Regional variation in forest health under long-term airpollution mitigated by lithological conditions

Mark Purdona,*, Emil Ciencialaa, Vaclav Metelkab, Jana Beranovaa,Iva Hunovac, Martin Cernya

aInstitute of Forest Ecosystem Research (IFER), 1544 Jılove u Prahy 254 01, Czech RepublicbMineralogy and Mineral Resources Faculty of Science, Institute of Geochemistry, Charles University,

Albertov 6, 128 43 Prague 2, Czech RepubliccCzech Hydrometeorological Institute (CHMI), Na Sabatce 17, 143 06 Prague 4, Komorany, Czech Republic

Received 14 February 2003; received in revised form 2 December 2003; accepted 20 February 2004

Abstract

Forest defoliation and discoloration have been monitored extensively in Europe over the past decade, yet the number of

published studies seeking to interpret these data in light of environmental parameters such as lithology and airborne pollution are

few. In this study we summarize and compare data on defoliation and discoloration of Norway spruce dominated stands from

three regions of the Czech Republic that differ in their lithology. In the Sumava and Krkonose regions these measures increased

over the monitoring period, which is interpreted as an effect of residual soil acidification. At Beskydy, a general stability in forest

health parameters was observed. Regional differences are attributed to underlying lithography—the greater calcium carbonate

content of the flysch bedrock at Beskydy provides better buffering against acid deposition. These results are supported by

evidence of similar trends in atmospheric pollution (ambient air concentrations and deposition) between Beskydy and the

Krkonose region and higher sulphur inputs than at Sumava. Stand elevation and age, collected as explanatory variables, did not

affect this interpretation. Additionally, in the Krkonose region forest health data were examined for four soil type categories

(extreme, acidic, enriched and nutritive) specific to forest conditions in the Czech Republic. Simple time series analysis of

defoliation and discoloration demonstrated that extreme and acidic soils accounted for the majority of the increasing trend of

forest decline in Krkonose. However, multivariate non-linear regression analysis using elevation and stand age revealed that

defoliation was not significantly different between acidic and nutritive soil type categories; rather, this was an artefact of the

experimental design. The implications of the research are that acidic and nutritive soil type categories respond similarly to acid

deposition while enriched, the most nutrient rich type category is most resistant. As such our results support the interpretation

that lithology is a factor mitigating forest decline in Norway spruce dominated forests in the Czech Republic. Our results have

implications for zonation strategies like those being used in Krkonose National Park which seek to prescribe specific restoration

measures based upon abiotic factors for acid-damaged forests.

# 2004 Elsevier B.V. All rights reserved.

Keywords: Acid deposition; Defoliation; Discoloration; Norway spruce; Soil acidification

1. Introduction

Forest defoliation and discoloration have been mon-

itored extensively in Europe over the past decade, yet

Forest Ecology and Management 195 (2004) 355–371

* Corresponding author. Present address: School of Geography

and the Environment, University of Oxford, Oxford OX1 3TB, UK.

Fax: þ44-1865-271929.

E-mail address: mark.purdon@green.oxford.ac.uk (M. Purdon).

0378-1127/$ – see front matter # 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.foreco.2004.02.039

the number of published studies seeking to interpret

these data in light of environmental parameters such as

lithology and airborne pollution are few. Forest degra-

dation and dieback in central Europe have tradition-

ally been linked with atmospheric pollution (Pelisek,

1983; Mazurski, 1986). Despite large-scale reductions

in atmospheric pollutants during the 1990s (Hunova

et al., 2004; Renner, 2002), forest dieback is still a

problem in areas of the Czech Republic. Results of the

Level I monitoring of the Czech ICP-Forests pro-

gramme show a pattern of worsening stand crown

condition since 1986 (Anonymous, 2001). Much of

the forest decline has been attributed to forest soil

acidification and nutrient degradation due to a com-

bination of previous periods of intense acidic deposi-

tion as well as a ‘‘borealization’’ effect resulting from

a 300-year tradition in Norway spruce (Picea abies

Karsten) monocultures (Fanta, 1997; Emmer et al.,

1998, 2000). Acid deposition resulting from high

ambient air concentrations of SO2 and NOx leads to

soil acidification by degrading the buffering capacity

of soils, resulting in Hþ induced cation leaching and

interference with cation uptake by Al substitution

(Schulze, 1989; Lawrence et al., 1995; Hruska and

Cienciala, 2001).

In the present study we examine defoliation and

discoloration data from three different subalpine

mountain forest regions of the Czech Republic (Bes-

kydy, Krkonose, and Sumava) where differences occur

in parent rock material. These data have been col-

lected by the Institute of Forest Ecosystem Research

(IFER) since 1990, using a modified UN/ECE ICP-

Forests methodology. In addition, for the Krkonose

region, we analyze these data under different soil type

categories developed specifically for the conditions of

the Czech Republic (Prusa, 2001). These soil type

categories are important because, along with an alti-

tudinal gradient, they form the basis for forest man-

agement in the country. Forests in Krkonose National

Park are currently undergoing restoration manage-

ment to mitigate the effects of soil acidification. A

key factor in this work is a new forest zonation, based

on forest health data described here and their relation

to stand conditions (Cerny et al., 1998; Cerny and

Moravcık, 1995). These authors identified elevation

and age as significant factors in the prediction of forest

health status in Krkonose National Park.

