o p e , were acidified at a n a c c e l e r a t i n g rate d u r i n g t h e last decades; p H d e c r e a s e d s u b s t a n tially in the topsoil as well as in the B- a n d C - h o r i z o n s (Hallb~icken a n d T a m m , 1986; F a l k e n g r e n - G r e r u p , 1 9 8 7 ) . N o c h a n g e s were f o u n d in n o r t h S w e d e n ( T a m m a n d Hallb~icken, 1988; G. Jacks, u n p u b l i s h e d data, 1989 ). Also, the e x c h a n g e a b l e base c a t i o n s ( N a , K, Mg, C a ) , w h i c h were s t u d i e d in ten profiles in the s o u t h e r n p r o v i n c e , Sk~ine, were f o u n d to be r e d u c e d c o n s i d e r a b l y o v e r the s t u d i e d 35 y e a r s ( F a l k e n g r e n - G r e r u p et al., 1987 ). T h e altered soil c h e m i s t r y s e e m s to be r e l a t e d to the d e p o s i t i o n g r a d i e n t o f air p o l l u t a n t s o v e r
0378-1127/90/$03.50
© 1990 - - Elsevier Science Publishers B.V.
38
U. FALKENGREN-GRERUP AND H. ERIKSSON
Sweden, and the enhanced soil acidification can therefore mainly be explained by the precipitation of acidifying substances. With increasing soil acidity, vital conditions for several plants change, which can lead to alterations in species composition and abundance. A review of 15-35-year-old studies in deciduous forests in south Sweden showed that many field-layer species were influenced (Falkengren-Grerup, 1986). Several species decreased in cover when the pH in the topsoil approached the lowest tolerable pH, and they disappeared when pH dropped beyond this limit. However, many species had increased in cover in spite of the soil acidification. Besides changes in competition among species, the most plausible explanation for the higher cover was the increased nitrogen deposition. This conclusion was drawn by Tyler (1987a) for the vegetation differences of varying N-deposition in Swedish sites. It has also been shown in European studies that the deposition of nitrogen and acidifying substances has caused the observed vegetation changes (Ballach et al., 1985; Wittig et al., 1985; Biirger, 1986; Tregenza, 1986; Kuhn et al., 1987). The specific causes of the vegetation changes in acidified forest soils are not known. A decrease in pH influences many chemical, and in the long run also the physical, soil properties. The solubility of P decreases, and the potentially toxic metals such as A1, Mn, Zn and Cd increase, while the pool of essential nutrients such as Ca, Mg and K decreases (Berd~n et al., 1987). The mineralization of nitrogen is affected, and might influence the proportion of ammonium and nitrate, which is important for the growth and vitality of several species (Bogner, 1968; Ingestad, 1976; Gutschick, 1981 ). The strong interactions among soil characteristics obstruct the separation of their biological effects. Soil pH and base saturation in beech forests of comparable properties as the studied sites are strongly correlated (Tyler et al., 1987 ). Tree age and cover, management of the forest, climate, and water conditions may vary even over small distances, and the influence on field-layer species is difficult to estimate. The effects on forest yield of increasing amounts of pollutants and acidification in forest soils have been studied during the last decades (e.g. Jonsson and Sundberg, 1972; Tveite and Abrahamsen, 1980; Jonsson and Svensson, 1982; Kramer, 1986; Bj6rkdahl and Eriksson, 1989). Many of the studies are based on survey data and concentrate on the relationships between forest increment and crown decline or differences in soil properties. However, up to now it has been difficult to demonstrate any clear growth changes with increasing amounts of acidifying elements in the precipitation. Studies of the current annual increment of spruce stands in south Sweden rather indicate an increase during the last decades (cf. Bj6rkdahl and Eriksson, 1989). Yield studies in West Germany also demonstrate a higher than expected increment over time for most species (Kenk, personal communication, 1988 ). A prob-
CHANGES IN SOIL, VEGETATION AND YIELD, 1947-1988, IN BEECH AND OAK
39
able explanation of this pattern is that the nitrogen input has had a positive effect and that the available base cations in soil have not yet become deficient. The purpose of this paper is to study changes over 40 years in permanent forest sample plots by chemical analysis of preserved and new soil samples from the C-horizon (pH, exchangeable Na, K, Ca, Mg, Zn, Mn, A1), reanalysis of the cover of field-layer species, and current measurements of forest yield. MATERIAL AND METHODS
