R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
LIFE HISTORIES OF
HYLOCOMIUM SPLENDENS,
A BOREAL FOREST MOSS
Lecture BZ 372,
spring 2003
Rune Halvorsen Økland
1
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
2
HYLOCOMIUM SPLENDENS: A MINI-PORTAIT I
 Characteristics:
- perennial, mainly clonal on the forest floor; one sporophyte per ca.
2000 segments
- modular, with annual periodicity in the emergence of new modules
that remain connected [as segment chains (= clonal fragments)]
until decomposing from below (after 2-20 years) or injured
- weft-building; wefts built by ‘reiteration of the architecture of whole
branching systems, including time-delayed repeats’
 The normal developmental cycle for a new module:
- single ramification; emergence of one new growing point (GP)
(usually sympodially) in spring from the one-year-old main axis
- the new growing point develops primary branches the first autumn, and
reaches maturity [becomes a mature segment(MS)] the second
summer at the age of c. 1.5 years
 Deviant developments:
 multiple ramification (two or more emergent GPs
 regeneration, the emergence of new growing points from dormant
buds on detached fragments or, with 1 or more years´ time delay,
from 2 year or older tissue
 termination (no offspring GP produced)
 loss (GP recovery failure)
 Terminology for clonal fragments and branching patterns:
 source and offspring segments used for interconnected segments,
irrespective of time of development
 mother segment, daughter segment, grandmother segment and
granddaughter segment refer to "normal" chains
 The species is predominantly ectohydric and poikilohydric; it changes
water content with the ambient air
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
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HYLOCOMIUM SPLENDENS: A MINI-PORTRAIT II
G0
S
G1
G2
G
Ms
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
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METHODS
 Study areas
– seven monitoring areas with old-growth boreal spruce forest
dominated by Vaccinium myrtillus; spread over S and C Norway
– sexual reproduction studied in 9 10×10 plots on top of a boulder
(1995–2000)
 Plots (1 m2), mostly 50, semi-randomly placed in each area, originally
used for monitoring understorey vegetation
– fixed subplots are used for demographic census from the time a
minimum of 8 or more Hylocomium splendens GPs were present
– a total of 119141 demography plots have been followed from 1990
– annual census between August 25 (i.e., after the new segment had
reached maturity) and October 10 (i.e., before the first snowfall) every
year
 Recorded features include:
– the fates of all GPs recorded the previous year;
– all new GPs, positions mapped
 morphological measurements for all mature segments (MSs)
 vertical position (6-point scale; % of mature segment visible from
above)
 Tagging of all GPs by plastic beads; sliced and provided with a slit
 The size (dry weight) of all recorded MSs
– estimated from a regression model that explains 91.3% of size
variation in the training set (328 MSs)
– size is expressed in log2 DW [in 10-4 g] units, an increase by one unit
then corresponding to a doubling of the size
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
METHODS: TAGGING
5
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
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SIZE RELATIONSHIPS OF INTERCONNECTED HYLOCOMIUM SPLENDENS MATURE SEGMENTS
Observations
(1) mother segment size explains c. 50% of variation in
offspring size in unbranched chains
(2) the summed sizes of segments arising by multiple
ramification is about the same as that of single offspring
the annual relative growth rate is negatively correlated
with mother segment size
Hypotheses supported by observations
(1) mature segments’ potential for producing offspring
is size dependent
(2) the size of offspring segments is controlled by
transport of water and nutrients to the developing
growing point from its source segment
environmental conditions during the growth period are
also important; very large segments are developed only
when external growth conditions are optimised
internal transport is negligible over distances longer than
one segment
environmental conditions during the growth period are
important
size of the grandmother segment explains only c. 5% of
variation in offspring segment size in unbranched chains
in chains with G1L regeneration, the size of the