Our hypotheses were (i) that forest degradation

varies in an important manner across these three

regions and (ii) that much of this can be attributed

to abiotic site factors such as bedrock and soils. A

secondary objective was to determine if the impor-

tance of elevation and stand age in explaining de-

foliation at Krkonose (i) applies to other forested

regions of the Czech Republic and (ii) if it is affected

by soil type. Though lacking experimental data on

lithology, we believe that results from this study can

serve to orientate future research, particularly for the

restoration of forested regions damaged by soil acid-

ification.

2. Materials and methods

2.1. Study area

2.1.1. General conditions

Data have been compiled from a network of forest

monitoring plots located in three regions of the Czech

Republic: Sumava, Krkonose, and Beskydy (Fig. 1).

All three are low-lying mountainous regions with

elevations not exceeding 1700 m. General conditions

are presented in Table 1. Krkonose is the coldest

region because the mountain range intercepts prevail-

ing westerly winds which bring in cold, wet oceanic

air masses from the Atlantic (Anonymous, 2002). In

comparison, climatic conditions in the Beskydy region

are slightly warmer (CHKO Beskydy, 2003, pers.

Table 1

General characteristics of the three study areas

Average temperature

(8C) (range)

Total precipitation

(mm) (range)

Altitude (m)

(range)

Difference in

altitude (m)

Krkonose 6–0 800–1400 400–1602 1202

Beskydy 7.8–2.3 900–1377 350–1328 978

Sumava 6.5–3.5 800–1600 600–1378 778

356 M. Purdon et al. / Forest Ecology and Management 195 (2004) 355–371

commun.). Typical conditions in Sumava are mild wet

weather mainly along river valleys, depending on

height above sea level, and cold wet weather (Anon-

ymous, 1999).

2.1.2. Geological conditions

The three study regions can be divided into two

geologic groups based on their lithology. The first one

including Sumava and Krkonose belongs to the crys-

talline part of the Bohemian Massif, while Beskydy is

a part of the Alpine–Carpathian system. A description

of the geology was derived from 1:500,000 and

1:50,000 scale maps developed by the Czech Geolo-

gical Survey (Kodym et al., 1967; Mencık, 1987; Pesl,

1990, 1993; Tasler, 1990; Vejnar, 1988), including

newly available GIS layers (Anonymous, 2003a). In

addition, the geochemical status of these regions was

drawn from 1:50,000 scale maps (Adamova, 1986,

1989, 1991a; Gurtlerova, 1991; Mrazek, 1990) des-

cribing the geochemical reactivity of bedrock, con-

sidering the lithological type and using the Xalk value,

ranging from 0.05 to 0.4 (mol kg�1) for common rock

types, where values greater than 0.4 mol kg�1 belong

to pure carbonate systems or extremely alkali rich

volcanic rocks

Xalk ðmol kg�1Þ

¼ Na þ K þ Li þ Ca þ Mg þ Ba þ Sr

Si þ Ti þ Al þ FeðII; IIIÞ þ Mn

þ Na þ K þ Li þ Ca þ Mg þ Ba þ Sr

(1)

The equation and methodology used are described by

Adamova (1991b).

Bedrock in the Krkonose and Sumava regions is

largely of medium to low geochemical reactivity, with

Xalk values ranging from 0.1 to 0.2 mol kg�1, and

likely originating from the Proterozoic to Paleozoic

periods. Krkonose is characterized primarily by meta-

morphic or igneous bedrock of which the predominant

lithological types are orthogneisses, schists, phyllites

Fig. 1. Map showing location of sampling regions in the Czech Republic.

M. Purdon et al. / Forest Ecology and Management 195 (2004) 355–371 357

and quartzites. A small area in the northern part of the

region is comprised of granites with low base content

(Mısar et al., 1983; Kodym et al., 1967). Calcium

carbonate is mainly present in small lentil shaped

bodies of crystalline limestone and erlan, and occur-

ring infrequently. Bedrock in Sumava is mostly meta-

morphic, but also a few igneous intrusive bodies. The

largest area is comprised of gneisses with only a few

intercalations of basic rocks and crystalline limestone

(Mısar et al., 1983; Kodym et al., 1967). The intrusive

bodies are spatially subordinated to the geneisses and

consist of different suites of granites (Mısar et al.,

1983; Baburek, 1996). Calcium carbonate is again

available only in small bodies of crystalline limestone

and is thus negligible.

ThegeologicalsettingofBeskydyisdifferentfromthe

two described above. It is a part of the Outer Carpathian

nappe system originating from the younger, Cretaceous

to Tertiary period. The study region is mainly comprised

of three geological formations: Godula, Istebna and

Solan.Theseformationsarecharacterizedbyalternating

sequences of calcareous or non-calcareous pelites, psa-

mites and conglomerates—the so-called flysch sedi-

mentation (Mencık et al., 1983; Pesl, 1990). Calcium

carbonate is present in the region, but varying over the

three formations, depending on lithological type (see

Table 2 modified from Elias (1970)). In the middle

Godula and Solan formations, bedrock was found

to be comprised of 1–10% calcium carbonate, with

Xalk values >0.25 mol kg�1 indicating high reactivity.

These two formations account for approximately 55%

of the Beskydy study area. The Istebna formation and

the lower part of the Godula formation demonstrate

Xalk values of 0.1–0.2 mol kg�1.