Permanent sample plots have been established during the 20th Century by the former Royal College of Forestry in oak and beech stands, mainly to study the effects of different thinning regimes on forest yield (Carbonnier, 1971, 1975). Soil samples were taken from the C-horizon; one portion was used immediately for mechanical analysis, and the other was saved for future study. Four oak (Quercus robur)and 15 beech (Fagussylvatica)plots with soil samples from 1947 to 52 (one from 1971 ) were resampled in 1988. All plots are situated in the provinces of Sk~ne and Halland in southern Sweden. Soils of the four oak plots are clayey (9-27% in the C-horizon) while only two of the beech plots exceed 5% ( 13 and 19%). In most plots the maximum root depth of the trees, visually estimated from the soil profiles, was 50-60 cm, exceptionally 80 cm. Tree age in 1988 was not high for any of the stands; for age classes (years) 50-59, 60-69, 70-79 and 80-89 there were respectively 1, 9, 5 and 0 beech stands and 1, 2, 0 and 1 oak stands. The methods used in 1988 were copied from the original study. Soil samples were taken at the 70-80-cm depth, usually pooled from 4-5 profiles (a single profile in five sample plots) spread over the investigation area of 0.251 ha. The humus layer (0-5 cm) was sampled only in 1988 as a composite sample of five cores ( 192.5 cm 3). The soil was air-dried and the < 2 m m fraction used for chemical analysis. Ten g of air-dried soil was shaken for 2 h with 50 ml distilled water and 0.2M KC1, and pH measured electrometrically in the supernatant liquid. To measure exchangeable cations, 10 g of air-dried soil was extracted with 50 ml 1M acid ammonium acetate, pH 4.8. The filtrates were analyzed for Na, K, Mg, Ca, Mn, Zn and AI by plasma emission spectroscopy (ICP). pH was also measured in the topsoil in samples taken in 1988. The same method as above was used, but with fresh soil. The field-layer vegetation was described in a circle of 2-m radius around the profiles using the Hult-Sernander-Du Rietz scale, which is logarithmic, with the cover degrees 0, 1 ( < 1 / 1 6 ) , 2 ( 1 / 1 6 - 1 / 8 ) , 3 ( 1 / 8 - 1 / 4 ) , 4 ( 1 / 4 1/2) and 5 ( > 1/2). Only one Swedish study of long-term changes in other chemical soil properties than pH has been published (Falkengren-Grerup et al., 1987). This
40
U. FALKENGREN-GRERUP AND H. ERIKSSON
study concerned changes over 35 years in ten profiles from forest, heathland and pasture ecosystems, studied in 1949-50 and 1984-85. The data were recalculated and included in this article for a comparison with the larger number of plots in this study (to be called '35-year-old plots' below). Combined, the results will cover a great range of soils and decrease the possibility of impact of storage of soil, year and m o n t h of sampling, climate, etc. The chemical analyses were the same as above, except that the < 0.6-mm fraction of soil was used and that pH was measured in 1 : 3 soil extract using distilled water or 1M KCI. To evaluate changes in the cover of single species, a large dataset is needed as soil changes are by no means the only causal factors. The 19 studied plots are presented together with 74 plots of deciduous (mainly beech), well-drained forest soils studied over 15-35 years (Falkengren-Grerup, 1986). The permanent sample plots of the beech and oak stands were initially established for yield purposes, with interest focused on the effects of different silvicultural measures, e.g. thinning regime and wood-quality development. Thinnings have been made according to a research program and revisions followed about every 5th year under the supervision of the Dept. of Forest Yield Research, Garpenberg. Stand characteristics such as stem number, mean diameter, mean and dominant height, basal area (cross-section area at breast height of all trees, per ha) and stem volume (volume above stump of all trees, per ha) were recorded at most or all reviews. The observed annual increment is computed as the difference between the basal area at the end of an investigation period before thinning and the basal area after thinning at the earlier review, divided by the number of years between the two measurements. As height determinations of standing trees are more susceptible to measurement errors, the basal-area increment is more discussed in this study. Fluctuations in basal growth-rate between periods are thus more dependent on climatic variation than on measurement errors. Functions for estimating current annual increment are published by Carbonnier for beech ( 1971 ) and oak (1975). These are based on data from the sample plots studied here up to 1967/1971 (beech/oak). Estimated increment is calculated from the following stand characteristics: stand age; mean diameter; mean diameter of the 100 largest trees per ha; dominant height; stem number; and basal area per ha; for oak, we also included site index (dominant height at a total age of 100 years ) and relative content of soil fraction < 0.06 mm. The calculated growth-rate represents increment at average climatic conditions. RESULTS
Soil The pH changes in the C-horizon were largest in soils with the highest orig-
CHANGES IN SOIL, VEGETATION AND YIELD, 1947-1988, IN BEECH AND OAK
pH H20
0.5-
~
0-
o
pH-
-0.5
pH KC!
0.5-
0 . . . .
o
a
B ~ - e,A, _ a oc~/ee~i~. . . . . . . . . .
o B
o
oB
-
o
O
o
°B
B~
-1.0-
B B
-1.5 -
3
o
-0.5 -
O
B
change -1.0 -
-2.0
41
o
I
I
I
4
5 pH 1947-52
6
o
o
o
o
-1.5 -
o
°
I
7
-2.0 3
I
I
I
I
4
5 pH 1947-52
6
7
Fig. 1. p H in 1 9 4 7 - 5 2 a n d t h e c h a n g e u p to 1988 in t h e u p p e r C - h o r i z o n in s t a n d s o f b e e c h ( B ) , o a k ( O ) a n d a y o u n g ( Y ) b e e c h soil s a m p l e d in 1971. I n c l u d e d a r e t e n 3 5 - y e a r - o l d p l o t s ( o ) , s t u d i e d in 1 9 4 9 - 5 0 a n d 1 9 8 4 - 8 5 .
