LIGHT SHORTAGE AS A MODIFYING FACTOR FOR GROWTH DYNAMICS AND WOOD ANATOMY IN YOUNG DECIDUOUS TREES - Brill
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
IAWA Journal, Vol. 23 (2), 2002: 121–141
LIGHT SHORTAGE AS A MODIFYING FACTOR FOR GROWTH
DYNAMICS AND WOOD ANATOMY IN YOUNG DECIDUOUS TREES
by
Silke Hoffmann & Fritz H. Schweingruber 1
Swiss Federal Research Institute WSL, Zürcher Strasse 11, 8903 Birmensdorf, Switzerland
SUMMARY
Suppressed trees growing under the canopy of mature forests exceed
the number of tall, dominant individuals by far. This paper focuses on
the wood structure of suppressed trees modified by light shortage. Sec-
ondly, the growth dynamics of suppressed deciduous trees within two
sites was reconstructed by internal (tree rings) and external (bud scale
scars) age determination. The social status of each specimen within the
natural regeneration changes with time. Suppressed plants could once
have held higher-ranking positions and individuals suffering from peri-
ods of suppression are able to recover after light conditions improve.
This is an important process for the long-term survival strategy of shade
tolerant tree species. Wood anatomy modified by suppression provides
additional information on tree growth through the following proper-
ties: low percentage of pores in earlywood, changed distribution of pores,
indistinct or absent growth ring boundaries, discontinuous growth rings.
The low percentage of pores in earlywood may be a means of identify-
ing light shortage in deciduous trees.
Key words: Light shortage, wood anatomy, stand dynamics, bud scale
scars, Acer platanoides, Acer pseudoplatanus, Carpinus betulus, Fagus
sylvatica, Fraxinus excelsior.
INTRODUCTION
During stand development, especially in the early period, many differentiating proc-
esses take place, mostly based on competition in the reduced light regime beneath the
canopy. Some of the trees die, others survive. We sought to determine whether it was
possible to see this development in wood anatomical features and clarify the way in
which light modifies the ontogenesis of the tree.
In addition to tree-ring width, wood anatomy provides important, detailed infor-
mation about the relationship between tree growth and environment. Studies on wood
anatomy have mainly been based on the trunk wood of big, mature trees of economic
importance (Carlquist 1988; Schweingruber 1990). Changes in the endogenously con-
trolled wood anatomical structure through exogenous factors enable the tree to sur-
1) Author for correspondence.
Downloaded from Brill.com12/21/2021 04:51:20AM
via free access122 IAWA Journal, Vol. 23 (2), 2002
vive under the current environmental conditions (Sass 1993). The wood anatomy of
big trees has to fulfil great demands for mechanical support as well as water transport
(Braun 1980). Suppressed trees are exposed to, e.g., low light and little water and
hence adaptations of the anatomical structures to these special conditions seem to be
necessary.
Few studies have been made on suppressed individuals growing under the canopy
of forest stands (Merz & Boyce 1956). One of the first studies relating light suppres-
sion to wood structure was made by Koltzenburg (1967). However, the trees she sam-
pled were growing in an experimental plantation, which can be a good simulation of
nature, but plants possibly react differently in their indigenous environment. Other
studies of suppressed trees are based on natural ecosystems, e.g. Baas et al. (1983),
Sass (1993), Wang & Lee (1989), Baumberger (1997), and Schöne & Schweingruber
(1999). However, they did not consider the continual changes occurring as a complex
ecosystem develops.
The aim of the present study was to compare the wood anatomical features of
seedlings growing under optimal light conditions with supppressed individuals in a
natural, heavily schaded site under a dense canopy of a mixed broad-leafed forest.
The temporal dimension represented by stem diameter and plant height reconstruc-
tion provided information about processes of competition and stand differentiation
during the past years. Furthermore the precision of age determination by counting
bud scale scars was investigated.
MATERIALS AND METHODS
Materials
Entire plants were uprooted from two sites of natural regeneration at an altitude of
550 m in the Ramerenwald near Birmensdorf, canton Zürich, Switzerland (longitude:
47° 21' 59 " E, latitude: 8° 27 ' 3 " N). Both sites are 1 m2 in size, close to the edge of
a former sprout seedling forest and approximately 50 m from each other. One sample
site (shade) is located under a close canopy with 1.6% relative light intensity RLI
(100% RLI = full daylight received by plants on open land). The brighter gap site
receives 2.6% RLI. According to Kraft’s classification (1884) all trees sampled are
suppressed ones (class 5), but within the natural regeneration, which we are focusing
on, there are also trees which are higher and have larger diameters than their neigh-
bours. They are relatively dominant and thus the term ‘dominant’ is used for them in
this study.
As controls, young trees from all species gathered in the forest were also taken
from the nursery of the WSL 2 as they had received full illumination (100% RLI).
The age of ten shaded beeches and hornbeams was exactly known (5 to 7 years). The
diameters ranged between 4 and 8 cm, heights between 3 and 5 m. The nursery lies
about 400 m distant from the forest sites and the climatic conditions are the same. The
soils of the two forest sites (lessivé) and the nursery are similar regarding soil acidity
2) Swiss Federal Research Institute WSL, CH-8903 Birmensdorf, Switzerland.
Downloaded from Brill.com12/21/2021 04:51:20AM
via free accessHoffmann & Schweingruber — Light shortage in young deciduous trees 123
and water regime. With a mean annual temperature of 8.5 °C and relatively high mean
precipitation (952 mm /year), the climate of Zürich (average from 1961 to 1990) is
humid. The mean minimum temperatures of December, January and February are
below 0 °C.
For the deciduous species found in the forest sites, see Table 1.
Table 1. Absolute and percent occurrence of all species in both forest sites.