regenerated segment is most strongly correlated with the
synchronously developed segment on the main axis than
with segments closer to it on the shoot chain
size dependence of ramification and regeneration
strong apical dominance, effected by basipetal transport
of plant substances
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
LIFE-CYCLE
GRAPH
7
Hylocomium splendens
S3
S4
G2
S5
GL
S6
D
G0
S7
S8
|
Based upon all transition in all areas, 1990–2002
Transitions associated with elasticities > 0.01 are
shown; line thickness proportional with elasticity
value
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
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TRANSITION MATRIX MODELLING
Matrix model for H. splendens for in all seven areas, 1990–2002:
D
G0
GL
GT
G2
S1
S2
S3
S4
S5
S6
S7
S8
D
0.000
0.003
0.012
0.001
0.136
0.001
0.002
0.003
0.005
0.006
0.005
0.002
0.001
G0
0.000
0.046
0.000
0.000
0.000
0.102
0.091
0.104
0.160
0.198
0.125
0.047
0.008
GL
0.000
0.039
0.000
0.000
0.000
0.067
0.100
0.120
0.194
0.213
0.155
0.047
0.009
GT
0.000
0.031
0.000
0.000
0.000
0.132
0.161
0.170
0.208
0.158
0.064
0.014
0.004
G2
0.000
0.023
0.000
0.000
0.000
0.191
0.204
0.186
0.150
0.097
0.037
0.012
0.002
: Note strong size-dependence of offspring
S1
0.950
0.008
0.005
0.046
0.000
0.163
0.095
0.055
0.021
0.007
0.002
0.001
0.000
S2
0.929
0.015
0.025
0.057
0.000
0.132
0.191
0.156
0.103
0.033
0.009
0.003
0.001
S3
0.941
0.020
0.037
0.043
0.000
0.078
0.124
0.190
0.216
0.103
0.029
0.005
0.001
S4
0.948
0.036
0.051
0.028
0.000
0.044
0.064
0.125
0.270
0.235
0.081
0.015
0.002
S5
0.947
0.063
0.090
0.022
0.000
0.029
0.027
0.055
0.165
0.307
0.215
0.065
0.011
S6
0.948
0.127
0.146
0.008
0.000
0.015
0.017
0.027
0.082
0.213
0.323
0.189
0.034
S7
0.953
0.221
0.194
0.006
0.000
0.011
0.008
0.015
0.040
0.128
0.282
0.309
0.137
S8
0.982
0.375
0.277
0.000
0.000
0.008
0.007
0.011
0.033
0.073
0.194
0.369
0.281
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
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DESCRIPTIVE DEMOGRAPHY I
 Size distribution (distribution vector), 1990–2002 (n = 38 354)
Number per 1000 MSs
Distribution on life-stages
250
200
150
Series1
100
50
0
G0
GL
GT
G2
S1
S2
S3
S4
S5
S6
S7
S8
Life-stage
: Size-distribution of mature segments is approximately lognormal
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
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DESCRIPTIVE DEMOGRAPHY II
 Probability for risk of termination, loss and loss by grazing
Probability
Risk of termination and loss
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Loss by grazing
Loss
Termination
G0 GL GT G2 S1 S2 S3 S4 S5 S6 S7 S8
Life-stage
: Strong size-dependence of termination risk (overall risk = 0.146)
: Loss risk fairly size-independent (overall risk = 0.063)
: Risk of loss by grazing highest for medium-large segments (overall
risk = 0.018)
 Probability for terminal regeneration of terminated segments, within
one year after termination took place
Probability
G1T regeneration probability
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
S1
S2
S3
S4
S5
S6
S7
Life-stage
: The tendency for terminated segments to regenerate terminally
within one year after termination is strongly size-dependent
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
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DESCRIPTIVE DEMOGRAPHY III
 Observed causes of termination and loss, data from all areas, 1990-98.
(all modules recorded as terminated and lost, also immigrated and
emigrated, are included.)
Term. Term.
at GP at MS
stage stage
Grazing incl. losses by rodent uprooting
Lost
Sum
In %
238
333
206
777
13.2
0
14
×
14
0.2
93
418
×
511
8.7
×
×
376
376
6.4
27
380
109
516
8.8
Burial by fungi
0
3
1
4
0.1
Burial in herb litter
4
83
23
110
1.9
Burial in ericaceous litter
20
184
29
233
4.0
Burial in coniferous litter
31
269
63
363
6.2
Burial in deciduous litter
72
345
110
527
8.8
Burial, agent not specified
18
141
70
229
3.9
157
1 364
713 2 234
37.9
Overgrown by algae
Discoloured [pale (incl. mammal
urination), dark etc.]
Detached
Burial by bryophytes
Unknown
5 894 100.0
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
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DESCRIPTIVE DEMOGRAPHY IV
 Number of offspring G0 ramifications per non-terminated segment
Ramification
Number of G0
offspring
0.5
0.4
0.3
0.2
0.1
0.0
S1
S2
S3
S4
S5
S6
S7
S8
Life-stage
: G0 ramification is strongly size dependent, with a threshold size of c.