inal pH and when measured in water extract (Fig. 1 ). Many beech stands were already quite acid 40 years ago, and no further changes seemed to occur below a pH of about 4.8/4.2 (H20/KC1, respectively). Several of the 35year-old plots were less acid when first studied. Adding these plots to the resuits confirmed the trend of large decreases from an originally higher pH. The levels of exchangeable base and metal cations studied decreased in most plots (Fig. 2). On average, the relative decrease was in the order: N a > M n > C a > Mg> Z n > K. After adding the 35-year-old plots, the following order was obtained: Na > Mn > Zn > Ca, Mg > K. Except for Zn, the results were consistent, showing two different patterns. For Na, Zn and Mn the relative change was largest at high original amounts; for K, Ca and Mg the decreases were similar independent of the original amounts. As the 35-year-old plots were richer, particularly in Zn, this is the probable cause of the discrepancy in the order of relative decrease among the ions mentioned above. The 35-year-old plots were poorer in Mg but the relative changes did not deviate from the other plots. Exchangeable A1 in the C horizon increased in practically all of the soils, and was on average doubled (Fig. 2). There was a tendency of a larger increase in soils of initially lower content. Most of the 35-year-old plots were richer in A1 in the original study, and the relative increase was therefore smaller. The beech plot originally sampled at a later date ( 1971 ) was quite acid and poor in base and metal cations. This might be the reason for the relatively small changes in the studied properties, but the time-factor probably contributes. The oak forests did not deviate much from the rest of the plots. The high original content of base cations is probably due to the clayey soils.
U. FALKENGREN-GRERUPAND H. ERIKSSON
42
Na
1000 -
K
1000o
100 remainder % 10-
-
I
-
"-v-n~
-
100-
o
B B
a
o o
.- .v - ~
oo°
so
B
B
- °-d,- . . .o . . . . .
%
ab o
10-
0
~kBo°
1
0.1
i
i
1
10
Ca
1000 -
1
0.1
I000
i
I
1
10
Mg
-
o
Oo_B
a 100-
. . . . .B . . B .
remainder
Y B a°-~
_-0-o-
o
R
BB
%
1
0.01
1000
;
#
O
Bo
-
_ o
B
o
oBo
B~
B
B
10-
I
I
I
i
I
10
100
1
0.01
100-
- - - - - - B . B : - 6 - ~ oo - - . . . . . . . . . . O o o o B o
10B
I
I
i
I
0.1
1
10
100
Mn
1000-
Zn
0.001
B
-,~-
o
0.1
1
_ ~
B
-
100remainder % 10-
_
O
B
10-
100-
B .
o o%~
"
.
.
.
.
o
o
[
I
I
0.01
0.1
1
1
0.01
I
I
0.1
I 1947-52
I
10 meq kg "1
A!
.
1000 -
.
BB B
oo a 100-
.
.
.
.
o
.
.
.
.
.
B . .
aa,~ .
.
remainder
0
o aB B o a _ . o _ g. o
--o
o
% 10-
I
10 1947-52
I
100 meq kg "1
Fig. 2. E x c h a n g e a b l e - c a t i o n p o o l s in 1 9 4 7 - 5 2 in the u p p e r C - h o r i z o n a n d the r e m a i n d e r in 1 9 8 4 - 8 8 as a p e r c e n t a g e o f the p o o l s in 1 9 4 7 - 5 2 . T h e b r o k e n line r e p r e s e n t s n o c h a n g e ( 1 0 0 % ) . F u r t h e r e x p l a n a t i o n s as in Fig. I.
CHANGES IN SOIL, VEGETATION AND YIELD, 1947-1988, IN BEECH AND OAK
43
Vegetation ~ The changes of cover in the field-layer are given in Table 1 for the 19 beech and oak plots and 74 deciduous forest plots. No direct comparisons of changes in the topsoil and the vegetation were possible for the 19 forest plots as only the C horizon was reanalyzed. However, all 35-year-old plots had reduced pH in the topsoil over the same period (Falkengren-Grerup, 1987), and as the changes in the C horizons in the two studies were similar, it is most probable that pH has decreased - or at least been unchanged - also in the topsoil of the 19 oak and beech plots studied in 1988. The distribution among the cover classes 0-5 is given for plots containing the species at least at one point in time (Table 1 ). Cover class 0 means that a species has disappeared since the previous time or has colonized the following point of time. Three groups appeared when the cover of single species in 194770 and 1984-88 was compared as to whether the number of plots with occurrence of a species: had increased (group 1 ); was unchanged (group 2 ); or had decreased (group 3). Group 1 consists of 12 species. The c o m m o n feature for these species was the increase from zero to higher cover classes, i.e. colonization of plots. Species which had colonized and attained low cover were Lactuca muralis, Dryopterisfilix-mas and Chamaenerion angustifolium. Colonizing or increasing from lower to higher cover classes were Rubus idaeus, Stellaria holostea, S. nemorum, Melica uniflora and, to some degree, Carex sylvatica and Milium effusum. Convallaria majalis, Poa nemoralis and Urtica dioica were present in a larger number of plots in 1984-88, but showed small or irregular changes among the cover classes. Group 2 consists of nine species with small changes in the number of plots where a species occurred. Among these species were the acid-tolerant Deschampsia flexuosa and Maianthemum bifolium, which did not change much in cover over time. A few species were noted for higher cover classes, e.g. Hepatica nobilis, Lamium galeobdolon and Aegopodium podagraria. Oxalis acetosella was more evenly distributed among the cover classes than earlier but the highest cover class was almost unrepresented. Galium odoratum was no longer found in the two highest cover classes; this change was probably the largest among the species. Group 3 consists of five species. Three species of originally low cover had disappeared from a majority of the plots, independent of pH in the topsoil. These species, Dentaria bulbifera, Pulmonaria officinalis and Polygonatum multiflorum are among the least acidophilous species in deciduous forests in south Sweden, usually found in soils with high base saturation. Luzula pilosa ~Nomenclature follows Lid (1974).