Proportion of tree species Absolute Percent
—————————— ——————————
Species Shade Gap Shade Gap
Maple (Acer pseudoplatanus L.) 10 2 23 6
Maple (Acer platanoides L.) 5 5 11 16
Hornbeam (Carpinus betulus L.) 15 14 34 44
Beech (Fagus sylvatica L.) 5 1 11 3
Ash (Fraxinus excelsior L.) 9 10 21 31
Methods
To determine the mutual effects of the plants on each other’s growth, as reflected
in stem increment, the position of each plant within each of the two 1 m2 sites inside
the forest was plotted (Fig. 1). For the anatomical investigation and the measurement
of tree ring width, cross sections (12 to 20 µm) were taken from each specimen at a
height of approx. 1 cm above soil level, to ensure that the first ring was included.
Preparations were bleached with eau de Javel, dyed with water soluble safranin, de-
hydrated with alcohol and xylol and finally conserved in Canada balsam (process
described in Schweingruber 1982). In each individual all rings were recorded, even
very narrow and tapering ones. The tangential diameter of earlywood pores was meas-
ured in several rings of each specimen and the circumference of the earlywood in
each ring was measured. Thus it was possible to compute the percentage of the
earlywood circumference made up by the pores. All anatomical parameters were
measured by means of the image analysis program “Image Pro Plus”.
Tree rings were counted to determine the age of each cross section and ring widths
were measured along two radii to reconstruct the diameter of each plant for every
year. To determine external age, bud scale scars along the primary shoot were counted.
To reconstruct the increment in plant height, annual shoot lengths were measured.
The age of dead plants according to both the bud scale scars and the tree rings was set
back by one year, because if they had died longer ago than that they would have
decayed and disappeared.
For checking the precision of external and internal age determination the number
of bud scale scars and tree rings of the beeches and hornbeams from the nursery were
compared with their actual age.
Downloaded from Brill.com12/21/2021 04:51:20AM
via free access124 IAWA Journal, Vol. 23 (2), 2002
cm shade 98 cm gap 98
100 100
80 80
60 60
40 40
20 20
0 0
0 20 40 60 80 100 0 20 40 60 80 100
cm cm
cm shade 94 cm gap 94
100 100
80 80
60 60
40 40
20 20
0 0
0 20 40 60 80 100 0 20 40 60 80 100
cm cm
Legend:
maple – hornbeam – beech – ash
diameter-scale (mm)
0–1 1–3 3–5 5–7 7–9 9–12
←
→
Fig. 1. Diameter development of the suppressed trees on the gap site (right) and the shade site
(left) in 4 -year intervals. Classification of diameter size is explained in the legend. Diameters
in 1998 range between 3 and 11 mm. The development of the diameters of the trees on the
shade side is continuous, the development on the gap site is more abrupt after 1990. The gap
was probably formed between 1990 and 1994.
Downloaded from Brill.com12/21/2021 04:51:20AM
via free accessHoffmann & Schweingruber — Light shortage in young deciduous trees 125
shade 90 gap 90
100 100
80 80
60 60
40 40
20 20
0 0
0 50 100 150 0 50 100 150
shade 86 gap 86
100 100
80 80
60 60
40 40
20 20
0 0
0 50 100 150 0 50 100 150
shade 82 gap 82
100 100
80 80
60 60
40 40
20 20
0 0
0 50 100 150 0 50 100 150
gap 78
(Figure 1 continued) 100
80
60
40
20
0
0 50 100 150
Downloaded from Brill.com12/21/2021 04:51:20AM
via free access126 IAWA Journal, Vol. 23 (2), 2002
age (shade)
20
18
bud-scale-scar age (years)
16
14
12
10
8
6
4
2
0
0 2 4 6 8 10 12 14 16 18 20
a ring age (years)
age (gap)
24
22
bud-scale-scar age (years)
20
18
16
14
12
10
8
6
4
2
0
0 2 4 6 8 10 12 14 16 18 20 22 24
b ring age (years)
0 maple; - hornbeam; beech; × ash; ---------------- 1: 1
Fig. 2. The age of plants, determined by counting bud scale scars (y-axis) and tree rings
(x-axis) on shade site (a) and gap site (b). Above the equal line, bud-scale-scar age exceeds
ring age, below this line ring age exceeds bud-scale-scar age.
RESULTS
Growth dynamics
Age detected by counting bud scale scars often exceeds age detected by counting
rings. This phenomenon was most conspicuous in the trees in shade (74%), but also
occurred in the gap (55%) (Fig. 2a, b). In all (shade) respectively most (gap) cases
hornbeam and ash exhibited more bud scale scars than tree rings whereas in beech
and maple the proportion was more balanced.
Downloaded from Brill.com12/21/2021 04:51:20AM
via free accessHoffmann & Schweingruber — Light shortage in young deciduous trees 127
The mean ring width curves of hornbeam, maple, beech and ash are shown in
Figure 3b–e, with an additional graph (Fig. 3a) showing all the single curves from
which the mean was derived for hornbeam as an example for illustration. The mean
curve for each species (Fig. 3b–e) gives an overview of the growth development in
the two different sites. On average, shade plants exhibit less growth in height and
diameter than plants in the gap, and in most cases their mean ring width curves lie
below those of the plants in the gap. All specimens of ash show decreasing ring widths
up to 1998, at which point 70% of the ash plants had died. Classification into height
and diameter ranks yields the following findings (Fig. 4a–d):
• Trees change their social status with regard to height as well as diameter during
stand differentiation. Some dominant individuals (e.g. maple no. 6 in 1998 on the
shade site in Fig. 4a) had been less dominant for several years. Suppressed trees
had never been absolutely dominant, but held higher-ranking positions (e.g. ash
no. 14, gap site in Fig. 4c).
• Changes in height rank are greater and occur more frequently than changes in
diameter rank (compare Fig. 4a with 4b and Fig. 4c with 4d).
• The tallest individuals in the upper third of the height ranking often have the larg-
est diameters, e.g. maple no. 25 in the gap site (Fig. 4c, d).
• The dominant trees in the upper third of the height or diameter ranking list are
mostly some of the oldest specimens in the natural regeneration sites, e.g. beech
no. 17 in the shade area (Fig. 4a, b).
In the five-year-old nursery beeches, twigs on the lower stem, and therefore shaded
by foliage higher up in the stem, showed the following features:
• They exhibited the same morphological features as the shoots of the suppressed
plants from the forest sites: in comparison to twigs receiving more incident light,
the annual shoot length and diameter are reduced.