2.2. Data collection

Defoliation and discoloration data were recorded

from 1990 to 2000 by IFER using a modified

ICP-Forests methodology (Cerny and Moravcık,

1995): this included a denser sampling plot grid

(1 km � 1 km) and estimations of percent total defo-

liation and intensity of discoloration based on per-

centages rather than ICP classes (0–4). Though plots

where systematically monitored regardless of tree

species composition, only data from plots dominated

by Norway spruce were of sufficient number for

statistical analysis conducted here. In addition, a

number of basic stand related data were recorded

annually: elevation, aspect, age, slope, and the num-

ber of tree species in each stand.

A forest soil type category map prepared for the

Krkonose region allowed us to assign plots to specific

soil type category classes. Soil type category is based

on soil characteristics as well as on a number of

understorey plant indicator species and is the basis

for forest management in the Czech Republic (Prusa,

2001). There are a total of 24 edaphic categories,

which are grouped into seven soil type categories of

which four were present in our study area (extreme,

Table 2

Approximate area, carbonate content and Xalk values of the Beskydy mountains study area

Stratigraphy Lithologic types Approximate

area (%)

Average clay

substance (%)

Average

calcite (%)

Xalk (mol kg�1)

Godulaa

Middle Psamites 40 15–50 0–3 >0.25

Calcareous psamites 35–40

Pelites 95–98 þUpper Psamites 20 10–60 0–2 0.1–0.2

Pelites 85–99 þ

Istebnaa Psamites 25 10–45 0 0.1–0.2

Calcareous psamites 20–30

Pelites 85–99 0

Solanb Psamites 15 Average 20.8 of carbonates >0.25

Pelites Average 8.3 of carbonates

a Elias (1970), dolomite not included, petrographic studies.b Pesl and Zurkova (1967), overall content of carbonates in samples (CaCO3, MgCO3), determined by complexometric titration.

358 M. Purdon et al. / Forest Ecology and Management 195 (2004) 355–371

acidic, enriched and nutritive). The general nutri-

tive status of these soil type categories proceeds in

the following manner, from poorest to richest:

extreme < acidic < nutritive < enriched (which is

particularly rich in N).

Tree forest health data were complimented by

air pollution data—ambient air concentrations and

deposition—obtained from hydrometeorological

monitoring stations maintained by the Czech Hydro-

meteorological Institute and the Czech Geological

Survey (Fig. 1). Data on ambient air concentrations

of SO2, NOx and O3 were collected from 1994 to

2000 at three monitoring stations: Beskydy (Bıly

Krız: 890 m altitude), Krkonose (Rychory: 1001 m

altitude) and Sumava (Churanov: 1122 m altitude). See

Hunova et al. (2004) for a description of sampling

methods. For measures of precipitation as well as

nitrate and sulphate deposition, data were obtained

from monitoring stations monitored from 1995 to

2001: Beskydy (Bıly Krız), Krkonose (Modry Potok:

1010 m altitude), and two for Sumava (Spalenec:

795 m altitude and Na lizu: 828 m altitude). Annual

wet atmospheric deposition (g m�2 per year) was

calculated from nitrate and sulphate ion concentrations

using the following equation:

D ðg m�2 per yearÞ ¼Xn

i¼1

cipi (2)

where ci is the ion concentration in the monthly

precipitation sample, pi is the monthly precipitation

amount measured at the relevant monitoring site, and

n is months in a year. It should be noted that the

method of deposition data collection between these

monitoring stations varied: at Beskydy deposition was

measured as wet-only samples while at all other

stations bulk deposition was monitored. We believe

that comparisons between these data are possible in

such rural areas. For example, Dixon et al. (1998)

demonstrated high similarity between both measure-

ment techniques in Florida. It should also be noted that

the method used for measuring dry deposition does not

account for aerosols, whose contribution may be sig-

nificant. Moreover deposition from fog and rime is not

taken in account due to the fact there is no relevant

data. The authors are fully aware, however, that the

contribution of fog and rime to the total atmospheric

deposition is significant in mountain areas.

2.3. Data analysis

Because the forest health data were generally

not normal, we used Kruskal–Wallis tests as a non-

parametric analogy to ANOVA, followed by Student–

Newman–Keuls post-hoc tests (Mathsoft, 1999) to

determine differences among regions and, at Krkonose,

among soil type categories. These same tests were used

to compare differences between elevation and age.

Linear regression was used to determine the amount

of variation in the defoliation and discoloration data

that could be explained by elevation and age. In

addition, for defoliation, a multiple non-linear regres-

sion equation was applied. This was based upon a

significant relationship between defoliation and eleva-

tion and age detected in a previous study in the

Krkonose region (Cerny et al., 1998):

defoliation ¼ ðp1 þ p2 � elevationÞ � agep3 (3)

We applied this equation to determine if the relation-

ship held across the other two regions, Beskydy and

Sumava, as well as across individual soil type cate-

gories at Krkonose. All regressions were conducted

using Sigma Plot 2000 (SPSS, 2000). Instead of using a

3D graph, results of Eq. (3) are shown in two separate

figures by using empirically determined parameters of

(p1, p2 and p3) to show the response of defoliation to

first elevation and then age. The first models the effect

of elevation on defoliation while holding age as a fixed

average in Eq. (3), while the second models the effect

of age while holding elevation fixed.