44
U. FALKENGREN-GRERUP AND H. ERIKSSON
TABLE 1 Changes in species cover between 1947-70 and 1984-88 in plots where the species at one or both times was represented Time
Group 1. Increased number of plots Carex sylvatica t1 t2 Chamaenerion angustifolium tl t2 Convallaria majalis t1 t2 Dryopteris filix-mas t1 t2 Lactuca muralis t1 t2 Melica uniflora t1 t2 Milium effusum t1 t2 Poa nemoralis t1 t2 Rubus idaeus tl t2 Stellaria holostea t1 t2 Stellaria n e m o r u m t1 t2 Urtica dioica t1 t2 Group 2. U n c h a n g e d n u m b e r of plots Aegopodium podagraria t1 t2 A thyrium filix-femina t1 t2 Deschampsia caespitosa t1 t2 Deschampsia flexuosa t1 t2 Galium odoratum t1 t2 Hepatica nobilis t1 t2 L a m i u m galeobdolon t1 t2 M a i a n t h e m u m bifolium t1 t2 Oxalis acetosella t1 t2
Cover class
0
1
9 2 9 3 6 3 10 3 11 2 14 3 15 5 14 8 23 7 9 3 16 3 9 4
4 8 3 8 6 8 5 12 4 13 13 16 15 18 22 24 17 20 17 12 11 19 8 11
2 3 3 4 4 4 6 6 7 12
12 5 7 6 7 4 14 11 15 20 12 5 43 22 21 17 33 24
1 4 11 7 8 14 10
No. plots in cover class 2
3
1
4
5
2 1 1
1
1
I 5
1 3
4
2
3
2
1 2 10
2
1 1 2
8 3 4
4 1 3 1
2 4
2 6
1 4
2 2
1 1 1 1 7
3
6 4
1 1 0
1
2
4 13 16
1 2 10 10 1 3 7 13
3 5 19
1 5 13
7
2 4 9
5 4 1
6
9 13
15 2
1-5
0-5
4 11 3 9 7 10 5 12 4 13 21 32 15 25 22 28 20 36 18 24 17 30 9 14
13
18 17 7 6 7 7 18 18 42 37 13 12 68 61 22 21 67 71
12 13 15 15 35 30 36 43 27 33 18
20 10 11 24 49 13 72 29 81
45
C H A N G E S IN SOIL, VEGETATION AND YIELD, 1947-1988, IN BEECH AND OAK
Time
Cover class
0
1
No. plots in cover class 2
3
4
5
1-5
0-5 18
G r o u p 3. D e c r e a s e d n u m b e r o f plots
Dentaria bulbifera
t1
1
17
17
t2
13
5
5
Luzula pilosa
tI
7
18
18
25
Mercurialisperennis
t2 tl t2
12 1 11
13 20 4
13 27 17
28
Polygonatum multiflorum
t1
2
9
9
11
t2
8
3
3
t1
2
18
1
19
t2
16
4
1
5
Pulrnonaria officinalis
2 2
2 5
2 3
1 3
21
N u m b e r o f plots is given for the cover classes 0 - 5 ( H u l t - S e r n a n d e r - D u Rietz scale). 10-lami gal + rubu ida stel nea~ ~- mere per + + dea~-'fl¢ aego pod meli uni stel hol + + +
mill eff 1 m
cover change +_0.1 -
c sylvat + c h a ~ ang
+
+
poa nean + hepa nob + +
de.so ca~ +
urti dio
+ lact+m~rryof-m . . . . . .
-4- . . . . . . . . . . . -I- . . . . . . . . . . . . . . . . . . . . . athy f-f + maia bif
+ poly mul
luzu pil + +eonv maj dentbul putm ,+ oIr r,
-1--
oxal ace gall odo + +
-10 --
I 0.1
. . . . . . . .
I 1
. . . . . . . .