• The number of bud scale scars (7) exceeded the actual age of the tree (5 years).
Wood anatomy
Figures 5 to 8 show microsections from maple, hornbeam, beech and ash. Tree
rings of the suppressed trees are narrower than those in dominant trees but the number,
distribution and size of the vessels also differ between trees from shady and those
from sunny sites. Cells seem to be less differentiated than in dominant specimens.
Although not always significant, all species studied show the same clear trend: per-
centage of vessel diameter of earlywood circumference increases with increasing light
availability (Fig. 10). The intensity of this trend varies between the diffuse-porous
maple, hornbeam and beech and the ring-porous ash.
It appears that earlywood pore diameter of maple (Fig. 5) correlates neither with
ring width (r = 0.16) nor with the age of the ring (r = 0.21). Vessel diameters (10– 45
µm) do not differ significantly between shade and gap site but do vary between gap
and nursery site (see Fig. 9). The percentage of vessels in earlywood shows an in-
creasing trend with increasing light availability (Fig. 10).
Downloaded from Brill.com12/21/2021 04:51:20AM
via free access128 IAWA Journal, Vol. 23 (2), 2002
Fig. 3. For legend, see next page.
mm tree-ring ring width ‘hornbeam’ (gap)
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
year: 89 90 91 92 93 94 95 96 97 98
a ———— single curves; ———— mean curve
mm mean ring width ‘hornbeam’
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
year: 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98
b 0
———— gap, n = 13; ————
- shade, n = 12
mm mean ring width ‘maple’
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
year: 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98
c 0
———— gap, n = 7; ————
- shade, n = 12
Downloaded from Brill.com12/21/2021 04:51:20AM
via free accessHoffmann & Schweingruber — Light shortage in young deciduous trees 129
mm mean ring width ‘beech’
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
year: 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98
d ————
0 gap, n = 1; ————
- shade, n = 5
mm mean ring width ‘ash’
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
year: 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98
e ————
0 gap, n = 7; ————
- shade, n = 4
←
←
Fig. 3a–e. Mean ring width curves for hornbeam, maple, beech and ash. As an example,
3a shows both the single curves and the mean curves for hornbeam from gap site.
With decreasing light availability the ray width decreases from 2– 4 to 1–2 rows of
cells. Maples suffering only slightly from light shortage exhibit a weak semi-ring-
porous pattern (Fig. 5 C). Under severe light shortage, they only exhibit a few vessels
dispersed over the whole tree ring (Fig. 5 D, inner part). Growth ring boundaries char-
acteristically consisting of tangentially flattened marginal parenchyma are easy to
detect, even in suppressed specimens. Maples are able to recover quickly after light
conditions improve (Fig. 5 D, arrow).
The mean vessel diameter of hornbeam also exhibits neither a relation to ring width
(r = 0.19), age of tree ring (r = 0.26) nor to illumination (Fig. 9). However, Figure 10
shows a significant increase in the percentage of pores in earlywood with increasing
Downloaded from Brill.com12/21/2021 04:51:20AM
via free accessFig. 4a. Rank in height on site ‘shade’ — For legend, see the next page Fig. 4b. Rank in diameter on site ‘shade’
130
year: 1986 87 88 89 90 91 92 93 94 95 96 97 98 year: 1982 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98
tree no: species tree no: species
1 40 40 40 31 31 31 31 31 31 31 16 6 6 1 maple 1 11 11 11 11 11 17 17 6 17 17 17 16 16 16 16 16 16 1 beech
2 41 17 17 24 24 16 16 16 16 16 6 16 16 2 beech 2 23 23 23 17 17 11 6 17 16 16 16 17 17 6 6 6 6 2 maple
3 17 41 24 17 43 24 24 17 17 17 17 17 17 3 beech 3 23 4 6 16 16 6 6 6 6 6 17 17 17 17 3 beech
4 22 43 43 16 17 17 17 43 6 6 31 31 31 4 hornbeam 4 23 4 11 7 7 24 24 24 24 24 24 24 24 4 beech
5 43 7 7 43 16 43 43 24 24 24 24 24 24 5 beech 5 23 7 11 11 43 43 43 43 43 43 11 11 5 maple
6 7 23 41 41 35 35 6 6 43 33 33 33 33 6 hornbeam 6 4 4 4 7 25 41 33 11 11 43 43 6 beech
7 38 22 6 40 6 41 35 35 41 43 43 43 43 7 beech 7 23 41 43 41 41 25 25 41 41 41 42 7 maple
8 23 12 28 7 41 33 41 21 33 41 41 41 41 8 beech 8 25 41 11 7 33 41 33 33 33 41 8 beech
9 12 25 16 6 7 6 21 41 21 21 21 21 21 9 hornbeam 9 23 25 18 33 7 11 25 42 42 33 9 hornbeam
10 25 38 25 15 15 15 15 33 35 35 35 35 35 10 hornbeam 10 18 4 11 11 7 10 10 4 21 10 hornbeam
11 24 24 23 32 40 32 33 15 15 15 32 32 32 11 ash 11 23 25 18 18 10 7 25 21 4 11 maple
12 6 6 31 11 32 7 32 32 32 32 15 15 15 12 hornbeam 12 33 4 10 18 42 4 10 25 12 maple