25∙10–4 = 3.2 mg
 Number of offspring G1L regenerated growing-points per segment
Number of G1L offspring
G1L regeneration
0.3
0.3
0.2
0.2
0.1
0.1
0.0
S1
S2
S3
S4
S5
S6
S7
S8
Life-stage
: G1L regeneration is dependent on the size of the amounts of
resources supplied by the shoot chain
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
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DESCRIPTIVE DEMOGRAPHY V
 The estimated long-term population growth rate, from the overall transition matrix, is λ = 1.0868
: Like most other bryophytes in boreal coniferous forests in Norway, Hylocomium splendens has increased in
abundance 1990–2002 (thereafter, populations have been more or less stable)
 The contribution to λ provided by each transition in the life-cycle graph is given by the elasticity matrix:
D
G0
GL
GT
G2
S1
S2
S3
S4
S5
S6
S7
S8
D
0.000
0.001
0.006
0.000
0.047
0.000
0.000
0.001
0.003
0.004
0.004
0.002
0.001
G0
0.000
0.002
0.000
0.000
0.000
0.002
0.003
0.004
0.008
0.013
0.010
0.005
0.001
GL
0.000
0.002
0.000
0.000
0.000
0.001
0.003
0.005
0.011
0.015
0.013
0.005
0.001
GT
0.000
0.000
0.000
0.000
0.000
0.001
0.001
0.002
0.003
0.003
0.002
0.000
0.000
G2
0.000
0.001
0.000
0.000
0.000
0.004
0.008
0.010
0.010
0.008
0.004
0.002
0.000
S1
0.006
0.000
0.000
0.002
0.000
0.003
0.003
0.002
0.001
0.000
0.000
0.000
0.000
S2
0.007
0.001
0.001
0.003
0.000
0.003
0.007
0.007
0.006
0.003
0.001
0.000
0.000
S3
0.009
0.001
0.003
0.002
0.000
0.002
0.005
0.011
0.016
0.010
0.003
0.001
0.000
S4
0.013
0.003
0.005
0.002
0.000
0.002
0.004
0.011
0.030
0.033
0.014
0.003
0.000
S5
0.015
0.007
0.011
0.002
0.000
0.001
0.002
0.006
0.022
0.051
0.044
0.016
0.003
S6
0.012
0.011
0.015
0.001
0.000
0.001
0.001
0.002
0.009
0.029
0.053
0.038
0.008
S7
0.007
0.011
0.011
0.000
0.000
0.000
0.000
0.001
0.002
0.009
0.025
0.034
0.018
S8
0.002
0.006
0.005
0.000
0.000
0.000
0.000
0.000
0.001
0.002
0.006
0.013
0.012
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
14
DESCRIPTIVE DEMOGRAPHY VI
 Comparing the actual distribution of ‘individuals’ on life stages with
the estimated distribution at stability, given constant transition
probabilities (found as the right eigenvector w of the transition matrix)
Frequency (sum S1 ...
S8 = 1000)
Comparison between observed and estimated
distributions
1000
800
600
Observed
400
Predicted
200
0
D G0 GL GT G2 S1 S2 S3 S4 S5 S6 S7 S8
Life-stage
: Populations are balanced, but the proportion of large segments is
expected to increase
 Individual fitness (number of offspring produced from one individual
within one transition period) for each life-stage (found as the left
eigenvector w of the transition matrix)
Number of offspring per
individual
Indiviudual fitness
2.5
2.0
1.5
1.0
0.5
0.0
D
G0
GL GT
G2
S1
S2
S3
Life-stage
: Fitness is size-dependent
S4
S5
S6
S7
S8
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
15
REPRODUCTIVE BIOLOGY
 Reproductive biological characteristics:
– dioecious (separate male and female plants)
– gametophyte haploid, sporophyte diploid, parasitic on gametophyte
– reproduction water-dependent
– germinating spores hardly observed in nature
 Data: From one boulder stone in Skedsmo, Akershus, with
exceptionally high sporophyte frequency
 Characteristics of the studied population:
– 4:1 female biased sex distribution
– among plants determined to sex, males are slightly larger than females
 Size-dependence of sporophyte production (frequency of female
segments that carry sporophytes)
Sporophyte frequency
0.40
0.30
0.20
0.10
0.00
2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8
Size class
: Demonstrates strong size dependence of sporophyte production
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
DISTRIBUTION OF CLONES
 Several clones co-occur and grow intermixed on the boulder stone
16
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
Female (2)
Female (?)
Male (1)
Male (12)
Male (13)
Male (?)
Unknown
17
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
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THE COST OF SEXUAL REPRODUCTION
 Proximate costs assessed by comparison of size development of cooccurring segments on female shoots from year t to year t – 1.