I
I
10
20
mean cover % Fig. 3. M e a n cover (%) in 1947-70 a n d its change up to 1984-88. M e a n cover is calculated from the class middle o f the cover classes 0 - 5 for the total n u m b e r of studied plots (n = 93). For species codes see text.
had also disappeared, but not to the same extent. Mercurialis perennis had disappeared from several sites but only those of lower cover classes. The picture is somewhat different when looking at the mean cover of each species in all studied plots, i.e. including plots which lacked the species at
46
U. FALKENGREN-GRERUPAND H. ERIKSSON
both observation times (Fig. 3). As the highest cover classes seldom were reached, and few species occurred in more than one third of the plots, the average cover usually was below 5%. At these low cover figures, changes from or to the highest cover class (class middle 75%) will influence the mean to a great extent. A large proportion of the species had increased in mean cover. Rubus idaeus, Mil. effusum, S. nemorum and Mel. uniflora had a relatively high increase due to colonization of plots but also to high cover in several plots. Other increasing species (Table 1, group 1 ) did not deviate much from species with small changes (group 2) in their average cover. Several of these species also increased over time, e.g. De. flexuosa, while G. odoratum and O. acetosella showed a marked decrease in mean cover. The substantial increase in mean cover ofL. galeobdolon and Mer. perennis was due to the higher cover classes in some plots. The disappearance from several plots will only have a small impact on the average cover.
Forest yield The mean of quotients between the observed and the estimated annual basalarea increment has been plotted against the central point of successive fiveyear periods. There are two curves for the beech plots, one representing all permanent sample plots available for yield studies in southern Sweden, and the other the fraction of plots where soil analysis was performed. The mean
1.2-
J
quotient 1.0 obs/exp
y
Y
0.8-
No. ofobs. Year
12/3 I 1945
26/16
32/22 I 1955
30/lff
30/19
I 1965
31/17
30/16 I 1975
11/16 I 1985
Fig. 4. Average quotient a n d s t a n d a r d error between observed a n d estimated basal-area increm e n t according to the function for beech stands ( C a r b o n n i e r , 1971 ). D a t a from all p e r m a n e n t beech sample plots in southern Sweden (solid) a n d from plots with repeated soil analysis ( d a s h e d ) . The n u m b e r s o f observed plots are given below.
CHANGES IN SOIL, VEGETATION AND YIELD, 1947-1988,1N BEECH AND OAK
47
1.2-
quotient 1.0 obs/exp
0.8-
No. of obs. Year
5
6
13
12
12
13
13
9
I
I
I
I
I
1945
1955
1965
1975
1985
Fig. 5. The average and standard error for quotients between observed and estimated basal area increment for all permanent oak stands in southern Sweden (Carbonnier, 19 75 ). Further explanations as in Fig. 4.
relative
change
0
%
-2--
~ v
~
___
t -4.8 No. of obs. Year
11/3
27/17
38/26
25/16
26/15
30/15
11/5
11/5
I
I
I
I
I
1945
1955
1965
1975
1985
Fig. 6. Relative changes of site index (dominant height at a total stand age of 100 years) for beech stands. Site index for beech according to revisions 1980-87 represents reference level ( z e r o ) . Negative values indicate lower index. Further explanations as in Fig. 4.
quotient for beech (Fig. 4) varied around 1.0 during 1945-75 but increased significantly (t-test) in 1976-85. The results were similar for both curves. The probable cause of the early variations is climatic conditions, but it is unlikely that favourable weather conditions should have existed during two successive periods. As only four oak plots were available for soil analyses, the growth changes over time are given for the total number of permanent oak plots. The quotient for oak (Fig. 5 ) varied irregularly over time and was only just approaching 1.0 after some periods of lower observed than expected increment in basal area. The changes in site index showed that the height in beech plots increased over time (Fig. 6 ), indicating a higher productivity as both height and basal
48
U. FALKENGREN-GRERUP AND H. ERIKSSON 2--
relative change %
No. of obs. Year
4
10
13
14
13
13
13
11
I
I
I
I
I
1945
1955
1965
1975
1985
Fig. 7. Relative changes of site index for all permanent oak stands in southern Sweden. Further explanations as in Figs. 4 and 5.