13 28 22 28 33 21 7 11 11 11 11 39 39 13 ash 13 23 10 4 4 23 23 25 12 13 maple
14 16 12 21 21 11 11 7 1 1 1 11 11 14 maple 14 9 37 37 15 21 23 15 14 ash
15 31 15 23 12 37 37 1 7 7 7 1 1 15 maple 15 23 28 21 4 15 15 23 15 maple
16 15 27 25 11 40 44 44 4 4 42 7 42 16 maple 16 9 28 21 7 7 28 16 maple
17 27 11 2 37 12 23 23 44 44 4 42 7 17 maple 17 44 23 18 35 28 32 17 hornbeam
18 11 21 27 2 44 2 37 37 37 44 4 4 18 maple 18 22 15 28 28 35 35 18 hornbeam
19 21 2 12 23 14 12 4 23 23 37 44 44 19 hornbeam 19 23 35 37 37 12 7 19 maple
20 2 32 33 28 2 14 12 25 42 23 37 37 20 ash 20 42 35 18 32 44 20 hornbeam
21 32 14 37 4 23 40 2 2 25 25 23 25 21 maple 21 44 44 44 37 36 21 ash
22 14 26 4 27 26 4 25 14 2 36 25 23 22 maple 22 9 9 36 18 18 22 maple
23 26 13 22 25 27 1 14 12 36 2 40 40 23 ash 23 22 22 32 36 22 23 maple
24 13 1 14 14 4 27 28 28 28 28 36 36 24 ash 24 3 36 22 44 30 24 hornbeam
25 1 38 26 26 25 25 27 42 14 40 28 28 25 maple 25 12 32 12 22 3 25 hornbeam
26 33 9 44 28 26 40 36 12 14 2 2 26 ash 26 3 9 30 14 26 hornbeam
27 37 3 22 3 28 9 9 29 12 14 14 27 hornbeam 27 30 30 9 8 27 hornbeam
28 4 13 3 22 3 26 27 9 29 29 29 28 maple 28 14 3 3 27 28 ash
29 9 44 13 1 9 42 3 3 3 12 12 29 ash 29 12 14 14 13 29 hornbeam
30 3 1 9 9 22 36 26 27 9 3 3 30 hornbeam 30 20 13 8 26 30 hornbeam
31 44 10 1 13 10 3 40 26 26 9 26 31 hornbeam 31 19 8 27 10 31 maple
32 10 38 10 10 36 10 10 10 27 26 19 32 maple 32 5 27 13 20 32 maple
33 35 38 36 13 22 29 40 10 27 9 33 hornbeam 33 31 20 26 19 33 maple
34 36 18 18 18 22 18 18 10 27 34 maple 34 34 19 20 5 34 maple
35 18 38 42 13 18 22 22 18 10 35 ash 35 2 5 19 9 35 hornbeam
36 42 8 29 13 19 19 19 18 36 maple 36 29 31 5 31 36 hornbeam
37 8 38 8 19 13 13 22 34 37 hornbeam 37 38 34 31 34 37 hornbeam
38 29 38 8 8 8 13 22 38 maple 38 39 2 34 2 38 hornbeam
39 19 38 38 30 30 30 39 hornbeam 39 40 29 2 29 39 ash
40 30 30 38 8 13 40 hornbeam 40 38 29 37 40 ash
41 39 38 38 41 ash 41 39 38 38 41 ash
42 34 20 42 maple 42 40 39 39 42 ash
43 20 8 43 hornbeam 43 40 40 43 ash
IAWA Journal, Vol. 23 (2), 2002
44 5 44 hornbeam 44
via free access
Downloaded from Brill.com12/21/2021 04:51:20AM(Figure 4 continued)
Fig. 4c. Rank in height on site ‘gap’ Fig. 4d. Rank in diameter on site ‘gap’
year: 1985 86 87 88 89 90 91 92 93 94 95 96 97 98 year: 1985 86 87 88 89 90 91 92 93 94 95 96 97 98
tree no: species tree no: species
1 14 18 9 9 9 9 32 32 32 31 24 24 25 25 1 maple 1 17 17 17 17 17 17 17 17 17 17 25 25 25 25 1 maple
2 18 14 18 26 19 8 25 8 19 32 19 19 19 19 2 maple 2 7 7 7 7 7 7 7 7 8 8 7 7 5 19 2 maple
3 9 14 18 24 26 8 31 8 24 32 25 31 31 3 hornbeam 3 15 15 15 15 15 8 8 8 25 25 15 15 19 5 3 hornbeam
4 10 31 18 19 19 19 24 19 9 31 24 24 4 maple 4 24 18 18 8 15 32 25 7 7 17 31 31 31 4 hornbeam
5 20 14 26 31 9 26 26 9 31 32 32 32 5 hornbeam 5 19 24 24 18 25 25 19 32 15 8 19 7 15 5 beech
6 16 7 3 27 26 24 31 8 25 9 9 8 6 hornbeam 6 9 19 19 24 31 15 32 15 31 31 17 15 7 6 maple
7 26 20 14 18 31 25 25 26 8 27 8 26 7 hornbeam 7 18 9 9 19 19 19 31 19 19 19 5 32 24 7 maple
8 31 10 31 14 20 20 9 25 26 8 26 9 8 hornbeam 8 8 9 18 31 15 31 32 32 8 24 32 8 hornbeam
9 7 27 11 11 27 27 20 23 27 26 27 27 9 ash 9 25 24 27 27 27 27 24 9 17 17 9 maple
10 27 16 27 1 24 9 1 27 23 5 5 7 10 maple 10 32 9 18 26 26 26 26 32 9 8 10 hornbeam
11 17 10 24 23 23 23 20 5 23 17 5 11 hornbeam 11 31 32 24 20 20 24 9 26 8 9 11 hornbeam
12 11 4 4 14 1 27 1 20 17 7 20 12 hornbeam 12 27 9 18 5 5 27 24 27 27 12 ash
13 22 7 3 18 10 17 17 1 20 20 17 13 maple 13 26 26 24 9 9 5 27 26 26 13 hornbeam
14 19 8 20 11 14 10 5 17 7 23 23 14 hornbeam 14 20 9 24 20 20 20 20 20 14 hornbeam
15 24 20 10 1 17 7 7 7 1 1 1 15 hornbeam 15 5 18 11 11 11 18 11 15 hornbeam
16 3 17 23 10 18 5 10 11 11 11 11 16 hornbeam 16 23 23 23 23 23 11 1 16 hornbeam
17 4 23 17 3 2 11 11 10 10 10 10 17 hornbeam 17 6 6 4 4 18 23 18 17 maple
18 8 32 7 4 11 18 18 18 15 15 15 18 beech 18 11 18 18 4 10 23 18 hornbeam
19 23 16 16 17 3 14 14 14 18 14 14 19 ash 19 4 6 10 10 1 10 19 hornbeam
20 32 30 13 7 4 2 2 2 14 18 18 20 maple 20 3 6 1 4 2 20 hornbeam
21 30 22 22 2 7 3 3 15 2 2 2 21 hornbeam 21 13 1 2 2 4 21 hornbeam
22 1 2 22 22 4 4 3 3 3 4 22 hornbeam 22 12 16 6 6 3 22 ash
23 13 32 16 16 6 6 4 4 4 3 23 ash 23 10 3 3 3 16 23 maple
24 2 30 13 30 16 15 6 6 6 16 24 maple 24 1 12 16 16 22 24 hornbeam
25 15 30 6 22 16 16 16 16 22 25 hornbeam 25 16 13 12 12 14 25 ash
26 25 12 12 13 22 22 22 22 29 26 ash 26 29 13 13 21 26 ash
27 12 6 13 30 13 13 13 13 33 27 ash 27 22 29 22 33 27 ash
28 6 15 15 12 12 12 12 12 6 28 ash 28 2 22 29 30 28 ash
29 33 15 30 29 29 29 12 29 ash 29 14 14 14 29 29 ash
30 5 29 29 30 30 30 21 30 ash 30 21 21 21 12 30 ash