Comparison made among the 0 type (without sporophytes in year t) and
the S type (with sporophytes in year t)
– Size development of singly ramifying segments, 0.66 log2 DM units
better for the 0 type than for the S type (randomisation test with correction
for size differences: P < 0.0001); the mass (back-transformed; in g) of an
average daughter segment produced by simple ramification of a
sporophytic mother segment is only 59% of the mass of the daughter of
a nonsporophytic mother segment of the same size.
– Abundance of multiply ramifying offspring: 21% of number of MSs in
0 and 13% in S; randomisation test with correction for size differences: P
< 0.0001
– Termination frequency: 5% in S and 1% in 0; randomisation test with
correction for size differences: P < 0.0001
 Ultimate costs assessed by stochastic matrix modelling of the fates of
0 and S subpopulations; difference in the population growth rate λ
assessed by comparing 1000 bootstrap matrix pairs.
– λ differed significantly between 0 and S (P = 0.001); no overlap among
95% CI were found.
– For 0, λ = 1.258, CI = [1.204, 1.319]; for S, λ = 1.091, CI = [1.020,
1.153]
– The strongest contributions to differences in λ (as assessed by LTRE
analyses) were made by transitions involving multiple ramification, that
contributed more strongly in the 0 subpopulation
 Sexual reproduction incurs somatic costs
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
ECOSYSTEM FUNCTION: NEIGHBOUR INTERACTIONS I
 Vertical distribution (based upon data 1992–97; n = 12,528 MSs;
classified to 6 V-classes according to proportion of MS visible from
above; V0: < 5% (buried); V1: 5–25%; V2: 25–75%; V3: 75–95%; V4:
95–100%; V5: emergent) and size
V0: mean =3.26a
0.5
0.4
V1: mean = 4.57c
0.5
0.4
0.3
0.2
0.1
0.0
0.3
0.2
0.1
0.0
S2 S3 S4 S5 S6 S7 S8
S2 S3 S4 S5 S6 S7 S8
V2: mean = 5.03e
0.5
0.4
V3: mean = 5.13e
0.5
0.4
0.3
0.2
0.1
0.0
0.3
0.2
0.1
0.0
S2 S3 S4 S5 S6 S7 S8
S2 S3 S4 S5 S6 S7 S8
V5: mean = 4.21b
V4: mean = 4.87d
0.5
0.5
0.4
0.4
0.3
0.3
0.2
0.1
0.2
0.1
0.0
0.0
S2 S3 S4 S5 S6 S7 S8
: The
S2 S3 S4 S5 S6 S7 S8
largest segments are found immersed in the bryophyte carpet just
below the top (V3)
: Burial is most unfavourable
: Emergence is unfavourable, but less strongly than burial
19
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
20
ECOSYSTEM FUNCTION: NEIGHBOUR INTERACTIONS II
 Vertical distribution and termination
Number of segments
3000
2500
2000
1500
1000
500
0
V0
V1
V2
V3
V4
V5
V-class
With offspring
Terminated
: Risk of termination is particularly large for buried segments, but
exposed segments also have higher termination rates than immersed
ones
 Vertical distribution and branching
Observed/expected
number
Observed/expected number of offspring of given type,
corrected for size
2.00
1.50
G0
1.00
G1L
G1T
0.50
0.00
V0
V1
V2
V3
V4
V5
V-category
: Development from dormant buds is dependent on radiation (note that
the V-level was recorded for the G1-regenerating MSs one year before
onset of regeneration)
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
ECOSYSTEM FUNCTION: NEIGHBOUR INTERACTIONS III
 Vertical variation in fitness
– Fitness not corrected for size differences among V-classes
1.2
cd
d
cd
c
1.0
b
0.8
0.6
a
a
0.4
0.2
0.0
V0
V1
V2
V3
V4
B
B
V5
– Size-corrected fitness
1.2
bB
B
V1
V2
b
1.0
0.8
0.6
a
a
0.4
0.2
0.0
V0
V3
V4
V5
: Fitness is dependent on vertical position in the bryophyte carpet
: This is accentuated by the more favourable size development of
segments in intermediate vertical positions
21
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
22
ECOSYSTEM FUNCTION: VERTICAL DYNAMICS
 Vertical dynamics
Transition
to V-class
V0
V1
V2
V3
V4
V5
Transition probabilities, from parent segment in V-class
V0
V1
V2
V3
V4
V5
0.177
0.126
0.091
0.085
0.444
0.250
0.166
0.185
0.167
0.133
0.090
0.047
0.151
0.218
0.177
0.095
0.238
0.228
0.105
0.166
0.189
0.201
0.155
0.221
0.106
0.139
0.182
0.301
0.219
0.314
0.027
0.042
0.047
0.072
0.127
0.318
: There is considerable vertical dynamics, although there is a strong
tendency to remain in the same vertical level
: Burial in litter may occur to segments regardless of level, while burial
by bryophytes is more likely occur to segments in low positions
: Escape from burial is much more frequent for litter burials
 Vertical size dynamics (change in log2 DM units for normally
ramifying MSs from one generation to the next)
Transition
to V-class
V0
V1
V2
V3
V4
V5
V0
–0.43
0.31
0.57
0.68
0.68
0.22
Transition from parent segment in V-class
V1
V2
V3
V4
–0.34
–0.56
–0.74
–0.71
0.18
0.02
–0.27
–0.24
0.48
0.22
0.16
–0.11
0.52
0.31
0.04
0.13
0.49
0.31
0.09
0.01
–0.31
–0.35
–0.36
–0.49
V5
–0.83
–0.20
–0.06
0.11
0.17
–0.27
: Persistently buried and emergent shoots will experience size reduction
