ay
b, P
ange
, D-8
No
.
ed
ree
growth at the expense of diameter growth. This change in allometry leads to rather cone-shaped stem
om ind
2005; Morgan et al., 2006). In addition to the direct growth reduc-
tion, ozone can induce long-term effects of practical importance like
the alteration of the competitive situations in mixed stands
trees or even stands under natural conditions (Kolb and Matyssek,
2001; Nunn et al., 2005b).
Nonetheless, a few results from field studies on adult trees are
available. Wipfler et al. (2005) found a decline in diameter growth
at breast height of about 20% on ca. 50-year-old spruce trees,
whereas the diameter growth of ca. 60-year-old beech trees
remained unaffected. Karlsson et al. (2006) reported on decline in
basal area increment of 4.6% in 19- to 35-years-old Norway spruce
at the tree level, and Braun et al. (2007) on a decrease of height
* Corresponding author. Tel.: þ49 8161 714710; fax: þ49 8161 714721.
E-mail address: h.pretzsch@lrz.tum.de (H. Pretzsch).
Contents lists availab
Environment
journal homepage: www.els
ARTICLE IN PRESS
Environmental Pollution xxx (2009) 1–10URL: http://www.wwk.forst.tu-muenchen.deincreased by factor two during the past century (Stockwell et al.,
1997; Volz and Kley,1988). Peak concentrations are decliningwhilst
the background ozone concentration is steadily increasing (Jonson
et al., 2006; Penkett, 1988). If the global emission trends continue,
ozone levels will rise by another 50% by the end of this century
(Meehl et al., 2007). The enhanced O3 regimes will impact the
vegetation andmay reduce forest productivity (Matyssek and Innes,
1999; Ska¨rby et al., 1998; Taylor et al., 1994) causing yield losses of
considerable economical importance (Ashmore, 2005; King et al.,
ozone on trees (e.g. leaf injuries) are well known (Matyssek and
Sandermann, 2003), only fragmentary assessments exist about
ozone effects on the productivity of mature forest trees and stands
(Matyssek and Innes,1999; Matyssek et al., 2007). Results about the
behavior of herbaceous plants and young trees have often been
obtained by performing ozone exposure experiments in phytotrons
or open-top chambers (Broadmeadow et al., 1999; Clark et al.,
2000; Dixon et al., 1998; Liu et al., 2004; Maurer and Matyssek,
1997). However, the results can hardly be transferred to matureoxidant has become a pollutant of great concern (Ashmore, 2005;
Sitch et al., 2007; Vingarzan, 2004). Tropospheric ozone levelsspread across major urban areas of the world and even to rural
regions. Towards the beginning of the 21st century, this photo-
(Dizengremel, 2001; Clark et al., 2000; Nunn et al., 2005a), other
studies use ozone as a stress factor to analyze the defense reaction
of plants in general (Sandermann et al., 1998). Although evaluations
dealing with chemical, physiological, and anatomical effects ofFree-air ozone fumigation
Stress response
Shoot allometry
Stem form factor
Tree height growth
Stem diameter growth
Volume growth
1. Introduction
High ozone regimes – resulting fr0269-7491/$ – see front matter  2009 Elsevier Ltd.
doi:10.1016/j.envpol.2009.07.035
Please cite this article in press as: Pretzsch,
ozone fumigation, Environ. Pollut. (2009), dforms and reduced stem stability in the case of spruce, and even neiloidal stem shapes in the case of
beech. Neglect of such ozone-induced changes in stem shape may lead to a flawed estimation of volume
growth. On the stand level, 2O3 caused, on average, a decrease of 10.2 m3 ha1 yr1 in European beech.
 2009 Elsevier Ltd. All rights reserved.
ustry and traffic – have
(Karnosky et al., 2005) leading to stand compositions which differ
from forest planning and required silvicultural interventions.
Many studies focused explicitly on ozone effects within plantsKeywords:
(1O3). Annual diameter growth, allocation pattern, stem form, and stem volume were quantified at the
individual tree and stand level. Ozone fumigation induced a shift in the resource allocation into heightAccepted 26 July 2009 through 2007 and can be compared with trees in the same stand under the ambient ozone regimeTree and stand growth of mature Norw
long-term ozone fumigation
Hans Pretzsch a,*, Jochen Dieler a, Rainer Matyssek
aChair for Forest Growth and Yield Science, Technische Universita¨t Mu¨nchen, Am Hoch
bChair for Ecophysiology of Plants, Technische Universita¨t Mu¨nchen, Am Hochanger 13
Ozone effects on tree growth and stem shape were investigated for
reaction patterns in growth rate and allometry under ozone exposure
a r t i c l e i n f o
Article history:
Received 22 July 2009
a b s t r a c t
In a 50- to 70-year-old mix
sylvatica L.) in Germany, tAll rights reserved.