Hoffmann & Schweingruber — Light shortage in young deciduous trees
31 29 33 33 21 21 21 13 31 ash 31 33 33 33 13 31 ash
32 21 33 33 33 30 32 ash 32 30 30 30 6 32 ash
Fig. 4. Classification into height and diameter ranks. Trees change their social status with regard to height as well as diameter during stand differen-
tiation. Some dominant trees had been less dominant for several years (e.g. maple no. 6 in 4a). Suppressed trees had never been absolutely dominant
but held higher ranking positions (e.g. ash no. 14 in 4c). Changes in height position are greater and happen more often than changes in diameter rank
(compare 4a with 4b and 4c with 4d).
131
via free access
Downloaded from Brill.com12/21/2021 04:51:20AM132 IAWA Journal, Vol. 23 (2), 2002
Legend to Figures 5–8. Histological cross sections, scale bars = 500 µm. – A: adult, dominant
specimen of the species. – B: juvenile specimen from the nursery of the WSL (receiving full
light). – C: suppressed individual from site ‘gap’ or ‘shade’ from the upper third of height
ranks. – D & E: individuals from the lowest third of the height ranks.
Fig. 5. Maple – Abrupt growth change (5D, arrow); recovery after light conditions improved.
Fig. 6. Hornbeam – Growth ring boundaries of juvenile hornbeam characteristically show a
discontinuous row of groups of thick-walled libriform fibres in the latewood (arrow in 6B).
Downloaded from Brill.com12/21/2021 04:51:20AM
via free accessHoffmann & Schweingruber — Light shortage in young deciduous trees 133
Fig. 7. Beech – In comparison with other species, the growth ring boundaries stay relatively
evident, identifiable by broadened rays and tangential flattened marginal parenchyma (arrow
in 7C). 7D (arrow) shows an abrupt growth change.
Fig. 8. Ash – Ash is a ring-porous species and tends to exhibit an increase in size of earlywood
pores with increasing light availability (8 A–E). Ash usually produces small latewood pores
(arrow, 8A), in suppressed trees these are often missing (8 C–E). Under severe light shortage
ash produces only discontinuous rings which in the preterminal period consist only of a few
vessels (arrows, 8 E).
Downloaded from Brill.com12/21/2021 04:51:20AM
via free access134 IAWA Journal, Vol. 23 (2), 2002
illumination. Pore density in latewood decreases and under severe light shortage only
a few pores appear in earlywood and none in latewood (Fig. 6 D). In contrast to the
stem wood of mature, dominant trees with usually aggregate rays, young specimens
and older suppressed specimens of hornbeam exhibit only uniseriate rays. Growth
ring boundaries of juvenile hornbeam characteristically show a discontinuous row of
groups of libriform fibre cells (arrow in Fig. 6 B). This attribute is manifest even in
suppressed samples (Fig. 6 C– E).
In beech, vessel diameter varies with age (r = 0.42) and varies slightly with ring
width (r = 0.3). Vessel diameter varies also with illumination (Fig. 9): vessel size
increases from shade to gap site but decreases from gap to nursery. Percentage of ves-
sel diameter of earlywood circumference increases with increasing light availability,
although not significantly (Fig. 10). Pore diameter in beech wood seems to be more
independent of light than pore diameter in ash (Fig. 10). With decreasing incident
light, the tendency to semi-porosity increases. In comparison with other species the
growth ring boundaries of beech remain relatively evident, identifiable by broadened
rays and tangentially flattened marginal parenchyma.
Ash was the only ring-porous species in this study. Ash exhibits a significant in-
crease in size of earlywood pores with increasing light availability (Fig. 9). There is a
high correlation between vessel diameter and ring width (r = 0.83) and also cambial
age (r = 0.43). Increasing light causes also a – partially – significant increase in per-
centage of pores in earlywood (Fig. 10). Dominant, mature ashes usually produce
small latewood pores (Fig. 8 A, arrow). In suppressed individuals these are often com-
pletely missing (Fig. 8 C– E). Under severe light shortage ash produces only discon-
tinuous rings of small earlywood pores (Fig. 8 D, E). Tapering rings occur more often
in suppressed than in dominant ashes, and rings in dying ashes consist only of a few
vessels (Fig. 8 E, arrows). The differences between vessels, parenchyma cells, ray
parenchyma and fibres become blurred and cell walls, though not actually measured,
seem to be thinner. Due to the arrangement of pores in a ring, it is usually easy to
detect the ring boundary. Dwarfed ashes do not exhibit clear ring boundaries, but in
most cases it was possible to identify the boundaries by means of discontinuous
earlywood vessel rows.