generation after generation
: Buried shoots rapidly recover if transferred to a more favourable
vertical position
: Emergent shoots respond less positively to a more favourable position
than V0 which are smaller and V1 which are larger; indicating that
emergence incurs loss of vitality in excess of what is indicated by the
reduction in size
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
23
ECOSYSTEM FUNCTION: IMPORTANCE OF PROCESSES IN
A VERTICAL PROFILE
100
Desiccation and
disturbance
Facilitation
Shading
Deeply buried
0
5
10
25
50
75
95
On top
Emergent
Slightly above
0
Relative importance of process
 Relative importance of three major processes and fitness
0.8
0.6
0.4
Position in the bryophyte carpet
(% visible from above)
: This sums up the points made above
Deeply
buried
0
5
10
25
50
75
95
On top
Slightly
above
Emergent
0
0.2
Relative fitness
1
1.2
Position in the bryophyte carpet
(% visible from above)
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
24
ECOSYSTEM FUNCTION: THE IMPORTANCE OF
BRYOPHYTE CARPET DENSITY I
 Mean segment size increases with increasing cover of the bryophyte
layer (data: 119 plots, followed 1990–94)
Size (log2 DM units)
8
7
6
5
4
3
2
0
20
40
60
80
100
Bryophyte cover (%)
: Size is positively density dependent in the studied system
 Danger of burial in the bryophyte carpet also increases with increasing
bryophyte cover
Frequency of burial (%)
25
20
15
10
5
0
0
20
40
60
80
100
Bryophyte cover (%)
: Increasing risk of burial with increasing density indicates negative
density dependence as well
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
25
ECOSYSTEM FUNCTION: THE IMPORTANCE OF
BRYOPHYTE CARPET DENSITY II
 Relationship between frequency of different branching patterns and
bryophyte carpet density (% cover)
Branching pattern
G0 ramification frequency, size-corrected
G1L regeneration frequency, size-corrected
G2 regeneration frequency
Termination risk, size-corrected
Loss risk
r
–0.1902
–0.3477
–0.2647
–0.1484
–0.0711
P
0.0383
0.0001
0.0037
>0.1
>0.1
: branching rates (ramification as well as regeneration) decreases with
increasing bryophyte carpet density, even after the effect of size has
been accounted for
: this is caused by dependence of development from dormant buds on
radiation
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
26
ECOSYSTEM FUNCTION: RELATIONSHIPS BETWEEN
HYLOCOMIUM SPLENDENS AND OTHER SPECIES IN THE
BRYOPHYTE CARPET
 Data: 85 plots (1 m2) in Vaccinium myrtillus-dominated spruce forest,
with nested subplots down to 6.25×6.25 cm; recording of bryophyte
species’ presences, and several environmental variables
 Relationships between layers:
Tree litter (tree influence)
Vascular plant cover, the
effect of litter partialled out
Bryophyte species Bryophyte cover
number
r
P
r
P
–0.1834 0.0464 –0.2890 0.0080
–0.3212 0.0027 –0.3401 0.0014
: dense vascular plant and tree layers act as strong stress factors for
bryophytes, with negative effects on species number as well as
bryophyte cover
: most likely, this negative effect is brought about by
– reduced size (growth) caused by light and moisture deprivation,
followed by decreasing branching and increased termination rates
– increased danger of burial in litter
 Interspecific associations:
– The observed number of positive associations exceeded the number
expected at random at all spatial scales; in the set of all 36 species as well
as a set of the 13 most common species (including Hylocomium
splendens)
– The number of negative associations was not different from the
expected number
: This underpins the conception of the boreal forest floor as a stressful and
disturbance-prone habitat for bryophytes in which positive intra- and
inter-specific interactions are important
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
27
POPULATION DYNAMICS I
 Data: Transition matrices for 7 areas × 12 one-year periods, with λ
estimates and elasticity matrices
 Variation in λ; single-factor ANOVAs
Factor
Area
Year
df
6
11
MSfactor MSresiduals
0.0163
0.0106
0.0400
0.0066
F
1.5363
6.0420
P
0.1776
<0.0001
 Variation in λ; two factors entered sequentially into ANOVA
Factor
Year
Area
Residuals
df
11
6
66
MS
0.0400
0.0164
0.0057
F
6.9722
2.8452
P
<0.0001
0.0158
: There is significant difference in population growth rates among years
: Differences among areas are significant only after variation among
years has been accounted for
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
28
POPULATION DYNAMICS II
 A life strategy corresponds to a closed loop in the life-cycle graph. The
Hylocomium splendens life-cycle graph with associated transition matrix
(all years, all areas) has 144 edges and 13 nodes and the number of unique
loops are
L = 144 – 13 + 1 = 132.