Though we conducted the above-mentioned linear

and multiple non-linear regressions of defoliation and

discoloration for all years when data were available,

results were similar between years and we present only

the 1997 data. This was the most recent year when data

availability allowed for comparisons between all three

regions.

3. Results

3.1. Long-term trends in atmospheric pollutants

between regions

General patterns in ambient air concentrations of

SO2, NOx and O3 since 1994 were similar between

regions, ozone in particular (Fig. 2A(i)). This is due to

M. Purdon et al. / Forest Ecology and Management 195 (2004) 355–371 359

NO

x (µ

g m

-3)

0

5

10

15

O3

(µg

m-3

)

0

5

60

80

100

Year

1994 1995 1996 1997 1998 1999 2000 2001 1994 1995 1996 1997 1998 1999 2000 2001

SO

2 (µ

g m

-3)

0

5

10

15

20

Krkonoše (Rýchory)Beskydy (Bílý Kriz)Šumava (Churánov)

A(i)

A(iii)

A(ii)

Year

Sul

phat

es (

g m

-2)

0

1

2

3

4

5

6

Nitr

ates

(g

m-2

)

0

1

2

3

4

5

6

Pre

cipi

tatio

n (m

m)

0

500

1000

1500

2000

Krkonoše (Modrý potok)Beskydy (Bílý Kriz)Šumava (Nalizu)Šumava (Spálenec)

B(i)

B(ii)

B(iii)

Fig. 2. Long-term trends (1994–2001) in (A) average annual ambient air concentrations of (i) O3, (ii) NOx and (iii) SO2 and (B) total annual (i) precipitation, (ii) nitrate and (iii)

sulphate deposition in the three study regions of the Czech Republic.

36

0M

.P

urd

on

eta

l./Fo

restE

colo

gy

an

dM

an

ag

emen

t1

95

(20

04

)3

55

–3

71

the fact that ozone concentrations depend very much

on meteorological conditions and are generally high in

rural regions. Similarities in SO2 and NOx were strong

between the Beskydy and Krkonose regions, while

concentrations in the Sumava region were slightly

reduced in comparison (Fig. 2A(ii) and (iii)). Con-

centrations of SO2 showed a strong decrease over

the monitoring period. European and Czech NOx

and SO2 limit values (EC, 1999, 2002; Czech Govern-

ment, 2002) were not exceeded in the period under

review.

Total annual precipitation was greatest at Krkonose

and Beskydy and lowest at the two Sumava stations

(Fig. 2B(i)). These differences are attributed to pre-

vailing winds, altitude and aspect of the monitoring

stations. Nitrate deposition was of the same magnitude

between regions (Fig. 2B(ii)), though deposition at the

two Sumava monitoring stations tended to be lower.

Nitrate deposition tended to remain stable over the

course of the monitoring period. Krkonose and Bes-

kydy were characterized by higher sulphate deposition

than the two Sumava monitoring stations, particularly

from 1997 to 2000 (Fig. 2B(iii)). Sulphate deposition

shows a general declining trend in all three regions.

We note however that nitrate and sulphate ion con-

centrations were similar between regions (results not

shown), indicating that deposition is mediated by the

amount of precipitation.

3.2. Regional differences

3.2.1. Differences in forest health parameters

between regions: Krkonose, Beskydy, and Sumava

Trees in the Krkonose region had significantly

higher defoliation than the other two regions

(Fig. 3A(i)). Kruskal–Wallis tests indicated significant

differences in defoliation amongst all three regions for

each year of the monitoring period (results not shown).

Defoliation in Sumava was marked by a clear increase

over time (slope ¼ 2:14, r2 ¼ 0:91), significantly

lower than in Beskydy until 1995, after which it

exceeded defoliation at Beskydy. From 1997 onward,

defoliation in Sumava appears to be reaching an upper

limit at around 35–40%. Linear relationships between

defoliation and time at Krkonose and Beskydy are not

as strong (r2 ¼ 0:29 and 0.06, respectively). Indeed,

defoliation at Beskydy remained within the 30–40%

range over the course of the monitoring period.

The intensity of discoloration was significantly high-

est in the Krkonose region, at least doubling that of the

other regions (Fig. 3A(ii)). From Kruskal–Wallis tests

showed discoloration in Sumava to be slightly greater

than in Beskydy, this being statistically significant in

all years except 1994 (results not shown). The data do

not show a linear relationship with time.

3.2.2. Regional differences related to elevation

and age

Forest monitoring plots were significantly higher

and older in Sumava, and lowest and youngest in

Beskydy (Fig. 4, Table 3). From Fig. 4 it is evident

that the distribution of elevation and age is greater at

Krkonose and Sumava than at Beskydy.

Independent linear regression analysis of the 1997

data (Fig. 5) demonstrated that defoliation and dis-

coloration increased both with elevation and with age

in the Krkonose region. In Sumava similar trends are

evident, but the coefficient of determination is lower.

Except for an r2 value of 0.10 between defoliation and

age, neither defoliation nor discoloration showed a

meaningful relationship with elevation and age at

Beskydy. Regression analyses conducted for the entire

monitoring period showed that these trends were

maintained (results not shown).