Fig. 9. Changes in earlywood-vessel diameters in relation to light availability. →
Legend:
maximum 5 significant (p = 5%)
quartile 75%
confidence median
interval
quartile 25%
minimum
Downloaded from Brill.com12/21/2021 04:51:20AM
via free accessHoffmann & Schweingruber — Light shortage in young deciduous trees 135
nursery
gap
shade
hornbeam
Fig. 9 — For legend see previous page.
beech
0.06 0.04 0.02 0.0 0.06 0.04 0.02
nursery
gap
shade
maple
ash
0.05 0.03 0.01 0.10 0.06 0.02
tangential vessel diameter (mm)
Downloaded from Brill.com12/21/2021 04:51:20AM
via free access136
maple beech
25
50
20
40
15
30
10
20
5
10
ash hornbeam
25
50
20
40
15
30
10
20
tangential vessel diameter of earlywood circumference (%)
5
10
shade gap nursery shade gap nursery
Fig. 10. Percentage of earlywood circumference made up by vessels — For legend see page 134.
IAWA Journal, Vol. 23 (2), 2002
via free access
Downloaded from Brill.com12/21/2021 04:51:20AMHoffmann & Schweingruber — Light shortage in young deciduous trees 137
DISCUSSION
Growth dynamics
Counting bud scale scars gives sometimes lower but in most cases higher ages
than counting growth rings (Fig. 2). A lower bud scale scar age is probably due to
difficulty in identifying scars close to the stem base caused by secondary thickening
and bark development (Schöne & Schweingruber 1999). On average the trees from
the gap site are older and have larger dimensions than those from the shady site.
Larger diameters cause less easily identifiable bud scale scars. Beech and maple con-
stitute in both sites usually the largest specimens (see Fig. 4), which explains the higher
rate of unidentifiable bud scale scars and, hence, more counted rings than inter-
nodes.
An explanation of the opposite case – higher values from counting scars – requires
a deeper insight into the growth behaviour of trees. There are two possibilities: sev-
eral rings could be completely missing or a second shoot (prolepsis) has been formed
in the same year, increasing the number of scars.
Exact dating and cross matching of tree-ring series for suppressed trees is difficult
because of tapering or missing rings, as has been frequently observed in the past
(Hartig 1869; Petersen 1899; Andrews & Gill 1939; Huber & Holdheide 1942; Roberts
1994). As early as 1899 Petersen described wedging and even missing growth rings
in diffuse- and ring-porous deciduous trees. Wedging rings were frequently observed
in the present study and thus the question of completely missing rings arises. Without
the possibility of cross matching time series, only the hypothesis of prolepsis can be
tested. In general, every tree species is able to form lammas shoots (“Johannistriebe”)
which are normally accompanied by false rings after a summer pause in growth.
Späth (1912) and Roloff (1989), who both studied dominant and suppressed trees,
never identified prolepsis in suppressed trees. The number of bud scale scars in shaded
beeches from the nursery exceeded the true age by about two years. The reason for
that phenomenon might be the “false Johannistrieb” (Späth 1912) which occurs as a
result of transplanting. Our own studies support the observations of Späth. Beeches
investigated in the present study had been transplanted twice and exhibit two more
internodes than real age. Gruber (1998) reported that beeches exhibiting endogenous-
ly induced prolepsis never produce false tree rings. However, the number of annual
shoots along the primary axis is always identical to the number of tree rings from the
year of germination.
Measurement along the primary axis of the trees investigated guaranteed that en-
dogenous prolepsis shoots were not counted. The number of bud scale scars did not
exceed real age in the case of light-suppressed trees. Thus, a lower number of tree
rings than of bud scale scars must be due to completely missing rings.
Cherubini et al. (1998) investigated the growth dynamics within a commercial
Norway spruce forest. The results emphasized the possibility of trees changing their
social status within the stand in the course of their life-span. In that study however,
statuses were reconstructed from tree rings; shoot lengths were not measured, so that
tree height could not be reconstructed. Different findings have been reported for a
Downloaded from Brill.com12/21/2021 04:51:20AM
via free access138 IAWA Journal, Vol. 23 (2), 2002
pine plantation (Sutton 1973); even-aged individuals in this artificial ecosystem never
changed their status, except that one dominant tree died and another one then became
dominant.
The current study shows the same findings as those of Cherubini et al. (1998) but
additionally shows a close relation between diameter and height position in natural
regeneration. On the basis of ranking individuals over the past ten years, some spe-
cies appear to have more competitive ability than others. At RLI 2.6% regeneration of
maple and beech developed successfully. Ash is suppressed if situated next to maple,
beech or hornbeam, even though it is known to be shade tolerant during its juvenility.
During the aggradation phase in the gap, RLI decreases partially to less than 2%
which is not enough for the successful establishment of ash (Emborg 1998) and prob-
ably the reason for the die back of ash on both forest sites.
The results of the present study demonstrate the variability of competitive situa-
tions in young stands. However, dramatic changes in dominance are seldom as long
light conditions do not change (Suner & Röhrig 1980; Poulsen & Platt 1989; Newbold
& Goldsmith 1990; Peltier et al. 1997; Gansert & Sprick 1998).
Wood anatomy
Different tree species respond in different ways to the same influence (Trendelen-
burg & Mayer-Wegelin 1955). We found the same in our case. The only trend all spe-
cies studied show is an increase in vessel proportion with increasing light availabil-
ity (Fig. 10). But how close is the relationship between this feature and the factor
light?
According to Grosser and Burger (1985), the wood of bonsai maples has smaller
vessels than the wood of ‘normal grown’ dominants whereas the number of vessels
increases. The sum of the entire vessel area remains of the same order of magnitude.
The maples in our study also showed a decrease in vessel diameter with increasing
suppression; however, the cause of the modifications is a different one. In contrast to
the bonsais, vessel proportion in earlywood of light-suppressed maples was lower
than in those under better light conditions. Thus earlywood circumference made up
by pores seems to be related to light regime.
Koltzenburg (1967) described the same phenomenon as Grosser and Burger (1985)
did for beeches suffering from light shortage. Our own study detected decreasing ves-
sel diameters in beech from gap to nursery, which could be due to age-trend (Bariska
& Bosshard 1974; Gartner 1995; Richie 1994). The features measured in beech from
the gap were obtained from only one specimen, which had been extremely suppressed
for the first ten years. Rings were impossible to distinguish or to measure so that rings
measured were older than those in beeches from shade and nursery sites.