 The relative importance of a life strategy, as defined by a loop, is given
by this loop’s characteristic elasticity, i.e. the elasticity for the transition
unique to that loop.
 Loop analysis requires a simplified life-cycle graph.
 For large transition matrices, summation of elasticities of different
regions in the transition matrix that may be associated with different
demographic processes is an alternative to loop analysis.
 Thirteen regions (processes) may be identified for Hylocomium
splendens, that can be grouped into three main strategies:
– G: vegetative growth (transition to a larger size class)
– S: survival (transition to the same or a smaller size class, or into the
diaspore bank
– B: branching (vegetative propagation)
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
29
POPULATION DYNAMICS III
 Quantifying the importance of different demographic processes for
Hylocomium splendens
Demographic process
Demographic
strategy
Summed
elasticity
P1a  growth of Sn to larger size
G
0.2328
P1b  size maintenance of Sn
S
0.2002
P1c  size reduction of Sn
S
0.1573
P1d  terminal regeneration from Sn
S
0.0125
P1e  development of G1T into Sn
G
0.0124
P2a  branching by multiple
ramification
B
P2b  branching by G1L regeneration
B
0.0505
P2c  branching by G2 regeneration
B
0.0472
P3  offset to the diaspore bank
S
0.0707
P4a  development of G0 into Sn
G
0.0456
P4b  development of G1L into Sn
G
0.0549
P4c  development of G2 into Sn
G
0.0459
P5  introduction of new growing
points
B
 Sums for main strategies: G = 0.3917, S = 0.4408, B = 0.1677
: Defines the ‘average importance’ of different processes
0.0464
0.0235
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
30
POPULATION DYNAMICS IV
1.25
 LNMDS ordination of 84 elasticity matrices shows gradients in lifehistory syndromes among areas and years
1.00
GN01
SO91
GU01
MDS2.2
0.50
0.75
GR94
SO98
GN93
RA95
GR95
PA00
GR92
GU94
RA98
PA98
RA01
OT91
GR90
GR91
PA91
GU90
OT94
0.25
PA94
PA90
GU91
GR96
SO01
RA92
SO99
RA97
RA96
RA91
SO95
GU93
GR97
RA93 PA96
RA99 PA99
GN92
GR00
SO00
GU92SO90
RA90
OT90 GU95
GR99
SO97PA92
GN98
GN96
PA95
GN00
SO96
RA94
GU98
PA97
GU00 OT95
SO93
GR98
SO94
GR93
GN91
GN97
GU97
OT93
PA01
GU99
GU96
OT96GN95
SO92
OT99
GN94
GR01
OT92
OT01
OT97
GN90OT00
RA00
OT98
0.00
GN99
PA93
0.0
0.5
1.0
MDS2.1
1.5
2.0
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
31
POPULATION DYNAMICS V
 Interpretation of ordination axes as gradients in life-history strategies is
obtained by correlating demographic processes (and, if available other
external information) with the scores obtained by the objects in the
analysis (i.e. the Year×Area combinations). As example is used the 13
demographic strategies above:
Demographic process
P1a  growth of Sn to larger size
P1b  size maintenance of Sn
P1c  size reduction of Sn
P1d  terminal regeneration from Sn
P1e  development of G1T into Sn
P2a  branching by multiple
ramification
P2b  branching by G1L regeneration
P2c  branching by G2 regeneration
P3  offset to the diaspore bank
P4a  development of G0 into Sn
P4b  development of G1L into Sn
P4c  development of G2 into Sn
P5  introduction of new growing
points
G
S
B
LNMDS 1
τ
P
LNMDS 2
τ
P
0.4917 <0.0001 0.0158 0.8317
0.0941 0.2051 0.2631 0.0004
–0.1044 0.1597 –0.3789 <0.0001
–0.5594 <0.0001 –0.0330 0.6569
–0.5683 <0.0001 –0.0425 0.5675
0.6334 <0.0001 –0.0766 0.3023
0.1261 –0.1845
<0.0001 0.2229
<0.0001 0.2085
<0.0001 0.0737
0.2863 –0.2212
<0.0001 0.2390
0.2626 –0.0445