area had increased more rapidly than expected. Site index of oak stands (Fig. 7 ), on the other hand, varied more and lacked the relatively stable increase with time that beech stands showed. DISCUSSION
In a comparative study of this kind, it is important that no systematic error distorts the results. As all soils were well-drained and groundwater did not reach the sample depth at either point in time, the C horizon can be seen as a relatively stable environment. The effect of annual and seasonal variations were diminished as the original studies were made at different years and seasons, and the repeated studies were made at the same season as in the first study. Differences in cover measures can arise between observers (Kennedy and Addison, 1987; Hermy, 1988 ). As the original studies were made by several persons and the repeated studies only by a few, the latter group must deviate from all earlier observers to create a systematic error. As cover was found to increase as well as decrease, it is probable that cover was not extremely overestimated in either direction. The C horizon was probably relatively unaffected by the direct root release of hydrogen ions for other cations, as only a fraction of the roots reached this level and the main nutrient uptake takes place in the upper soil levels. In spite of this, the changes of the chemical properties in the upper C horizon were quite pronounced. Soil pH over 35 years decreased to different extents in a north/south gradient in Sweden and seemed to approach some kind of steady-state value related to the degree of acid deposition (G. Jacks, unpublished data, 1989). This steady-state pH increased towards the north of Sweden and also towards greater soil depths within a region. The pH value in our study, beyond which
CHANGES IN SOIL, VEGETATION AND YIELD, 1947-1988, IN BEECH AND OAK
49
no further decreases occurred, was 4.8 (H20) in the C horizon, which conformed to the values in the Swedish gradient. Factors such as differences in forest growth, climate and soil formation are also positively correlated with the pattern of acid deposition. These factors have a more long-term effect and have smaller effect on the observed changes during the investigation period. There was a smaller decrease in pH (KC1) than in pH (n20), which partly is due to the fact that pH is a logarithmic measurement of hydrogen ions and that pH (KC1) gives a lower pH-value. The difference between the two pH measurements has become smaller in these C-horizon samples. This was also characteristic for acid mineral soils in beech forests in Sk~ne (Tyler, 1987b ). The small change in pH (KC1) in the relatively acid soils in that study is a consequence of the changes from silicate/cation buffering to aluminium buffering (Ulrich, 1981 ). The more acid the soil, the more will base cations be replaced by aluminium rather than by hydrogen ions. Our study also showed a considerable increase in exchangeable A1. The exchangeable-cation pools of the C horizon were reduced over time in the following order: Na > Mn > Zn > Ca, Mg > K. Sodium is weakly adsorbed by clay minerals and therefore susceptile to leaching, while K ions have a much higher affinity for clay minerals, particularly 2: 1. Accordingly, a larger negative budget is often found for Na than for K in Soil water of acid forests in south Sweden (Bergkvist, 1987 ). On average, the remainder of exchangeable Na was 20%, Mn and Zn 30-50% and Ca, Mg and K 50-70% after 3540 years. As about the same figures were found also in more upper soil layers (Falkengren-Grerup et al., 1987 ), the removal of these elements must partly be an incorporation in the biomass and partly a leaching to deeper horizons, perhaps to surface waters or even to groundwater. The study of changes in the field-layer species was complemented by adding 74 plots from deciduous forests studied in 1984-85 (Falkengren-Grerup, 1986) to the 19 permanent sample plots studied in 1988. The data support each other for all species except Deschampsiaflexuosa. The increase in cover in the acidified soils has become too small to be significant. In all plots taken together, more species increased in cover and occurrence than decreased. The increasing species, however, conceal the fact that some species tended to decrease in cover in the most-acid soils. Some decreasing species also responded more strongly on the more-acid soils. Light is an important factor for the field-layer, especially in the dark beech forests. An altered management causing a more-open stand could therefore result in a moreabundant vegetation. However, the thinning regime for the permanent sampiing plots causes only a short lighter period as the degree of tree cover is regained after about two years (Svensson et al., 1987 ). By adding an element that has been scarce in forest ecosystems, increased growth might be expected if competition or other nutrients are not restricting. The nitrogen content in precipitation has more than doubled since 1955
50
U. FALKENGREN-GRERUP AND H. ERIKSSON
(Anonymous, 1986) and the total deposition to forest ecosystems is about 15-20 kg h a - 1 (Westling, 1989). This increase ought to promote nitrophilous species, and higher covers were also found for, e.g. Rubus idaeus, Stellaria nemorum, Chamaenerion angustifolium and Aegopodium podagraria. Another feature that might be advantageous for a species in a changing environment is longevity of the individual. The long-lived Hepatica nobilis (Inghe and Tamm, 1985 ), that usually occurs on less-acid soils, was found to increase where already established but did not colonize new plots. However, other relatively long-lived species with nutrient reserves and translocation in the rhizomes decreased in the most-acid soils (Mercurialis perennis), or over the entire pH-range ( Dentaria bulbifera, Pulmonaria officinalis, Polygonatum