Multiple non-linear regression output of the 1997

defoliation data (Fig. 6A) showed an improvement in

the amount of variation explained at Krkonose and

Sumava due to the combined relationship of age and

elevation (r2 ¼ 0:48 and 0.17, respectively). At Bes-

kydy however, the non-linear model did not improve

over r2 values of the linear model (r2 ¼ 0:08). Though

all three regions did demonstrate that defoliation

increases with elevation and age, approaching an

upper limit with the latter, all three regions showed

different responses. It is also apparent that the reduced

fit at Beskydy is due to a less important response to

elevation. Multiple non-linear regression analyses of

all years found these patterns to be sustained over the

entire 10-year monitoring period (results not shown).

3.3. Differences between soil type categories

3.3.1. Defoliation and discoloration among soil

type categories in the Krkonose region

From 1993 to 1997, defoliation is consistently

highest on extreme, and then acidic soil type categories

M. Purdon et al. / Forest Ecology and Management 195 (2004) 355–371 361

Year

1988 1990 1992 1994 1996 1998 2000 2002

% D

efol

iatio

n

0

10

20

30

40

50

60

70

KrkonoseBeskydySumava

Year

1988 1990 1992 1994 1996 1998 2000 2002

% D

isco

lora

tion

0

5

10

15

20

25

30

35

KrkonoseBeskydySumava

A(i) A(ii)

Year

1992 1993 1994 1995 1996 1997 1998 1999

% D

efol

iatio

n

0

10

20

30

40

50

60

70ExtremeAcidicEnrichedNutritive

Year

1992 1993 1994 1995 1996 1997 1998 1999

% D

isco

lora

tion

0

5

10

15

20

25

30

35

ExtremeAcidicEnrichedNutritive

B(i) B(ii)

Fig. 3. Defoliation (%) and discoloration (%) in Norway spruce dominated plots for (A and B) three regions of the Czech Republic and (C and D) the four soil type categories of the

Krkonose region.

36

2M

.P

urd

on

eta

l./Fo

restE

colo

gy

an

dM

an

ag

emen

t1

95

(20

04

)3

55

–3

71

followed by nutritive and enriched (Fig. 3B(i)). Defo-

liation on these latter two soil type categories demon-

strates quite similar responses, not showing significant

differences via Kruskal–Wallis tests (results not

shown). By 1998 however, significant differences

between acidic, nutritive and enriched were found

not to exist. In terms of change over time, only

defoliation on extreme sites shows a slight, linear

increase over the monitoring period (r2 ¼ 0:51).

Values of r2 for other soil type categories are less

significant and are not shown.

Results of Kruskal–Wallis tests (results not shown)

indicate that discoloration was not significantly dif-

ferent between soil type categories until 1995, after

which significant differences are found between

extreme-acidic soils and nutritive-enriched soils

(Fig. 3B(ii)). On the first two soil type categories,

discoloration increases with a peak in 1996 followed

by a return to lower levels. Nutritive and enriched soils

do not show such a strong peak. Extreme also dis-

sociates itself from acidic for the period 1996–1998.

3.3.2. Differences in elevation and age between

soil type categories in the Krkonose region

Soil type categories were characterized by impor-

tant differences in elevation and stand age (Fig. 4,

Table 3). At one extreme were extreme soils that were

characteristic of stands of highest elevation and oldest

Krkonoše Beskydy Šumava

0

50

100

150

200

400

600

800

1000

1200

1400A

ge (

yr)

Ele

vatio

n (m

)

Age (yr)

Elevation (m)

Extreme Acidic Enriched Nutritive

50

100

150

200

500

700

900

1100

1300

Age

(yr

)E

leva

tion

(m)

Age (yr)

Elevation (m)

(A) (B)

Fig. 4. Box plots of elevation and plot age for (A) the three study regions and (B) the four soil type categories of the Krkonose region.

Table 3

Mean values (and standard deviation) of explanatory variables for all three regions

Explanatory

variable

Regional level Soil type categories at Krkonose

Krkonose Beskydy Sumava Extreme Acidic Enriched Nutritive

Elevation (m) 922b (188) 704c (122) 1007a (146) 1134a (167) 938b (167) 817c (115) 784c (147)

Age (years) 110b (42.3) 89.9c (27.1) 113a (31.9) 132a (45.1) 110b (38.2) 91.1b (37) 97.5b (37.5)

Mean results followed by different letters indicate significant differences between treatments as determined through Kruskal–Wallis/Student–

Newman–Keuls testing. Standard deviations are given in parenthesis.

M. Purdon et al. / Forest Ecology and Management 195 (2004) 355–371 363

500 750 1000 1250

% D

efo

liati

on

0

20

40

60

80

100

500 750 100 1250 500 750 1000 1250

50 125 20050 125 20050 125 2000

20

40

60

80

100

r2 = 0.43 r2 = 0.02 r2 = 0.11

Krkonoše Beskydy Šumava

Elevation (m)

DEFOLIATION

r2 = 0.29 r2 = 0.10 r2 = 0.12

% D

efo

liati

on

Stand Age (yr)

50 125 200

% D

isco

lora

tio

n

0

20

40

60

50 125 200 50 125 200

DISCOLORATION

Krkonoše Beskydy Šumava

500 750 1000 1250500 750 1000 1250500 750 1000 1250

% D

isco

lora

tio

n

0

20

40

60r2 = 0.41 r2 = 0.00 r2 = 0.08

Elevation (m)

r2 = 0.12 r2 = 0.01

Stand Age (yr)

r2 = 0.01

Fig. 5. Linear regression of 1997 defoliation and discoloration data with elevation and age over the three study regions of the Czech Republic.