Diffuse-porous species transport water throughout the whole sapwood (Huber 1956;
Eckstein et al. 1974). Thus, at the onset of the vegetation period, their earlywood
vessels are less important than in ring-porous species. According to Peszlen (1994)
cambium age has significant effects on the anatomical features of (poplar) wood.
Furthermore, Gartner (1995) ascertained great intra-individual variability in xylem.
Amplitude of vessel diameter, vessel area, fibre length and ray area between pith and
Downloaded from Brill.com12/21/2021 04:51:20AM
via free accessHoffmann & Schweingruber — Light shortage in young deciduous trees 139
bark within one individual varies much more than wood from the same part of the
trees between individuals from two different sites. For that reason we compared juve-
nile forest trees with a maximum age of twenty-two years with likewise juvenile trees
from the nursery.
Vessel width is a question of ‘efficiency and safety’ (Huber 1935; Zimmermann
1983). Ring-porous species, with their wide vessel elements in stems, transport up to
7000 times more water, bearing a 7000 times higher risk of cavitation and collapse of
connected adjacent cells than diffuse-porous species with narrow vessels. Ash as a
ring-porous species has a different strategy for survival than e.g. maple. As water is
conducted only in the outermost ring, the efficiency of the earlywood is an important
factor for the first weeks of the vegetation period (Zimmermann 1983). Thus, in ash
the earlywood vessel diameter increases significantly with improving light condi-
tions (Fig. 9).
In hornbeam the percentage of vessels in earlywood increases significantly, al-
though there is no correlation between vessel diameter and light, cambial age or ring
width. According to Sass (1993) and Baas et al. (1984), vessel diameter changes with
different water regimes, which is related to the lower risk of embolisms in narrow
vessels (Huber 1935; Zimmermann 1982). Light shortage does not incorporate this
risk but leads to lower photosynthetic rates and hence lower production of material
(Tognetti et al. 1994). Thus, only the minimum number of each type of cell can be
formed to maintain the functions of mechanical support and ascent of sap.
CONCLUSION AND OUTLOOK
In principle all suppressed trees are capable of recovering after improvement in light
conditions. Suppressed trees under shady canopies stay in a ‘position of waiting’,
ready to instantly assume the status of a tree which dies.
Counting bud scale scars provides, at least with suppressed trees under a close
canopy, the option of determining the minimum age of plants without killing them.
Further studies on growth dynamics, even in mature stands containing large trees,
could reinforce the current findings.
The results of the present study suggest a means of identifying light shortage in
deciduous trees through low vessel percentage in earlywood. To distinguish signs of
light shortage from those of e.g. drought or cold, investigation of deciduous trees,
e.g. bonsai-like ashes in crevices or in other extreme ecological situations, must be
conducted. Publications on the ascent of water in trees (e.g. Zimmermann 1983; Anfo-
dillo et al. 1993), as well as most wood anatomical studies, deal with mature, domi-
nant trees. Investigations of sap flow in suppressed trees would be necessary for a
better understanding of the observed structural differences.
Intra-annual growth of trees and related interactions between trees is more or less
still an enigma, above all in natural stands. The development of the latest tree ring of
different species within a stand from the beginning to the end of the vegetation period
would provide valuable data for further investigation.
Downloaded from Brill.com12/21/2021 04:51:20AM
via free access140 IAWA Journal, Vol. 23 (2), 2002
ACKNOWLEDGEMENTS
The present study was funded by a doctoral scholarship from the Swiss National Science Founda-
tion (no. 31-52’349.97) to the first author. We would like to thank A. Burkart and C. Cattaneo for
taking samples from the nursery and O.U. Bräker for advice with the image analysis. We are espe-
cially grateful to P. Cherubini for critical reading and interesting discussions, A. Rigling for advice
with the statistical methods and to M.J. Sieber for the English corrections.
REFERENCES
Andrews, S.R. & L.S. Gill. 1939. Determining the time, branches on living trees have been
dead. Jagd und Forst 37. Washington D.C.
Anfodillo, T., G.B. Sigalotti, M. Tomasi, P. Semenzato & R. Valentini. 1993. Applications of
thermal imaging technique in the study of the ascent of sap in wood species. Plant, Cell
and Environment 16: 997–1001.
Baas, P., C.-L. Lee, X.Y. Zhang, K.-M. Cui & Y.F. Deng. 1984. Some effects of dwarf growth
on wood structure. IAWA Bull. n.s. 5: 45–63.
Baas, P, E. Werker & A. Fahn. 1983. Some ecological trends in vessel characters. IAWA Bull.
n.s. 4: 2–3.
Bariska, M. & H.H. Bosshard. 1974. Einfluss des Kambiumalters auf die Xylembildung, dar-
gestellt am Merkmalen der Mikrozugfestigkeit von Buchenholz. Holz Roh- Werkst. 32:
19–23.
Baumberger, C. 1997. Minimale Lebensbedingungen und deren Ausdruck in holzanatomischen
Strukturen. Diplomarbeit, Univ. Bern.
Braun, H. J. 1980. Bau und Leben der Bäume. Rombach Verlag, Freiburg.
Carlquist, S. 1988. Comparative wood anatomy. Systematic, ecological and evolutionary as-
pects of dicotyledon wood. Springer Verlag, Berlin, Heidelberg, New York etc.
Cherubini, P., M. Dobbertin & J. Innes. 1998. Potential sampling bias in long-term forest growth
trends reconstructed from tree rings: A case study from the Italian Alps. For. Ecol. Man-
agem. 109: 103–118.
Eckstein, D., E. Frisse & W. Liese. 1974. Holzanatomische Untersuchungen an umweltge-
schädigten Strassenbäumen der Hamburger Innenstadt. Eur. J. For. Path. 4: 232–244.
Emborg, J. 1998. Understory light conditions and regeneration with respect to the structural
dynamics of a near-natural temperate deciduous forest in Denmark. For. Ecol. Managem.
106: 83–95.
Gansert, D. & W. Sprick. 1998. Storage and mobilization of non-structural carbohydrates and
biomass development of beech seedlings (Fagus sylvatica) under different light regimes.