0.0130
0.0027
0.0050
0.3208
0.0029
0.0013
0.5493
0.4808 <0.0001 0.1495
–0.4028 <0.0001 –0.2447
0.0654 0.3784 0.2780
0.0441
0.0010
0.0002
0.1136
–0.5863
–0.5663
0.6403
0.0792
–0.5863
–0.0832
Other properties:
Demographic process
λ – population growth rate
log2 DM – mean size
log2 D – H. splendens density
V – average vertical position
LNMDS 1
τ
P
LNMDS 2
τ
P
0.4073 <0.0001 0.1736
0.3855 <0.0001 0.0146
–0.0092 0.9016 0.0204
–0.3561 <0.0001 –0.0369
0.0194
0.8438
0.7839
0.6518
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
32
POPULATION DYNAMICS VI
 Variation along LNMDS 1; single-factor ANOVAs
Factor
Area
Year
df
6
11
MSfactor MSresiduals
0.8816
0.1149
0.4580
0.1264
F
7.6697
3.6232
P
<0.0001
0.0004
 Variation along LNMDS 1; two factors entered sequentially into
ANOVA
Factor
Area
Year
Residuals
df
6
11
66
MS
0.8816
0.4580
0.0578
F
P
15.2624 <0.0001
7.9297 <0.0001
 Variation along LNMDS 2; single-factor ANOVAs
Factor
Area
Year
df
6
11
MSfactor MSresiduals
0.0762
0.0356
0.0390
0.0384
F
2.1396
1.0155
P
0.0582
0.4419
 Variation along LNMDS 2; two factors entered sequentially into
ANOVA
Factor
Area
Year
Residuals
df
6
11
66
MS
0.0762
0.0390
0.0350
F
2.1747
1.1147
P
0.0564
0.3642
: There are two main life-strategy gradients:
(1) from predominantly small shoots, visible from above, with high
importance of size maintenance and terminal regeneration, and
branching mainly by regeneration from older parts; to larger shoots,
high importance of size increase and ramification; associated with a
gradient in population growth rate
(2) a minor life-strategy gradient that highlights an alternative route to
high λ, by massive regeneration from older parts (most notably, after
rodent peak years)
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
33
POPULATION DYNAMICS VII
 Causes of broad-scale demographic variation:
– In a smaller set (2 areas×6 years) it is shown that growth (MS size) and
several demographic characteristics related to size are favoured by a
humid climate with long growing seasons; i.e. that population
development is dependent mainly on climatic conditions
– Other important factors are rodent grazing
– A study of the importance of climatic conditions for demographic
variation is in progress
 The massive population increase observed for Hylocomium splendens
in the study areas 1990–2002, with an average λ = 1.0868, accords with
the recorded abundance increase for significantly more forest-floor
bryophyte species than expected from a null model in boreal coniferous
forests (in vegetation monitoring)
: There is a development going on towards a more closed bryophyte layer;
from 2002 the cover of bryophytes in Norwegian boreal forests has
remained stable
: This may have important consequences for the boreal forest ecosystem,
as bryophytes interact with other organisms, e.g. by providing a less
favourable environment for seed germination and seedling survival
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
POPULATION DYNAMICS VIII
 Changes in bryophyte species’ abundances
34
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
KNOWLEDGE GAPS
 A better understanding of factors responsible for population dynamics
at the Area scale
– an improved model for relationships between climate and bryophyte
population dynamics is needed
– which demographic transitions contribute the most to variation in λ
 A better understanding of the dynamics of interactions between
neighbours; size relationships, etc.