In the upper left-hand corner of each graph is the calculated r2 value for the regression.

364 M. Purdon et al. / Forest Ecology and Management 195 (2004) 355–371

Elevation (m)

200 400 600 800 1000 1200 1400 1600

Def

olia

tion

(%)

0

25

30

35

40

45

50

55

60

Krkonose (r2 = 0.48)Beskydy (r2 = 0.08) Sumava (r2 = 0.17)

Age (yr)

0 50 100 150 200 250

Def

olia

tion

(%)

0

25

30

35

40

45

50

55

60

Krkonose (r2 = 0.48)Beskydy ( r 2 = 0.08) Sumava (r 2 = 0.17)

A(i) A(ii)

Elevation (m)

400 600 800 1000 1200 1400

Def

olia

tion

(%)

0

25

30

35

40

45

50

55

60

Extreme (r2 = 0.53)Acidic (r2 = 0.40)Enriched (r 2 = 0.07)Nutritive (r 2 = 0.57)

Age (yr)

0 50 100 150 200 250

Def

olia

tion

(%)

0

25

30

35

40

45

50

55

60

Extreme (r2 = 0.53)Acidic (r2 = 0.40)Enriched (r2 = 0.07)Nutritive (r2 = 0.57)

B(i) B(ii)

Fig. 6. Results of multiple non-linear regression using Eq. (3) on 1997 data from (A) the three study regions and (B) the four soil type categories of the Krkonose region. To obtain

the regression lines, average values of age and elevation were inserted as fixed values into Eq. (3) along with empirically determined parameters (p1, p2, and p3). For the regions

these are average age and elevation, 106.5 years and 907.5 m, respectively. For the four soil type categories of the Krkonose region, these are age ¼ 104:9 years and 842.8 m.

M.

Pu

rdo

net

al./F

orest

Eco

log

ya

nd

Ma

na

gem

ent

19

5(2

00

4)

35

5–

37

13

65

750 1000 1250

% D

efo

liati

on

0

20

40

60

80

100

750 1000 1250 750 1000 1250 750 1000 1250

r2 = 0.43 r 2 = 0.34 r2 = 0.04 r2 = 0.46

Elevation (m)

Extreme Acidic Enriched Nutritive

DEFOLIATION

750 1000 1250750 1000 1250

% D

isco

lora

tio

n

0

20

40

60

750 1000 1250 750 1000 1250

r2 = 0. 37 r2 = 0.23 r2 = 0.23 r2 = 0.57

Elevation (m)

DISCOLORATION

Extreme Acidic Enriched Nutritive

50 125 200

% D

efo

liati

on

0

20

40

60

80

100

50 125 200 50 125 200 50 125 200

r2 = 0.42 r2 = 0.23 r 2 = 0.01 r2 = 0.33

Stand Age (yr)

Stand Age (yr)

50 125 200

% D

isco

lora

tio

n

0

20

40

60

50 125 200 50 125 200 50 125 200

r2 = 0.08 r2 = 0.02 r2 = 0.00 r2 = 0. 28

Fig. 7. Linear regression of 1997 defoliation and discoloration with elevation and age over the four soil type categories in the Krkonose

region. In the upper left-hand corner of each graph is the calculated r2 value for each regression.

366 M. Purdon et al. / Forest Ecology and Management 195 (2004) 355–371

age. The elevation of acidic soils was significantly

less, but greater still than the nutritive and enriched

soil type categories. Though all younger than extreme

plots, the ages of the other three type categories were

similar.

From linear regressions of 1997 forest health para-

meters (Fig. 7) it can be observed that on extreme and

acidic sites, defoliation showed a significant relation-

ship with both explanatory variables, while the varia-

tion in discoloration was only significantly explained

by elevation. For nutritive soil type categories a linear

relationship of increasing defoliation and discolora-

tion is discernible for both elevation and age. Enriched

sites showed weakest relationships with elevation and

age, only showing significant relationships between

discoloration and elevation. These results were main-

tained over the monitoring period (results not shown).

For defoliation, the multiple non-linear model

resulted in an improved fit for all soil type categories:

r2 values were 0.53, 0.40, 0.07 and 0.57, respectively,

for extreme, acidic, enriched and nutritive soil type

categories. Plots of the independent regressions using

Eq. (3) demonstrates that defoliation increases with

elevation and age for all soil type categories (Fig. 6B(i)

and (ii)). It is important to note here however, that of

the four soil type categories, acidic and nutritive soil

type categories show very similar responses.

4. Discussion

4.1. Inter-regional variation in forest health status

There is a marked difference in forest health status

between regions which we attribute to lithology. Both

defoliation and discoloration are most severe at Krko-

nose and, to a lesser extent, at Sumava. More impor-

tantly defoliation in the Sumava and Krkonose regions

increased over time, but was generally stable in the

Beskydy region at the 30–40% range. This is espe-

cially important for Sumava which, at the beginning of

the monitoring period, posted the lowest levels of

defoliation but surpasses Beskydy by the year 2000.

We note that though the ‘‘stable’’ amount of defolia-

tion at Beskydy is high relative to other European

countries, it is not surprising considering that the

Czech Republic has continuously reported amongst

the highest defoliation values of European ICP forests

and has been subject to some of the continent’s worst

pollution. Differences between regions in terms of

discoloration are similar, but no linear increase over

time is discernible.