multiflorum ). In spite of soil acidification, acid-tolerant species did not increase distinctly. Deschampsia flexuosa, Maianthemum bifolium and Luzula pilosa showed small changes and the quite tolerant Oxalis acetosella rather decreased. This is probably not due to increased light competition with other species, as the vegetation in the acid soils seldom covers the whole ground and has been relatively unchanged over the period (Falkengren-Grerup, 1986). The competition could rather be for nutrients in the rhizosphere, including tree roots. There might also be a response to an antagonism between A1 and Ca, Mg, P or to an increase of toxic elements, e.g. A1 or Mn, although D. flexuosa is known to be tolerant (Rorison, 1985, 1986). The increase of yield in the beech stands during the last ten years is contradictory to the demonstrated decreases of the nutrient pools. Whether the increase in yield will be persistent or not cannot be extrapolated from this material. The oak plots did not show any trend in growth changes. Unfortunately, the small number of oak soils which could be chemically analyzed does not illustrate the influence of the different soil chemical properties. As to the physical soil properties of the different soils, the permanent sample plots of beech had on average 28% and the oak plots 42% of particles < 0.06 mm. The differences in soil properties between the oak and beech stands are probable causes for the different growth patterns for the two species during the last decades. Most of the beech plots were relatively young at the time of the first soil sampling. The biomass of the beech plots has increased dramatically, which can be examplified from an average beech plot in the province of Halland (T54: 1-4, Carbonnier 1971 ). The stem volume in 1951 was 43 m 3 ha -~, in 1988 180 m 3 ha-1, and removed in thinnings was 181 m 3 ha-~. The increment in stem volume during the whole period was thus 318 m 3 h a - ~. An approximative conversion to biomass for the whole stand including bole, branches, twigs, leaves, stump and roots indicate a biomass increase including the removed stemwood of 250 t ha -~. The incorporation of base cations into the biomass most certainly affects the exchangeable amounts in the top-
CHANGES IN SOIL, VEGETATION AND YIELD, 1947-1988, IN BEECH AND OAK
51
soil, but might also to some degree affect the C horizon, as many studies demonstrate considerable amounts of roots in this horizon (e.g. Vyskot, 1976; NSrgaard Nielsen, 1988 ), although the studied plots showed a shallower root depth. Unfortunately, the lack of soil samples from the A and B horizons makes it impossible to present a total budget of the studied chemical elements. The yield increase of beech stands in 1976-87 is most probably not caused by favourable weather conditions. A common method to correct observed values of stand increment is to use the so-called annual ring indices. Such indices are presented for spruce but not for beech in south Sweden. The mean index for 1974-85 was 101 for spruce (Persson, 1986), which indicates normal weather. During the period 1910-1984 it has not at any time occurred that the mean annual ring indices for two successive periods both have exceeded the average value very much. Fertilization experiments with nitrogen offer another explanation of the increased yield in beech stands. Experiments in spruce stands in south Sweden gave increased wood production even on relatively fertile sites (Fahlroth, 1970). The growth increase in the beech stands may therefore be interpreted as a fertilization effect caused by the increased nitrogen deposition. This effect seems still to overwhelm the effects of the decrease of cations in the soil. The important question now is, how long will the fertilization effect exist and when will the indicated imbalances in nutrient supply influence the stand increment? Given the present state of knowledge it is difficult to give a sound answer to this question. ACKNOWLEDGEMENTS
The chemical analysis of soil and the repeated description of ground vegetation was financed by the World Wide Fund for Nature. We thank G. Tyler for comments on the manuscript, K. Olsson for field assistance, E. Sj/SstdSm for laboratory work and K. Karlsson for computer help.
REFERENCES
Anonymous, 1986. Sura och frrsurade vatten (Acid and acidified waters). National Swedish Environmental Protection Board, Solna, 180 pp. Ballach, H-J., Greven, H. and Wittig, R., 1985. Biomonitoring in Waldgebieten NordrheinWestfalens. Staub Reinhalt. Luft, 45: 567-573. Berdrn, M., Nilsson, S.I., Rosrn, K. and Tyler, G., 1987. Soil acidification. Extent, causes and consequences. Swed. Environ. Prot. Board, Solna, Rep. 3292: 1-164. Bergkvist, B., 1987. Soil solution chemistry and metal budgets of spruce forest ecosystems in s. Sweden. Water Air Soil Pollut., 33:131-154. Bjrrkdahl, G. and Eriksson, H., 1989. Effects of forest decline on increment in Norway spruce
52
U. FALKENGREN-GRERUP AND H. ERIKSSON