H., et al., Tree and stand grow
oi:10.1016/j.envpol.2009.07.0spruce and European beech under
hilip Wipfler a
r 13, D-85354 Freising, Germany
5354 Freising, Germany
rway spruce and European beech; the study reveals species-specific
stand of Norway spruce (Picea abies (L.) Karst.) and European beech (Fagus
cohorts have been exposed to double ambient ozone (2O3) from 2000
le at ScienceDirect
al Pollution
evier .com/locate/envpolth of mature Norway spruce and European beech under long-term
35

enta
ARTICLE IN PRESSgrowth by 4.7% in 60- to 180-year-old beech stands. Studies on
black cherry and yellow poplar revealed O3-induced stem radial
growth losses by 8–12% and 30–43%, respectively (Somers et al.,
1998). Vollenweider et al. (2003) derived stem radial growth losses
of 28% from a long-term study on black cherry. Yet, such growth
losses are either not applied to the whole tree or they are up-scaled
to the tree and stand level via modeling (Laurence et al., 2001),
often based on unclear assumptions about alterations of stem
shape and shift of form factor (Deckmyn et al., 2007). Hence,
knowledge about the differential response of tree organs and
dimensions to ozone, which is the ultimate expression of resource
allocation at the whole-plant level under stress impact and, hence,
a pre-requisite for understanding both ecological performance and
economic yield, is still missing (Matyssek et al., 2005).
Some further answers may be provided by the large-scale ozone
fumigation experiment ‘‘Kranzberger Forst’’ near Freising in
southern Bavaria, which started in 2000 and provides 8 years of
data. The experiment was conducted on mature trees of Norway
spruce (Picea abies (L.) Karst.) and European beech (Fagus sylvatica
L.) in a mixed stand under natural growing conditions, whose
reaction to ozone fumigation is poorly understood. Previous studies
were focused either on diameter or height development (Matyssek
et al., 1993, 2007;Wipfler et al., 2005). Alterations in stem form and
changes in productivity on stand level which are highly relevant for
forest practice had not been considered. Here, besides changes in
diameter and height, also changes in the stem form have been
recorded precisely and are compared to adjacent non-fumigated
trees of the same stand. By using the increment trend method
(Deutscher Verband Forstlicher Forschungsanstalten, 1988;
Pretzsch, 2009) initial growth differences between the target and
reference collectives can be eliminated. This method allows for
accurate quantification of tree growth reaction and exact quanti-
fication of the loss of volume growth. Overall, this study focuses on
the three following questions:
Q1: Does the annual diameter increment of Norway spruce and
European beech trees after 8 years of 2O3 exposure differ from
trees under the unchanged 1O3 regime prevailing at the site?
Q2: Does long-term 2O3 exposure alter the height–diameter
allometry of the stems of Norway spruce and European beech?
Q3: Do the mean periodic increments of diameter, basal area,
height, the change of the form factor, and the resulting volume
show response to enhanced ozone exposure?
In a first report after only three years of ozone exposure, we
found a 22% decrease of radial stem increment for Norway spruce
while European beech showed no change on the basis of successive
stem diameter measurements (Wipfler et al., 2005). This report, in
contrast, reveals long-term effects after 8 years of ozone exposure
on the basis of tree ring analysis, height increment measurements
and retrospective analysis of stem form development.
2. Material and methods
2.1. Stand and sample tree characteristics
The experimental plot ‘‘Kranzberger Forst’’ is under survey since 1994 and is
located at 113904200E, 482501200N in the ecological region 12.8 ‘‘Tertia¨res Hu¨gelland.
Oberbayerisches Tertia¨rhu¨gelland’’ in southern Bavaria near Freising, 35 km north-
east of Munich. The altitude is 490 m above sea level. The research plot has a rect-
angular shape of 50100m. Mean annual temperature is 7.0–7.5 C and
precipitation 730–890 mm per annum. The corresponding temperature and rainfall
during the vegetation period are 14.0–15.0 C and 410–520 mm, respectively. The
prevailing soil is parabrown soil, based on loess and tends to pseudo-gley. The
potential natural vegetation is a Galio-odorati-Fagetum association, dominated by
European beech (Pretzsch and Schu¨tze, 2009).
H. Pretzsch et al. / Environm2The experimental design comprises pure stands of Norway spruce and European
beech and in-between a stand section in which both species are mixed as individual
Please cite this article in press as: Pretzsch, H., et al., Tree and stand gro
ozone fumigation, Environ. Pollut. (2009), doi:10.1016/j.envpol.2009.07.0trees or clusters. The ozone fumigation experiment was established in the mixed
zone of the stand. The ages of the spruce and beech trees were determined as 56 2
and 66 4 years, respectively, in 2007. The characteristics of the stands are
summarized in Table 1 which reflects the growing conditions from the beginning
through the end of the analyzed period and refers to the neighboring pure stands of
Norway spruce and European beech each under the ambient ozone regime. As no
thinning measures were carried out since 10–20 years before the first survey in
1994, the reduction in stem number between 1994 and 2007 is solely due to self-
thinning.