Forest dieback in central Europe has been attributed

to be the direct effect of acid deposition and air

pollution which disrupt the soil nutrient balance

(Mazurski, 1986; Schulze, 1989). Accordingly, it

had been assumed that reductions in direct acid

deposition would result directly in improvements in

forest health. However, the increase in defoliation in

the Sumava and Krkonose regions has occurred

despite a decrease in atmospheric pollutant concen-

trations and deposition in these regions, particularly of

sulphur. As such, results from Krkonose and Sumava

support the hypothesis put forth by Likens et al. (1996)

of a residual effect of prior periods of acid deposition.

In the Czech context, soil acidification induced by the

high ambient air concentrations of pollutants is com-

pounded by the ecology of Norway spruce monocul-

tures. In comparison to deciduous species, Norway

spruce has a greater capacity to intercept pollutants

and higher litter acidity (Augusto et al., 1998, 2002;

Binkley and Valentine, 1991) and is also less efficient

in nutrient cycling (Emmer et al., 1998; Murach,

1985). Although there is a trend to promote a selection

system of forest management, management of even-

aged stands based on Norway spruce remains the

predominant strategy on state-run forests, which

represent 61% of the Czech forest land (Anonymous,

2003b).

We propose that the underlying reason for increas-

ing defoliation and higher discoloration in the Krko-

nose and Sumava regions and their stability at

Beskydy is due to differences in the buffering capacity

of the lithology between regions. Rock weathering—

particularly through hydrolysis which consumes Hþ—

is one of the most important buffers of soil acidity

(Johnson, 1984; Binkley and Richter, 1987; Kram

et al., 1997). Buffering from bedrock weathering

would be greater at the Beskydy region, than at the

geologically older Sumava and Krkonose regions. The

dominant, silicate minerals in Krkonose (granite,

muscovite and K-Feldspars) and Sumava (biotite)

are at the more weathered end of the mineral weath-

ering sequence of Goldich (1938), which has been

demonstrated to be consistent with dissolution (buf-

fering) patterns of minerals (Li et al., 1988; White

M. Purdon et al. / Forest Ecology and Management 195 (2004) 355–371 367

et al., 1996). Such silicate bedrock has lower pH

buffering and a slower response to acidic inputs.

The flysch bedrock of the Beskydy region has a higher

buffering capacity because of its greater content of

calcium carbonate, an important buffer (Schlesinger,

1997). Furthermore, higher pH values can be corre-

lated with lower solubility of Al3þ (Van Hees et al.,

2001) and thus the toxic effect of aluminum on the

plants can be relatively lower. The conclusion that

Beskydy has a greater buffering capacity is supported

by its relatively higher alkaline reactivity values

(>0.25) of the middle part of Godula formation, which

forms the core of the mountain range occupying

higher elevations and Solan formation in the southern

part of the study region. Together these two regions

comprise approximately 55% of the Beskydy study

area.

In opposition to our main conclusion, it could also

be argued that forests in Beskydy were healthier

simply because the sampling plots were of lower

altitude—acid deposition increases with altitude

(Lawrence et al., 1999). However, though there was

a 100 m difference between their monitoring station

elevations, atmospheric pollution was similar between

Beskydy and Krkonose. Furthermore, a pattern of

increasing defoliation is most salient in the Sumava

region, which had lowest observed ambient sulphur

concentrations and deposition over the monitoring

period. Another point of consideration is that our

study does not take into consideration the manage-

ment history of the three regions and the possible

impacts of liming. Because of these uncertainties, the

importance we attribute to lithology in mitigating

forest dieback in Beskydy certainly requires verifica-

tion by detailed geological sampling in all three

regions. This is especially necessary in light of recent

studies showing atmospheric inputs of cation nutrients

to be more important than weathering sources for

shallow-rooted species, such as Norway spruce (Ken-

nedy et al., 2002). In support of this, we note that

defoliation in Norway spruce stands is correlated with

the Ca/Al ratios of only the organic soil layer and not

the mineral soil (Hruska et al., 2001). This may

indicate that in Norway spruce monocultures, bedrock

weathering is more important as an acid buffer than as

a source of nutrients.

Our results also bear importance to the development

of restoration strategies for forests damaged by acid

rain. While elevation and age have been used as an

effective basis for a forest restoration zonation strat-

egy in Krkonose National Park there (Cerny et al.,

1998), such a mitigation strategy is only applicable in

the Sumava region and is not possible at Beskydy.

Regression analysis has demonstrated that forest

health parameters at Beskydy showed weak if not

insignificant relationships with stand age and

elevation. However, this lack of a relationship is an

artefact of the monitoring design. Not only are the

means of these explanatory variables least at Beskydy,

but their distribution is also most constricted. In other

words, the lack of a relationship between forest health

parameters and elevation and age at the Beskydy sites

is not due to the lack of a significant relationship with

these variables, but to their reduced distribution in the

allocation of monitoring plots.

4.2. Soil type category as a contributing factor to

forest health status

Our results also support the hypothesis that soil

conditions are a factor contributing to stand suscept-

ibility to defoliation and discoloration. Simple time

series analysis of trends in defoliation and discolora-

tion demonstrated that most of the increasing trend in

defoliation in Krkonose was occurring on extreme

and, to a lesser extent, acidic soil type categories.