(Picea abies (L.) Karst) in southern Sweden. In: K. Bjor and B. Halvorsen (Editors), Air Pollution as Stress Factor in Nordic Forests. Medd. Norsk Inst. Skogforsk., 42: 19-36. Bogner, W., 1968. Experimentelle Priifung von Waldbodenpflanzen aufihre Anspriiche and die Form der Stickstoffern~ihrung. Mitt. Ver. Forstl. Standortsk. Forstpflanzenz., 18:115-124. BiJrger, R., 1986. Ver~inderungen der Bodenvegetation als Indikator ftir m/Sgliche landschafts/3kologische Folgen des Waldsterbens. Projekt europ~iisches Forschungszentrum ftir Massnahmen zur Luftreinhaltung. KFK-PEF-Berichte, 4: 375-384. Carbonnier, C., 1971. Bokens produktion i s6dra Sverige (Yield of beech in southern Sweden). Stud. For. Suec., 91: 1-89. Carbonnier, C., 1975. Produktionen i kulturbest/tnd av ek i s/Sdra Sverige (Yield of oak plantations in southern Sweden). Stud. For. Suec., 125: 1-89. Fahlroth, S., 1970. Gran p~i god bonitet - analys av ett g6dslingsf6rs6k (Spruce on a fertile site --analysis of a fertilization experiment). F6reningen Skogstr~idsf6r~idling, Inst. f. Skogsf6rb~ittring, ~,rsbok, pp. 76-86. Falkengren-Grerup, U., 1986. Soil acidification and vegetation changes in deciduous forest in southern Sweden. Oecologia, 70: 339-347. Falkengren-Grerup, U., 1987. Long-term changes in pH of forest soils in southern Sweden. Environ. Pollut., 43: 79-90. Falkengren-Grerup, U., Linnermark, N. and Tyler, G., 1987. Changes in acidity and cation pools of south Swedish soils between 1949 and 1985. Chemosphere, 16: 2239-2248. Gutschick, V.P., 1981. Evolved Strategies and Vegetation Processes. Wiley, Chichester. Hallb~icken, L. and Tamm, C.O., 1986. Changes in soil acidity from 1927 to 1982-1984 in a forest area of south-west Sweden. Scand. J. For. Res., 1:219-232. Hermy, M., 1988. Accuracy of visual cover assessments in predicting standing crop and environmental correlation in deciduous forests. Vegetatio, 75:57-64. Ingestad, T., 1976. Nitrogen and cation nutrition of three ecologically different plants. Physiol. Plant., 38: 29-34. lnghe, O. and Tamm, C.O., 1985. Survival and flowering of perennial herbs. IV. The behaviour of Hepatica nobilis and Sanicula europaea on permanent plots during 1943-1981. Oikos, 45: 400-420. Jonsson, B. and Sundberg, R., 1972. Has the acidification by atmospheric pollution caused a growth reduction in Swedish forests? R. Coll. For., Dep. For. Yield Res. Rep. Uppsat., 20: 9-14. Jonsson, B. and Svensson, L-G., 1982. A study of the effects of air pollution on forest yield. Swed. Univ. Agric. Sci., Sect. For. Mensur. Manage. Rep., 9: 9-43. Kennedy, K.A. and Addison, P.A., 1987. Some considerations for the use of visual estimates of plant cover in biomonitoring. J. Ecol., 75:151-157. Kramer, H., 1986. Relation between crown parameters and volume increment of Picea abies stands damaged by environmental pollution. Scand. J. For. Res., 1:251-269. Kuhm N., Amiet, R. and Hufschmid, N., 1987. Vedindernngen in der Waldvegetation der Schweiz infolge N~ihrstoffanreicherungen aus der Atmosph~ire. Allg. Forst JagdZtg., 158: 7784. Lid, J., 19741 Norsk og Svensk Flora. Det Norske Samlaget, Oslo. Linnermark, N., 1960. Podsol och brunjord (Podsols and brown soils) I-II. Summary in English. Publ. Inst. Mineral. Paleontol. Quart. Geol., Univ. Lund, Sweden, 75: 1-233. N/Srgaard Nielsen, C.C., 1988. EinfliJsse von Plantzenabstand und Sturmzahlhaltung auf Wurzelforme, Wurzelbiomass, Verankerung sowie auf die Biomasseverteilung im Hinblick auf die Sturmfestigkeit bei Fichte. Thesis, Univ. G/Sttingen, Part 2, pp. 19-26. Persson, O., 1986. The Atvidaberg thinning experiment. Swed. Univ. Agric. Sci., Dep. For. Yield Res. Rep., 18: 12-16.
CHANGES IN SOIL, VEGETATION AND YIELD, 1947-1988, IN BEECH AND OAK
53
Rorison, I.H., 1985. Nitrogen source and the tolerance ofDeschampsiaflexuosa, Holcus lanatus and Bromus erectus to aluminium during seedling growth. J. Ecol., 73: 83-90. Rorison, I.H., 1986. The response of plants to acid soils. Experentia, 42: 357-362. Svensson, J., Bjerk6n, J., M/Lrtensson, B-L. and Einarsson, E., 1987. Kronslutenhet och dessf6r~indring i gallrade bokbest~nd (crown density and its change in thinned beech stands ). Swedish University of Agricultural Science, Dept. Forest Yield Research (stencil), 13 pp. Tamm, C.O. and Hallb~icken, L., 1988. Changes in soil acidity from the 1920s to the 1980s in two forest areas with different acid deposition. Ambio, 17:56-61. Tregenza, N.J.C., 1986. Acidification effects on the flora of Cornwall. Cornwall Trust for Nature Conservation, Cornw. Conserv. Rev. Rep., 1: 1-21. Tveite, B. and Abrahamsen, G., 1980. Effects of artificial acid rain on the growth and nutrient status of trees. In: T.C. Hutchinson and M. Havas (Editors), Effects of Acid Precipitation on Terrestrial Ecosystems. Plenum, New York, pp. 305-318. Tyler, G., 1987a. Probable effects of soil acidification and nitrogen deposition on the floristic composition of oak (Quercus robur L. ) forest. Flora Jena, 179:165-170. Tyler, G., 1987b. Acidification and chemical properties of Fagus sylvatica L. forest soils. Scand. J. For. Res., 2:263-271. Tyler, G., Berggren, D., Bergkvist, B., Falkengren-Grerup, U., Folkeson, L. and Riihling, A., 1987. Soil acidification and metal solubility in forests of southern Sweden. In: T.C. Hutchinson and K.M. Meema (Editors), Effects of Atmospheric Pollutants on Forests, Wetlands and Agricultural Ecosystems. NATO ASI Series, Vol. G 16, Springer, Berlin, pp. 347-359. Ulrich, B., 1981. Okologische Gruppierung von B6den nach ihrem chemischen Bodenzustand. Z. Pflanzenern~ihr. Bodenkd., 144: 289-305. Vyskot, M., 1976. Tree story biomass in lowland forests in south Moravia. Rocnik, 86-sesit 10: 57-74. Westling, O., 1989. Nedfall av luftf6roreningar i Sk/me. (Deposition of atmospheric pollutants ) Swed. Environ. Res. Inst., Rep., 1-14. Wittig, R., Ballach, H.J. and Brandt, C.J., 1985. Increase of number of acid indicators in the herb layer of the millet grass-beech forest of the Westphalian Bight. Angew. Bot., 59:219232.