2.1.1. Ozone fumigation within the stand
Within the mixed stand zone of the experimental plot ‘‘Kranzberger Forst’’ the
ozone fumigation experiment was initiated in 2000. It covers one of the groups of
beech trees together with neighboring spruces, comprising the most intensively
studied section of the experimental site (Pretzsch et al., 1998). This part of the stand
is growing under self-thinning conditions and was fumigated with ozone by means
of ‘Kranzberg Ozone Fumigation Experiment’ (KROFEX), representing a free-air
methodology of O3 release (Karnosky et al., 2007; Nunn et al., 2002; Werner and
Fabian, 2002) from spring 2000 through fall 2007. Five neighboring beech and
spruce trees were experimentally exposed to a fluctuating double ambient ozone
regime (2O3), allowing O3 levels of 150 nl l1 at maximum to prevent acute O3
injury. A corresponding group of trees growing under the unchanged ambient air at
the forest site (1O3) served as control. Due to the prevailing west winds, the
unfumigated trees are located upwind. O3 levels generated by 2O3 were within the
range of those occurring under unchanged forest conditions, although the enhanced
frequency of the experimental O3 levels warranted a chronically elevated O3 expo-
sure (Matyssek et al., 2007). The 2O3 regime was maintained during the growing
season of each year (April through November), defined as the time span between
flush and autumnal shedding of leaves in beech. In this way, the achieved experi-
mental period of 8 consecutive years was unprecedented for studying the response
of adult forest trees to a controlled, elevated O3 regime under stand conditions.
2.1.2. Measurements at tree and stand level
At the date of the plot establishment in autumn 1994, the precise positions of all
trees were determined by theodolite (LEICA TC500); diameter at breast height was
documented by girth tapes; and tree and crown heights were measured with
ultrasonic hypsometer (HAGLO¨F VERTEX). Since 1999, measurements of the diam-
eter at breast height are available for all trees in the stand. Based on permanent girth
tapes, the values were read by monthly intervals during the vegetation period. Due
to the permanent installation and the additional vernier scale, these tapes allow
measurements of an accuracy of 1 mm. The differences of the January value of two
successive years are defined as annual diameter growth. Measurements of tree
height and crown height were re-measured in 1994, 1999, 2002 and 2007 on sample
trees. These data were used to construct height–diameter curves to estimate the
height of all trees.
2.1.3. Sample trees
In contrast to previous reports (Nunn et al., 2005a; Matyssek et al., 2007;
Wipfler et al., 2005) about ozone effects on tree and stand growth in Kranzberg, this
study includes the complete 8-years time series of the ozone fumigation. This study
is based on the diameter and height measurements at the survey times (1994, 1999,
2007) and additional increment cores from a selected set of fumigated trees and
non-fumigated trees. To guarantee comparability of the data, the sampled trees all
possessed a dominant or co-dominant position within the stand. The increment
cores additionally allow an annual resolution of growth differences.
For the evaluation of questions Q1–Q3, we selected two different samples
(Table 2) due to different demands on data resolution and precision. The sample for
Q1 and Q3 consists of 11 spruces and 10 beeches: 6 reference spruce and 5 reference
beech trees (1O3), and 5 spruce and 5 beech trees under double ambient ozone
(2O3). Aside from basic yield measurements, such as diameter at breast height or
tree height, stem diameter was also measured at a height of 0.6 m as well as in 50
and 70% of tree height from a crane. At every tree height, breast height included,
increment cores were taken in order to trace back increment and stem shape
development (Fig. 1b). Increment data are available back to the pith. This allows on
the one hand an annual resolution of the diameter development (Q1) and on the
other hand very precise determination of the (periodic) form factor and volume
development (Q3). The sample for analyzing the height–diameter allometry (Q2)
consists of 11 spruces and 7 beeches under ambient ozone and 11 spruces and 6
beeches under double ambient ozone, respectively. Height and diameter were
measured in 1994, 1999, and 2007 (Fig. 1a). This sample includes the Q1/Q3 trees in
the experiment and other trees for which passive ozone samplers indicated similarly
high ozone levels during the 8 years of fumigation.
Fig. 1a displays the measurements for detecting changes in the height–diameter
allometry, and Fig. 1b the measurement of diameter and sampling of increment
cores in various tree heights in order to reveal any changes of the form factor (f) of
the stem by long-term ozone fumigation.
The two non-fumigated pure stands of Norway spruce and European beech
l Pollution xxx (2009) 1–10(Table 1) provide the basis to assess the change in yield on stand level under double
ambient ozone. Both stands are far enough away and unaffected by the ozone
wth of mature Norway spruce and European beech under long-term
35