Extreme soils would be most susceptible to acid

damage because they are at relatively higher eleva-

tions (thus likely receiving greater acid deposition

(Lawrence et al., 1999)). In turn, because of the

generally colder conditions, Extreme soils would have

slower nutrient cycling rates (Prusa, 2001), which can

reduce weathering rates of base cations. Low base

cation concentrations predispose soils to Al release

and toxicity (Bohan et al., 1998; Sverdrup and Warf-

vinge, 1993).

Forests on the other three soil type categories were

healthier in terms of defoliation and discoloration, but

differences between them were more difficult to dis-

cern. From the simple time-series analyses, acidic soil

type categories appear to be prone to defoliation and

discoloration while enriched and nutritive most resis-

tant. One possible explanation is that acid deposition

would be greater on acidic sites because of their higher

elevation (Lawrence et al., 1999). However, when

combining the relationship of elevation and stand

368 M. Purdon et al. / Forest Ecology and Management 195 (2004) 355–371

age, defoliation on acidic and nutritive soil type

categories demonstrates the same response pattern.

This result indicates that defoliation on these two soil

type categories is proceeding in the same manner.

This is a surprising result given the lower pH of

acidic sites, a quality that would incline these soils

to have a lower buffering capacity and we address this

below. These same results also indicate defoliation

and discoloration were lowest on enriched soils. This

is consistent with the interpretation that it is consid-

ered to be the most nutrient rich and thus offering

greatest buffering capacity, resulting in least forest

decline.

How then to explain the different response pattern

in forest health status on acidic and nutritive soil type

categories between the simple time-series analysis and

the non-linear multiple regression? Again, the distri-

bution of sampling plots over elevation and stand age

is important. Acidic soils are found over the full range

of elevation and age classes, making them more

susceptible to the influence of these site variables.

From the response pattern resulting from the com-

bined relationship of elevation it can be predicted that

if nutritive soils were present over the same range,

they would post similar values of defoliation and

discoloration in the simple time-series analysis. Thus,

differences in forest health status between these two

soil type categories is due to differences in their

elevation and stand age, not to their inherent nutrient

status. The similarity in defoliation on acidic and

nutritive soil type categories may be attributed to

the ability of humic and fulvic acids, which lead to

the lower pH conditions that characterize the acidic

soil type category, to bind Al and other metals into

organic complexes and thus prevent Al toxicity

(Hruska et al., 1996). Acids deposited in the form

of H2SO4 and HNO3 do not possess this ability to form

acid complexes and mitigate Al release—there are

thus conditions where the soil is acidic but not toxic

(Hruska, 2001).

We conclude that under Czech conditions, forest

restoration strategies should be designed to treat acidic

and nutritive soil type categories similarly. Given the

similarities in responses we can say that three soil type

category groupings should be managed separately: (i)

extreme soils, (ii) acidic and nutritive and (iii)

enriched soils. Before initiating any such reforms, it

will be necessary to validate the acid neutralizing

capacity of the soil type categories via more rigorous

soil sampling.

5. Conclusions

In conclusion, long-term trends in defoliation and

discoloration in plots dominated by Norway spruce

varied between regions. Overall, defoliation was a

more sensitive indicator and demonstrated more sig-

nificant results than discoloration. In the Sumava and

Krkonose regions these variables were greater or

increasing over the monitoring period, while at Bes-

kydy a general stability was observed. These regional

differences were not found to be attributable to stand

elevation and age. Rather we attributed patterns in

defoliation and discoloration to differences in litho-

graphy between regions. In Beskydy, the flysch bed-

rock possesses more calcium carbonate and other

alkaline rich minerals to buffer effectively against

acid deposition. Forest restoration strategies in Bes-

kydy will need a different orientation than those in

Krkonose and Sumava. In the latter regions, forest

management must more urgently promote the intro-

duction of suitable broadleaved species in order to

create a more diverse species and age structure of

forest stands.

In the Krkonose region, results from soil type

categories specific for the Czech Republic region

showed that soil conditions help mitigate defoliation

and discoloration. From simple time series analysis,

forest health parameters were poorest on extreme and

acidic soils but stable on nutritive and enriched.

However, this interpretation is too simplistic. Patterns

in defoliation on acidic and nutritive sites were similar

when accounting for the relationship between expla-

natory variables, indicating that differences in forest

health status between these two soil type categories is

not due to the inherent qualities of the soils them-

selves. Enriched soils on the other hand did not show

any relationship to the explanatory variables and we

conclude that reduced levels of forest decline here are

due to its higher nutrient status. We thus propose that

forest restoration in the Krkonose accounts for these

differences by applying a management regime differ-

entiating between three instead of four soil type

categories, namely (i) extreme, (ii) acidic and nutritive

and (iii) enriched.

M. Purdon et al. / Forest Ecology and Management 195 (2004) 355–371 369

Acknowledgements

The authors would like to thank Jan Apltauer, Petr

Blazek, Milos Sedlacek and Petr Vopenka at IFER for

their technical assistance during this paper. We also

thank the Czech Hydrometeorological Institute and

Czech Geological Survey for maintaining air pollution

data. Thanks are also due to Thuy Nguyen-Xuan and

Catherine Boudreault who aided with statistical ana-

lyses and to Radka Kozakova for obtaining some key

books. The comments of two anonymous reviewers

significantly improved the quality of this article.

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