 Dynamics of populations at the plot scale (< 1 m2)
– are the gradients the same as on the broad scale
– relationships between gradients in population dynamics and
environmental factors
 A better understanding of factors determining the fate of individuals,
e.g.
– how loss rate is related to terrain slope and segment size
– scales on which termination occurs (single shoots, shoot groups etc.)
 Future population change
– can only be determined by continuation of vegetation monitoring and
population biological studies
35
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
36
REFERENCES
 Used in the lecture
Økland, R.H. 1994. Patterns of bryophyte associations at different scales in a Norwegian boreal
spruce forest. - J. Veg. Sci. 5: 127-138.
Økland, R.H. 1995. Bryophyte and lichen persistence patterns in a Norwegian boreal coniferous
forest. - Lindbergia 19: 50-62.
Økland, R.H. 1995. Population biology of the clonal moss Hylocomium splendens in
Norwegian boreal spruce forests. I. Demography. - J. Ecol. 83: 697-712. [H1]
Økland, R.H. & Økland, T. 1996. Population biology of the clonal moss Hylocomium
splendens in Norwegian boreal spruce forests. II. Effects of density. - J. Ecol. 84: 63-69.
[H2]
Økland, R.H. 1997. Population biology of the clonal moss Hylocomium splendens in
Norwegian boreal spruce forests. III. Six-year demographic variation in two areas. Lindbergia 22: 49-68. [H3]
Økland, R.H. 2000. Population biology of the clonal moss Hylocomium splendens in
Norwegian boreal spruce forests. 5. Vertical dynamics of individual shoot segments. Oikos 88: 449-469. [H5]
Rydgren, K. & Økland, R.H. 2001. Sporophyte production in the clonal moss Hylocomium
splendens: the importance of shoot density - J. Bryol. 23: 91-96. [H7]
Rydgren, K. & Økland, R.H. 2002. Ultimate costs of sexual reproduction in the clonal moss
Hylocomium splendens.  Ecology 83: 1573-1579. [H9]
Rydgren, K. & Økland, R.H. 2002. Life cycle graphs and matrix modelling of bryophyte
populations.  Lindbergia 27: 81-89.
Rydgren, K. & Økland, R.H. 2002. Sex distribution and sporophyte frequency in a population
of the clonal moss Hylocomium splendens.  J. Bryol. 24: 207-214 [H10]
Rydgren, K. & Økland, R.H. in press. Short-term costs of sexual reproduction in the clonal
moss Hylocomium splendens.  Bryologist, accepted 2002 12 [H8].
Økland, T., Bakkestuen, V., Økland, R.H. & Eilertsen, O. 2004. Changes in forest understorey
vegetation in Norway related to long-term soil acidification and climatic change. - J. Veg.
Sci. 15: 437-448.
 Other references related to Hylocomium splendens population
dynamics
Økland, R.H., Steinnes, E. & Økland, T. 1997. Element concentrations in the boreal forest
moss, Hylocomium splendens: variation due to segment size, branching patterns and
pigmentation. - J. Bryol. 19: 673-686.
Rydgren, K. & Økland, R.H. & Økland, T. 1998. Population biology of the clonal moss
Hylocomium splendens in Norwegian boreal spruce forests. 4. Effects of simulated finescale disturbance. - Oikos 82: 5-19. [H4]
Økland, T., Økland, R. & Steinnes, E. 1999. Variation in element concentrations in
Hylocomium splendens in Norway, in relation to gradients in vegetation and local
environmental factors. - Pl. Soil 209: 71-83.
Rydgren, K., de Kroon, H., Økland, R.H. & van Groenendael, J.M. 2001. Effects of fine-scale
disturbances on the demography and population dynamics of the clonal moss
Hylocomium splendens. - J. Ecol. 89: 395-405. [H6]
R.H. Økland: Life histories of Hylocomium splendens in Norwegian boreal forests. Lecture BZ372, 2003
37
Økland, R.H. & Bakkestuen, V. 2004. Fine-scale spatial patterns in populations of the clonal
moss Hylocomium splendens partly reflect structuring processes in the boreal forest floor.
– Oikos 106: 565-575 [H11]
Cronberg, N., Rydgren, K. & Økland, R.H. Clonal structure and genet-level sex ratios suggest
different roles of vegetative and sexual reproduction in the clonal moss Hylocomium
splendens. – Ecography, accepted 05 08 [H12]
Rydgren, K., Cronberg, N. & Økland, R.H. Factors influencing reproductive success in the
clonal moss, Hylocomium splendens. – Oecologia, accepted 05 10 [H13]