Trees 12: 247–257.
Gartner, B.L. 1995. Patterns of xylem variation within a tree and their hydraulic and mechani-
cal consequences. In: B.L. Gartner (ed.), Plant stems: physiology and functional morphol-
ogy. Academic Press, San Diego, New York, Boston, London.
Grosser, D. & P. Burger. 1985. Holzanatomische Untersuchungen an japanischen Zwergbäumen
(Bonsai) und kümmerwüchsigen Bäumen. Holz Roh- Werkst. 43: 6.
Gruber, F. 1998. Kombinierte Altersbestimmung und Altersentwicklung von Jungbuchen (Fagus
sylvatica L.). Flora 193: 59–73.
Hartig, R. 1869. Das Aussetzen der Jahrringe bei unterdrückten Stämmen. Zeitschr. Forst- und
Jagdwesen. Springer-Verlag, Berlin.
Huber, B. 1935. Die physiologische Bedeutung der Ring- und Zerstreutporigkeit. Ber. Dtsch.
Bot. Ges. 53: 711–119.
Downloaded from Brill.com12/21/2021 04:51:20AM
via free accessHoffmann & Schweingruber — Light shortage in young deciduous trees 141
Huber, B. 1956. Die Gefässleitung. In: O. Stocker (ed.), Handbuch der Pflanzenphysiologie
(Encyclopaedia of Plant Physiology). Vol. 3: 541–582. Springer-Verlag, Berlin, Göttingen,
Heidelberg.
Huber, B. & W. Holdheide. 1942. Jahrringchronologische Untersuchungen an Hölzern der
bronzezeitlichen Wasserburg Buchau am Federsee. Ber. Dtsch. Bot. Ges. 60: 261–287.
Koltzenburg, C. 1967. Der Einfluss von Lichtgenuss, soziologischer Stellung und des Standortes
auf Holzeigenschaften der Rotbuche (Fagus sylvatica L.) IUFRO, 14. Kongress, München.
Band 9, Sekt. 41: 210–235.
Kraft, G. 1884. Beiträge zur Lehre von den Durchforstungen, Schlagstellungen und Lichtungs-
hieben. Hannover.
Merz, R.W. & S.G. Boyce. 1956. Age of oak “seedlings”. J. Forestry 54: 774–775.
Newbold, A. J. & E.B. Goldsmith. 1990. Regeneration of oak and beech: a literature review.
Discussion papers in Conservation No. 33, University College London.
Peltier, A., M.C. Touzet, C. Armengaud & J.F. Ponge. 1997. Establishment of Fagus sylvatica
and Fraxinus excelsior in an old-growth beech forest. J. of Vegetation Sciences 8: 13–20.
Peszlen, I. 1994. Influence of age on selected anatomical properties of Populus clones.
IAWA J. 14: 311–321.
Petersen, O.G. 1899. Aarringstudier. Tidsskrift f. Skovvaesen, Raekke B11: 190–220.
Poulson, T.L. & W. J. Platt. 1989. Gap light regimes influence diversity. Ecology 70: 553–555.
Richie, G.A. 1994. Maturation of Douglas-fir: Changes in stem, branch and foliage character-
istics associated with ontogenetic aging. Tree Physiology 14: 1245–1259.
Roberts, S.D. 1994. The occurrence of non-ring producing branches (NRP) in Abies lasiocarpa.
Trees 8: 263–267.
Roloff, A. 1989. Kronenentwicklung und Vitalitätsbeurteilung ausgewählter Baumarten der
gemässigten Breiten. Schriften Forstlichen Fakultät Univ. Göttingen und Niedersächsischen
Forstlichen Versuchsanstalt, Bd. 93. J.D. Sauerländer’s Verlag, Frankfurt a. M.
Sass, U. 1993. Die Gefässe der Buche als ökologische Variabel. Dissertation des Fachbereichs
Biologie der Universität Hamburg.
Schöne, B. & F.H. Schweingruber. 1999. Verzwergte Laubhölzer; anatomische und morpholo-
gische Besonderheiten sowie ökologische Bedeutung. Schweiz. Z. Forstwes. 150: 132–141.
Schweingruber, F.H. 1982. Microscopic wood anatomy. Flück-Wirth, Internationale Buchhand-
lung für Botanik und Naturwissenschaften, Teufen.
Schweingruber, F.H. 1990. Anatomie europäischer Hölzer: ein Atlas zur Bestimmung europä-
ischer Baum-, Strauch- und Zwergstrauchhölzer. Haupt-Verlag, Bern, Stuttgart.
Späth, H.L. 1912. Der Johannistrieb. Ein Beitrag zur Kenntnis der Periodizität und Jahrring-
bildung sommergrüner Holzgewächse. Verlagsbuchhandlung Paul Parey, Berlin.
Suner, A. & E. Röhrig. 1980. Die Entwicklung der Buchenverjüngung in Abhängigkeit von
der Auflichtung des Altbestandes. Forstarchiv 51: 145–149.
Sutton, W.R.T. 1973. Changes in tree dominance and form in a young radiata pine stand. N. Z.
J. For. Sci. 3: 323–330.
Tognetti, R., M. Michelozzi & M. Borghetti. 1994. Response to light of shade-grown beech
seedlings subjected to different watering regimes. Tree Physiology 14: 7–9, 751–758.
Trendelenburg, R. & H. Mayer-Wegelin. 1955. Das Holz als Rohstoff. Carl Hanser , München.
Wang, Y.F. & C.L. Lee. 1989. Comparative studies on woods of three species of normal and
dwarf trees. Acta Bot. Sinica 31: 12–18.
Zimmermann, M.H. 1982. Functional xylem anatomy of angiosperm trees. In: P. Baas (ed.),
New perspectives in wood anatomy. Martinus Nijhoff Verlag / Dr. W. Junk Publishers, The
Hague, Boston, London.
Zimmermann, M.H. 1983. Xylem structure and the ascent of sap. Springer-Verlag, Berlin, etc.
Downloaded from Brill.com12/21/2021 04:51:20AM
via free accessYou can also read
